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Incorrect Desaturate help article

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Sphinx.
Filter Optimizer

Posts: 1750
Filters: 39
Quote
Help states:
Lightness – based on the HSB color model, taking the B channel as a grayscale value. This method is provided for compatibility with Adobe® Photoshop® which uses this method in its 'Desaturate' adjustment. For more information on the HSB (HSV) color model, see this Wikipedia article.
(source)


Not sure what it outputs in "Lightness" mode, but it isn't B from HSB model (which indeed would be useful in there, along with min. rgb and med. rgb, so we don't have to set up switches etc for multiple grayscale method selections..see this request)..

EDIT: Further inspection tells me that the Lightness output is "med. rgb", i.e. (min(r,g,b) + max(r,g,b)) / 2
Njyldgarkn init/prepare process x no. of render blocks x no. of passes
Posted: October 25, 2011 9:24 am   Details E-Mail
Dmitry Sapelnikov
Filter Forge, Inc. AKA Egret
Posts: 76
Filters: 5
Yes, you're right.
It's a mistake in the manual. Desaturate uses the HLS model in the "Lightness" mode.
Lightness in the HLS model is calculated as
(max(R, G, B) + min(R, G, B)) / 2,
while the HSB model uses
max(R, G, B)

It seems you've received another 'bug point' smile;)
Posted: October 26, 2011 10:37 am   Details E-Mail
Sphinx.
Filter Optimizer

Posts: 1750
Filters: 39
Quote
It seems you've received another 'bug point'


Nah, share that amongst the programmers (first time is free). Each scripting issue fixed will be rewarded with new points from my account smile:-p

Btw now that I have your attention.. how about adding some more grayscale output modes to that Desat. component and thereby make it more useful?
Njyldgarkn init/prepare process x no. of render blocks x no. of passes
Posted: October 26, 2011 10:55 am   Details E-Mail
Dmitry Sapelnikov
Filter Forge, Inc. AKA Egret
Posts: 76
Filters: 5
I could say "probably".
Actually it seems really strange that the HSY has been chosen and the HSB model hasn't been added. I bet there was a good reason not to include HSB. So the issue needs a little investigation.
Posted: October 26, 2011 2:04 pm   Details E-Mail

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