Arcady- JPEGs offer by far the most compression, but they are also what is called a lossy (not lousey) format- there is some degrading of the image. Most other formats offer optional LZW compression, the same type used in a ZIP file, which will typically only compress a photo about 25 to 40% (but does a lot better on areas of solid color). Compressed BMPs are very rare (but it is in the spec), other than that it is a toss up, a LZW compresssed TIF is about the same size a compressed Photoshop file or whatever. I use Photoshop format on most all the stuff on my computer, but I have 24 GB of disk space, I put the textute maps of the file I put on the web as JPEGs. There is also the new PNG format, but I haven't used it, some have said it is non-lossy and compresses better than LZW, I don't know that for sure.