Sampling - Advanced

Tabble Of Contents

• Overview
• Sampling
• Unified Sampling
• Filter
• Overrides
• Denoising
• Optix Settings
• Altus Settings
• Texture Sampling

Overview

Sampling

Interactive Rendering

Sets which rendering mode will be used when starting an Interactive Rendering session, like when hitting the Start / Stop IPR button found in the Redshift Render View.

• Progressive (default) - Intended for fast interactive feedback that favors speed over clean renders.
• Bucket - Intended for high quality final renders that favors high quality clean renders over speed.

Final Rendering

Sets which rendering mode will be used when starting a new Render / Batch Render, like when hitting the Render button found in the  Redshift Render View.

• Progressive - Intended for fast interactive feedback that favors speed over clean renders.
• Bucket (default) - Intended for high quality final renders that high quality clean renders over speed. Bucket mode is always recommended for final renders .

Rendering Modes

Bucket

Bucket rendering refers to Redshift's high quality final rendering mode. Bucket mode splits the framebuffer into a grid of squares to be worked on one at a time until the entire framebuffer is finished rendering. These squares are referred to as buckets and systems with more than one GPU will render multiple buckets at a time. A bucket is only ever rendered by a single GPU, so the maximum number of simultaneous bucket renders is limited by the number of GPUs setup for rendering in Redshift.

Bucket mode supports all renderer features and uses unified sampling.

Progressive 

Progressive rendering refers to Redshift's interactive rendering mode. It renders the framebuffer in multiple passes which start noisy and get progressively cleaner. It is useful for getting fast feedback when shaders, meshes or lights are edited.

Progressive rendering is controlled exclusively by the Progressive Passes setting.

When progressive rendering is enabled, certain renderer features and options have no effect. These are:

• All unified sampling settings (including filtering)
• Point-based subsurface scattering. If you're using point-based SSS, ray-traced SSS (with equivalent settings) will be used instead when doing progressive rendering.
• Photon mapping (including caustics). Redshift's photon mapping implementation is computed as a separate pass so it's only available to production (non-progressive) renders
• Irradiance cache, irradiance point cloud. These are not needed because progressive rendering computes GI in a brute-force way.
• All parameters that have to do with "number of samples". Examples include the number of samples for Depth-Of-Field, number of samples for glossy reflections or refractions, number of area light samples, etc.

Progressive Passes

Controls the maximum number of passes that Progressive rendering mode can reach and therefore controls the maximum achievable visual quality of Progressive mode. The higher the number of Progressive Passes the higher the render quality and the less visual noise, default is 1024 passes.

Since Progressive mode can be used in either Interactive Rendering or Final Rendering the behavior of this setting differs depending on the rendering mode and the situation.

• Progressive Passes with Interactive Rendering - In Interactive Rendering the Progressive render will only reach the maximum number of Progressive Passes if given the necessary amount of time between scene edits and changes. 
  • For example: If a scene edit takes place before the maximum number of Progressive Passes is reached then a new updated Progressive render will be started and again begin to build back up to the maximum number of Progressive Passes.

• Progressive Passes with Final Rendering - In Final Rendering the Progressive render will always reach the maximum number of Progressive passes before moving on to the next frame, no more and no fewer.
  • For example: If your maximum number of Progressive Passes is set to 64 then each frame will be rendered for as long as it takes to reach the 64th pass. Once the 64th pass is reached, Redshift will move onto the next frame and then start the process over for each frame until the entire batch is finished.

Unified Sampling

Automatic Sampling

When enabled Redshift will automatically optimize the sample counts per-pixel by using 'Automatic Sampling' which aims to simplify scene setup by removing any reliance on manually tweaking sample counts. The minimum and maximum number of samples to shoot per pixel is controlled by Redshift in relation to the noise present in the scene and the value set by the Threshold parameter.

When disabled, Redshift will disable 'Automatic Sampling' at which point the Samples Min and Samples Max parameters are revealed so you can manually control the minimum and maximum number of samples to shoot per pixel.

The Threshold parameter is still used when Automatic Sampling is disabled but it operates within the confines of the manually set Samples Min and Samples Max parameters. 

Threshold

This setting controls how sensitive the noise detection algorithm will be. Threshold may also be referred to as the 'Adaptive Error Threshold.;

• Lower numbers detect noise more aggressively which means that more rays will be shot per pixel - resulting in less visual noise.
• Higher numbers detect noise less aggressively which means fewer rays will be shot per pixel - resulting in more visual noise.

It is recommended that you use the 'show samples' feature to visualize the effect of this setting. The default 0.01 value should work well for a variety of scenes. For production-quality results, we recommend lower settings such as 0.003.

Threshold: 0.100 Render Time (Min:Sec) : 0:44 Automatic Sampling: Enabled	0.010 3:20	0.005 7:53	0.001 22:50

Show Samples

This option enables a debug rendering mode which shows the numbers of rays that were shot for each pixel in a grayscale form.

Darker pixels mean that fewer rays were shot while brighter pixels mean that more rays were shot. A pure white color means that 'max samples' rays were shot for that pixel.

When Show Samples is enabled, the noisy parts of the image will typically be brighter because the unified sampler will shoot more rays to try and clean up the noise. 

Random Noise Pattern

When enabled Redshift will randomise the sampling noise pattern on each frame, by default this is enabled.

Techniques such as depth of field, motion blur, brute-force GI, glossy reflections/refractions, AO and area lighting share the same noise pattern so when sample counts for these effects are not high enough and the noise is visible, noise can appear to be 'stuck' on the camera when rendering an animation. Randomize Noise Pattern makes the noise look more like moving TV static or film grain. In some cases this can be more visually appealing.

 

Filter

The Filter defines how the per-pixel samples will be combined together to produce the final pixel color together with the filter Size parameter. There are five options:

• Box - blurriest filter
• Triangle
• Gauss (default) - most "neutral" filter
• Mitchell
• Lanczos - sharpest filter

You can control the final 'blurriness' of the filter using the "Filter Size" parameter. A thing to remember here is that, the sharper the filter type, the larger the filter size typically needs to be. For example, Gaussian filters work fine with values like 2.0, 2.5 and 3.0 while Mitchell typically works best with values like 3.0, 4.0 or 5.0.
A sharpening filter such as Mitchell or Lanczos in conjunction with a small filter size (like 2.0) will accentuate pixel 'jaggies' as well as noise!

Size

The filter Size controls the final "blurriness" of the filter. In general the sharper the filter type the larger the filter size needs to be.

For example, Gaussian filters work fine with values like 2.0, 2.5 and 3.0 while Mitchell typically works best with values like 3.0, 4.0 or 5.0.

Filter: Gauss Size 2.0 A bit too sharp around the rings.	Gauss 2.0 A bit too sharp around the rings.	Mitchell 2.0 Very sharp features. Almost as if antialiasing is disabled. Mitchell filters require larger sizes!	Mitchell 3.0 Still a bit aliased but looking better.	Mitchell 4.0 Sharp and relatively smooth. The Mitchell filter typically works best with sizes like 4.0 and 5.0

Max Subsample Intensity

Limits the maximum value of intensity for each individual sample. The higher the 'Max Subsample Intensity' the harder the renderer has to work to antialias the image.

Usually monitors can show colors ranging from black (0.0, 0.0, 0.0) to white (1.0, 1.0, 1.0). Any color that is brighter than white (like 10.0, for example) will still be rendered as white. But the internal workings of a renderer  do care about these "overbright" colors.

Scenes containing very bright lighting and/or strong emissive materials can be very hard to antialias. The reason has to do with sample filtering: say a pixel was rendered with 64 samples. If most of these samples are mid-gray (0.5, 0.5, 0.5) but there is a single sample that is extremely bright (100.0, 100.0, 100.0), that sample will 'dominate' the final pixel color.

Max Subsample Intensity: 128 All the rings are smooth except the self- illuminated one. That part of the image looks as if no antialiasing is enabled.	4.0 While there is a little bit of improvement, the self- illuminating ring still shows aliasing artifacts!	1.0 The self-illuminating ring now renders smoothly.

Max Secondary Ray Intensity

Limits the maximum intensity value for secondary rays like glossy reflection and global illumination rays.

This feature is useful for reducing fire-flies that may appear in glossy reflections or refractions, which can occur when a small percentage of rays are unlucky enough to sample extremely hot light sources, while most of the rays do not. The ideal solution would be to use as many rays as it takes to clean up the noise caused by fire-flies, but often this is not practical since many thousand, if not infinite, ray samples would be required.

Clamping glossy samples is a simple (though not physically correct) solution, which helps ensure that hot samples are no brighter than a specified maximum amount.

Denoising

Enabled

The Denoising Enabled checkbox allows you to quickly toggle denoising on and off.

Denoising lets you easily render images at a reduced baseline quality (lower sample counts) and increased speed at the expense of some potential accuracy. Denoising can only do so much and a balance must be struck between the baseline unified sampling quality and the denoising engine of choice in order to find what works best for your project. For more information please see  this page.

Engine

Sets the denoising engine used when denoising is enabled.

Redshift has three built-in denoising engines and they can easily be switched between here, each one with their own general pros and cons.

• OptiX - Very fast and can be used during interactive rendering but can have more trouble cleaning noise compared to alternatives. 
• Altust Single - Slower (renders the frame once before denoising) and non-interactive but produces good results for final quality renders. 
• Altus Dual - Slowest (renders the frame twice before denoising) and non-interactive but produces great results for final quality renders.

For more information on Denoising and the different Denoising Engines please see  this page.

The images below were rendered with low sample counts in order to better demonstrate the differences of the different Denoising Engines.

Denoising: Off Render Time (Min:Sec) : 0:43	OptiX 0:44	Altus Single 0:49	Altus Dual 1:24

Denoise AOVs

When enabled - by default, it allows Redshift to denoise AOVs.

When disabled, denoising will not occur on AOVs even if denoising is enabled at the individual AOV level.

Automatically Create AOVs

When enabled - by default, Redshift will automatically add any AOVs that are needed to achieve its denoising results for the specified denoising engine. When disabled the user will need to manually add the necessary AOVs depending on the current denoising engine.

• AOVs used by Altus - Diffuse Albedo, World Position and Bump Normals
• AOVs used by Optix - Diffuse Albedo and Bump Normals

Show Additional Buffers

When enabled the additional image buffers used for denoising are revealed in the Render View AOV list. This can be useful when diagnosing denoising.

While Redshift is rendering it generates additional images ("buffers") which are essential for the denoising process. These buffers are normally hidden from  Redshift's Render View but if you enable "Show Additional Buffers", those buffers will appear in the Render View's AOV list and will be previewable. 

Save Additional Buffers

When enabled the additional image buffers required for denoising are saved out before the denoising takes place, this lets you to denoise the renders after the fact with Altus.

Optix Settings

Bucket Denoise Overhead

Controls how much time is allowed for denoising, as a percentage of the total rendering time when using  Bucket rendering mode.

This can be a helpful setting to adjust depending on the demands of your scene and in particular with large-resolution renders since Redshift denoises the entire frame after each bucket.

See the table below for some example values and their behavior.

 

Bucket Denoise Overhead Value	Behavior
0.0	Only execute OptiX denoising once after all buckets are finished rendering.
0.1	Allow OptiX denoising to take up to 0.1% of the time it has taken to render after each bucket.
10	Allow OptiX denoising to take up to 10% of the time it has taken to render after each bucket.
100	Allow OptiX denoising as much time as it needs after each bucket.

Progressive Denoise Overhead

The Progressive Denoise Overhead value controls how often OptiX is executed with  Progressive rendering mode.

See the table below for some example values and their behavior.

 

Progressive Denoise Overhead Value	Behavior
0	Only execute OptiX denoising once after the progressive render finishes rendering (by reaching the maximum number of Progressive Passes.)
0.1	Allow OptiX denoising to take up to 0.1% of the time it has taken to render after each pass.
10	Allow OptiX denoising to take up to 10% of the time it has taken to render after each pass.
100	Execute OptiX denoising after every pass.

Altus Settings

Altus Single / Altus Dual

"Altus Single" means that the frame will be rendered once and then Altus will execute denoising. "Altus Dual" means that the frame will be rendered twice. The two images are then compared to find and remove the noise.

The newer Single Pass technique can determine per-pixel noise in a single render pass. This approach is much more natural as it doesn't double the render time.

kc1

Controls how much high-frequency detail will be retained (i.e. sharp image features)

Lower kc1 values will retain more high-frequency detail while higher values will make the denoising stronger in those areas. I.e. it will produce smoother results but it might lose details.

kc2

Controls how much medium-frequency detail will be retained

Lower kc2 values will retain more medium-frequency detail while higher values will make the denoising stronger in those areas. I.e. it will produce smoother results but it might lose details.

kc4

Controls how much low-frequency detail will be retained (i.e. chunky image features)

Lower kc4 values will retain more low-frequency detail while higher values will make the denoising stronger in those areas. I.e. it will produce smoother results but it might lose details.

kf

Controls how much influence the additional AOV image buffers are used to affect the denoising results.

Lower values shift the denoising result in the direction of an overall more noisy image but one that retains more of its original details, deriving more of an influence from the additional AOVs.

Higher values shift the denoising result in the direction of a smoother and less noisy image, deriving less of an influence from the additional AOVs.

Texture Sampling

Primary Rays

Sets the texture mapping method for primary rays. The methods to choose from are:

• Anisotropic - High quality texture mapping but slower
• Bilinear - More blurry texture mapping but faster
• Point - More blocky texture mapping but faster

Additional Bump Bias

Sets a global bias to bump and normal map fidelity, -2 by default.

Lower values can  increase the sharpness of the bump / normal maps by decreasing the MIP-map levels used.

This setting can be used to quickly bias all the bump and normal maps in your scene in a particular direction. 

Copy Pre-Converted Textures to Cache Folder

The option "Copy Pre-Converted Textures to Cache Folder" is used in junction with textures that have been pre-converted using the ' TextureProcessor' tool.

By default this option is enabled, the assumption being that the local texture cache folder has better IO performance than the source texture folder, which is common for example when source textures are stored on slower network drives or when the local texture cache folder is on an SSD drive while the source texture folder is on a mechanical drive. By copying the pre-converted textures to the local machine cache folder, the out-of-core texture file streaming during rendering can be significantly faster, which can have a significant impact on rendering performance. This option should be disabled when the IO performance of the texture cache folder is equal to or lower than that of the source texture folder.