On Sun, Nov 2, 2008 at 12:02 AM, Martin Nordholts <[EMAIL PROTECTED]> wrote:
> David Gowers wrote:
>> Hi,
>> On Sat, Nov 1, 2008 at 11:06 PM, Martin Nordholts <[EMAIL PROTECTED]> wrote:
>> Actually, I didn't understand  why you grouped them with Difference
>> (even given your explanation of 'can produce completely different
>> colors'); I would have grouped them with Overlay, since they both
>> provide darkening ( on one side of 128) and lightening (on the other
>> side of 128),
> I had them grouped with Overlay for a while but ended up putting them
> under Difference since Grain Extract can look very similar to
> Difference. And from an aesthetic point of view it looks better to have
> 3 and 3-groups than 5 and 1-groups.
>> I'm a bit puzzled as to why Multiply is paired thusly with Screen --
>> Divide is closer to being the opposite of Multiply IMO (from a visual
>> inspection div(mul(x)) and mul(div(x)) are closer to the original x
>> than scr(mul(x)) or mul(scr(x)) )
> One have to differentiate between mathematical similarities of the
> blending formulas and the effect the modes have on the colours we
> perceive. From this point of view Multiply pairs better when Screen than
> with Divide.
No, that's what I was saying -- from VISUAL inspection.I didn'c check
the numbers, just how it looked when I painted in div mode then
multiply mode with same color, etc..

> Actually from this point of view Divide and Subtract should probably be
> moved to the Difference category. They can produce completely new
> colours as well. Addition doesn't really have a counterpart (Addition is
> Linear Dodge in PS and GIMP has no Linear Burn counterpart).

Linear Burn is exactly a reversed Subtract, yes? that is,
result = dest - (1-src)
 rather than
result = dest - src

> The problem with introducing Linear Burn to GIMP is the name; what
> should it be called? One alternative would of course be to call Addition
> Linear Dodge instead.

I like that. For layer mode usage. (for painting, the current Subtract
behaviour is more symmetric with Add than Linear Burn would be.)

I think it would be wise to plan for eventually having the layer modes
list something like the toolbox tools currently are:
a large set, with each item individually hideable (and new ones
installable -- though they would have to be visually differentiated so
the user knew they might not load in a 'baseline' GIMP install).
Perhaps the disabled ones could be left in an 'others' "submenu" to
leave them accessible while reducing their interaction speed cost.

So, we could consider which ones would be the least valuable, and let
that inform the sorting.
For example:

* Color mode is markedly inferior to PS Color mode (because it uses
HSL, rather than LAB colorspace, the transference is not only of color
data but some intensity data.). It's important to include some Color
mode, however if we can get Color mode working in LAB space, we should
probably show that by default and hide old style Color mode.
* Also consider doing the same with Hue and Saturation, using a polar
transform of LAB (ie. LCH),
hue transfers only the angle, saturation transfers only the radius.

Personally, only about 7 of the layer modes have any use to me:
   normal dissolve difference multiply divide grainMerge grainExtract
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