anyone knows color management ???

[boarder's paradise]

Hi folks. If you know what "color management" is, maybe you can help me:

I have this color chart (PNG file):



I open it with IrfanView, and save it as JPEG with 100% quality and with color subsampling disabled, to get the best possible JPEG quality that IrfanView offers. This is the JPEG file that IrfanView produces:

http://img184.imageshack.us/img184/4564/a3gencolorhighwwwfhoemdjv4.jpg

Most (but not all) of the colors are DIFFERENT to the picture above! The red pixels in this image denote different pixels:



How is this possible ? It surely isn't related to color management (given that IrfanView assumes sRGB by default for both the input and the output), but what is it then? I always thought that it's mostly edges that suffer from jpeg compression (that's where you see artefacts, etc.). But why can't jpeg save large areas with the same color correctly, even when color subsampling is disabled ??

Thanks for any help!

[boarder's paradise]

By the way, if you want to try it out yourself using IrfanView, it's easy:

1) Download the first two files I posted above (PNG file and its JPEG-conversion)
2) open PNG file in IrfanView
3) press F12 for drawing tools
4) select the color-picker
5) look for the field L1 on the color chart and click anywhere inside it
6) in IrfanView's tools palette click on the color you just picked
7) click "define custom colors"
8) you see the RGB values 62, 39, 50
9) do the same with the jpeg file
10) you see the RGB values 62, 38, 51

Or do you see other values ??

[Sam_Zen]

I don't use color management, but I slightly remember earlier topics about this phenomenon with the values.

[Sam_Zen]

Sorry I wouldn't know.

[boarder's paradise]

ok, thanks anyway

[Skippybox]

Are you talking about a thread like this?

I don't use color management. It's another thing to worry about and learn...

My impression is that JPG changes the colors as it sees fit to achieve it's goals in compression. Quite lossy is it indeed! A file is never the same. How do you think it achieves such small file size even at 100%? If it did preserve color, I would think it would be far more competitive with PNG, yet it is not. Even 2 color images come out very strange with JPG at 100%.

[boarder's paradise]

My impression is that JPG changes the colors as it sees fit to achieve it's goals in compression. Quite lossy is it indeed! A file is never the same.

hey skippybox, sorry for the late reply ...
Yes, from what I've seen you are right. But I claim, that it wouldn't be necessary.

How do you think it achieves such small file size even at 100%? If it did preserve color, I would think it would be far more competitive with PNG, yet it is not.

What I wanted to point out is that many color patches above keep exactly the same value after jpeg compression, others change ... but there is no reason for changing the color or large areas, and it's not what users would expect from jpeg files.

Even 2 color images come out very strange with JPG at 100%.

I'd be very interested in seeing this. Can you post examples here ?
cheers & thanks