GNOME Bugzilla – Bug 51009
uneditable alpha channel on TGA files under Gimp 1.2/Irix 6.5
Last modified: 2009-08-15 18:40:50 UTC
When running the Gimp 1.2, under Irix 6.5 on an SGI O2, if I try to save a targa image with an alpha channel the way I do it under Photoshop, it will convert the image to black and white. It seems that it is loosing the alpha channel. When I re-open the image (targa), I get a b&w image with only one channel. I posted images of what I get at the following url http://cadre.sjsu.edu/~ndufort/gimp/ screen_a.png: image I create under the gimp, with rgb channels and an alpha channel. I saved as a targa image the way I do it under Photoshop. screen_b.png: image I get when open the targa file I just created a minute ago. In Photoshop, I can save a targa image with my four channels seperatly (red, green, blue and alpha). Now if I want to modify the alpha later or in another program, I can't edit the file anymore. Someone on the gimp newsgroup told me that it was considered a bug. Could you confirm me if this is a bug? I did find a way to do my transparency, but this is not the way other programs would do it (by keeping the information for each channel -rgb, seperate from each other). And it makes it very challenging dealing with alpha channels since I am restricted to targa. thanks. nico
It looks like only a (grayscale) layer mask or channel mask was saved in your TGA file, instead of saving the whole image as you expected. This could be a duplicate of an old bug that I re-submitted today as bug #51114. If this is the case, then the only thing that you would have to do in order to make sure that your image is correctly saved with transparency in the TGA file is to click on the current layer in the Layers, Channels and Paths dialog (and maybe select "Apply Layer Mask" if a mask is active). That would explain why others (including myself) have no problems saving a TGA image with an alpha channel. Could you please try the following and see if it works for you: - Create a new image, fill it with some pattern (for example, the wooden pattern that you used in your examples). - In the "Layers, Channels and Paths" dialog, right-click on the layer and select "Add Alpha Channel" and then "Add Layer Mask". - Draw something in the mask so that some areas become transparent. - Right-click on the layer again and select "Apply Layer Mask". - Save the image as TGA. - Load the TGA image in the Gimp or any other tool. Please report if you got the correct result or if you got only some black & white image (in which case this could be an IRIX-specific bug).
For what I just saw in the "TARGA+ALPHA CHANNEL" thread in comp.graphics.apps.gimp and from the additional wood2.xcf image that you provided on your web page, I conclude that the problem came from two things: - A misunderstanding of how to attach an alpha channel to an image. In the Gimp, this is done with a layer mask, and not with a channel mask (which is nothing else than a saved selection). I suggest that you read chapter 4 of the book "Grokking the GIMP", available on-line from: http://gimp-savvy.com/BOOK/index.html?node42.html - A duplicate of bug #51114, which caused the new channel to be saved to the TGA file instead of saving the whole image as you intended. Therefore, I will close this bug and mark it as a duplicate of #51114.
*** This bug has been marked as a duplicate of 51114 ***
The fix for bug #51114 was part of the stable release 1.2.3. Closing this bug.