I have a problem with The GIMP ... it is performins some undesired scaling
of my RGB values when I change alpha value.

The situation is as follows. I have an application which can generate TIFF
images. If I use this program to generate an image of some color, say RGB
= [20, 30, 40] for all pixels, and set alpha = 255 for all pixels, and
then load the generated image in GIMP, then everything is fine. Color
picker says the color of all pixels is [20, 30, 40], and alpha 255.

But then if I generate a new image, exact same colors, but alpha = 128,
and load the image in GIMP, then color picker says the color is [40, 60,
80], i.e., double the real values (although GIMP does tell me the right
alpha value, 128).

I might add that loading the image with 'xv' tells me that the color in
fact is [20, 30, 40], even though 'xv' cannot tell me what the alpha value

If I generate another image, same color values, but e.g. alpha 10, then
color picker in GIMP says, alpha = 10, but by now the color values have
been scales so much, that the colorbalance is not the same anymore, e.g.,
RGB = [237, 245, 255]. In this last example I am unsure about the exact
result values (I was testing last night on my machine at home, and don't
remember the exact values).

In summary: it seems GIMP is scaling the RGB values in response to alpha,
alpha = 128 leads to double RGB values, alpha = 64 leads to four times the
actual RGB values, etc.

Have I misunderstood something?



Gimp-user mailing list

Reply via email to