Message-Id: <mailto:199503110234.UAA22101@library.wustl.edu> Date: Fri, 10 Mar 1995 20:46:31 -0500 From: Bob Rosenberg <mailto:rarosenb@GANDALF.RUTGERS.EDU> Subject: Re: JPEG and image size To: Multiple recipients of list IMAGELIB
> I'm afraid I don't quite know how to phrase this question, but here
>goes. I know that when you use JPEG you can choose what degree to which
>the algorithm will compress a file, and this degree affects file size and
>image quality in opposite directions. 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.
>
> An example of the information I'm looking for, with completely made-up
>figures, is: at 75% a 1 megabyte file turns into 300k.
>
>Thank you very much,
>kim brookes, in grant proposal hell
>Schlesinger Library, Radcliffe College
mailto:>mailto:k_brookes@harvard.edu >
The degradation of the image depends on the compression, but it also depends on the nature of the image. Images with lots of color look better than high-contrast images with little color, for example. The latter tend to get "halos"--bright borders around dark lines--at relatively low compression. In a test on a large (21Mb), high-resolution image with a fair number of colors, compression of 10:1 lost little information. But that question of loss is also relative to the use planned for the image. I think most users agree that 10:1 compression of colorful images loses very little in quality. Compression is more meaningful (for you and the granting agencies) than the program's "quality" measure. A few trials will give you the compression equivalent for a given "quality" reduction.Good luck getting Charon to ferry you back on your way out.
Robert Rosenberg + Supposing is good, Thomas Edison Papers + but finding out Rutgers University + is better. New Brunswick, NJ 08903 + --Twain mailto:rarosenb@gandalf.rutgers.edu