How the RGB Limit Filter Works
The RGB Limit filter processes your video in 32-bit floating-point RGB color space and
then outputs the native color space of your footage (either RGB or Y´C
). The high
precision of this color space minimizes quality loss in your video during processing.
The RGB Limit filter affects only RGB-equivalent values above the Clamp Levels Above
parameter value and below the Clamp Levels Below parameter value. The filter applies
up to three stages of level reduction at a time, as necessary:
Â Clamping: Levels above the Clamp Levels Above parameter value are clamped to the
parameter value. Levels below the Clamp Levels Below parameter value are clamped
to the parameter value. For example, if the Clamp Levels Above slider is set to 100
percent, all RGB levels above 100 percent are clamped to 100 percent.
Â Chroma desaturation: After clamping, any pixel with an RGB level above the
Desaturate or Darken Levels Above parameter value is desaturated until the red,
green, or blue channel reaches the parameter value. Desaturation is an effect easily
understood in Y´C
color space: the color difference channels are merely reduced.
However, in RGB color space, desaturation is achieved by reducing the level of the
color channel with the highest level while simultaneously increasing the levels of the
two channels with lower levels. This reduces saturation while maintaining the same
luma level. A pixel with equal RGB channel levels has no saturation (in other words,
the pixel is black-and-white only—like the luma channel in Y´C
color space) and
therefore cannot be desaturated.
Â Luma reduction: Finally, for any RGB levels that still remain above the Desaturate or
Darken Levels Above parameter value after desaturation, luma levels are reduced so
they are at the level set by the Desaturate or Darken Levels Above slider. Reducing
luma levels in RGB color space is achieved by simply reducing the levels of all three
Color Correction and Video Quality Control