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Most digital cameras save images in only one file type: JPEG (Joint Photographers Expert Group). But even if this is the case with your camera, read on, because you're going to discover something disturbing about JPEG files. And what you can do about it.
If you own a professional digital camera, or one designed for serious enthusiasts, you'll probably have one or two other options: TIFF (Tagged Image File Format) and RAW (Raw isn't an acronym. It denotes files that have been saved exactly as they were recorded by the image sensor.)
JPEG files have an advantage that make them the favorite of most camera manufacturers - they compress. That's why your camera probably offers three options for saving JPEG images - typically they are Small, Medium and Large. Each option indicates a different degree of compression… and compression actually throws picture data away.
For most snapshooters, this isn't a problem, because only “duplicate” data is lost. But the greater the compression, the greater the amount of data that's discarded… and the greater the amount of fine detail that's lost.
TIFF files, on the other hand, are larger, because they're not compressed. That means you can save many fewer TIFF files on a memory card than JPEG files. How many less? A 6 MP Nikon D100 can store about 150 – 175 JPEG files with minimal compression on a 512 MB compact flash card. The same card will only hold about 27 6 MP TIFF files.
In other words, you can get more than six times as many JPEG's in the same amount of memory. That's about 3 MB per JPEG file vs. about 19 MB per TIFF.
Finally, there are RAW files. They're about half the size of TIFF files, and have one other big advantage. Because they contain the data just as the image sensor “saw” it – unprocessed in any way - professionals find that these files provide them with the best opportunity to recreate on paper (or on screen) the scene as they envisioned it when they shot it.