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Old Oct 8, 2006, 8:33 AM   #1
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What causes the file size to change on a photo. I have notice this when I check the size of my photos. I use AV mode. Some of my photo size are 3.3 MB, 2.8 MB etc..
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Old Oct 8, 2006, 10:14 AM   #2
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The amount of similar information, all black, blue sky, etc. and the ISO setting (higher means larger). This is assuming you don't change any quality settings between shots. The compression algorithms map out similar information and stores it along with a mathematical decompression algorithm. So a large area of the exact same information can be represented by one unit of compression. This is an overly simplified explanation but you get the idea. To see how ISO settings impact image size, look at the number of estimated remaining shots at ISO 100, then set your camera to it's maximum ISO. The number of remaining shots should be reduced.
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Old Oct 9, 2006, 12:55 PM   #3
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An underexposed 'noisy' image will also have a bigger file size...

-> RAW files are constant (unless they are embedded with JPEG)
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Old Oct 10, 2006, 4:53 PM   #4
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As NHL mentions - it is the amount of information and how it is handled that has a great effect on file size.

This is why many of us prefer shooting in RAW. This file format is all the information the camera records (think of it as a digital negative). Jpegs converted from RAW files will also, in general, be larger than those produced 'in-camera'.

If you are not anticipating several modifications of the original image, Jpegs work just fine.

As mentioned earlier, just setup a standard shot and take one of each resolution your camera offers. It will give you a perfect reference for the future. Oh, yeah, be sure to view all images at 100%...you will see some very obvious differences.
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