Select the rendering engine.

Determines how the image will be rendered.

Note: When rendering for IPR, Karma will use progressive rendering until the IPR preview passes are complete.

Karma breaks down an image into multiple buckets for rendering. This is the side length (in pixels) of the square bucket. The default is 32, specifying a 32 pixel x 32 pixel bucket. Threads operate at the bucket level, so it might be useful to lower the bucket size if there are only a few buckets that are particularly expensive. That way the expensive areas can be divided across more threads.

For example, if the image is mostly empty, but there’s a distant object that fits within single 32 x 32 bucket, then that object will only be rendered using 1 thread. If you switch to a 16 x 16 bucket, then the object might be split across 4 buckets and have 4 threads working on it.

Ideally changing the bucket size doesn’t change the results, but Karma measures variance across pixels within the current bucket, so if you set it to a low value, for example 4, Karma only has 4 x 4 = 16 pixels to look at, so Karma will tend to make very poor variance estimates. This can show up as black pixels, where pixel rendering terminated prematurely due to a bad variance estimate.

Specifies which buckets are rendered first. Values can be:

Note: When rendering to mplay, the user can click to focus on an area to render.

The number of transparent samples to be shaded as a ray travels through partially opaque objects. Increasing this value will result in less noise in partially opaque objects and is generally less costly than increasing Pixel samples, Volume Step Rate, or Min and Max ray samples. This parameter will not have any effect on noise from Indirect Sources however.

When set to Path Traced, maximum of 1 indirect ray is generated per bounce. When set to Automatic, the number of indirect rays is calculated based on initial noise estimate, target noise threshold, and the maximum number of camera rays. Also note that under Automatic mode, number of samples for direct lighting is adjusted based on noise estimate as well.

Depth at which indirect rays start to get stochastically pruned based on ray throughput.

Whether Karma should perform uniform sampling of lights or whether rendering should use the light tree. The light tree can be significantly faster for scenes that have large numbers of lights.

Some lights cannot be added to the light tree, and will all be sampled by Karma:

• Dome Lights

• Distant Lights

• Point Lights

• Lights with Light Filters

• Lights with shaping controls (i.e. spot lights)

This is a global control to improve sampling quality for all lights. This acts as a multiplier on the individual light quality controls. Increasing the quality will improve direct light sampling as well as shadows/occlusion.

If this is on, Karma does a pre-render to roughly estimate of the light in the scene, and uses that to guide indirect diffuse rays, rather than just relying on the BSDF sampling distribution. This can improve “difficult” lighting (for example, caustics, and mostly indirect lighting), but can make “easy” lighting noisier. Before using this, you can try rendering direct and indirect AOVs to see where the noise is. If the noise is mostly caused by the direct lighting, there’s no point in turning on path guiding.

Number of pixel samples to use for prepass render when Indirect Guiding is enabled. Recommended minimum is 10% of pixel samples under Path Traced convergence mode, or the same number of pixel samples under Automatic convergence mode. Grid-like artifacts can show up in the final render when this value is too low and not enough data is collected. It’s recommended to keep this value above 64.

Applies blur to spatial component of path guiding samples while training. Can be increased to reduce grid-like artifacts at the cost of efficiency.

Applies blur to directional component of path guiding samples while training. Can be increased to reduce grid-like artifacts at the cost of efficiency.

The minimum distance used when testing if secondary rays from a surface intersect with other objects in the scene. The distance is measure from surface along the direction of the ray. Objects within the ray bias distance are ignored.

Roughness parameter in GGX BSDFs are clamped by the maximum roughness value propagated down the ray chain in pathtracing. Enabling this option can cut out a lot of noise in indirect specular (in particular, cases where glossy surface is reflected by a rough specular surface) at the cost of a bit of accuracy.

The maximum value a shading sample is allowed to contribute to an LPE image plane to reduce appearance of “fireflies” caused by undersampling of extremely bright light sources. Note that reducing this value can result in an overall reduction in the amount of light in your scene.

When enabled, indirect bounces use Color Limit value and Indirect Color Limit parameter is ignored.

Color limit applied to indirect bounce only. Note that this parameter is ignored unless Shared Color Limit toggle is disabled.

Enable depth of field rendering.

If there are no lights in the scene, a headlight is created by default. To disable, turn off this checkbox.

Disable all lighting and material evaluation, using only the display color to shade primitives.

When rendering in headlight mode, perform this many ambient occlusion samples per shade.

When rendering in headlight mode with ambient occlusion shading, this distance is used for occlusion testing. Smaller values will result in faster, but less accurate shading.

The color of the depthcue fog for disabled lighting.

The alpha for depthcue fog when lighting is disabled.

The near/far distance for depth cue fog when lighting is disabled. If the far distance is less than the near distance, fog will be disabled.

Specifies a camera that is used for dicing complicated surfaces. This can provide consistent dicing of surfaces when the viewing camera is moving.

This parameter controls the shading quality scale factor for geometry that is not directly visible to the camera. For geometry that is outside the field of view (ie. visible only to secondary rays), karma will smoothly reduce the shading quality based on the angle between the geometry and the edge of the viewing frustum. Smaller values can increase performance particularly in scenes where the camera is within the displacement bound of nearby geometry, where it permits the hidden primitives to be diced more coarsely than those that are directly visible.

This parameter is a global multiplier for dicing quality of all objects.

Image filters post-process the filtered pixels to produce the final image. This parameter takes a string containg a JSON-encoded list of filters and their arguments. Usually you don’t need to craft this value by hand, it’s computed by the Karma LOP from the values of filter-related parameters. See Karma filters for more information.

Specifies the distribution of samples over pixels. A box filter will distribute samples randomly over the interior of each individual pixel. A Gaussian filter will distribute samples in a disk around the pixel center, but with a Gaussian distribution (instead of a uniform distribution).

This is the size of the Pixel Filter. A Guassian filter with a filter size of 1.8 will be slightly less blurry than a Gaussian filter with a filter size of 2.0.

Sample filters are used to modify samples before they are sent to pixel filters.

This parameter specifies a list of filters. These filters are specified as a JSON list.

When rendering, a Pixel Oracle tells karma which pixels need additional sampling and which pixels are converged. This parameter tells karma which oracle to use.

“Off” disables Background IPR Filter. “Auto” enables it only for IPR. “On” enables it for both IPR and off-line rendering.

JSON list of image filters specifically for background image preview and slap-comp of shadows and other holdout elements.

Whether to use a fixed size cache (karma:global:cachesize) or whether to use a proportion of physical memory (karma:global:cacheratio)

The proportion of physical memory Karma will use for its unified cache.

For example, with the default vm_cacheratio of 0.25 and 16 Gb of physical memory, Karma will use 4 Gb for its unified cache.

The unified cache stores dynamic, unloadable data used by the render including the following:

• 2D .rat texture tiles

• 3D .i3d texture tiles

• 3D .pc point cloud pages (when not preloaded into memory)

Note: This value is only used for off-line rendering, not IPR.

An explicit memory limit for the unified shading cache. This is deprecated in favor of using the Cache Memory Ratio.

Note: This value is only used for off-line rendering, not IPR.

Normally, geometry settings specified in the render settings LOP provide default values for objects. Each object can override the value of the default.

This parameter specifies a pattern of object property names whose values will taken from the render settings, overriding any per-object settings. For example, setting the pattern to “diffuselimit” will override the diffuse limit for all objects with the value specified on the render settings LOP.

This is the random seed to use for the render.

Enabling this option will cause karma to stop the render with an error if it encounters a missing texture map.

A whitespace-separated list of shading component names that will be computed for export. If you have defined new component labels in your materials, these can be added to the list so that they are exported for per-component export planes. If you are not using some components, remove them from the list to improve render efficiency.

PBR light exports assume that this list is complete - that is, all components created by shaders are listed. If there are unlisted components, light exports may be missing illumination from these components.

A space-separated list of component types that will behave like diffuse bounces. This will affect which reflection scope is used based on the ray type and also which bounce limit to use. Uncategorized component types are assumed to be reflections.

A space-separated list of component types that will behave like refract bounces. This will affect which reflection scope is used based on the ray type and also which bounce limit to use. Uncategorized component types are assumed to be reflections.

A space-separated list of component types that will behave like volume bounces. This will affect which reflection scope is used based on the ray type and also which bounce limit to use. Uncategorized component types are assumed to be reflections.

A space-separated list of component types that will behave like subsurface scatter bounces. This will affect which reflection scope is used based on the ray type and also which bounce limit to use. Uncategorized component types are assumed to be reflections.

Whether to enable motion blur. Changing this in the display options will require a restart of the render.

This parameter lets you choose what type of geometry velocity blur to do on an object, if any. Separate from transform blur and deformation blur, you can render motion blur based on point movement, using attributes stored on the points that record change over time. You should use this type of blur if the number points in the geometry changes over time (for example, a particle simulation where points are born and die).

If your geometry changes topology frame-to-frame, Karma will not be able to interpolate the geometry to correctly calculate Motion Blur. In these cases, motion blur can use a velocities and/or accelerations attribute which is consistent even while the underlying geometry is changing. The surface of a fluid simulation is a good example of this. In this case, and other types of simulation data, the solvers will automatically create the velocity attribute.

When this is set to “Velocity Blur” or “Acceleration Blur”, deformation blur is not applied to the object. When this is set to “Acceleration Blur”, use the karma:object:geosamples property to set the number of acceleration samples.

The number of sub-frame samples to compute when rendering deformation motion blur over the shutter open time. The default is 1 (sample only at the start of the shutter time), giving no deformation blur by default. If you want rapidly deforming geometry to blur properly, you must increase this value to 2 or more. Note that this value is limited by the number of sub-samples available in the USD file being rendered. An exception to this is the USD Skel deformer which allows.

“Deformation” may refer to simple transformations at the Geometry (SOP) level, or actual surface deformation, such as a character or object which changes shape rapidly over the course of a frame.

Objects whose deformations are quite complex within a single frame will require a higher number of Geo Time Samples.

Deformation blur also lets you blur attribute change over the shutter time. For example, if point colors are changing rapidly as the object moves, you can blur the Cd attribute.

Increasing the number of Geo Time Samples can have an impact on the amount of memory Karma uses. For each additional Sample, Karma must retain a copy of the geometry in memory while it samples across the shutter time. When optimizing your renders, it is a good idea to find the minimum number of Geo Time Samples necessary to create a smooth motion trail.

Deformation blur is ignored for objects that have Velocity motion blur turned on.

The number of samples to compute when rendering transformation motion blur over the shutter open time. The default is 2 samples (at the start and end of the shutter time), giving one blurred segment.

If you have object moving and changing direction extremely quickly, you might want to increase the number of samples to capture the sub-frame direction changes.

In the above example, it requires 40 transformation samples to correctly render the complex motion that occurs within one frame. (This amount of change within a single frame is very unusual and only used as a demonstration.)

Transformation blur simulates blur by interpolating each object’s transformation between frames, so it’s cheap to compute but does not capture surface deformation. To enable blurring deforming geometry, increase karma:object:geosamples.

When defining motion blur on instances, the transform of each instance can be blurred in addition to any motion blur occurring on the prototype. This option controls how the instance will compute the motion blur of the transform on each instance. For example, when instancing prototypes to a particle system, you'd likely want to use velocity blur to compute motion blur (the transform on the prototype would be blurred by the velocity on the particles).

When motion blur on instances is computed using Accleration Blur or Deformation Blur, this parameter specifies the number of motion segments used for motion blur.

Velocity multiplier used to reduce or exaggerate amount of motion blur on volumes.

Specifies the quality of indirect diffuse shading. A value of one translates to roughly one additional diffuse sample per shading computation. A sample of 4 translates to roughly 4 additional diffuse samples per shading computation.

Specifies the quality of indirect reflection shading. A value of one translates to roughly one additional reflection sample per shading computation. A sample of 4 translates to roughly 4 additional reflection samples per shading computation.

Specifies the quality of indirect refraction shading. A value of one translates to roughly one additional refraction sample per shading computation. A sample of 4 translates to roughly 4 additional refraction samples per shading computation.

Specifies the quality of indirect volumetric shading. A value of one translates to roughly one additional volumetric sample per shading computation. A sample of 4 translates to roughly 4 additional volumetric samples per shading computation.

Specifies the quality of indirect sub-surface scattering shading. A value of one translates to roughly one additional sub-surface scattering sample per shading computation. A sample of 4 translates to roughly 4 additional sub-surface scattering samples per shading computation.

How finely or coarsely a volume is sampled as a ray travels through it. Volumetric objects are made up of 3d structures called Voxels, the value of this parameter represents the number of voxels a ray will travel through before performing another sample.

The default value is 0.25, which means that every one of every four voxels will be sampled. A value of 1 would mean that all voxels are sampled and a value of 2 would mean that all voxels are sampled twice. This means that the volume step rate value behaves in a similar way to pixel samples, acting as a multiplier on the total number of samples for volumetric objects.

Keep in mind that increasing the volume step rate can dramatically increase render times, so it should only be adjusted when necessary. Also, while increasing the default from 0.25 can reduce volumetric noise, increasing the value beyond 1 will rarely see similar results.

Noise threshold to determine the number of indirect rays cast for indirect bounce when the Convergence Mode is set to “Automatic”. Decreasing this threshold (for example, to 0.001) will theoretically send more indirect rays and decrease noise, however the “extra” rays will likely be cancelled out by the Max Ray Samples parameter. The correct way to decrease noise is to increase the number of samples per pixel, rather than change this threshold.

If you are using Variance Pixel Oracle, you should set the same value for both threshold parameters. Setting the oracle’s threshold lower may make the indirect component reach its threshold sooner and cast fewer indirect rays, but the oracle decides to cast more expensive camera rays because the amount of final noise in the beauty pass is higher than the oracle’s threshold.

Minimum number of rays to cast in per-component variance anti-aliasing.

Maximum number of rays to cast in per-component variance anti-aliasing.

Some volume primitives can use a filter during evaluation of volume channels. This specifies the filter. The default box filter is fast to evaluate and produces sharp renders for most smooth fluid simulations. If your voxel data contains aliasing (stairstepping along edges), you may need to use a larger filter width or smoother filter to produce acceptable results. For aliased volume data, gauss is a good filter with a filter width of 1.5.

• point

• box

• gauss

• bartlett

• blackman

• catrom

• hanning

• mitchell

This specifies the filter width for the “Volume Filter” property. The filter width is specified in number of voxels. Larger filter widths take longer to render and produce blurrier renders, but may be necessary to combat aliasing in some kinds of voxel data.

The number of times diffuse rays can propagate through your scene.

Unlike the Reflect and Refract Limits, this parameter will increase the overall amount of light in your scene and contribute to the majority of global illumination. With this parameter set above zero diffuse surfaces will accumulate light from other objects in addition to direct light sources.

In this example, increasing the Diffuse Limit has a dramatic effect on the appearance of the final image. To replicate realistic lighting conditions, it is often necessary to increase the Diffuse Limit. However, since the amount of light contribution usually decreases with each diffuse bounce, increasing the Diffuse Limit beyond 4 does little to improve the visual fidelity of a scene. Additionally, increasing the Diffuse Limit can dramatically increase noise levels and render times.

The number of times a ray can be reflected in your scene.

This example shows a classic “Hall of Mirrors” scenario with the subject placed between two mirrors.

This effectively creates an infinite series of reflections.

From this camera angle the reflection limits are very obvious and have a large impact on the accuracy of the final image. However, in most cases the reflection limit will be more subtle, allowing you to reduce the number of reflections in your scene and optimize the time it takes to render them.

Remember that the first time a light source is reflected in an object, it is considered a direct reflection. Therefore, even with Reflect Limit set to 0, you will still see specular reflections of light sources.

This parameter control the number of times a ray be refracted in your scene.

This example shows a simple scene with ten grids all in a row.

By applying a refractive shader, we will be able see through the grids to an image of a sunset in the background.

From this camera angle, in order for the image to be accurate, the refraction limit must match the number of grids that that are in the scene. However, most scenes will not have this number of refractive objects all in a row and so it is possible to reduce the refract limit without affecting the final image while also reducing the time it takes to render them.

Keep in mind that this Refract Limit refers to the number of surfaces that the ray must travel through, not the number of objects.

Remember that the first time a light source is refracted through a surface, it is considered a direct refraction. Therefore, even with Refract Limit set to 0, you will see refractions of Light Sources. However, since most objects in your scene will have at least two surfaces between it and the light source, direct refractions are often not evident in your final render.

The number of times a volumetric ray can propagate through a scene. It functions in a similar fashion to the Diffuse Limit parameter.

Increasing the Volume Limit parameter will result in much more realistic volumetric effects. This is especially noticeable in situations where only part of a volume is receiving direct lighting. Also, in order for a volumetric object to receive indirect light from other objects, the Volume Limit parameter must be set above 0.

With the Volume Limit set to values above zero, the fog volume takes on the characteristic light scattering you would expect from light traveling through a volume. However, as with the Diffuse Limit, the light contribution generally decreases with each bounced ray and therefore using values above 4 does not necessarily result in a noticeably more realistic image.

Also, increasing the value of this parameter can dramatically increase the amount of time spent rendering volumetric images.

The number of times a SSS ray can propagate through a scene. It functions in a similar fashion to the Diffuse Limit parameter.

Whether to render this object as if it was a uniform-density volume. Using this property on surface geometry is more efficient than actually creating a volume object of uniform density, since the renderer can assume that the volume density is uniform and place samples more optimally. The surface normal of the surface is used to determine which side of the surface will render as a volume - the normal will point away from the interior. The surface need not be closed - if the surface is not closed, the volume will extend an infinite distance away from the surface. Non-closed surfaces may produce unexpected results near the edge of the surface, so try to keep the viewing camera away from the edges.

Determines how the samples are distributed when rendering a uniform volume (karma:object:volumeuniform is enabled). This parameter must match the density on the uniform volume shader in order to produce correct results.

The number of samples to generate when rendering a uniform volume (karma:object:volumeuniform is enabled). The samples will be distributed so as to produce an equal image contribution if they were all equal in brightness.

Controls the visibility of an object to different types of rays using a category expression. This parameter generalizes the Phantom and Renderable toggles and allows more specific control over the visibility of an object to the different ray types supported by karma and VEX.

For example, to create a phantom object, set the expression to “-primary”. To create an unrenderable object, set the expression to the empty string “”. These tokens correspond to the string given to “raystyle” in the VEX trace() and gather() functions.

If there are no normals on an object, any edges with a dihedral angle greater than this value will be cusped. For compatibility with mantra, Karma will also look for a detail attribute named vm_cuspangle (which takes priority over the setting).

When this is set to “Matte” mode, the object will be considered to be a cutout matte. Any lighting contribution and alpha of the object will be redirected to LPE AOVs with “holdouts” prefix. Holdout Mode does not affect the utility AOVs such as ray:hitP and ray:hitN. “Background” mode is similar to “Matte”, except it’s used for background plate so it will appear “pre-lit” in indirect bounces, multiplied by shadow contribution. Diffuse albedo of the shader is used to determine the pre-lit irradiance.

Adjust shading position of shadow rays to avoid self-shadowing artifact on low-poly mesh due to discrepancy between smooth normals and face normals.

Custom label assigned to lights or objects for use with light path expression.

For compound BSDFs with refractive components, only apply direct lighting for lights that belong in specified location. A light ray facing the same direction as geometry normal is considered “Outside”. For transparent material that are solid/closed-manifold, setting this parameter to “Outside” can improve render performance by reducing noise in direct lighting and cut down on wasted shadow rays.

Allows evaluation of glossy BSDF that’s seen by indirect diffuse bounce. This is a brute-force solution which may require significant number of diffuse rays to resolve, especially if Caustics Roughness Clamp parameter is set to very small value or Indirect Guiding feature is disabled.

Increasing this value can make caustics less noisy at the cost of accuracy.

Any object with an emissive material will generate light within the scene. If an object is significant enough (eg size, brightness, etc…) then it is possible for Karma to treat that object as if it were an explicit lightsource (similar to regular lights), meaning the emitted light will be handled much more efficiently. But doing so will add extra overhead elsewhere in the system (eg increased memory usage, slower update times, etc…).

There are three options. “No” will set the object as not being a lightsource. “Yes” will set the object as being a lightsource. “Auto” (default) means Karma will use an internal heuristic to decide if the object should be treated as a lightsource.

A multiplier for the effect of this emissive object on the diffuse, SSS, and volume response of materials

A multiplier for the effect of this emissive object on the reflection and refraction response of materials

When enabled, the object will turn into a “light portal” that only lets in certain portion of dome lights based on portal geometry visibility.

Space-separated list of dome lights to associate this portal with.

When rendering point clouds, they can be rendered as camera oriented discs, spheres or discs oriented to the normal attribute.

When rendering curves, they can be rendered as ribbons oriented to face the camera, rounded tubes or ribbons oriented to the normal attribute attached to the points.

USD supports Curve Basis types that may not be supported directly in Houdini. In some cases, you may want to override the Houdini curve basis. For example, if you have linear curves in Houdini, you may want to render them with a Bezier, B-Spline or Catmull-Rom basis. This menu will force Karma to override the basis that’s tied to the USD primitives.

Note that the topology of the curves must match the target basis. For example, when selecting any cubic curve basis, every curves must have at least 4 vertices. For the Bezier basis, curves must have 4 + 3*N vertices.

If enabled, geometry that are facing away from the camera are not rendered.

This parameter controls the geometric subdivision resolution for smooth surfaces (subdivision surfaces and displaced surfaces). With all other parameters at their defaults, a value of 1 means that approximately 1 micropolygon will be created per pixel. A higher value will generate smaller micropolygons meaning that more shading will occur - but the quality will be higher.

The effect of changing the shading quality is to increase or decrease the amount of shading by a factor of karma:object:dicingquality squared - so a shading quality of 2 will perform 4 times as much shading and a shading quality of 0.5 will perform 1/4 times as much shading.

This property controls the tesselation levels for nearly flat primitives. By increasing the value, more primitives will be considered flat and will be sub-divided less. Turn this option down for more accurate (less optimized) nearly-flat surfaces.