[Cin] Cingg'divide mode, very divisive!

[Andrew Randrianasulu]

вс, 6 нояб. 2022 г., 00:52 Igor Vladimirsky <sitelve at gmail.com>:

>
>
> ср, 2 нояб. 2022 г. в 12:53, Andrew Randrianasulu <randrianasulu at gmail.com
> >:
>
>> So, as Igor noticed CinGG's divide and subtract modes do not behave like
>> they behaved in Cin HV/CV/CVE I digged into matter a bit and found few
>> confusing (for me, amateur) things......
>>
>  But moreover, according to documentation CinGG composites tracks a bit
>> backward comparing to photo editors:
>>
>>
>  I found this in my archive.
>

Very cool, thanks!

So, for your specific preferences does inverting S and D in overlayframe.h
for subtract and divide return familiar behavior, especially with  huge use
of reroute/inversion? I do not think making it new default unconditionally
will be good, because some modes compositing this way and some - that way
add too much confusion, but a) you can use personal patch and hopefully b)
I'll find some way to make this behavior configurable ....



In 2016,  I asked GoodGuy about the Divide blend mode.
> I showed him a quote from from Changelog 2.1
> https://github.com/cinelerra-cv-team/cinelerra-cv/blob/master/cinelerra/CHANGELOG.2.1
> Quote:*" For overlaying, divide behavior is the same as the Gimp.*
> New overlaying algorithm: Max takes the maximum r, g, and b values."
>
> *GG's answer:*
> *------------------------------------*
>
>
>
>
>
>
>
>
>
>
>
>
> *"This is the math form Gimp currently uses:STD_BLEND + (Sa == 0.0 || Dc /
> Sc > Da / Sa ?  Sa * Da : Dc * Sa * Sa / Sc)HV 4.6.1 (and CV) actually
> uses:(Sc > 0 ? Dc / Sc : 1)Cin5 actually uses:(Dc > 0 ? Sc / Dc : 0)So,
> none of these look like Gimp. But Divide is a bit squirrelly.  It can fail
> on a per pixel basis because of divide by zero.  I prefer src (top track) /
> dst (btm track) with divide by zero as black (not white).  I think this is
> the way most would like to see it work, since it is a stack of operations,
> and it easier to work up from zero, than down from 1."*
> *---------------------------------------*
>
> ----------------------------------------
>
> This is from CGG'code
> Cinelerra-GG
> // DIVIDE       [Sa + Da - Sa*Da, Sc*(1 - Da) + Dc*(1 - Sa) +  Sc / Dc]
> // SUBTRACT     [(Sa - Da), (Sc - Dc)]
>
>
> But in HV and CV*, the Subtract and Divide blend modes work the same way
> as GIMP, Photoshop, Adobe Premiere Pro, EDIUS
>
> *GIMP*
> Divide mode multiplies each pixel value in the lower layer by 256 and then
> divides that by the corresponding pixel value of the upper layer plus one.
> Subtract mode subtracts the pixel values of the upper layer from the pixel
> values of the lower layer.
>
> *Photoshop*
> https://photoblogstop.com/photoshop/photoshop-blend-modes-explained
> Divide
> Background layer ÷ Active layer = Quotient
> Subtract
> B minus A
>
> *Adobe Premiere Pro*
> https://helpx.adobe.com/premiere-pro/using/blending-modes.html
> Divide
> Divides underlying color by source color. If the source color is white,
> the result color is the underlying color. Result color values can be
> greater than 1.0 in 32-bpc projects.
> Subtract
> Subtracts the source file from the underlying color. If the source color
> is black, the result color is the underlying color. Result color values can
> be less than 0 in 32-bpc project
>
> *EDIUS *(quote from its manual)
> Subtract
> Subtracts the overlay color values from the background.
>
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