peter sikking wrote:
> actually a question for peter (yahvuu): how complete is this overview?

most notably, the porter-duff modes are not listed.
I'll have a look to make the overview as complete as possible.


> first, I know now why our Darken section is one Shorter that our
> Lighten one: we are missing "subtractive" (that needs a name not
> soooo close to our Subtract).

yeah, in photoshop, the names are:
  'subtractive'  =>  'linear burn'
  'additive'     =>  'linear dodge'
which is a lot better.

It's still not perfect though, as the most prominent property of burn/dodge
is the capability to increase the local contrast -- which is not featured
by their 'linear' counterparts. But at least the confusion of 'subtractive'
not actually using a subtraction term in the formula is avoided.


Actually, i think the old 'subtract' mode should be removed,
when 'subtractive' gets added: just invert the blend layer and
you get the old 'subtract' mode back.

Along the same lines, what is the right to exist for 'divide'?
- it's just 'dogde' with an inverted blend layer.

An accepted pair of this type is grain extract/merge, for which
useful techniques exist [1], but also for dodge/divide?!?
If so, possibly the rest of the modes are candidates for
'mode bloat', too, say a new mode: 'multiply with inverted blend layer'...

Under GEGL, this technique of using a blend mode twice in conjunction
with an inverted blend layer should probably provided by a macro?!?


... well, and if go with such macros, 'dodge' is just the complement
of 'burn', which is a shortcut for inverting both the input layers
as well as the result. But this clearly goes too far against the
history of image editors. Just thinking aloud...


greetings,
yahvuu    (i'll try to stick with the nick name, easier for everbody)


[1] 
https://lists.xcf.berkeley.edu/lists/gimp-developer/2008-November/021116.html


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