Viz Artist User Guide
Version 5.1 | Published October 31, 2023 ©
Tonemapping
Tonemapping is a technique that converts color values from a high dynamic range (HDR) to a low dynamic range (LDR) a display can output.
The tonemapping shader is directly integrated into the Viz Engine Render Pipeline and is applied as the last step of the main rendering process, just before the image is processed for video output. The filmic tonemapping operator proposed by John Hable is used.
To enable the tonemapping post effect, go to the Scene's Rendering Settings and enable tonemapping under Lens Effects. Be sure to enable post-processing effects in the Scene Editor to have a preview of it while editing its properties. When the tonemapping post process effect is enabled, a tonemapping node is added to the Render Graph, which contains values to configure the tonemapping curve, contrast, exposure and lift, gamma and gain.
The order of the adjustments to the input color is:
-
Exposure
-
Saturation
-
Contrast
-
Tonemap
-
Lift/Gamma/Gain
Exposure / Saturation / Contrast
|
Parameter |
Description |
|
exposure |
Adjusts the exposure of the input pixels. |
|
saturation |
Adjusts the saturation of the input pixels. |
|
contrast |
Adjusts the contrast of the input pixels. |
Examples
|
Screenshot |
Information |
|
|
Default Settings contrast = 1
|
|
|
exposure = 0.5 |
|
|
contrast = 1.2 |
|
|
saturation = 0.2 |
Tonemapping Operator
The function that is applied on the HDR input colors can be configured using multiple parameters in the Render Graph node. To see how the operator works check out the interactive graph.
Parameters
|
Parameter |
Description |
|
shoulderStrength |
Defines the shape of the curve. |
|
whitePoint |
Defines the value in the input that translates to 1 in the output. All values below are squeezed into the range from 0 to 1, everything above results in values larger than 1. |
Examples
|
Screenshot |
Information |
|
|
Tonemapping Disabled |
|
|
Tonemapping Enabled Default values. |
|
|
Tonemapping Enabled Adjusted values compared to the default ones, to have a slightly improved saturation. |
Color Correction
Color correction is done after tonemapping and applies the so called Lift, Gamma and Gain input values: output = (input * gain + lift) ^ gamma.
The formula being used is mentioned in https://en.wikipedia.org/wiki/ASC_CDL.
To see what the separate values do check out the interactive graph.
Parameters
|
Parameter |
Type |
Description |
|
gain |
Multiplier |
Adjusts highlights. |
|
lift |
Offset |
Adjusts brightness. |
|
gamma |
Exponent |
Adjusts mid-tones. |
Examples
|
Screenshot |
Description |
|
|
Default Settings lift = 0 for red green and blue channel |
|
|
Adjusted lift for red and green channels, leaving blue untouched. |
|
|
Adjusted gamma for red and green channels, leaving blue untouched. |
|
|
Adjusted gain for blue channel, leaving red and green channels untouched. |
Credits
Environment image is taken from https://hdrihaven.com/hdri/?h=leadenhall_market.