Why is the imagedata value different from Win32 to MacOS platforms?

[Joel Guillod]

For image processing I have to extract the RGB values from an  
imagedata of an image but I got different results under MacOSX and  
Win32.
I found that the imagedata values is different between the two  
platform: every color component of pixels is slighty changed. I have  
not found in the documentation such a change depending on the  
platform. Notice that <the text of image> is identical between both  
platform.

Could anyone give me a clue?

Is there an easy other way to get the exact RGB array on both platforms?

Thanks!