This may not be the right place to pose such a question; if so, direct me elsewhere. I've read what Real World Color Management says about color spaces. profile connection spaces, and intermediate color spaces, and I think I understand the general ideas. But when I try to figure out what is going on in specific applications, it seems to all fall apart. In particular, I am finding it hard to figure out how device profiles relate to color spaces. Let me give you an example. I've been doing some experiments with xsane and gimp 2.4. Depending on which options I choose for xsane and gimp, the RGB values for a given pixel that xsane reports on preview may or may not be the same as those that gimp reports for the same pixel. (Either xsane of gimp make be making the change, depending on the choice.) What appears on the screen in xsane and gimp looks the same in any case, as long as color management is enabled, but I haven't actually tried to make spot reading with an instrument to be sure. So presumably the applications are doing what they should, but I'm uneasy about just what they are doing. I understand that profiles allow conversion from what an input device produces to what an output device shows, and there is supposed to be an intermediate called the profile connection space. What I don't understand is how the actual RGB values in the image file may be related to theoretical values in the profile connection space. (I know that the PCS may not be an RGB space, but if I understand correctly, the difference is one of making the appropriate mathematical transformation, and in principle one could think of the PCS a being an RGB space.) In cases like that I discussed above, the PCS doesn't actually seem to exist anywhere, except perhaps abstractly as an intermediate step in translating from one device to another. Also, I am a little unclear how the values identifying the color in an abstract CIE color space relate to any of this. Presumably, the values in that space range over the full gamut of possible colors that a normal human viewer can see under standard viewing conditions, while various devices like monitors and printers can only produce a limited subset of those colors. So would it be accurate in some sense to say that the CIE color space is that for which the device is the average human viewing system? Although, it must be wrong, can we think of there being an RGB pixel in the visual cortex? In that sense, we could say that we are always converting from one device to another, and the object is that where you end up, a human viewer's brain, the final result is close to what the same human brain would record---under standard viewing conditions---directly from the source? Being confused, I'm not sure I'm really asking about what is bothering me, but any comments or suggestions about where to look would be appreciated. In particular, it would be nice to be able to follow the details of what the various applications I use actually do. -- Leonard Evens <len@xxxxxxxxxxxxxxxxxxxxx> Mathematics Department, Northwestern University