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Will Data Compression Degrade Quality of .jpg Images?


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Each time a .jpg file is opened and closed in Photoshop it recompresses and the image degrades (loss, or modification of information).

 

Does the use of data compression in Retrospect or hardware cause this same type of degradation? Thanks.

 

[Retrospect version 6.0.204; Mac OS 10.3.9; 750MB RAM; backing up 60G from internal 8OG via Firewire to OWC HD 250G.]

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No, since Retrospect's compression isn't lossy (unlike JPEG, which IS lossy). Nor are the tape drive's hardware compression lossy.

 

Why are you still running 6.0 when 6.1 is a free update?

 

"Each time a .jpg file is opened and closed in Photoshop it recompresses..."

You left out two IMPORTANT steps there. You missed to point out that the image is edited and re-saved (=re-compressed) before being closed.

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I'm not sure, but I think Retrospect skips compressing files that are already compressed, such as JPEGs (with some compression algorithms, attempting to compress an already compressed file will actually create a larger file). Even if it does compress them, it's lossless as Lennart said.

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