On Sun, Aug 1, 2010 at 1:04 PM, Bill Skaggs <weska...@gmail.com> wrote:
> It would be much better not to use the word "tool"in this way.

I agree terminology is going to be difficult.  I get the impression
you are only thinking about color, but I'm not.  Maybe it's clearer if
I use the terms "Image layer" and "Blend layer".

So our layer tree has an image on the bottom and an image on the top.
Where the top image has alpha, the bottom image can been seen through,
as it is today.

Now, instead of making the layer mode "Multiply" (or 'screen' or
'saturation' or 'lighten' (which have the same issues as color), etc),
the user inserts a "Blend Layer" between the images.  This "Blend
Layer" is a "Multiply" type, and the "Multiply Blend Layer" has
properties associated with it.  One of these is "Color Space".

Further, this "Blend Layer" has a gray(/alpha) mask so that the layer
effect may apply to only a portion of the image.  Further still,
multiple "Blend Layers" may reside between the two images.

So for example, picture a bottom layer of a frog sitting on a log.
Above that is a "Desaturation Blend Layer" in the HSY color space,
making it appear black and white.  Above that is "Lighten Blend Layer"
that is a graymask of the frog, making only the frog appear slightly
puched-out.  Above that is a color image layer of a butterfly (or
something) near the frog.

Your graph now resembles:
- [Image]: Butterfly
- [Blend]: Lighten (Lab), Frog mask
- [Blend]: Desaturate (HSY)
- [Image]: Frog on a log

I'm thinking that some color tools could become unnecessary if you do
this (just create a blend layer and flatten the image...), but I'm not
advocating their removal.

I'm also thinking that 'layer modes' could be useful when you have
multiple blend layers, but they wouldn't be as problematic as they are
all gray masks (add, subtract, etc. are all well-defined.)

> backward compatibility.  If you can find a way to make the Hue/Saturation
> tool work better, there's no strong reason it couldn't be put into Gimp.
> Changing layer modes that are stored in XCF files is more problematic.

I'm not sure where this is coming from, but so it's clear: I think
that Hue/Saturation is essentially unfixable.  If you want to work in
L*a*b space, such ideas don't exist.  You would either need a color
space selector and a complicated tool, or a tool for each colorspace
type.  And layer modes go away altogether.

Instead you get a "Blend Layer" that performs the operations of the
tool, using the color space specified in the properties of this "Blend
Layer".  And instead of constraining your image using a selection, the
"Blend Layer" retains a gray mask indicating the affected pixels.
The gray, in this case, replacing (or augmenting) an opacity slider.

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