Irradiance Cache (Legacy) (CineRender Global Illumination)

These settings are available, as part of the optional Global Illumination effect, in the Detailed view of PhotoRendering Settings for the CineRender engine.

These parameters are available if GI Method is set to Irradiance Cache (Legacy).

For more information, see Options for Primary Method.

Generally speaking, the predefined values in these additional settings do not have to be modified.

General

Interpolation Method

Different algorithms can be used to calculate the transition between light and dark regions and between color values between the Shading points.

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Least Squares: This function essentially calculates a curve based on a limited number of points.

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Delaunay: In contrast to the Least Squares interpolation method, only neighboring records and not those located further away will be included in the interpolation for rendering. However, in order to achieve homogeneous dispersion of light, the Record Density, a.k.a. shading point density, should be very high. The Record Density parameter offers several Delaunay preset options that can be used for this purpose (see Record Density, below).

The Delaunay option is in fact intended for use in special circumstances and is not really suited for use in “normal” renderings.

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None: If this option is selected, no smoothing will take place.

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Weighted Average: This method of interpolation works similarly to the Least Squares method, except that it only interpolates between values (whereas the Least Squares method can also extrapolate, i.e. for brighter or darker results than those represented by the defined values). This method can prevent artifacting when using low-quality GI settings. Furthermore, this method will render faster than the Least Squares method. Disadvantage: The dispersion of light is less homogeneous than when using the Least Squares method.

Distance Map

If, in relation to the total number of image pixels, only very few Shading points are interpolated, primarily soft shadows will be created and many details will be lost or smoothed too much. This can, for example, lead to light seeping through polygons. For example: in the form of sunlight seeping through an outer wall and being visible somewhere in the room. Enabling the Distance Map option can prevent this from happening - but will also increase render times accordingly.

Check Record Visibility

Record Density

This value defines the density and dispersion of the Shading points in the prepass phase. The information that these Shading points gather about the Stochastic Samples will then be interpolated between the Shading points to create soft transitions. The more Shading points that exist, the more exact the transition between light and dark regions in the scene will be - and the longer the Prepass and total render time will be.

Method: This parameter contains a set of predefined parameters that are by default optimized for most uses. Only under special circumstances should you change the option to Custom and modify these parameters yourself.

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Preview: As the name suggests, a preview will be rendered quickly - with correspondingly “poor” values that make a quick rendering possible. These “poor” values will result in many GI details being lost or in faulty rendering.

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Low/Medium/High/High (Details): These four options are optimized for use with the Least Squares interpolation method and result in differing levels of quality.

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Low (Delaunay)/Medium (Delaunay)/High (Delaunay): These three options are designed for use with the Delauney interpolation method. This interpolation method requires a very dense dispersion of shading points.

Min Rate/Max Rate

When the program creates an Irradiance Cache, it initially starts with a lower image resolution (Min. Rate) and progresses to the final IR resolution (Max. Rate). A value of 0 results in full resolution (pixel size 1*1), a value of -1 results in a pixel size of 2*2, a value of -2 = results in a pixel size of 4*4, and so on. The Min Rate value should logically be smaller than the Max Rate value. Positive values can also be applied, which will allow cache Records in the sub-pixel range (can be useful for SubPolygon Displacement if details are lost).

These resolutions apply only to IR calculations. Since the Irradiance Cache can be scaled relatively easily (i.e. lower IR resolution at larger image resolution), good results can often be achieved even when using smaller resolutions. Hence, these two parameters offer great potential for shortening render times, especially for brightly illuminated, low-detail scenes.

Radius

This parameter defines the maximum distance between shading points. The lower the value the more densely the points will lie together. This parameter primarily affects non-critical regions of the scene such as flat, clear surfaces. The effect of this parameter is also dependent on the Density Control value.

Minimum Radius

This parameter defines the minimum distance between shading points. It primarily affects the critical regions of the scene such as corners, edges, etc. The lower the value the more densely the shading points will lie at these regions. This parameter works in proportion to the Radius parameter above, i.e. if this value is halved, the Minimum Radius value will be halved as well.

The Minimum Radius parameter primarily affects areas in which details are important (e.g. subtle shadows). However, too many shading points in these areas can cause problems.

To make subtle details visible, use the Details Enhancement parameters instead.

See Details Enhancement, below.

Density Control

In contrast to the previous two parameters that primarily affect critical or non-critical regions, this parameter affects the shading points globally throughout the scene. The higher the value the greater the density.

Use Proximity Correction

This parameter is responsible for having neighboring shading points “assist” each other in critical regions and pass on information regarding the proximity of geometry. New shading points are created and calculated during this process.

This behavior can be disabled here, which will save some render time but also result in poorer render quality (especially at corners and edges).This option should be disabled if you are using a Max. Rate value of less than 0. Otherwise unnecessary calculations will result.

Smoothing

Increasing the Smoothing effect results in more lost details, but also in a more homogeneous dispersion of light.

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Method: Use the pop-up to define the level of smoothing. Select Custom to manually define the Records and Scale values below.

The Records and Scale values limit the number of shading points to be used.

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Records: The Records parameter defines, for each pixel to be rendered, the maximum number of surrounding Records in the Irradiance Cache that should be included in the interpolation of color and brightness for that pixel. If, however, the Scale value is so low that not enough Records can be included in the interpolation, it may result in fewer Records being included.

The lower the parameter value, the fewer Records that will be included in the final interpolation and the less homogeneous the rendering will turn out. Higher values will result in more smoothing but also take correspondingly longer to render.

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Scale: This parameter serves to spatially limit the Records included in the interpolation process. The larger the value, the more Records will be included and the softer the interpolation will be - and the longer it will take to render. Alternatively the Records parameter can be used for this purpose.

Cache Refinement

The previously described parameters all dealt with the placement of shading points based on a scene’s geometric properties. But what if a coarse, dark GI shadow disturbs the entire image?

This is where the Cache Refinement parameter comes in: It compares the Records in the Irradiance Cache and generates additional Records (i.e. shading points) in areas with high contrast (brightness and color) in order to refine and render these areas more precisely.

Tip: Refining the cache can greatly increase the number of Records in the Irradiance Cache, which will not necessarily improve the render quality. Especially when applied in conjunction with incorrect smoothing, this can lead to very grainy results. Hence, only refine the cache if absolutely necessary.

Higher Cache Refinement settings will lead to longer render times but not necessarily to better render quality.

Passes [0..4]: Use this setting to set the frequency with which the cache should be defined. Each new pass includes the results of the previous pass and refines it further by creating additional shading points in critical areas.

Color Threshold: This value defines the degree to which (neighboring) cache Records can deviate from each other with regard to their color (intensity) before additional shading points (“Samples”) are added. The lower the value, the lower the deviation threshold will be and the more samples will be added.

Cutoff: This value includes differences in intensity. The lower the value, the greater the differences between Records have to be for the color correction to apply. A value of 0 will turn cache refinement off.

Strength: This parameter is used to adjust the cache refinement’s overall sample density. A value of 0 will turn cache refinement off, whereas larger values will increase the number of shading points (“Samples”) correspondingly while taking into account Color Threshold and Cutoff values.

Details Enhancement

The Irradiance Cache method renders noise-free and much faster than other sampling methods, but entails compromises on details that lie in shadowed areas. This can result in the omission of finer details, such as tile grouting, during the smoothing process. Enabling Details Enhancement will counteract this by sending additional samples specifically to these areas. The effect is similar to Ambient Occlusion.

In a nutshell: Subtle geometry details are accentuated.

In order to save render time and avoid over-emphasizing finer details, either Ambient Occlusion or the Details Enhancement option should be used, but not both. Using both can make fine details visually too dominant. Since enabling the Details Enhancement option will send additional samples into the scene, you may also want to consider reducing the Record Density value.

The Details Enhancement parameters include options to counteract a characteristic of the Irradiance Cache - the “blurring” (smoothing) of details such as subtle shadows. The enhancement of details uses the QMC Sampling method in critical areas (for each relevant pixel) like corners, edges, cavities, etc. The Details Enhancement functionality can be seen as a special type of Ambient Occlusion whereby indirect light is included.

Note that the internal Irradiance Cache will be calculated differently (the algorithm will be aware of the subsequent detail enhancements and will calculate the critical areas differently) if this option is disabled. However you do it, the Details Enhancement will be calculated separately for each rendered image, i.e. re-using a saved cache will reduce render times.

If you apply Details Enhancement, you can lower the other Irradiance Cache settings (especially those pertaining to Record Density).

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Details Enhancement: Check this box to enable the Details Enhancement parameter.

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Adaptive: Enabling this option can be an advantage in some circumstances, e.g. several small areas are more grainy than others. Additional samples will then be rendered in these areas.

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Estimate Secondary: This mode renders faster and offers good results for most applications. However, certain areas will be rendered too dark or too colorful as opposed to a pure QMC rendering (GI Mode QMC), which in most cases doesn’t matter at all. If desired, this behavior can also be disabled (note that grainy renderings can result, in which case the Quality Ratio value should be raised).

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Radius: Use this setting to define the radius within which neighboring objects, corners and edges should be included. Lower values result in only elements in the immediate proximity being “seen”, whereas larger values will “see” elements correspondingly far away. Larger values will also result in higher precision and therefore longer render times.

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Quality Ratio: As mentioned, QMC Sampling will take place in critical areas. The Quality Ratio defines how many samples should be used per pixel, which in turn simply defines the graininess of the Details Enhancement. Larger values result in less grainy, softer results but require correspondingly longer render times.

Quality Ratio is an autonomous value that works independently of the rest of the IR settings (a value of 100% is equivalent to 64 samples).

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Mode: The options in this drop-down menu are for test purposes only so the effects of the detail enhancement, which are often very subtle, can be made more visible. You can select from the following options:

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Combine (Normal): Renders accurate results.

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Details Only (Preview): Renders detail enhancement without GI. Makes the detail enhancement the most visible of all the options.

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Global Only (Preview): Renders indirect illumination only.