yahvuu 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.

I am interested in that. modes are like a box of chocolates,
you'll never know what you gonna get.

> 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.

well, we cannot rename addition (and it is a clear name at that),
and linear burn is really not where I would like to go.

After a look at the math (thanks for that) and a bit of brainstorming
with nonsense names like "addition against all odds" or "orchestral
addition in the dark" I arrived at something that does work:
"Dark addition" (because it is an addition, shifted full range
towards black).

> 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.

no no no. everything stays there and keeps its name. file and user
backward compatibility is needed here. that sounds very 'developer',
and I fight a lot of these battles on the other side, but in
this case it is true.

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

it is a straightforward mathematical mode, maybe used to
prepare a mask for further use. it is part of the
difference group that provides all kinds of mind-bending
(inverting) stuff. after moving grain merge out I am happy
to leave that group as-is.

> 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'...


avoiding mode bloat is a good one.
but please do not mix up the different reasons why modes are there
right now. Like having a set of 'layer math' or simply results oriented
(burn, lighten only). you see there are some very subtle reasons to
add a new mode or not.

I had some more fun with the heat maps in
<http://yahvuu.files.wordpress.com/2009/09/table-brightness-1600.png>
and I think I start to understand the algorithm-aesthetics better.
as you pointed out, the lighten and darken groups are exclusively
red or blue, which means that something like freeze/reflect
do not fit there. then our overlay group modes have equal areas of
red and blue in it. this makes heat/glow a better candidate then
the two rows above or the one below them.

then again there is no artistic value in that...

     --ps

         founder + principal interaction architect
             man + machine interface works

         http://mmiworks.net/blog : on interaction architecture



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