GIMP Version: 2.6.11
Operating System: Windows
OS Version: XP - SP3
GIMP Experience: Beginner Level

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How do I make a color on my image the transparent background to my image?
Also, what file format should I use to make sure it works and when I use the image it will be transparent where I say it should be?

There's a number of ways to do this, and the best way to do this depends on exactly what you're trying to do.

So, what are you trying to do?

First off, PNGs support transparency. So you will want to save the image in that format. As for the first question, like TST said, more info is needed. Maybe you could post the image and note what you are trying to do. If it's a solid color background, removing it would allow for transparency, assuming your goal is to add a different background.

I got a little logo. I am going to use it in Silverlight in a XAML file on top of another image and so the edges and other parts need to be transparent. I have the imag sitting in te GIMP file right now and right now the color is already the same constantly throughout the image to be the transparent color.

Have you tried the color select tool? <---looks like that. It should be able to accurately select the background with a single click. You can then just hit the delete key on your keyboard to remove the background.

You could also try this:

select the brush tool
in the tool options, there is a "mode" drop down menu. Set that to "color erase."
set your foreground color to whatever color you want to erase
brush everything off of the layer.

here is the logo in questioni

Definitely try the color erase function I mentioned earlier. I think it may be one of your simplest solutions in this case.

Use the Color picker to pick the background color. It becomes the FG color in the color boxes.



Colors > Color to Alpha > Drag the color you picked into the color bar.



Your logo cleaned up very nicely just doing those two steps. It doesn't always happen that easily. Below are my results but I recommend that you also do those steps to help familiarize yourself with those particular aspects of GIMP. Just an added note here: alpha means transparent. When you do Color to Alpha you are changing a particular color to transparency.

There's always more than one way to skin a cat. I completely forgot about color to alpha.

Oh, yes. There are many ways to do the same thing in GIMP. Color to Alpha is one of my favorite tools.

Gimp is so versatile.

2 of the 3 methods are news to me, so good work guys!

gimp is awesome.

This is a feature I didn't know about. I went into the brush mode and I can't find any drop down menu where it says "Set that to "color erase.". Could someone please guide me to where it is? It looks like it would be handy for some thingys. thanx

Molly,

In the brush tool options the drop down menu should be at the top.

Hot dog, I never thought it would be in with the modes. Funny but I didn't see it there before. thanks Draconian

Edit: I just tried it.
I made a duplicate, set it to erase, set the foreground to white, cuz that is the color I wanted to get rid of. It erased the white, but it darkened the other colors and I think, made them transparent. Was this the correct way? What do I do to get the colors back that I didn't want to erase?

Yes, what it does is it pulls all of whatever color you choose out. Some artists who draw a photo and scan their image in use this tool to erase around the edges of their drawing without interfereing with the actual edges. The advantage is that the slight opacity that comes out of the other colors is barely noticeable, so it's a lot more forgiving than the erase tool. They explain how it all works here: http://docs.gimp.org/2.6/en/gimp-tools-paint.html under "color erase" toward the bottom of the page.

That is one cool trick. Thank you!!!

It's kind of like Color to Alpha. I would suspect that the two are inter-connected.

Very interesting way to use a brush!