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image calculations – gray channel?
I am working on a large scale video masking project extracting figures from 100’s of video clips of existing footage. My workflow combines AE with imagineer systems Motor to create excellent roto mattes. combining these mattes with image calculations of fine detail areas such as hair in AE.
my question is what does the gray channel in calculations represent? how can one understand this channel option?
Is there a known formula of channel mixing that the gray arrives from (eg photoshop uses a calc of roughly 30% red, 40%green, 20% to arrive at desaturate command)
Is this knowledge available?
Many thanks in advance
Paul Richards
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3 Replies
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[Paul Richards] “my question is what does the gray channel in calculations represent? how can one understand this channel option?
Is there a known formula of channel mixing that the gray arrives from (eg photoshop uses a calc of roughly 30% red, 40%green, 20% to arrive at desaturate command)”
If you want to mix the 3 color channels in varying amounts to end up with a grayscale image then I would recommend looking at the Color Correction > Channel Mixer effect.
I’ll have to look into Calculations a bit more.
Darby Edelen
Designer
Left Coast Digital
Santa Cruz, CA -
Darby Edelen
If you want to mix the 3 color channels in varying amounts to end up with a grayscale image then I would recommend looking at the Color Correction > Channel Mixer effect.”
Hi, yes thanks – my question relates to the specific channel mix that corresponds to the gray channel in calculations, which of course could be generated within channel mixer at some point.
has anybody seen this information published?
It otherwise renders calculations as an inaccurate art – contradicting the specificity inferred by its name
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AE help says:
“Gray converts all color channel values for a pixel to the luminance value of the original pixel.”
Luminance is a weighted sum of RGB values (although I’m sure Adobe uses the term luminance when they mean luma, which is a weighted sum of gamma corrected R’G’B’ values). The weighting of the R’G’B’ channels in the calculation of luma in AE appears to follow the Rec. 601 standard which is:
Y’ = 0.299 R’ + 0.587 G’ + .114 B’
Or (in Channel Mixer for example) 29.9% Red, 58.7% Green and 11.4% Blue.
Darby Edelen
Designer
Left Coast Digital
Santa Cruz, CA
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