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List:       gimp-developer
Subject:    Re: [Gimp-developer] Enhancement request - Use alpha channel for
From:       Snake Arsenic <snakearsenic () gmail ! com>
Date:       2008-07-20 17:46:47
Message-ID: 48837A07.6030709 () gmail ! com
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That sounds really good Joao, I was thinking of a "use layer as alpha" 
overriding

option for the TGA save dialog(which eliminates the layer being used in the final image
other than to serve as the alpha channel, of course).

I'm also thinking of an "extract alpha to layer" option
in a menu such as transparency or as a filter that also performs the function of
setting the alpha channel to 1.0 in all pixels of that layer.

This could provide easy editing of multiple layers with individual masks/alpha as
the combined alpha has messed up the mapping in a few cases as well as providing an easy
method of re-editing an image if the original is lost as TGA files only have one layer.

It also makes it easy to hide all unnecessary layers before using this "extract alpha channel"
function to extract the correct information if more than one layer is present.

The reason I say TGA is because that is the only format I know
of being used in this way and is very common for a wide range of 3d applications.

What do you think of these ideas on top on Joao's?

Joao S. O. Bueno wrote:
> On Sunday 20 July 2008, Raphaël Quinet wrote:
>   
>> On Sun, 20 Jul 2008 21:22:11 +1000, Snake Arsenic 
>>     
> <snakearsenic@gmail.com> 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 <image> 
> 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 requesterś (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
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>>     
>
>
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