Shel Belinkoff wrote: > So, if JPEG loses, or throws away, a lot of information, why are the files > when converted to TIFF (or PSD) so large? Where does the extra info come > from? And why does Photoshop show the smaller JPEG file to be the size of > the larger TIFF or PSD file.
Without going into a bunch of information theory, it's because there is more than one way to represent an rectangular array of pixel colors. Some are more efficient of storage than others, even ignoring compression (a la JPEG). For example, converting an 8-bit (uncompressed) TIFF to a 16-bit (uncompressed) TIFF, the doubling in size is probably pretty obvious. Same number of pixels, twice as many bits per pixel, twice as many bits total. The JPEG, when decompressed, fills the same rectangular array of pixel colors that the TIFF does, but not with the same fidelity to the original. If you take the TIFF, compress it to different JPEG files with different levels of compression, then compare the decompressed JPEG images to the TIFF image, you'll find there are differences. JPEG throws away data primarily in the very high and very low spatial frequency ranges (fast color changes and slow color changes) and that's the cause of both the differences with the original and the compressed storage size. -- Thanks, DougF (KG4LMZ) -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
