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Old May 14, 2003, 4:23 PM   #1
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Default Understanding JPG files

For anyone that is curious about the JPG questions below, I have posted answers to these after having recently had to answer them.

Comments welcome: http://www.trevoli.com/tutorial2.htm

1)***After loading a photo only once, will a repeated save/modify cycle continue to degrade the image?

2) Why does the file size grow or shrink when I make a change to a photo, and then resave?

3) Why does a camera generated image that is 1.4MB, go down to 386k when an apparently low compression level of 92 is used?

4) Is there any industry standard that defines what the amount of compression is for a given number?
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Old May 14, 2003, 8:30 PM   #2
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I find it intriguing that Photo Finale doesn't lose picture quality on subsequent resaves of a JPEG file. Could you be a little more specific as to how it does that? For example, if you renamed the picture and reloaded the renamed file, wouldn't you get some picture degradation when you saved it a second time? I'd be interested to know how the program keeps up with the original data.
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Old May 14, 2003, 9:30 PM   #3
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Quote:
Originally Posted by lg
I find it intriguing that Photo Finale doesn't lose picture quality on subsequent resaves of a JPEG file. Could you be a little more specific as to how it does that? For example, if you renamed the picture and reloaded the renamed file, wouldn't you get some picture degradation when you saved it a second time? I'd be interested to know how the program keeps up with the original data.
lg,
I think that you misunderstand the explanation in that website. Me too ,I find the text confusing and not so clear. But, the from last paragraph:
Quote:
The same logic applies for Save-As. Using Save-As 100 times in a row only incurs one generation of loss. But Save-As, then re-load 100 times would cause 100 generations of loss.
IMO, I think that all photo editors behave so, not only PhotoFinale.
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Old May 15, 2003, 3:57 PM   #4
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The last poster was correct - the article should apple to all JPG software.

The article was intended as a forum contribution on JPG, not something specific to our software.

If there are specific parts that are confusing I would like to clarify them and appreciate any feedback.
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Old May 15, 2003, 10:35 PM   #5
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Thanks for the clarification, KCan and lwhitney. I guess I should have read it more thoroughly.
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