Re: luminance channel in AE

[kirk tabalotny] "My bed-time reading lately is about colour theory - is my life out of balance or what?"

Glad I'm not the only one =)

You should already know, then, that luminance is based on human perception which is more sensitive to green than red, and more sensitive to red than blue.

There are several ways to preserve this model of sensitivity in AE, one of which is the default Color Correction > Tint effect. Alternatively, you can place a Solid color layer at the top of a composition with 0% saturation (pure white, black or gray works) and set it to the 'Color' blend mode. Also, the same results can be achieved with the Color Correction > Channel Mixer effect as long as the weighting is modeled after human perception...

Just to complicate things, video doesn't generally use luminance, but rather luma which consists of gamma encoded luminance... yikes! Different color spaces (SDTV, HDTV, etc.) can apply different gamma curves to the values and apply different weightings to the luminosity values. The former generally doesn't pose a problem, since the inverse gamma curve should be applied farther down the pipeline (e.g. at display)... The latter, I swear, can be useful information if you want to use Channel Mixer.

HDTV for example uses these coefficients: 0.2126 R' + 0.7152 G' + 0.0722 B'

So you can emulate the default Color Correction > Tint effect with values of 21.26 Red 71.52 Green and 7.22 Blue in the HDTV color profile or come up with your own similar or dissimilar values (because lets face it... human perception can be so boring).




Darby Edelen
Lead Designer
Left Coast Digital
Santa Cruz, CA