Convert video to gray using custom color filter.

A description of the accepted options follows.

cb

Set the chroma blue spot. Allowed range is from -1 to 1. Default value is 0.

cr

Set the chroma red spot. Allowed range is from -1 to 1. Default value is 0.

size

Set the color filter size. Allowed range is from .1 to 10. Default value is 1.

high

Set the highlights strength. Allowed range is from 0 to 1. Default value is 0.