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Re: compression strategy

  • Subject: Re: [iris-photos] compression strategy
  • From: Cathy <kittencampi@earthlink.net>
  • Date: Mon, 28 Jun 2004 13:15:52 -0700

oneofcultivars@aol.com wrote:
In a message dated 6/28/2004 10:25:45 AM Central Daylight Time, kittencampi@earthlink.net writes:

JPEG compression formulas don't produce linear results. The scale you see as you save an image to JPG is a quality index scale.

I do not see a scale identified as such when using PhotoStudio to resize photos.
If you are resizing by dimensions or dpi it wouldn't be a factor. If you are using a RESIZE command it possibly could be taking all the guess work out of jpg compression. Each time you use the SAVE command to jpg format it will use the default compression index.  Use the SAVE AS  command and you should see the scale.(probably reflecting the default setting.) Even at the 100 setting(no compression) there is always some loss when resaved to jpg format. resaving with compression increases the loss. For example the JI pollenating jpg at  a 50 index resaved at a 50 index would result in a 26% loss in detail. Small losses in detail are not that noticeable on the computer but do appear in printing. Editing photos for printing is usually done in TIFF format  which is LARGE file but lossless but no compression. Jpg( JPEG-Joint Photograph Exchange Graphics?) was done to make small files for internet transfer.

On the other hand, when scannin' images to a specific size I am given percentage reduction information for the scan being sized. Is this the same, or similar to, the scale to which you refer?
Dunno. specific size dimensions - no; specific size dpi - no but file size - - probably. I will send you a small jpg compression checker from www.mediachance.com. It is helpfull to know how compressed an image is before you start to work on it.

Prechate the other info and response.

FWIW: Fun With Internet Whackos <laughin'>
Ah Hah! Now yu're getting personal :-D

Michael M.

Bill Burleson

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