Part of this problem can also be the fact that you can create either 4 colour images (Cyan Magenta Yellow blacK) or 3 colour images (Red Green Blue). Some programs do not convert between the two very well, (software settings) this would be when saving from 3 colur to 4 colour in most cases.
And dont forget what you see on screen is affected by your screen (RGB) settings of brightness and contrast and as output by one piece of software, open the image in another program and there may be variations, same will occur when printing to different style of printers, ie bubble jet or colour laser or colour seperation for offset printing.
See also the commetn about gamma settings.
Darryl Jenkins Perth Western Australia