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Hidden layer after using the "Color to Alpha" function.

Jan 2, 2011, 09:12 (This post was last modified: Jan 2, 2011 09:13 by Gaijin77.)
Post: #1
Hidden layer after using the "Color to Alpha" function.
Hi, I'm encountering a problem creating transparent png files for some T-shirt designs and was hoping someone might know why. Basically, I use the "color to alpha" function to make a certain color transparent and everything looks OK in gimp but when I print the T-shirt I find that the transparent part is still there. At first I thought it was a problem with the printing but when I checked the image in Microsoft Paint I could see that the color that was supposed to be transparent was still there. I'm wondering if anyone on the forum knows why this might be and how I might stop it happening. I have this problem whenever I use the color to alpha function and it is getting quite frustrating. I've attached a file to this thread so that you can see what I mean. When I open this file in gimp the only visible color is yellow and the rest of the image is transparent. However, if I open it in Microsoft Paint I can still see the green outline that I thought I had erased (turned transparent) in Gimp. I'd be very grateful for any advice.

Thanks,
Daniel


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Jan 2, 2011, 10:56
Post: #2
RE: Hidden layer after using the "Color to Alpha" function.
Thanks for your quick reply. I totally agree that MS-Paint is a complete lemon. The only reason I use it is to check for any "hidden layers" that might end up on my T-shirts. I use CafePress (a print-on-demand website) to print the T-shirts and for some reason these "hidden layers" I can only see in MS-Paint keep getting printed on the T-shirts. If you click on my attachment, select [Save image as...] to save the original file (not the thumbnail) and open it in MS-Paint what do you see? I see a yellow knot with a green outline against a black background. I understand that the black background is MS-Paint's way of dealing with transparency, but I can't figure out why the green outline that I colored to alpha is still there...
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Jan 3, 2011, 04:49
Post: #3
RE: Hidden layer after using the "Color to Alpha" function.
Yeah, it's weird because everything looks fine in GIMP and pretty much every other software I've used except MS-Paint. It even looks fine in the preview software on the CafePress site. The first time I knew there was a problem was when the T-shirts came back printed with the colors I thought I had removed using the color-to-alpha function. I've also noticed that I don't have this problem if I save the file as a GIF, then reopen it and save it as a PNG, so perhaps that is a workaround I can use. The only downside is that the file size seems to get reduced which I'm guessing would indicate a loss of resolution.

Also, just a couple of questions about the terminology you use as I'm new to this forum and want to make sure I understand correctly:

What do you mean by de-aliased borders?
What do you mean by C2A?
What do you mean by IIRC? (I'm guessing you mean "If I remember correctly" but just want to be sure!).

Thanks for your help, it is really appreciated.

Cheers,
Daniel
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