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Direct Lighting
Direct Lighting renders previews faster. Direct Lighting is not unbiased, and shouldn't be used when you are aiming for photorealism. However, it is useful when creating quick animations or renders (Figure 1).
Figure 1: The Direct Lighting kernel parameters
Direct Lighting Kernel Parameters
Quality
- Max. Samples - This sets the maximum number of samples per pixel before the rendering process stops. The higher the number of samples per pixel, the cleaner the render. For quick animations and scenes with predominantly direct lighting, a low amount of samples (500-1000) will suffice. In scenes with lots of indirect lighting and mesh lights, you may need several thousand samples to get a clean render.
- Global Illumination Mode - There are three different modes:
- None - Only direct lighting from the sun or area lights is included. Shadowed areas receive no contribution and are black.
- Ambient Occlusion - Standard ambient occlusion. This mode often provides realistic images, but offers no color bleeding.
- - Indirect diffuse, with a configuration to set the number of indirect diffuse bounces. This gives a Global Illumination quality that is in between Ambient Occlusion and Pathtracing, but without caustics. It is much faster than Pathtracing and PMC.
- Depth - Controls the number of times a ray can refract before dying. Higher numbers mean higher render times, but more color bleeding and more details in transparent materials. Low numbers introduce artifacts or turn some refractions into pure black.
- Glossy Depth - Controls the number of times a ray can reflect before dying. Higher numbers mean higher render times, and numbers below 4 can introduce artifacts or turn some reflections into pure black.
- Diffuse Depth - Gives the maximum number of diffuse reflections when you set Global Illumination Mode to Diffuse.
- Ray Epsilon - The distance to offset new rays so they don't intersect with the originating geometry. If a scene's scale is too large, precision artifacts like concentric circles can appear. In that case, increasing Ray Epsilon makes the artifacts disappear.
- Filter Size - Sets the pixel size for filtering the render, and improves aliasing artifacts in the render. This can also reduce noise, but if you set the filter too high, then the image becomes blurry.
- AO Distance - Ambient Occlusion distance in units.
- AO Ambient Texture - Sets the Ambient Occlusion environment texture for AO rays. If this isn't specified, OctaneRender® uses the environment instead.
- Alpha Shadows - Allows any object with transparency (Specular materials, materials with opacity settings and alpha channels) to cast a proper shadow instead of behaving as a solid object.
- Irradiance Mode - Renders the first surface as a white . This mode is similar to Clay Mode - however, it only applies to the first bounce. It disables the Bump channel and makes samples that are blocked by back faces transparent.
Alpha Channel
- Alpha Channel - Removes the background and renders it transparent (zero alpha). This is useful for compositing the render over another image without the background being present.
- Keep Environment - Used with the Alpha Channel setting. It allows OctaneRender to render the background with zero alpha, but the background is still visible in the final render. This gives more flexibility to compositing images.
Light
Sampling
- Path Term. Power - This parameter provides a system to tweak samples/second vs. convergence (how fast noise vanishes). Increasing this value causes the kernels to keep shorter paths and spend less time on dark areas (meaning they stay noisy longer), but it increases samples/second. Reducing this value causes kernels to trace longer paths on average, and spend more time on dark areas. In short, high values increase the render speed, but leads to higher noise in dark areas.
- Coherent Ratio - When enabled for Path Tracing or Direct Lighting kernels, the render becomes noise-free faster. However, it also causes flickering while rendering animations. For still images and action-heavy animations, this option saves some time.
- Static Noise - When enabled, the noise is static (doesn't change between frames). This is disabled by default. The noise is fully static as long as you use the same GPU architecture for rendering. Using different architectures produces slightly different numerical errors, which manifest as small differences in noise patterns every time rendering restarts on the frame.
- Parallel Samples - Controls how many samples are calculated in parallel. If set to a small value, OctaneRender requires less memory to store the samples state, but renders are slower. If set to a high value, then OctaneRender needs more graphics memory, but renders are faster. The change in performance depends on the scene, the GPU architecture, and the number of shader processors available on the GPU.
- Max. Tile Samples - Controls the number of samples per pixel that OctaneRender uses for rendering before it stores the result in the film buffer. Higher numbers mean results arrive less often at the film buffer, but it reduces CPU overhead during rendering, which improves performance.
- Minimize Net Traffic - When enabled, OctaneRender distributes only the same tile to the net render slaves until it reaches the max samples/pixel for that tile, and then OctaneRender distributes the next tile to the slaves. This option doesn't affect work done by local GPUs.
Adaptive Sampling
- Adaptive Sampling - Provides options to the kernel to disable sampling for pixels that reach a specified noise level.
- Noise Threshold - Specifies the smallest relative noise level. When a pixel's noise estimate is less than this value, then the pixel's sampling switches off. You can get good values in the range of 0.01 to 0.03. The default is 0.02.
- Min. Adaptive Samples - Specifies the minimum number of samples to calculate before adaptive sampling activates. The noise estimate of a pixel is just an estimate with a large initial error, so the higher the noise threshold, the higher you should set this parameter to avoid artifacts.
- Pixel Grouping - Specifies the number of pixels that are handled together. If all pixels of a group have reached the specified noise level, sampling stops for these pixels.
- Expected Exposure - This value should be close to the same value as the image exposure, otherwise set it to 0 to ignore these settings. The default value is 0. Adaptive sampling uses this parameter to determine the bright and dark pixels, which depends on the Exposure setting in the OctaneRender Imager. If the value is not 0, Adaptive Sampling tweaks/reduces the noise estimate of very dark areas of the image. It also increases the Min. Adaptive Samples limit for very dark areas, because very dark areas don't always find paths to light sources, resulting in over-optimistic noise estimates.
Deep Image
- Deep Image - Enables rendering deep pixel images used for deep image compositing.
- Maximum Depth Samples - Sets the maximum number of depth samples per pixel. The PBR Render Target uses this when you enable Deep Image rendering.
- Depth Tolerance - OctaneRender merges the depth samples whose relative depth difference falls below this tolerance value. The PBR Render Target uses this when you enable Deep Image rendering.
Toon Shading
- Toon Shadow Ambient - Ambient modifier for Toon Shadowing.
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