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

[Andrew Randrianasulu]

can you check if attached patch fixes subtract mode or makes it even more
broken?



вс, 30 окт. 2022 г., 20:58 Andrew Randrianasulu <randrianasulu at gmail.com>:

>
>
> вс, 30 окт. 2022 г., 17:21 Phyllis Smith <phylsmith2017 at gmail.com>:
>
>> 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...
>>>
>>
>
>
> or may be i get layers order wrong /
>
>
>
>> 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.
>>
>
> I found some python description of Adobe's blend modes .... also, blending
> and compositing can be two stages of more complex process??
>
>
> https://github.com/psd-tools/image-blender/blob/master/src/image_blender.pyx
>
>
> see divide/subtract grouped together ...
>
>
>
>> 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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