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| Wilbert |
| Posted: Feb 3 2011, 08:24 PM |
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Advanced Member
Group: Members
Posts: 132
Member No.: 6270
Joined: 11-September 03
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Hi Avery!
I made a HSVAdjust plugin for AviSynth (i need to include HSL/HSI yet, but that's not important here) and i compared it to the build-in filter in Virtualdub (1.9.11).
When using a blankclip of R=235,G=0,B=0 with "hue=35,saturation=75%" i got the following values (formulas from wikipedia):
M = 235, m=0 => C=235
H = 60*( G - B )/C = 60*(0-0)/235 = 0
S = C/M = 235/235 = 1
V = M = 235
S' = 0.75*S = 0.75
H' = 0 + 35 = 35
V' = 0+1*235 = 235
Hi = int(H'/60) = 0
f = H'/60 - Hi = 0.5833
R = V' = 235
G = V'*(1-(1-f)*S') = 161.5566 = 162
B = V'*(1-S') = 58.75 = 59
The output of Virtualdub seems to be very different: R=206, G=132, B=29. Any idea why it's that way off? |
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| phaeron |
| Posted: Feb 5 2011, 07:21 PM |
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Virtualdub Developer
Group: Administrator
Posts: 7773
Member No.: 61
Joined: 30-July 02
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The saturation calculations are different, because VirtualDub's filter converges to the midrange as saturation goes to zero instead of the top. According to Wikipedia, this is actually an HSL model instead of HSV, although there's probably some differing opinions on this. I don't remember where I got the original model from -- might have been Graphics Gems I.
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| Wilbert |
| Posted: Feb 12 2011, 09:35 PM |
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Advanced Member
Group: Members
Posts: 132
Member No.: 6270
Joined: 11-September 03
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Thanks for your clarification! For the ones who are interested:
M = 235, m=0 => C=235
H = 60*( G - B )/C = 60*(0-0)/235 = 0
L = (M+m)/2 = 117,50
S = C/(255-|2L-255|) = 235/235 = 1
S' = 0.75*S = 0.75
H' = 0 + 35 = 35
L' = 0+1*117,50 = 117,50
C' = (255-|255-2L'|)*S' = 176,25
m' = L' - C'/2 = 29,375
Hi = int(H'/60) = 0
f = H'/60 - Hi = 0.5833
R = C' + m' = 205,625 = 206
G = f*C' + m' = 132,1875 = 132
B = m' = 29,375 = 29 |
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