Color correction nodes in compositing networks appear with a blue background. Houdini collapses consecutive color correction nodes into one operation, saving memory, improving performance and avoiding clipping/quantization issues.
The Bright, Contrast, and Gamma operations can optionally affect individual channels.
|To adjust…||Use this operator|
|Brightness, Contrast, and Gamma for the overall image,|
|Map one color range to another|
|Clamp minimum and/or maximum color values|
|Hue, saturation, and/or value|
Black point and white point
For planes with integer data, by default 0 means black and the maximum value (which depends on whether you are using 8, 16, or 32-bit integers) is white. However, you can adjust which level corresponds to black and which level corresponds to white. This allows you to reduce the head and foot clipping errors at the expense of quantization errors.
For planes with floating point data, 0 is always black and the maximum value is always white. You cannot set black and white points for floating point data.
For example, a 16 bit image with black and white points set at 24,000 and 40,000 gives you 16,000 levels between black and white, and quite a bit of head and foot room (the full range is -1.5 to 2.6).
Houdini always displays color values as a range from 0 to 1. So, if you adjust the black/white points, you can have values less than 0 or greater than 1, which reduces clipping of values during calculations.
For example, for an 8-bit integer channel, you could set the black point to 64 and the white point to 192. In Houdini, the 0 color value now corresponds to a value of 64 in the channel, and the 1 color value now corresponds to a value of 192 in the channel. So, the range of color values you can use in Houdini is now from (0-64)/(192-64) = -0.5 to (255-64)/(192-64) = 1.492.
To set the black point and white point of an image, use the Levels operator.