[Cin] Fwd: cingg vs gimp 2.10 compositing mode divide

[Phyllis Smith]

The below  is very possible (except for the gimp comparison) meaning we may
be making black where it should be white.  But as Andrew implied old
projects may suddenly provide different unexpected results if we change it.

> I think you see, we are making black areas where gimp was making white
> areas...
>

Much work was performed to follow one of many versions of the Overlays from
various other software packages.  In the Description section of the
Overlays chapter in the manual, it states:
Divide: Divides source color by destination color. If the source color is
white, the
result color is the underlying color. The resulting image is often lighter.
*Mathformula used is different than that used by Gimp*; there is no SVG
equivalent.
https://cinelerra-gg.org/download/CinelerraGG_Manual/Arithmetic_Group.html

I believe that CinGG when rewriting the code several years ago attempted to
follow the algorithm that currently existed in Cinelerra HV version at the
time, but the image I had included earlier comparing CinGG with HV 4.6.1 is
so different.  One or the other is inconsistent.  Changing it to match Gimp
is not desirable, however it would be great to fix an obvious bug.

On Sun, Oct 30, 2022 at 1:59 AM Andrew Randrianasulu via Cin <
cin at lists.cinelerra-gg.org> wrote:

> but should we blindly  follow gimp ? Again, gimp tend to have bigger mode
> list ) may be right thing to do  is leave some of our modes intact (they
> might be buggy but graphics art can utilize that, too) and add
> gimp/svg/oldcin compatible modes ?
>


>
> ---------- Forwarded message ---------
> От: Андрей Рандрианасулу <randrik at mail.ru>
> Date: сб, 29 окт. 2022 г., 18:43
> Subject: cingg vs gimp 2.10 compositing mode divide
> To: randrianasulu <randrianasulu at gmail.com>
>
>
>
> I think you see, we are making black areas where gimp was making white
> areas...
> --
> Андрей  Рандрианасулу
> --
> Cin mailing list
> Cin at lists.cinelerra-gg.org
> https://lists.cinelerra-gg.org/mailman/listinfo/cin
>
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