thank you guys for all the inputs,
For the moment I changed the color setting in CS2 to adobe RGB, it seems that the quality loss is better than before.
in a close up human potrait photo the loss is still significant but in a landscape pics with less detail (like clear blue sky and a green field from far) the loss is not so much.
I'll have a go with lightroom as suggested
Why not try editing in Adobe's RAW processor? It's pretty easy after you understand the terms. The terms can be defined simply by doing a few searches in Google. Last, even if you don't really understand the terms, the sliders give you visual clues as to what they are doing, and you can trust your eyes in this respect and ignore the definitions. I read a book on Adobe RAW, and these are my notes:
1) Is there any advantage to using PSCS2 Photo filters when you are shooting and using Adobe Raw? No.
2) Is there any image degradation adjusting white balance in Adobe Raw as compared to setting the white balance manually with a gray card in the camera? No, or at least much less than when in PS.
Tabs are in fairly logical order.
1) EXPOSURE: Although third down, this is what you need to get right before going to white balance IF you need more than a .25 exposure adjustment. If less, than use WB first. Affects entire tonal range, but is mainly a white balance tool.
2) WHITE BALANCE: White Balance: If only a small exposure adjustment is needed, then set white balance first.
(a) Temperature: Tint = white balance. Temperature = blue (cold) ----- yellow (warm)
( Tint: green ----- red
© White balance sampler: Use this sometimes to get a rough WB, then use temperature. Do not sample a specular highlight however.
Exposure and white balance are critical to RAW.
3) BRIGHTNESS & CONTRAST: Shapes entire tonality of image.
(a) Shadows are presented before this slider, but most of the time better to do this first because shadows is a black point set point and will have big changes in the entire image.
( Brightness first: Changes midtown brightness w/o changing end point tonal range.
© Contrast second: positive brightens values above the midpoint set by brightness and darkens values below that midpoint. Negative settings darken values above mid point and brightens those below.
IN BOTH CASES BRIGHTNESS AND CONTRAST DO NOT CHANGE THE END POINTS—black and white points.
(d) Contrast will have a more obvious effect on the darker ¾ tones than the brighter values.
(e) To brighten the dark ¾ tones w/o affecting midtones, reduce contrast. It is better than using brightness. If image goes flat, use shadows to get it back.
4) SHADOWS: sets black point, and has big effect on image!
(a) If shadows have important detail, set to zero or leave at least some headroom. Then use P.S. for finer control.
(a) Sharpness: preview only. Use PS for sharpening.
6) LUMINANCE SMOOTHING
(a) Luminance noise is random speckled variations in tone that usually increase with ISO speed. Noise of this sort is more concentrated in darker zones. Simply raise the slider until it disappears. Does impact sharpening.
7) COLOR NOISE REDUCTION
(a) Random magenta and green splotches in the dark areas, or, in some cameras, around highlights. Raise slider until it goes away. Has less impact on sharpness than luminance smoothing. Default is good all around.
NOTE: ENLARGE and PAN to see effects of both, or you will not see them.
LENS TAB: Chromatic Aberration: little effect on entire image.
RC = Red/Cyan fringing