VRay System

General

In this section you can control variety of VRay parameters. These are divided into the following sections:

Parameters

Raycaster parameters

Here you can control various parameters of VRay's Binary Space Partitioning (BSP) tree.

One of the basic operations that VRay must perform is raycasting - determining if a given ray intersects any geometry in the scene, and if so - identifying that geometry. The simplest way to implement this would be to test the ray against every single render primitive (triangle) in the scene. Obviously, in scenes with thousands or millions of triangles this is going to be very slow. To speed this process, VRay organizes the scene geometry into a special data structure, called a binary space partitioning (BSP) tree.

The BSP tree is a hierarchical data structure, built by subdividing the scene in two parts, then looking at each of those two parts and subdividing them in turn, if necessary and so on. Those "parts" are called nodes of the tree. At the top of the hierarchy is the root node - which represents the bounding box of the whole scene; at the bottom of the hierarchy are the leaf nodes - they contain references to actual triangles from the scene.

Max tree depth - the maximum depth of the tree. Larger values will cause VRay to take more memory, but the rendering will be faster - up to some critical point. Values beyond that critical point (which is different for every scene) will start to slow things down. Smaller values for this parameter will cause the BSP tree to take less memory, but rendering will be slower.

Min leaf size - the minimum size of a leaf node. Normally this is set to 0.0, which means that VRay will subdivide the scene geometry regardless of the scene size. By setting this to a different value, you can make VRay to quit subdividing, if the size of a node is below a given value.

Face/level coef - controls the maximum amount of triangles in a leaf node. If this value is lower, rendering will be faster, but the BSP tree will take more memory - up to some critical point (which is different for every scene). Values below that critical point will make the rendering slower.

Default geometry - internally VRay maintains four raycasting engines. All of them are built around the idea of a BSP tree, but have different uses. The engines can be grouped into raycasters for non-motion blurred and for motion blurred geometry, as well as for static and dynamic geometry. This parameter determines the type of geometry for standard 3dsmax objects. Note that some objects (displacement-mapped objects, VRayProxy and VRayFur objects, for example) always generate dynamic geometry.

Static geometry is precompiled into an acceleration structure at the beginning of the rendering and remains there until the end of the frame. Note that static raycasters are not limited in any way and will consume as much memory as necessary.

Dynamic geometry is loaded and unloaded on the fly depending on which part of the scene is being rendered. The total memory taken up by the dynamic raycasters can be controlled within certain limits.

Dynamic memory limit - the total RAM limit for the dynamic raycasters. Note that this limit is divided between the number of rendering threads. If you specify 400 MB total limit, for example, and you have a dual processor machine with multithreading enabled, then each rendering thread will use 200 MB for its dynamic raycaster. If this limit is too low, and geometry needs to be loaded and unloaded very often, this may turn out to be slower than rendering in single-threaded mode.

Render region division

Here you can control various parameters of VRay's rendering regions (buckets). The bucket is an essential part of the distributed rendering system of VRay. A bucket is a rectangular part of the currently rendered frame that is rendered independently from other buckets. Buckets can be sent to idle LAN machines for processing and/or can be distributed between several CPUs. Because a bucket can be processed only by a single processor the division of the frame in too small a number of buckets can prevent the optimal utilization of computational resources (some CPUs stay idle all the time). However the division of the frame in too many buckets can slow down the rendering because there is a some time overhead related with each bucket (bucket setup, LAN transfer, etc).

X - determines the maximum region width in pixels (Region W/H is selected) or the number of regions in the horizontal direction (when Region Count is selected)

Y - determines the maximum region height in pixels (Region W/H is selected) or the number of regions in the vertical direction (when Region Count is selected)

Region sequence - determines the order in which the regions are rendered. Note that the default Triangulation sequence is best if you use a lof of dynamic geometry (displacement-mapped objects, VRayProxy or VRayFur objects), since it walks through the image in a very consistent manner so that geometry that was generated for previous buckets can be used for the next buckets. The other sequences tend to jump from one end of the image to another which is not good with dynamic geometry.

Reverse sequence - reverses the Region sequence order

Note: When the Image Sampler is set to Adaptive Sampler the size of the buckets will be rounded up to the nearest number which is a power of 2.

Previous render

This parameter determines what should be done with the previous image in the virtual frame buffer when rendering starts. The possible values are:

Unchanged - no changes will be made - the virtual frame buffer remains the same;

Cross - every second pixel of the image will be set to black;

Fields - every other line of the image will be set to black;

Darken - the colors in the image will be darkened.

Note that this parameter has no effect on the final result of the rendering; it is implemented simply as a convenient way to distinguish between parts from the current frame being rendered, and part left over from the previous rendering.

Distributed rendering

Distributed rendering is the process of computing a single image over several different machines. Note that this is different from distributing the frame over several CPU's in a single machine, which is called multithreading. VRay supports multithreading, as well as distributed rendering.

Before you can use the distributed rendering option, you must determine the machines that will take part in the computations. Both 3dsmax and VRay need to be properly installed on those machines, although they don't need to be authorized. You must make sure that the VRay spawner application is running on those machines - either as a service, or as a stand-alone application. Refer to the Installation section for more details on configuring and running the VRay spawner.

For additional information on distributed rendering, please refer to the dedicated Distributed rendering section.

Distributed rendering - this checkbox specifies whether VRay will use distributed rendering.

Settings... - this button opens the VRay Networking settings dialog. See the Distributed rendering section for more information.

ShadeContext compatibility

VRay carries all its computations in world space. However, some 3dsmax plugins (notably atmospherics) take it as granted that the renderer works in camera space, because this is what the default scanline renderer does. To preserve compatibility with such plugins, VRay emulates work in camera space by converting the various points and vectors passed to and from other plugins.

In addition to slowing down VRay by forcing it to convert values all the time, working in camera space messes up with camera modifiers such as the Technical camera script. This why you have the option of turning off the camera-space emulation.

Frame stamp

The frame stamp is a convenient way to put some short text over the rendered images. It can be useful in many ways - for example, in network rendering, to quickly determine which frames were rendered by which machine. The frame stamp is one line of text, which appears at the bottom of the image.

Checkbox - turns the frame stamp on and off.

Edit box - here you enter the text you wish to appear in the images. You can also use some special keywords, all of which begin with the percent symbol (%). The keywords are replaced by VRay with the corresponding value:

Keyword	Meaning
%vrayversion	the current version of VRay
%filename	the name of the current scene file
%frame	the number of the current frame
%primitives *	the number of unique intersectable primitives generated for the current frame*
%rendertime	the render time for the current frame
%computername	the network name of the computer
%date	the current system date
%time	the current system time
%w	the width of the image in pixels
%h	the height of the image in pixels
%camera	the name of the camera for this frame (if rendering from a camera, empty string otherwise)
%	the value of any VRay parameter, given its MaxScript name (see section on MaxScript)
%ram	the amount of physical memory (in KBytes) installed on the system
%vmem	the amount of virtual memory (in KBytes) available on the system
%mhz	the clock speed of the system CPU(s)
%os	the operating system

* An intersectable primitive is a primitive that provides a direct method for intersection with a ray (such as a triangle, the infinite plane generated by a VRayPlane plugin etc). Most often, the number of these primitives is the same as the number of triangles (faces) processed by VRay for the current frame. Note that this may be different from the total number of triangles in the scene. With the dynamic raycaster, only geometry that is actually needed is generated and accounted for. Geometry that is not generated is not included in this count.

Font - this button allows you to choose a font and font attributes for the text in the frame stamp.

Full width - when this option is checked, the frame stamp will take the whole width of the image, otherwise the stamp will be only as wide as the text is.

Justify - specifies the position of the stamp:

Left - the stamp is placed on the left of the image.

Center - the stamp is centered.

Right - the stamp is placed on the right side of the image.

Object Settings / Light Settings

These buttons bring up the dialogs for the local object and light settings.

Presets

This button brings up the presets dialog.

VRay Camera

VRay Camera

General

The camera rollout controls the way the scene geometry is projected onto the image.

Parameters

Camera type

The cameras in VRay generally define the rays that are cast into the scene, which essentially is how the scene is projected onto the screen. VRay supports several camera types: Standard, Spherical, Cylindrical (point), Cylindrical (ortho), Box and Fish eye. Orthographic views are supported too.

Override FOV - with this setting you can override the 3dsmax's FOV angle. This is because some VRay camera types can take FOV ranges from 0 to 360 degrees, whereas the cameras in 3dsmax are limited to 180 degrees.

FOV - here you specify the FOV angle (only when Override FOV is turned on and the current camera type supports FOV angle).

Height - here you can specify the height of the Cylindrical (ortho) camera. Note: this setting is available only when the Type is set to Cylindrical (ortho).

Auto-fit - this setting controls the auto-fit option of the Fish-eye camera. When Auto-fit is enabled VRay will calculate the Dist value automatically so that the rendered image fits horizontally with the image's dimensions.

Dist - this setting applies only to the Fish-eye camera. The Fish-eye camera is simulated as a Standard camera pointed to an absolutely reflective sphere (with a radius of 1.0) that reflects the scene into the camera's shutter. The Dist value contorts how far is the camera from the sphere's center (which is how much of the sphere will be captured by the camera). Note: this setting has no effect when the Auto-fit option is enabled.

Curve - this setting applies only to the Fish-eye camera. This setting contorts the way the rendered image is warped. A value of 1.0 corresponds to a real world Fish-eye camera. As the value approaches 0.0 the warping is increased. As the value approaches 2.0 the warping is reduced. Note: in fact this value controls the angle at which rays are reflected by the virtual sphere of the camera.

Type - from this list you can select the type of the camera. The available types are Standard, Spherical, Cylindrical (point), Cylindrical (ortho), Box, Fish eye. See the Examples section for a more detailed discussion on camera types.

Standard - this is a standard pinhole camera.

Spherical - this is a spherical camera which means that the camera lenses has spherical form.

Cylindrical (point) - with this type of camera all rays have a common origin - they are cast from the center of the cylinder. In the vertical direction the camera acts as a pinhole camera and in the horizontal direction it acts as a spherical camera.

Cylindrical (ortho) - in vertical direction the camera acts as an orthographic view and in the horizontal direction it acts as a spherical camera.

Box - the box camera is simply 6 standard cameras placed on the sides of a box. This type of camera is excellent for generation of environment maps for cube mapping. It may be very useful for GI too - you can calculate the irradiance map with a Box camera, save it to file and you can reuse it with a Standard camera that can be pointed at any direction.

Fish eye - this special type of camera captures the scene as if it is normal pinhole camera pointed at an absolutely reflective sphere which reflects the scene into the camera's shutter. You can use the Dist/FOV settings to control what part of the sphere will be captured by the camera. The red arc in the diagram corresponds to the FOV angle. Note that the sphere has always a radius of 1.0.

Depth of field

On - turns the depth-of-field effect on.

Aperture - this is the size of the virtual camera aperture, in world units. Small aperture sizes reduce the DOF effect, larger sizes produce more blur.

Center bias - this determines the uniformity of the DOF effect. A value of 0.0 means that light passes uniformly through the aperture. Positive values mean that light is concentrated towards the rim of the aperture, while negative values concentrate light at the center.

Focal distance - determines the distance from the camera at which objects will be in perfect focus. Objects closer or farther than that distance will be blurred.

Get from camera - when this option is on, the Focal distance is determined from the camera target, if the rendering is done from a camera view.

Sides - this option allows you to simulate the polygonal shape of the aperture of real-world cameras. When this option is off, the shape is assumed to be perfectly circular.

Rotation - specifies the orientation of the aperture shape.

Anisotropy - this option allows the stretching of the bokeh effect horizontally or vertically. Positive values stretch the effect in the vertical direction. Negative values stretch it in the horizontal direction.

Subdivs - controls the quality of the DOF effect. Lower values are computed faster, but produce more noise in the image. Higher values smooth out the noise, but take more time to render. Note that the quality of sampling also depends on the settings of the QMC sampler as well as on the chosen Image sampler.

Motion blur

On - turns motion blur on.

Duration - specifies the duration, in frames, during which the camera shutter is open.

Interval center - specifies the middle of the motion blur interval with respect to the 3dsmax frame. A value of 0.5 means that the middle of the motion blur interval is halfway between the frames. A value of 0.0 means that the middle of the interval is at the exact frame position.

Bias - this controls the bias of the motion blur effect. A value of 0.0 means that the light passes uniformly during the whole motion blur interval. Positive values mean that light is concentrated towards the end of the interval, while negative values concentrate light towards the beginning.

Prepass samples - this controls how many samples in time will be computed during irradiance map calculations.

Blur particles as mesh - this option controls the blurring of particle systems. When this is on, particles will be blurred like normal meshes. However, many particle systems change the number of particles between frames. You can turn off this option to compute the motion blur from the velocity of the particles instead.

Geometry samples - this determines the number of geometry segments used to approximate motion blur. Objects are assumed to move linearly between geometry samples. For fast rotating objects, you need to increase this to get correct motion blur. Note that more geometry samples increase the memory consumption, since more geometry copies are kept in memory.

Subdivs - determines the quality of the motion blur. Lower values are computed faster, but produce more noise in the image. Higher values smooth out the noise, but take more time to render. Note that the quality of sampling also depends on the settings of the QMC sampler as well as on the chosen Image sampler.

Notes

• Depth of field is supported only for the Standard camera type. Other camera types do not produce depth of field effect at this time.
• When DOF and motion blur are both enabled, they are sampled together using the higher of the two Subdivs parameters.

VRay Default Displacement

General

This section allows you to control displacement of objects with displacement materials, which do not have a VRayDisplacementMod modifier applied.

Parameters

Override Max's - when this option is on, VRay will render objects with displacement materials using its own internal microtriangle displacement. When this option is off, the objects will be rendered with the standard 3dsmax displacement.

Edge length - this determines the quality of the displacement. Each triangle of the original mesh is subdivided into a number of subtriangles. More subtriangles mean more detail in the displacement, slower rendering times and more RAM usage. Less subtriangles mean less detail, faster rendering and less RAM. The meaning of Edge length depends on the View-dependent parameter below.

View-dependent - when this is on, Edge length determines the maximum length of a subtriangle edge, in pixels. A value of 1.0 means that the longest edge of each subtriangle will be about one pixel long when projected on the screen. When View-dependent is off, Edge length is the maximum subtriangle edge length in world units.

Max. subdivs - this controls the maximum subtriangles generated from any triangle of the original mesh. The value is in fact the square root of the maximum number of subtriangles. For example, a value of 256 means that at most 256 x 256 = 65536 subtriangles will be generated for any given original triangle. It is not a good idea to keep this value very high. If you need to use higher values, it will be better to tesselate the original mesh itself into smaller triangles instead. From build 1.45.20 onward, the actual subdivisions for a triangle are rounded up to the nearest power of two (this makes it easier to avoid gaps because of different tesselation on neighboring triangles).

Tight bounds - when this is on, VRay will try to compute the exact bounding volume of the displaced triangles from the original mesh. This requires pre-sampling of the displacement texture, but the rendering will be faster, if the texture has large black or white areas. However, if the displacement texture is slow to evaluate and varies a lot between full black and white, if may be faster to turn this option off. When it is off, VRay will assume worst-case bounding volumes, and will not presample the texture.

Notes

• The default displacement amount is based on the bounding box of an object. Therefore, it is not a good choice when you have deforming objects. In that case, you should apply a VRayDisplacementMod modifier, which supports constant displacement amount.

VRay Color Mapping

Ray Color Mapping

Search keywords: color mapping, tone mapping, burn-out, overexpose

General

Color mapping (also called tone mapping) can be used to apply color transformations on the final image colors. Sometimes an image can contain a higher range of colors that can be displayed on a computer screen. Color mapping has the task of re-mapping the image values to be suitable for display purposes.

Parameters

Type - this is the type of transformation used. These are the possible types:

Linear multiply - this mode will simply multiply the final image colors based on their brightness are. Color components that are too bright (above 1.0 or 255) will be clipped. This can result in burnt out spots near bright light sources.

Exponential - this mode will saturate the colors based on their brightness. This can be useful to prevent burn-outs in very bright areas (for example around light sources etc). This mode will not clip bright colors, but will instead saturate them.

HSV exponential - this mode is very similar to the Exponential mode, but it will preserve the color hue and saturation, instead of washing out the color towards white.

Intensity exponential - this mode is similar to the Exponential one, but it will preserve the ratio of the RGB color components and will only affect the intensity of the colors.

Gamma correction - this mode applies a gamma curve to the colors. In this case, the Dark multiplier is a general multiplier for the colors before they are gamma-corrected. The Bright multiplier is the inverse of the gamma value (f.e. for gamma 2.2, the Bright multiplier must be 0.4545).

Intensity gamma - this mode applies a gamma curve to the intensity of the colors, instead of each channel (r/g/b) independently.

Reinhard - this mode is a blend between exponential-style color mapping and linear mapping. If the Burn value is 1.0, the result is linear color mapping and if the Burn value is 0.0, the result is exponential-style mapping.

Dark multiplier - this is the multiplier for dark colors.

Bright multiplier - this is the multiplier for bright colors.

Gamma - this parameter allows the user to control the gamma correction for the output image regardless of the color mapping mode. Note that the value here is the inverse of the one used for the Gamma correction color mapping type. For example, to correct the image for a 2.2-gamma display, you should set the Gamma parameter simply to 2.2.

Sub-pixel mapping - this option controls whether color mapping will be applied to the final image pixels, or to the individual sub-pixel samples. In older versions of VRay, this option was always assumed to be on, however its default value is now off as this produces more correct renderings, especially if you use the universal settings approach.

Affect background - if this is off, color mapping will not affect colors belonging to the background.

Clamp output - if this is on, colors will be clamped after color mapping. In some situations, this may be undesirable (for example, if you wish to antialias hdr parts of the image, too) - in that case, turn clamping off.

VRay Environment

General

The Environment section in VRay render parameters is where you can specify a color and a map to be used during GI and reflection/refraction calculations. If you don't specify a color/map then the MAX's background color and map will be used instead.

Parameters

GI Environment (skylight)

This group allows you to override the 3dsmax Environment settings for indirect illumination calculations. The effect of changing the GI environment is similar to skylight.

Override MAX's - with this option turned on VRay will use the specified environment color and/or texture during GI calculations.

Color - lets you specify the background (skylight) color.

Multiplier - a multiplier for the color value. Note that the multiplier does not affect the environment texture (if present). Use an Output map to control the brightness of the environment map if the map itself does not have brightness controls.

Texture - lets you choose a background texture.

Reflection/refraction environment

This group allows you to override the 3dsmax Environment settings when reflections and refractions are calculated. Note that you can also override the reflection/refraction environment on a per material basis (see VRayMtl) or a per map basis (see VRayMap).

Override MAX's - with this option turned on VRay will use the specified Color and Texture during GI and reflection/refraction calculations.

Color - lets you specify the background (skylight) color.

Multiplier - a multiplier for the color value. Note that the multiplier does not affect the environment texture (if present). Use an Output map to control the brightness of the environment map, if the map itself does not have brightness controls.

Texture - lets you choose a background texture

VRay Caustics

General

VRay supports the rendering of the caustics effects. In order to produce this effect you must have proper caustics generators and caustics receivers in the scene (for information how to make an object a caustics generator/receiver read the Object settings and Lights settings sections in Render parameters > System > Object/Light settings. The settings in this parameter section control the generation of the photon map (an explanation of the photon map can be found in the Terminology section).

Parameters

On - turns caustic on and off.

Multiplier - this multiplier controls the strength of the caustics. It is global and applies to all light sources that generate caustics. If you want different multipliers for the different light sources then you should use the local light settings. Note: this multiplier is cumulative with the multipliers in the local light settings.

Search dist - when VRay traces a photon that hits an object in some point the raytracer searches for other photons on the same plane in the surrounding area (search area). The search area in fact is a circle with center the original photon and its radius is equal to the Search dist value.

Max photons - when VRay traces a photon that hits an object in some point and counts the photons in the surrounding area it then averages the illumination of that area based on the number of the photons in it. If the photons are more than Max photons VRay will only take the first Max photons of them.

Max density - this parameter allows you to limit the resolution (and this the memory) of the photon map. Whenever VRay needs to store a new photon in the caustics photon map, it will first look if there are any other photons within a distance specified by Max density. If there is already a suitable photon in the map, VRay will just add the energy of the new photon to the one in the map. Otherwise, VRay will store the new photon in the photon map. Using this options allows you to shoot many photons (and thus get smoother results) while keeping the size of the caustics photon map manageable.

Mode - controls the mode of the irradiance map:

New map - when this option is selected a new photon map will be generated. It will overwrite any previous photon map left over from previous rendering.

Save to file - hit this button if you want to save an already generated photon map in a file.

From file - when you enable this option VRay will not compute the photon map but will load it from a file. Hit the Browse button on the right to specify the file name.

Don't delete - when checked, VRay will keep the photon map in memory after the scene rendering has finished. Otherwise the map will be deleted and the memory it takes will be freed. This option can be especially useful if you want to compute the photon map for a particular scene only once and then reuse it for further rendering.

Auto save - when this is turned on, VRay will automatically save the caustics photon map to the provided file when rendering is complete.

Switch to saved map - this option is only available if Auto save is on. It will cause VRay to automatically set the mode to From file with the file name of the newly saved map.

Notes

Caustics also depend on th

VRay rQMC Sampler

General

rQMC (randomized Quasi Monte Carlo) sampling is employed throughout VRay for every "blurry" value - antialiasing, depth of field, indirect illumination, area lights, glossy reflection/refraction, translucency, motion blur etc. rQMC sampling is used to determine what samples should be taken and, ultimately, which rays to trace.

Instead of having separate methods for sampling each of those blurry values, VRay has a single unified framework that determines how many and what exactly samples to be taken for a particular value, depending on the context in which that value is required. This framework is called the rQMC sampler.

Note that although similar in concept, the sampling method employed by VRay is different from strict QMC sampling in that the number sequences that are used have higher discrepancy than pure QMC methods (but still lower one compared to pure random Monte Carlo methods).

The actual number of samples for any blurry value is determined based on three factors:

• The subdivs value supplied by the user for a particular blurry effect. This is multiplied by the Global subdivs multiplier (see below).
• The importance of the value (for example, dark glossy reflections can do with fewer samples than bright ones, since the effect of the reflection on the final result is smaller; distant area lights require fewer samples than closer ones etc). Basing the number of samples allocated for a value on importance is called importance sampling.
• The variance (think "noise") of the samples taken for a particular value - if the samples are not very different from each other, then the value can do with fewer samples; if the samples are very different, then a larger number of them will be necessary to get a good result. This basically works by looking at the samples as they are computed one by one and deciding, after each new sample, if more samples are required. This technique is called early termination or adaptive sampling.

For more information on the relationship and effects of these parameters, please refer to the tutorials section.

Parameters

Amount - controls the extent to which the number of samples depends on the importance of a blurry value. It also controls the minimum number of samples that will be taken. A value of 1.0 means full adaptation; a value of 0.0 means no adaptation.

Min samples - determines the minimum number of samples that must be made before the early termination algorithm is used. Higher values will slow things down but will make the early termination algorithm more reliable.

Noise threshold - controls VRay's judgment of when a blurry value is "good enough" to be used. This directly translates to noise in the result. Smaller values mean less noise, more samples and higher quality. A value of 0.0 means that no adaptation will be performed.

Global subdivs multiplier - this will multiply all subdivs values everywhere during rendering; you can use this to quickly increase/decrease sampling quality everywhere. This affects everything, except for the lightmap, photon map, caustics and aa subdivs. Everything else (dof, moblur, irradiance map, qmc GI, area lights, area shadows, glossy reflections/refractions) is affected by this parameter.

Time independent - when this option is On, the rQMC pattern will be the same from frame to frame in an animation. Since this may be undesirable in some cases, you can turn this option Off to make the rQMC pattern change with time. Note that re-rendering the same frame will produce the same result in both cases.

VRay Global Photon Map

Ray Global Photon Map

General

The global photon map is somewhat similar to the irradiance map. It is also used to represent the lighting in the scene, and it is a collection of points in 3D space (a point cloud). However, the photon map is built in a different way. It is built by tracing particles (photons) emitted by the scene lights. Those photons bounce around the scene and hit various surfaces. The hit points are stored in the photon map.

Reconstructing the illumination from the photon map is also different from the irradiance map. With the irradiance map, a simple interpolation is used to blend the nearby GI samples. With the photon map, we need to estimate the photon density at a given point. The idea of density estimation is central to the photon map. VRay can use several methods for density estimation, each with its own advantages and disadvantages. Usually these methods are based on looking for the photons that are nearest to the shaded point.

Note that in general, the photon map provides a less accurate approximation of the scene illumination than the irradiance map, especially when it comes to small details. The irradiance map is built adaptively, whereas the photon map is not. Also a major disadvantage of the photon map is the boundary bias. This unwanted effect is mostly visible around corners and object edges, which appear darker than they should be. The irradiance map can also exhibit boundary bias, however its adaptive nature allows one to decrease the effect greatly. Another disadvantage of the photon map is that it cannot simulate illumination from skylight. This is because the photons need an actual surface to be emitted from. The skylight, at least in VRay, is not a surface actually present in the scene.

On the other hand, the photon map is view-independent and can be computed relatively quickly. This makes it ideal for approximating the scene illumination when used together with more accurate methods like direct computation or the irradiance map.

Parameters

Note that the building of the photon map is also controlled by the photon settings of individual lights in the scene. See the Light settings dialog for more information.

Bounces - this parameter controls the number of light bounces approximated by the photon map. More bounces produce a more reallistic result, but take more time and memory.

Auto search dist - when this is on, VRay will try to compute a suitable distance within which to search for photons. Sometimes the computed distance is ok, in other cases it might be too big (which will slow down the rendering) or too small (which will produce a more noisy result).

Search dist - this option is only available when Auto search dist is off. It allows you to specify the photon search distance manually. Keep in mind that this value depends on the size of your scene. Lower values will speed up the rendering but may produce more noisy results. Larger values will slow down the rendering but may produce smoother results.

Max photons - this option specifies how many photons will be taken into consideration when approximating the irradiance at the shaded point. More photons mean a smoother (and more blurry) result and may also slow down the rendering. Smaller values mean a more noisy result but will render faster.

Multipler - this allows you to control the brightness of the photon map.

Max density - this parameter allows you to limit the resolution (and thus the memory) of the photon map. Whenever VRay needs to store a new photon in the photon map, it will first look if there are any other photons within a distance specified by Max density. If there is already a suitable photon in the map, VRay will just add the energy of the new photon to the one in the map. Otherwise, VRay will store the new photon in the photon map. Using this options allows you to shoot many photons (and thus get smoother results) while keeping the size of the photon map manageable.

Convert to irradiance map - this will cause VRay to precompute the irradiance at the photon hit points stored in the photon map. This allows fewer photons to be used when interpolated the irradiance during rendering, while keeping the result relatively smooth. It is important to note that the resulting map stores irradiance, but is not the same as the irradiance cache used by VRay for primary diffuse bounces.

Interp. samples - this controls how many irradiance samples will be taken from the photon map once it is converted to an irradiance map. Larger values produce smoother results, but may be slower; smaller values produces more noisy results but rendering is faster.

Convex hull area estimate - when this is off, VRay will use a simplified algorithm for computing the area, covered by a number of photons (by only taking the distance to the farthest photon). This algorithm may cause corners to be darker. Using the convex hull area estimate avoids the dark corners problem, but is slower and not as robust.

Store direct light - when this is on, VRay will store direct illumination in the photon map as well. This may speed up the irradiance map or QMC GI, when used as a primary engine, and there are lots of lights in the scene. When this is off, direct lighting will be computed always by tracing the necessary rays. This may slow things down if there are lots of lights in the scene.

Retrace threshold - when this is greater than 0.0, VRay will use direct QMC GI near corners, instead of the photon map, in order to obtain a more accurate result and to avoid splotches in these areas. This may slow down the rendering. When this is 0.0, the photon map will be used always, which will be faster, but may produce artifacts near corners or in places where objects are close to each other.

Retrace bounces - controls how many bounces will be made when retracing corners. If Retrace threshold is 0.0, then this parameter is ignored. Typically this should be equal to the Bounces parameter.

Notes

• The photon map cannot simulate secondary illumination due to skylight. The photon map is mostly useful for interior scenes with artificial lighting or relatively small windows.
• The photon map works only with VRay materials. Standard materials will receive GI, but will not generate any photons.

VRay Quasi-Monte Carlo GI

Search Keywords: QMC, Quasi-Monte Carlo, GI

General

This section is available only if you have chosen Quasi-Monte Carlo GI as either the primary or the secondary GI engine.

The Quasi-Monte Carlo method for computing global illumination is a brute-force approach. It recomputes the GI value for every single shaded point separately and independently from other points. While very slow, this method is very accurate, especially if you have many small details in the scene.

To speed up Quasi-Monte Carlo GI, you can use a faster method (the photon map or the light map) for approximating secondary GI bounces, while using the Quasi-Monte Carlo method for the primary bounces.

Parameters

Subdivs - this determines the number of samples used to approximate GI. Note that this is not the exact number of rays that VRay will trace. The number of rays is proportional to the square of this number, but also depends on the settings in the QMC sampler rollout. Depth - this parameter is available only if Quasi-Monte Carlo GI is selected as a secondary GI engine. It co

VRay Light Cache

General

Light caching (sometimes also called light mapping) is a technique for approximating the global illumination in a scene. This method was developed originally by Chaos Group specifically for the VRay renderer. It is very similar to photon mapping, but without many of its limitations.

The light cache is built by tracing many many eye paths from the camera. Each of the bounces in the path stores the illumination from the rest of the path into a 3d structure, very similar to the photon map. On the other hand, in a sense, it is the exact opposite of the photon map, which traces paths from the lights, and stores the accumulated energy from the beginning of the path into the photon map.

Although very simple, the light-caching approach has many advantages over the photon map:

• It is easier to set up. We only have the camera to trace rays from, as opposed to the photon map, which must process each light in the scene and usually requires separate setup for each light.
• The light-caching approach works efficiently with any lights - including skylight, self-illuminated objects, non-physical lights, photometric lights etc. In contrast, the photon map is limited in the lighting effects it can reproduce - for example, the photon map cannot reproduce the illumination from skylight or from standard omni lights without inverse-square falloff.
• The light cache produces correct results in corners and around small objects. The photon map, on the other hand, relies on tricky density estimation schemes, which often produce wrong results in these cases, either darkening or brightening those areas.
• In many cases the light cache can be visualized directly for very fast and smooth previews of the lighting in the scene.

Even with these advantages, light caching is similar in speed to the photon map and can produce approximations to the global lighting in a scene very quickly. In addition, the light cache can be used successfully for adding GI effects to animations.

Of course, the light cache has some limitations:

• Like the irradiance map, it is view-dependent and is generated for a particular position of the camera.
• Like the photon map, the light cache is not adaptive. The illumination is computed at a fixed resolution, which is determined by the user.
• The light cache does not work very well with bump maps.

Parameters

Subdivs - this determines how many paths are traced from the camera. The actual number of paths is the square of the subdivs (the default 1000 subdivs mean that 1 000 000 paths will be traced from the camera).

Sample size - this determines the spacing of the samples in the light cache. Smaller numbers mean that the samples will be closer to each other, the light cache will preserve sharp details in lighting, but it will be more noisy and will take more memory. Larger numbers will smooth out the light cache but will loose detail. This value can be either in world units or relative to the image size, depending on light cache Scale mode.

Scale - this parameter determines the units of the Sample size and the Filter size:

Screen - the units are fractions of the final image (a value of 1.0 means the samples will be as large as the whole image). Samples that are closer to the camera will be smaller, and samples that are far away will be larger. Note that the units do not depend on the image resolution. This value is best suited for stills or animations where the light cache needs to be computed at each frame.

World - the sizes are fixed in world units everywhere. This can affect the quality of the samples - samples that are close to the camera will be sampled more often and will appear smoother, while samples that are far away will be noisier. This value might work better for fly-through animations, since it will force constant sample density everywhere.

Store direct light - with this option, the light cache will also store and interpolate direct light. This can be useful for scenes with many lights and irradiance map or direct GI method for the primary diffuse bounces, since direct lighting will be computed from the light cache, instead of sampling each and every light. Note that only the diffuse illumination produced by the scene lights will be stored. If you want to use the light cache directly for approximating the GI while keeping the direct lighting sharp, uncheck this option.

Show calc. phase - turning this option on will show the paths that are traced. This does not affect the calculation of the light cache and is provided only as a feedback to the user. This option is ignored when rendering to fields - in that case, the calculation phase is never displayed.

Pre-filter - when this is turned on, the samples in the light cache are filtered before rendering. Note that this is different from the normal light cache filtering (see below) which happens during rendering. Prefiltering is performed by examining each sample in turn, and modifying it so that it represents the average of the given number of nearby samples. More prefilter samples mean a more blurry and less noisy light cache. Prefiltering is computed once after a new light cache is computed or loaded from disk.

Filter - this determines the type of render-time filter for the light cache. The filter determines how irradiance is interpolated from the samples in the light cache.

None - no filtering is performed. The nearest sample to the shaded point is taken as the irradiance value. This is the fastest option, but it may produce artifacts near corners, if the light cache is noisy. You can use pre-filtering (see above) to decrease that noise. This option works best if the light cache is used for secondary bounces only or for testing purposes.

Nearest - this filter looks up the nearest samples to the shading point and averages their value. This filter is not suitable for direct visualization of the light cache, but is useful if you use the light cache for secondary bounces. A property of this filter is that is adapts to the sample density of the light cache and is computed for a nearly constant time. The Interpolation samples parameter determines how many of the nearest samples to look up from the light cache.

Fixed - this filter looks up and averages all samples from the light cache that fall within a certain distance from the shaded point. This filter produces smooth results and is suitable for direct visualization of the light cache (when it is used as the primary GI engine). The size of the filter is determined by the Filter size parameter. Larger values blur the light cache and smooth out noise. Typical values for the Filter size are 2-6 times larger than the Sample size. Note that Filter size uses the same scale as the Sample size and its meaning depends on the Scale parameter.

Use light cache for glossy rays - if this option is on, the light cache will be used to compute lighting for glossy rays as well, in addition to normal GI rays. This can speed up rendering of scenes with glossy reflections quite a lot.

Number of passes - the light cache is computed in several passes, which are then combined into the final light cache. Each pass is rendered in a separate thread independently of the other passes. This ensures that the light cache is consistent across computers with different number of CPUs. In general, a light cache computed with smaller number of passes may be less noisy than a light cache computed with more passes, for the same number of samples; however small number of passes cannot be distributed effectively across several threads.

For single-processor non-hyperthreading machines, the number of passes can be set to 1 for best results.

Mode - determines the rendering mode of the light cache:

Progressive path tracing - in this mode, the light cache algorithm is used to sample the final image progressively. For a discussion of this mode see the tutorial.

Single frame - this will compute a new light cache for each frame of an animation.

Fly-through - this will compute a light cache for an entire fly-through animation, assuming that the camera position/orientation is the only thing that changes. The movement of the camera in the active time segment only is taken in consideration. Note that it may be better to use World Scale for fly-through animations. The light cache is computed only at the first rendered frame and is reused without changes for subsequent frames.

From file - in this mode the light cache is loaded from a file. The light cache file does not include the prefiltering of the light cache; prefiltering is performed after the light cache is loaded, so that you can adjust it without the need to recompute the light cache.

Notes

• Do not set the Adaptation by importance amount in the QMC sampler rollup to 0.0 when using the light cache, as this will cause excessive render times.
• Do not apply perfectly white or very close to white materials to a majority of the objects in the scene, as this will cause excessive render times. This is because the amount of reflected light in the scene will decrease very gradually and the light cache will have to trace longer paths. Also avoid materials that have one of their RGB components set to maximum (255) or above.
• If you want to use the light cache for animation, you should choose a large enough value for the Filter size in order to remove the flickering in the GI.
• There is no difference between light caches computed for primary bounces (direct visualization) and for secondary bounces. You can safely use light caches computed in one of these modes for the other.
• Similar to the photon map, you can get "light leaks" with the light cache around very thin surfaces with substantially different illumination on both sides. Currently there is no way to avoid this, except to avoid having very thin objects; also the effec

VRay Irradiance map

General

This section allows the user to control and fine-tune various aspects of the irradiance map. This section is enabled only when the irradiance map is chosen as the GI method for primary diffuse bounces.

Some background for understanding how the irradiance map works is necessary in order to grasp the meaning of these parameters.

Irradiance is a function defined for any point in the 3D space and represents the light arriving at this point from all possible directions. In general, irradiance is different in every point and in every direction. However, there are two useful restrictions that can be made. The first is the surface irradiance - which is the irradiance arriving at points which lie on the surface of objects in the scene. This is a natural restriction since we are usually interested in the illumination of objects in the scene, and objects are usually defined through their surface. The second restriction is that of diffuse surface irradiance - which is the total amount of light arriving at a given surface point, disregarding the direction from which it comes.

In more simple terms, one can think of the diffuse surface irradiance as being the visible color of a surface, if we assume that its material is purely white and diffuse.

In VRay, the term irradiance map refers to a method of efficiently computing the diffuse surface irradiance for objects in the scene. Since not all parts of the scene have the same detail in indirect illumination, it makes sense to compute GI more accurately in the important parts (e.g. where objects are close to each other, or in places with sharp GI shadows), and less accurately in uninteresting parts (e.g. large uniformly lit areas). The irradiance map is therefore built adaptively. This is done by rendering the image several times (each rendering is called a pass) with the rendering resolution being doubled with each pass. The idea is to start with a low resolution (say a quarter of the resolution of the final image) and work up to the final image resolution.

The irradiance map is in fact a collection of points in 3d space (a point cloud) along with the computed indirect illumination at those points. When an object is hit during a GI pass, VRay looks into the irradiance map to see if there are any points similar in position and orientation to the current one. From those already computed points, VRay can extract various information (i.e. if there are any objects close by, how fast the indirect illumination is varying etc). Based on that information, VRay decides if the indirect illumination for the current point can be adequately interpolated from the points already in the irradiance map, or not. If not, the indirect illumination for the current point is computed, and that point is stored in the irradiance map.

Parameters

Built-in presets

Current preset - this dropdown list allows you to choose from several presets for some of the irradiance map parameters. You can use these to quickly set the color, normal and distance thresholds, as well as the min/max rates. The following presets are available:

• Very low - this preset is only useful for preview purposes to show the general lighting in the scene.
• Low - a low-quality preset for preview purposes
• Medium - a medium quality preset; works fine in many situations in scenes which have don't small details.
• Medium animation - a medium quality preset targeted at reducing flickering in animations - the Distance threshold is higher.
• High - a high-quality preset that works in most situations, even for scenes with small details as well as for most animations.
• High animation - a high-quality preset that can be used if the High preset produces flickering in animations - the Distance threshold is higher.
• Very high - a very high quality preset; can be used for scenes with extremely small and intricate details.

Note that the presets are targeted for a typical 640x480 image. Larger images usually can do with lower Min/Max rates than those specified in the presets.

Basic parameters

Min rate - this value determines the resolution for the first GI pass. A value of 0 means the resolution will be the same as the resolution of the final rendered image, which will make the irradiance map similar to the direct computation method. A value of -1 means the resolution will be half that of the final image and so on. You would usually want to keep this negative, so that GI is quickly computed for large and flat regions in the image. This parameter is similar to (although not the same as) the Min rate parameter of the Adaptive subdivision image sampler.

Max rate - this value determines the resolution of the last GI pass. This is similar to (although not the same as) the Max rate parameter of the Adaptive subdivision image sampler.

Color threshold (Clr thresh) - this parameter controls how sensitive the irradiance map algorithm is to changes in indirect lighting. Larger values mean less sensitivity; smaller values make the irradiance map more sensitive to light changes (thus producing higher quality images).

Normal threshold (Nrm thresh) - this parameter controls how sensitive the irradiance map is to changes in surface normals and small surface details. Larger values mean less sensitivity; smaller values make the irradiance map more sensitive to surface curvature and small details.

Distance threshold (Dist thresh) - this parameter controls how sensitive the irradiance map is to distance between surfaces. A value of 0.0 means the irradiance map will not depend on object proximity at all; higher values place more samples in places where objects are close to each other.

Hemispheric subdivs (HSph. subdivs) - this controls the quality of individual GI samples. Smaller values make things faster, but may produce blotchy result. Higher values produce smoother images. This is similar to the Subdivs parameter for direct computation. Note that this is not the actual number of rays that will be traced. The actual number of rays is proportional to the square of this value and also depends on the settings in the rQMC sampler rollout.

Interpolation samples (Interp. samples) - this is the number of GI samples that will be used to interpolate the indirect illumination at a given point. Larger values tend to blur the detail in GI although the result will be smoother. Smaller values produce results with more detail, but may produce blotchiness if low Hemispheric subdivs are used.

Options

Show samples - when this option is on, VRay will show visually the samples in the irradiance map as small dots in the scene.

Show calc phase - when this option is on, VRay will show the irradiance map passes as the irradiance map is calculated. This will give you a rough idea of the indirect illumination even before the final rendering is complete. Note that turning this on slows the calculations a little bit, especially for large images. This option is ignored when rendering to fields - in that case, the calculation phase is never displayed.

Show direct light - this option is only available when Show calc phase is on. It will cause VRay to show direct lighting for primary diffuse bounces in addition to indirect lighting while the irradiance map is being calculated. Note that VRay does not really need to compute this. The option is only for convenience. This does not mean that direct lighting is not calculated at all - it is, but only for secondary diffuse bounces (only for GI purposes).

Detail enhancement

Detail enhancement is a method for bringing additional detail to the irradiance map in the case where there are small details in the image. Due to its limited resolution, the irradiance map typically blurs the GI in these areas or produces splotchy and flickering results. The detail enhancement option is a way to calculate those smaller details with a high-precision QMC sampling method. This is similar to how an ambient occlusion pass works, but is more precise as it takes into account bounced light.

On - turns on detail enhancement for the irradiance map. Note that an irradiance map calculated in this mode should not be used without the detail option. When detail enhancement is On, you can use lower irradiance map settings and higher Interpolation samples. This is because the irradiance map is only used to capture the general far-off lighting, while direct sampling is used for the closer detail areas.

Scale - this determines the units for the Radius parameter:

Screen - the radius is in image pixels.

World - the radius is in world units.

Radius - this determines the radius for the detail enhancement effect. Smaller radius means that smaller parts around the details in the image are sampled with higher precision - this would be faster but may be less precise. Larger radius means that more of the scene will use the higher precision sampling and may be slower, but more precise. This is similar to a radius parameter for an ambient occlusion pass.

Subdivs mult. - this determines the number of samples taken for the high-precision sampling as a percentage of the irradiance map Hemispheric subdivs. A value of 1.0 means that the same number of subdivs will be used as for the regular irradiance map samples. Lower values will make the detail-enhanced areas more noisy, but faster to render.

Advanced options

Interpolation type - this option is used during rendering. It selects the method for interpolating the GI value from the samples in the irradiance map.

Weighted average - this method will do a simple blend between the GI samples in the irradiance map based on the distance to the point of interpolation and the difference in the normals. While simple and fast, this method tends to produce a blochiness in the result

Least squares fit - the default method; it will try to compute a GI value that best fits in among the samples from the irradiance map. Produces smoother results than the weighted average method, but is slower. Also, ringing artifacts may appear in places where both the contrast and density of the irradiance map samples change over a small area.

Delone triangulation - all other methods of interpolation are blurry methods - that is, they will tend to blur the details in indirect illumination. Also, the blurry methods are prone to density bias (see below for a description). In difference, the Delone triangulation method is a non-blurry method and will preserve the detail while avoiding density bias. Since it is non-blurry, the result might look more noisy (blurring tends to hide noise). More samples will be needed to get a sufficiently smooth result. This can be done either by increasing the hemispheric subdivs of the irradiance map samples, or by decreasing the Noise threshold value in the QMC sampler rollout.

Least squares with Voronoi weights - this is a modification of the least squares fit method aimed at avoiding the ringing at sharp boundaries by taking in consideration the density of the samples in the irradiance map. The method is quite slow and its effectiveness is currently somewhat questionable.

Although all interpolation types have their uses, it probably makes most sense to use either Least squares fit or Delone triangulation. Being a blurry method, Least squares fit will hide noise and will produce a smooth result. It is perfect for scenes with large smooth surfaces. Delone triangulation is a more exact method, which usually requires more hemispheric subdivs and high Max irradiance map rate (and therefore more rendering time), but produces accurate results without blurring. This is especially obvious in scenes where there are a lot of small details.

Sample lookup - this option is used during rendering. It selects the method of choosing suitable points from the irradiance map to be used as basis for the interpolation.

Nearest - this method will simply choose those samples from the irradiance map which are closest to the point of interpolation. (How many points will be chosen is determined by the value of the Interpolation samples parameter.) This is the fastest lookup method and was the only one available in early versions of VRay. A drawback of this method is that in places where the density of the samples in the irradiance map changes, it will pick more samples from the area with higher density. When a blurry interpolation method is used, this leads to the so-called density bias which may lead to incorrect interpolation and artifacts in such places (mostly GI shadow boundaries).

Nearest quad-balanced - this is an extension of the nearest lookup method aimed at avoiding density bias. It divides the space about the interpolated point in four areas and tries to find an equal number of samples in all of them (hence the name quad-balanced). The method is a little slower than the simple Nearest lookup, but in general performs very well. A drawback is that sometimes, in its attempt to find samples, it may pick samples that are far away and not relevant to the interpolated point.

Precalculated overlapping - this method was introduced in an attempt to avoid the drawbacks of the two previous ones. It requires a preprocessing step of the samples in the irradiance map during which a radius of influence is computed for each sample. This radius is larger for samples in places of low density, and smaller for places of higher density. When interpolating the irradiance at a point, the method will choose every sample that contains that point within its radius of influence. An advantage of this method is that when used with a blurry interpolation method it producses a continuous (smooth) function. Even though the method requires a preprocessing step, it is often faster than the other two. These two properties make it ideal for high-quality results. A drawback of this method is that sometimes lonely samples that are far-away can influence the wrong part of the scene. Also, it tends to blur the GI solution more than the other methods.

Density-based - the default method; it combines the Nearest and the Precalculated overlapping methods and is very effective in reducing ringing artifacts and artifacts due to low sampling rates. This method also requires a preprocessing step in order to compute sample density, but it performs a nearest neighbour look-up to choose the most suitable samples while taking sample density in account.

Being the fastest of the three methods, Nearest lookup may be used for preview purposes. Nearest quad-balanced performs fairly well in the majority of cases. Precalculated overlapping is fast and in many cases performs very well, but may tend to blur the GI solution. The Density-based method produces very good results in the majority of cases and is the default method.

Note that the lookup method is mostly important when using a blurry interpolation method. When using Delone triangulation, the sample lookup method does not influence the result very much.

Calc. pass interpolation samples - this is used during irradiance map calculation. It represents the number of already computed samples that will be used to guide the sampling algorithm. Good values are between 10 and 25. Low values may speed the calculation pass, but may not provide sufficient information. Higher values will be slower and will cause additional sampling. In general, this parameter should be left to the default value of 15.

Use current pass samples - this is used during irradiance map calculation. When checked, this will cause VRay to use all irradiance map samples computed so far. Unchecking it will allow VRay to use only samples collected during previous passes, but not those computing earlier during the current pass. Keeping this checked will usually cause VRay to take less samples (and therefore compute the irradiance map faster). That means that on multiprocessor machines, several threads will be modifying the irradiance map at the same time. Because of the asynchronous nature of this process, there is no guarantee that the rendering the same image twice will produce the same irradiance map. Normally this is not a problem at all and it is recommended to keep this option checked.

Randomize samples - this is used during irradiance map calculation. When it is checked, the image samples will be randomly jittered. Unchecking it will produce samples that are aligned in a grid on the screen. In general, this option should be kept checked in order to avoid artifacts caused by regular sampling.

Check sample visibility - this is used during rendering. It will cause VRay to use only those samples from the irradiance map, which are directly visible from the interpolated point. This may be useful for preventing "light leaks" through thin walls with very different illumination on both sides. However it will also slow the rendering, since VRay will trace additional rays to determine sample visibility.

Mode

Mode - this groups of controls allow the user to select the way the irradiance map is (re)used.

Bucket mode - in this mode, a separate irradiance map is used for each rendered region ("bucket"). This is especially useful since it allows the irradiance map computations to be effectively distributed among several computers when using distributed rendering. Bucket mode can be slower that the Single frame mode, since an additional border must be computed around each region in order to reduce edge artifacts between neighboring regions. Even so, there may be such artifacts. They can be further reduced by using higher settings for the irradiance map (the High preset, more hemispheric subdivs and/or smaller Noise threshold for the QMC sampler).

Single frame - the default mode; a single irradiance map is computed for the whole image, and a new irradiance map is computed for each frame. During distributed rendering, each render server will compute its own full-image irradiance map. This is the mode to use when rendering animations of moving objects. In doing so one must make sure that the irradiance map is of sufficiently high quality to avoid flickering.

Multiframe incremental - this mode is useful when rendering a sequence of frames (not necessarily consequtive) where only the camera moves around (so-called fly-through animations). VRay will compute a new full-image irradiance map for the first rendered frame; for all other frames VRay will try to reuse and refine the irradiance map that has been computed so far. If the irradiance map is of sufficiently high quality as to avoid flickering, this mode can also be used in network rendering - each rendering server will compute and refine its own local irradiance map.

From file - in this mode VRay will simply load the irradiance map from the supplied file at the start of the rendering sequence and will use this map for all the frames in the animation. No new irradiance map will be computed. This mode can be used for fly-through animations and will work well in network rendering mode.

Add to current map - in this mode VRay will compute a completely new irradiance map and will add it to the map that is already in memory. This mode is useful when compiling an irradiance map to render multiple views of a static scene.

Incremental add to current map - in this mode VRay will use the irradiance map that is already in memory and will only refine it in places that don't have enough detail. This mode is useful when compiling an irradiance map to render multiple views of a static scene or a fly-through animation.

The irradiance map mode that should be used depends on the particular rendering task - a static scene, a static scene rendered from multiple views, a fly-through animation or an animation with moving objects. Refer to the tutorials section for more information.

Irradiance map control buttons

There are some more buttons in this group that allow one to perform certain operations on the irradiance map:

Browse - this button allows the user to select the irradiance map file which will be loaded if the From file mode is selected. Alternatively, the user can enter the path and name of the file directly in the edit box.

Save to file - this will save to file the irradiance map which is currently in memory. Note that the Don't delete option in the On render end group must be turned on. Otherwise VRay will automatically delete the irradiance map at the end of the rendering process.

Reset irradiance map - this will clear the irradiance map from memory.

On render end

This group of controls instructs VRay what to do with the irradiance map at the end of the rendering process.

Don't delete - the default for this option is on, which means that VRay will keep the irradiance map in memory until the next rendering. If this option is cleared, VRay will delete the irradiance map when rendering is complete. This means that you will not be able to save the map manually afterwards.

Auto save - if this option is set, VRay will automatically save the irradiance map to the specified file at the end of the rendering. This mode is particularly useful if you want to send the irradiance map for rendering on a different machine through network rendering.

Switch to saved map - this option is only available if the Auto save option is turned on. If Switch to saved map is on, then VRay will also automatically set the irradiance map mode to From file and will set the file name to be that of the map that was just saved.

VRay Indirect illumination (GI)

General

Approaches to indirect illumination

VRay implements several approaches for computing indirect illumination with different trade-offs between quality and speed:

• Direct computation - this is the simplest approach; indirect illumination is computed independently for each shaded surface point by tracing a number of rays in different directions on the hemisphere above that point.
  
  Advantages:
  • this approach preserves all the detail (e.g. small and sharp shadows) in the indirect lighting;
  • direct computation is free from defects like flickering in animations;
  • no additional memory is required;
  • indirect illumination in the case of motion-blurred moving objects is computed correctly.
    
  Disadvantages:
  • the approach is very slow for complex images (e.g. interior lighting);
  • direct computation tends to produce noise in the images, which can be avoided only by shooting a larger number of rays, thus slowing it even more.
    
• Irradiance map - this approach is based on irradiance caching; the basic idea is to compute the indirect illumination only at some points in the scene, and interpolate for the rest of the points.
  
  Advantages:
  • the irradiance map is very fast compared to direct computation, especially for scenes with large flat areas;
  • the noise inherent to direct computation is greatly reduced;
  • the irradiance map can be saved an re-used to speed up calculations of different views for the same scene and of fly-through animations;
  • the irradiance map can also be used to accelerate direct diffuse lighting from area light sources.
    
  Disadvantages:
  • some details in indirect lighting can be lost or blurred due to the interpolation;
  • if low settings are used, flickering may occur when rendering animations;
  • the irradiance map requires additional memory;
  • indirect illumination with motion-blurred moving objects is not entirely correct and may lead to noise (although in most cases this is not noticeable).
    
• Photon map - this approach is based on tracing particles starting from the light sources and bouncing around the scene. This is useful for interior or semi-interior scenes whith lots of lights or small windows. The photon map usually does not produce good enough results to be used directly; however it can be used as a rough approximation to the lighting in the scene to speed the calculation of GI through direct computation or irradiance map.
  
  Advantages:
  • the photon map can produce a rough approximation of the lighting in the scene very quickly;
  • the photon map can be saved an re-used to speed up calculation of different views for the same scene and of fly-through animations;
  • the photon map is view-independent.
    
  Disadvantages:
  • the photon map usually is not suitable for direct visualization;
  • requires additional memory;
  • in VRay's implementation, illumination involving motion-blurred moving objects is not entirely correct (although this is not a problem in most cases).
  • the photon map needs actual lights in order to work; it cannot be used to produce indirect illumination caused by environment lights (skylight).
    
• Light map - light mapping is a technique for approximating the global illumination in a scene. It is very similar to photon mapping, but without many of its limitations. The light map is built by tracing many many eye paths from the camera. Each of the bounces in the path stores the illumination from the rest of the path into a 3d structure, very similar to the photon map. The light map is a universal GI solution that can be used for both interior or exterior scenes, either directly or as a secondary bounce approximation when used with the irradiance map or the direct GI method.
  
  Advantages:
  • the lightmap is easy to set up. We only have the camera to trace rays from, as opposed to the photon map, which must process each light in the scene and usually requires separate setup for each light.
  • the light-mapping approach works efficiently with any lights - including skylight, self-illuminated objects, non-physical lights, photometric lights etc. In contrast, the photon map is limited in the lighting effects it can reproduce - for example, the photon map cannot reproduce the illumination from skylight or from standard omni lights without inverse-square falloff.
  • the light map produces correct results in corners and around small objects. The photon map, on the other hand, relies on tricky density estimation schemes, which often produce wrong results in these cases, either darkening or brightening those areas.
  • in many cases the light map can be visualized directly for very fast and smooth previews of the lighting in the scene.

  Disadvantages:

  • like the irradiance map, the light map is view-dependent and is generated for a particular position of the camera. However, it generates an approximation for indirectly visible parts of the scene as well - for example, one light map can approximate completely the GI in a closed room;
  • currently the light map works only with VRay materials;
  • like the photon map, the light map is not adaptive. The irradiance is computed at a fixed resolution, which is determined by the user;
  • the light map does not work very well with bump maps; use the irradiance map or direct GI if you want to achieve better results with bump maps.
  • lighting involving motion-blurred moving objects is not entirely correct, but is very smooth since the lightmap blurs GI in time as well (as opposed to the irradiance map, where each sample is computed at a particular instant of time).

Which method to use? That depends on the task at hand. The Examples section can help you in choosing a suitable method for your scene.

Primary and secondary bounces

The indirect illumination controls in VRay are divided into two large sections: controls concerning primary diffuse bounces and controls concerning secondary diffuse bounces. A primary diffuse bounce occurs when a shaded point is directly visible by the camera, or through specular reflective or refractive surfaces. A secondary bounce occurs when a shaded point is used in GI calculations.

Parameters

On - turns indirect illumination on and off.

GI caustics

GI caustics represent light that has gone through one diffuse, and one or several specular reflections (or refractions). GI caustics can can be generated by skylight, or self-illuminated objects, for example. However, caustics caused by direct lights cannot be simulated in this way. You must use the separate Caustics section to control direct light caustics. Note that GI caustics are usually hard to sample and may introduce noise in the GI solution.

Refractive GI caustics - this allows indirect lighting to pass through transparent objects (glass etc). Note that this is not the same as Caustics, which represent direct light going through transparent objects. You need refractive GI caustics to get skylight through windows, for example.

Reflective GI caustics - this allows indirect light to be reflected from specular objects (mirrors etc). Note that this is not the same as Caustics, which represent direct light going through specular surfaces. This is off by default, becase reflective GI caustics usually contribute little to the final illumination, while often they produce undesired sublte noise.

Post-processing

These controls allow additional modification of the indirect illumination, before it is added to the final rendering. The default values ensure a physically accurate result; however the user may want to modify the way GI looks for artistic purposes.

Saturation - controls the saturation of the GI; a value of 0.0 means that all color will be removed from the GI solution and will be in shades of grey only. The default value of 1.0 means the GI solution remains unmodified. Values above 1.0 boost the colors in the GI solution.

Contrast - this parameter works together with Contrast base to boost the contrast of the GI solution. When Contrast is 0.0, the GI solution becomes completely uniform with the value defined by Contrast base. A value of 1.0 means the solution remains unmodified. Values higher that 1.0 boost the contrast.

Contrast base - this parameter determines the base for the contrast boost. It defines the GI values that remain unchanged during the contrast calculations.

Save maps per frame - if this is on, VRay will save the GI maps (irradiance, photon, caustic, light maps) that have the auto-save option enabled, at the end of each frame. Note that the maps will always be written to the same file. If this option is off, VRay will write the maps only once at the end of the rendering.

First (primary) diffuse bounces

Multiplier - this value determines how much primary diffuse bounces contribute to the final image illumination. Note that the default value of 1.0 produces a physically accurate image. Other values are possible, but not physically plausible.

Primary GI engine - the list box specifies the method to be used for primary diffuse bounces.

Irradiance map - selecting this will cause VRay to use an irradiance map for primary diffuse bounces. See the Irradiance map section for more information.

Global photon map - selecting this option will cause VRay to use a photon map for primary diffuse bounces. This mode is useful when setting up the parameters of the global photon map. Usually it does not produce good enough results for final renderings when used as a primary GI engine. See the Global photon map section for more information.

Quasi-Monte Carlo - selecting this method will cause VRay to use direct computation for primary diffuse bounces. See the Quasi-Monte Carlo GI section for more information.

Light map - this chooses the light map as the primary GI engine. See the Light map section for more information.

Secondary diffuse bounces

Multiplier - this determines the effect of secondary diffuse bounces on the scene illumination. Values close to 1.0 may tend to wash out the scene, while values around 0.0 may produce a dark image. Note that the default value of 1.0 produces physically accurate results. While other values are possible, they are not physically plausible.

Secondary diffuse bounces method - this parameter determines how VRay will calculate secondary diffuse bounces.

None - no secondary bounces will be computed. Use this option to produce skylit images without indirect color bleeding.

Global photon map - selecting this option will cause VRay to use a photon map for primary diffuse bounces. This mode is useful when setting up the parameters of the global photon map. Usually it does not produce good enough results for final renderings when used as a primary GI engine. See the Global photon map section for more information.

Quasi-Monte Carlo - selecting this method will cause VRay to use direct computation for primary diffuse bounces. See the Quasi-Monte Carlo GI section for more information.

Light map - this chooses the light map as the primary GI engine. See the Light map section for more information.

Notes

• VRay does not have a separate skylight system. The skylight effect can be achieved by setting the background color or environment map in MAX's environment dialog, or in VRay's own Environment rollout.
• You will get physically accurate lighting if you set both the primary and secondary GI multipliers to their default value of 1.0. While other values are possible, they will not produce a physically accurate result.