Luminance vs Lightness

[Todd Kopriva]

The luminance calculation is a weighted average of the color channels that approximates how you perceive brightness, while lightness is just an average of the largest and smallest channels without regard to perception.

But you didn’t mention your context. In some plug-ins and other parts of various software interfaces and descriptions, people use these terms sloppily. So, don’t rely 100% on the reality of any given context matching the academic distinction in my first paragraph.

———————————————————————————————————
Todd Kopriva, Adobe Systems Incorporated
putting the ‘T’ back in ‘RTFM’ : After Effects Help on the Web
———————————————————————————————————

[Jonathan Marte]

Thanks! That does answer my question!

[Filip Vandueren]

After Effect’s weghing for Luminance formula seems to be roughly:

R: 30.5%
G: 53%
B: 16.5%

Lightness strangely is not just the average as in (R+G+B)/3
but appears to be (Max(R,G,B)+Min(R,G,B))/2 if that makes sense.

These observations are based on the Channel Combiner effect, where the two terms ar used next to each other.

[Filip Vandueren]

Incidentally the Y in YUV in the same effect
is Luminance but mapped between 16 and 236 instead of 0-255

[Todd Kopriva]

One wrinkle is that the weightings aren’t identical across plug-ins, because some plug-in developers have been… um… not careful in researching their numbers.

———————————————————————————————————
Todd Kopriva, Adobe Systems Incorporated
putting the ‘T’ back in ‘RTFM’ : After Effects Help on the Web
———————————————————————————————————