CMYK file size smaller then RGB... Why?

[apart...@adobeforums.com]

I have been receiving some very simple files from a colleague and her file sizes are a 10th of what mine are. The confusing part is she is sending them in CMYK and I convert them to RGB. Theoretically they should be smaller. Dimensions and resolution are exactly the same and both are 8 bits per channel and no color profiles. She might be using an older version of Photoshop than me (currently CS3). Anyone have any ideas?

[steve_g...@adobeforums.com]

What are the formats? And where are you getting the file size readings?

[J_Ma...@adobeforums.com]

These are uncompressed file sizes? My guess, given that you say how simple they are, and the 10:1 ratio, that she's using LZW compression or RLE compression on the file. Both lossless and should be fine.

no color profiles

You should check with her to determine her working CMYK color space (in her PS color settings) and then assign that CMYK profile before converting to RGB. Then you want to embed your RGB profile or convert to sRGB and strip the profile before posting to the web.