Message-Id: <mailto:199503151323.HAA03721@library.wustl.edu> Date: Wed, 15 Mar 1995 08:20:10 +0400 From: Terry Lund <mailto:lund@PCD.KODAK.COM> Subject: Re: JPEG and image size To: Multiple recipients of list IMAGELIB
At 5:10 PM 3/10/95, Sandeep Somaiya wrote:>kim brookes <mailto:k_brookes@harvard.edu> wrote:
>>> 1. What degree, or percentage, or whatever the proper term is, have people
>>> used without losing an unacceptable amount of image information,
>>>2. can someone give me an example of the change in file size using this
>>> degree.
>
>JPEG lets one select file size vs. image quality tradeoff by selecting a
>quality setting. This quality setting or Q-factor usually ranges from 0-100
>or 0-4 or a high-medium-low scale or excellent-good-normal-bad kind of a
>scale depending on yor software.
[snip] - Good summary of the tradeoffs was provided by Sandeep, and other replies previously posted. I'm a few days behind this listserv.
>
>These are approximations. Results vary from image-to-image and acceptable
>quality defination varies from observer-to-observer.
>And standard disclaimer applies.
>
I would just add that the results obtained from JPEG are also strongly dependent on the quality of the scan data of the "original", and the size of the image and viewing conditions on output.
Some years ago we did testing of JPEG with 2K by 3K images scanned from 35mm negatives (24 bit color data). We had one demonstration with a compression ratio of about 150 to 1, and the output was a 4x6 inch print, and we had some heated discussions about which was the original and which was the reconstructed picture, because it was so hard to tell the difference between the two prints, and in fact, the first set of prints were accidently mislabled. The artifacts were real subtle for that particular picture. That is the high end of anything I have seen, but we had very high quality scan data to start with, and we also has a fairly small print on output (the print was done at 500 pixels per inch, so we used the full 2K by 3K data for the print)
Terry Lund Phone: 716-726-0533 Digital and Applied Imaging FAX: 716-726-0500 Eastman Kodak Company 901 Elmgrove Road KNET/KMX: 236-0533 Rochester, NY 14653-5218 Internal Mail: 3/1//EP/35218