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  1. I have the dubious task next week of explaining image formats (jpg, tiff, raw) to a group of non-photographers (OK don't ask!). So I did some prep, and came unstuck in the detail. I'd always assumed that for raw files a rule of thumb that the pixel dimensions (width by height) times 3 (red, green, blue) would give a reasonable approximation to the filesize. But this simply isn't true. For example a 5472 by 3448 image (Canon Raw (Cr2)) only occupies 23,300 Kbytes on disk. I've played around with 8, 12,14 pixel depth, and understand that 1K is 1024 bytes, but I cannot make the numbers add up. My conclusion is that although Canon Raw is "uncompressed" it actually uses a "lossless" compression technique (e.g. given a string of identical pixels it records the colour of one pixel and the length of the string) and expands the string when the file is opened (e.g. in Lightroom) Is my assumption correct? Help needed & much appreciated!