My guess would be the IDL file is upside down in the Y direction, but it would be hard to say without knowing how you are comparing the RGB values. If you reverse the IDL image in Y (image = reverse(image,2)) does that help the comparison? IDL is the only software in the world (AFAIK) that thinks the (0,0) pixel is in the lower-left corner. Everyone else believes it is in the upper-left corner.

Hi David, Yes, I think that's the case. Also, he has tried already that, if I understood correctly, on a previous post (this post was a duplicate from another one, see a few post below). Thanks!, Fernando