Swapping color gradients with Gimp

Question

I have a logo that I would like to use on a shirt that has a black to white gradient throughout the logo. Since the shirt may end up being blue and the color printed on the shirt yellow, I want to make the logo's gradient go as follows:

• From: black to white
• To: transparent to yellow

Is this possible to do in GIMP using one of its color tools?

Answer 1

You want to convert a B->W gradient to transparent->yellow?

1. Add an alpha channel to the layer, if it hasn't already got one.
2. Make a selection that covers the gradient area fairly accurately. I am assuming this is necessary because the gradient colors may be used in other areas of the design (which you don't want to affect). If you have areas where the gradient mixes with the background, you may want to feather the selection.
3. Layer->Transparency->Color to Alpha . Choose black as the color to convert.
4. Colors->Levels. Select Blue channel. Set the second (rightmost) 'Output Levels' value to 0 (it would have previously been 255).
5. Done.

A more flexible approach would involve creating a transparent->yellow gradient (as in, making one in the gradient editor, not putting one on the image :). Step 3 could then be 'Colors->Gradient Map' (with no step 4 needed.). However this requires gradient-editing skills.

Answer 2

I wrote a small tutorial about how to use a transparent gradient in gimp. Maybe it can help you

http://infofreund.de/gimp-transparent-gradient/