how to change the color that's used for transparency automatically, or programmatically?

Question

For every picture (e.g. bmp, png), a transparent point actually does have a color

The transparency is either

• defined by alpha channel mask (e.g. in PNG)
• or one of the colors is defined as transparent, and the viewer program is responsible to replace pixels with this color - as transparent.

I have a strange scenario, where one program knows transparency, the other doesn't so it shows the original color.

So

I want to replace the color only in the pixels where it is defined to be transparent. I need it all to be defined as white, while keeping it transparent

I can pre-convert my input to be a specific format, if it helps the process.

For now my toolbox includes: ImageMagick, Gimp, python programming (PIL) and maybe more, but I don't know how to do this specific task with these tools.

Answer 1

try:

 convert infile -fill white -opaque none outfile