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DJofTexas
05-09-2006, 08:11 PM
I have a technical question: do jpg files lose data every time you turn on and off your computer?

I know they lose it with each save; looking back at old jpgs I've archived on my hard drive, I am starting to wonder if there is loss with each time a computer is turned on and off.

Is there any format that can do some compression without the lossiness of jpg?
At present, I use the following strategy to prevent loss of data on my digital photos:
I burn my photos directly from the memory card to a CD for archiving.

I am pc based, so whatever compression format needs to be compatible with that.

I am experimenting with the png format now. For years, I used .tif, but with the amount of photos I do and the size of the files, I can't afford the storage that would be required for me to store everything as a .tif file.

I am interested in any advise in this area. It's a conundrum I've studied a long while.

Thanks

DJ

David Metsky
05-09-2006, 09:05 PM
No, turning your computer on and off has no impact on the files stored on your computer. They only lose information when they are resampled or reimaged. This occurs only when you do a "save" of a JPG image that you brought into an image editing program. If you use "save as" and a different file name, your original will not lose any information.

If you keep the originals on your hard drive, they will always contain all the info that came off your camera.

-dave-

Norm in Fujino
05-10-2006, 09:26 PM
I have a technical question: do jpg files lose data every time you turn on and off your computer?

I know they lose it with each save; looking back at old jpgs I've archived on my hard drive, I am starting to wonder if there is loss with each time a computer is turned on and off.

Is there any format that can do some compression without the lossiness of jpg?
At present, I use the following strategy to prevent loss of data on my digital photos:
I burn my photos directly from the memory card to a CD for archiving.


I would not use compression software with any photograph I felt worth saving. As David noted, merely copying photos to hd or cd/dvd causes no change to the file or image. The jpep compression only comes into play when you open a file in an editing program, then resave it (CTRL-S) under the same name. If you save under a different name, the newly named file will have slight (depending on the original quality setting) degradation, but the file with the original name will remain unchanged. Alternately, use "save as copy" which has the same effect.

In practice, though, if you shoot at your camera's highest jpeg quality setting, you can probably resave a jpeg numerous times before any visible artifacts occur. YMMV.
If you're concerned about historical archiving, never change the original photographs, and only resave copies.