On Sun, 20 Jul 2008 21:22:11 +1000, Snake Arsenic wrote:

Okay I made a feature request at http://bugzilla.gnome.org/show_bug.cgi?id=543810 but it's missing a solution that will not remove any functionality. [...]

I think that it would be a big mistake to use the alpha channel for anything else than transparency. I assume that you are asking for this because you have some program (I don't know which one) that is incorrectly using the alpha channel to store bump map information or something else that is not related to transparency. It is likely that this program doesn't use a file format that supports layers or independent channels, so its authors of have decided to hijack the alpha channel in some existing file format.

The correct way to solve this problem is to use layers instead of abusing the alpha channel (or maybe additional channels, but I think that using layers would be more convenient in this case). With layers, it is very easy to toggle the visibility of the image or the bump map layer, specular map layer or whatever else you are working on.

So instead of extending the mistakes done by the authors of some other software, it would be much better to know what file format has been subverted, and to perform the conversion in the file plug-in: * When the plug-in loads a file that uses this strange format, it would convert the alpha channel into a layer and mark that layer (using a special name like the GIF plug-in does for animations, because that can be edited easily by the user if necessary). * You would then be free to edit the image in GIMP and modify the layer containing what should be visible or the layer containing the bump map.
* When saving the file, the plug-in would detect that some layers have a special name and would then combine these layers in a way that can be read by whatever other program you are using.

So I suggest that you: 1) Identify what file formats need some special treatment. 2) Check if there is a way to detect what files using that format are special, so that we do not have to ask the user every time if a file using that file format should be read in the intended way (alpha channel = transparency) or in the non-standard way (bump map). 3) Suggest improvements to the corresponding file plug-ins, instead of requesting major changes in the GIMP core.

-Raphaël

On Sunday 20 July 2008, Raphaël Quinet wrote:

On Sun, 20 Jul 2008 21:22:11 +1000, Snake Arsenic

wrote:

Okay I made a feature request at
http://bugzilla.gnome.org/show_bug.cgi?id=543810 but it's missing a solution that will not remove any functionality. [...]

Hi!
Going beyond all of Raphael's excelent remarks, I still see some issues here :
1) The ability to "ciew teh layer sans transparency" and "edit the alpha channel as if it where any other channel" is provided in GIMP - you copy the alpha channel to the layer's mask, and edit it (the layer's mask).

2) The request indeed points a thing: GIMP _has_ the ability to set each channel "visible" or not - in the layers channel. If the channel is disabled in the channels dialog, channel cvaleus are considere as zero for all display operations. However, setting the alpha channel to zero in this way - which is what gimp does -is useless - you just can't see anything in the image, as it is rendered with alpha = 0 for all layers.
I'd suggest that when the alpha channekll si disabled in the channel dialog, image is rendered with alpha =1.0 (255) insetead. That would:
a) enable the feature thought when the ability to run channel'son and off was included;
b) Make gimp attend the requester? (Snake) needs.

Maybe the bug request should be chanegd accordingly?

Moreover - I really think it is a more usefull (even if seldom used) behavior for disabling the alpha. What do you say of doing it?

I think that it would be a big mistake to use the alpha channel for anything else than transparency. I assume that you are asking for this because you have some program (I don't know which one) that is incorrectly using the alpha channel to store bump map information or something else that is not related to transparency. It is likely that this program doesn't use a file format that supports layers or independent channels, so its authors of have decided to hijack the alpha channel in some existing file format.

The correct way to solve this problem is to use layers instead of abusing the alpha channel (or maybe additional channels, but I think that using layers would be more convenient in this case). With layers, it is very easy to toggle the visibility of the image or the bump map layer, specular map layer or whatever else you are working on.

So instead of extending the mistakes done by the authors of some other software, it would be much better to know what file format has been subverted, and to perform the conversion in the file plug-in: * When the plug-in loads a file that uses this strange format, it would convert the alpha channel into a layer and mark that layer (using a special name like the GIF plug-in does for animations, because that can be edited easily by the user if necessary).
* You would then be free to edit the image in GIMP and modify the layer containing what should be visible or the layer containing the bump map.
* When saving the file, the plug-in would detect that some layers have a special name and would then combine these layers in a way that can be read by whatever other program you are using.

So I suggest that you: 1) Identify what file formats need some special treatment. 2) Check if there is a way to detect what files using that format are special, so that we do not have to ask the user every time if a file using that file format should be read in the intended way (alpha channel = transparency) or in the non-standard way (bump map). 3) Suggest improvements to the corresponding file plug-ins, instead of requesting major changes in the GIMP core. -Raphaël