Faxes would be "bi-level" images, and the best

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Post #59,682 by a6l6e6x 10/26/02 10:31:36 PM Reply	Faxes would be "bi-level" images, and the best compression results would come from [link\|http://www.cl.cam.ac.uk/~mgk25/jbigkit/\|JBIG] (Joint Bi-level Image experts Group) standards group. * Close to state-of-the-art lossless compression ratio for high resolution bi-level images. * Around 1.1 to 1.5 times better compression ratio on typical scanned documents compared to G4 fax compression (ITU-T T.6), which has been the best compression algorithm for scanned documents available prior to JBIG. * Up to 30 times better compression of scanned images with dithered images compared to G4 fax compression. * Around 2 times better compression on typical 300 dpi documents compared to 'gzip -9' on raw bitmaps. * Around 3-4 times better compression than GIF on typical 300 dpi documents. etc. Alex "I have a truly marvelous demonstration of this proposition which this margin is too narrow to contain. -- Pierre de Fermat (1601-1665)
Post #59,852 by Arkadiy 10/28/02 10:11:22 AM Reply	I thought faxes support gray-scale? -- We have only 2 things to worry about: That things will never get back to normal, and that they already have.
Post #59,965 by a6l6e6x 10/28/02 9:37:20 PM Reply	No. Group 3/group 4 compression of a fax is bi-level. Now, you can use it for [link\|http://desktoppub.about.com/library/weekly/aa090600a.htm\|halftone] images. But any given pixel is either black or white. Your eye and brain integrate the pixels over the local area to see grays. This is exactly what you have in a newspaper picture. On any given spot you either have or not have ink. The local ratio of black to white in an area gives you the effect of grays. Pull out your magnifying glass and take a close look. Alex "I have a truly marvelous demonstration of this proposition which this margin is too narrow to contain. -- Pierre de Fermat (1601-1665)

Dunno where to put this - graphic compression - (broomberg) - (9) - Oct. 24, 2002, 07:35:34 PM EDT

jpegs are lossy - (imric) - (2) - Oct. 24, 2002, 07:43:42 PM EDT

jpegs don't *have* to be lossy - (wharris2) - Oct. 24, 2002, 08:40:28 PM EDT

Yup I know - (broomberg) - Oct. 24, 2002, 09:10:21 PM EDT

PNG or JPEG - (admin) - (2) - Oct. 24, 2002, 08:03:14 PM EDT

Thanks on the QA - (broomberg) - Oct. 24, 2002, 09:16:37 PM EDT

More to the point (follow the line...) - (kmself) - Oct. 24, 2002, 11:32:05 PM EDT

Faxes would be "bi-level" images, and the best - (a6l6e6x) - (2) - Oct. 26, 2002, 10:31:36 PM EDT

I thought faxes support gray-scale? -NT - (Arkadiy) - (1) - Oct. 28, 2002, 10:11:22 AM EST

No. Group 3/group 4 compression of a fax is bi-level. - (a6l6e6x) - Oct. 28, 2002, 09:37:20 PM EST

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