Problem: Painting (e.g. with wacom-board) complex athmospheric perspective with overlapping objects.

Solution suggestion: A parent base layer determines alpha values for a dependent stack of child layers above the base layer. Then the last layer on top of the child stack e.g. could be the "athmosphere color" for the silhouette of the base layer.

People suggest as workaround the "alpha to selection" feature. But if the silhouette of the base layer has transparency gradients, e.g. when painting clouds, every addition of color to child layers will nevertheless end up opaque in the child layer.

Especially when painting on alpha masks of the child layers to evolve the forms gradually a "clipping mask layer" is in fact the only possibilty of producing complex scenes with athmospheric depth.

yahvuu schrieb:

Hi all,

On Sun, May 17, 2009 at 10:39 PM, Daniel Johannsen wrote:

Solution suggestion: A parent base layer determines alpha values for a dependent stack of child layers above the base layer. Then the last layer on top of the child stack e.g. could be the "athmosphere color" for the silhouette of the base layer.

i wonder, is what you're proposing the same as the 'group layers masks' described in
https://lists.xcf.berkeley.edu/lists/gimp-developer/2009-April/022118.html ?

Is this already covered by http://bugzilla.gnome.org/show_bug.cgi?id=51112 ?

Do you envision a user interface for this? The UI Brainstorm always welcomes cool mock-ups: http://gimp-brainstorm.blogspot.com/

greetings, peter

Hi to all,
yes your links point in the right direction. I agree, the term "layer group mask" hits the mark.
I only like to add, that in the layer group it is the alpha value of the lowest layer in the group
which provides the masking effect for the grouped layers above. (And not a layer in the middle or on top of the group.)

I am not surprised, that this feature is used a lot in photoshop (here it is called "clipping mask").

Some examples in order to stress how important this is for the painting process:

1)One can start with searching for a good composition by defining only silhouettes.
Then, in dependency of the silhouette, you can add volume and texture layers above the silhouette.

2)Often the shapes are not known in advance. Then they are dependend of normally subsequent painting steps
like adding volume and texture layers. With layer group masks one can quickly correct all the layers of the object only by manipulating the base shape layer.

3)Painting objects made of transparent materials like colored glass. The layer group mask feature would look like the following: * top layer: highlights (dependent)
* middle layer: glass texture (dependent) * underlying layer: glass shape in the color of the glass with 50% opacity (defines the transparency for the dependent layers)

regards, Daniel.

yahvuu schrieb:

Hi,

Daniel Johannsen schrieb:

I only like to add, that in the layer group it is the alpha value of the lowest layer in the group
which provides the masking effect for the grouped layers above. (And not a layer in the middle or on top of the group.)

hmm, special-casing the bottom layer seems a bit odd to me. I'd expect the layer group mask to be a property of the layer group and that all layers within that group have independent transparency of their own.

Looking at your examples, i assume the photoshop behaviour is convenient because you usually start with a layer and subsequently turn that into a layer group. Assuming correctly?

greetings, peter

Hi,
yes, your assumption is right. I start the painting process with layers only for shapes and silhouettes.
Then i add a "layer group" with the mask property (or in photoshop-terms a group of "clipping mask"-layers)
to each of the shape-layers. The layers inside the layer group mask define volume, texture, athmospheric perspective, etc. of the shape they are connected to.

So to say, the layer group mask has the property of a transparency value. This value is defined
by the alpha-value of the layer the group is assigned to.

Here is a link that shows the photoshop approach quite well: http://photoshopcontest.com/tutorials/23/clipping-mask-101.html

You are absolutely right, every layer in the layer group should maintain their independent transparency,
but in addition inherit the transparency of their layer group mask.

greetings, daniel