Re: Re: How do I edit the alpha channel?

[Dale Welch <mlist8@xxxxxxxxxxx>]

take a look at layer masks.
i believe on youtube there are a number of tutorials discussing it.

http://www.youtube.com/results?search_query=gimp+mask+layer&search_type=&aq=f

Make sure the layers window is open (Windows/Layers) or ctrl-L
right click on your layer (in layer window) and choose add alpha channel
right click and choose add layer mask
                 choose "layer's alpha channel"
right click and choose "show layer mask"
you can now switch between editing the mask or the picture buy click on
the thimbnail of the image or the mask in the layer window.
however it only shows the mask in the editing/viewing window if you
right click and choose "show layer mask".

--- dale

maspeir wrote:
> What I have is two files. One is a (now) 24-bit RGB file containing the sprite images. The other is black and white (mask) file of the same sprite images. Where the mask file is black, the sprite would be drawn, where it is white, the background would show through.
>
> What I need to do is take these two file and merge them into one file with the mask image in the alpha channel. I'm going to load the file into an OpenGL texture by reading the PNG file. What I have been trying to do, without success, is open the mask file, copy the image and paste it into the alpha channel of the color image. The resulting PNG file needs to be in RGBA format.
>
> --- In gimpi@xxxxxxxxxxxxxxx, "Owen" <rcook@...> wrote:
>   
>>     
>>> I am trying to use GIMP as a sprite creation/editing tool. I'm working
>>> on recreating an old Macintosh game that my dad was developing in the
>>> early 90's. The sprites he used were 8-bit color and had separate
>>> 1-bit masks (black and white). I've converted the images from the
>>> Macintosh PICT format to PNG and opened them with GIMP, but once I add
>>> the alpha channel to the sprite image, I have no way of adding the
>>> black and white mask image to the channel. I've tried everything and
>>> what documentation I could find on GIMP's site doesn't actually
>>> mention how to add pixels to the alpha channel.
>>>
>>> Without the ability to actually add anything to an alpha channel, the
>>> feature is useless, so I know that I'm missing something or doing
>>> something wrong. I really need to merge these files into a single RGBA
>>> image.
>>>
>>> If it matters any, I'm using GIMP in Windows.
>>>
>>> Any help would be greatly appreciated.
>>>       
>>
>> I am not quite sure what you are doing, but once you get the image
>> into gimp, save it as an xcf file. That is gimp's native format
>>
>> Then, working on the xcf file, open the layers dialog
>>
>> Right click on the layer and you will be able to add alpha channels,
>> layer masks and do all sorts of operations
>>
>> After you finish, save it in some usable format, like png
>>
>>
>> HTH
>>
>>
>>
>> -- 
>>
>>
>>
>> Owen
>>
>>     
>
>
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