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Original bmp file .. appx 20mb jpg compression 2: 217kb jpg compression 15: 79kb jpg compression 30: 51kb ..reccommended jpg comression 50: 36kb ..reccommended jpg compression 150: 20kb.
Even 20kb version was adequate for pictures say up to 5 by 3 inches on an 800 by 600 pixel screen resolution. 30 to 60kb seems a good trade off between file size and quality, but file size you get relates to picture composition. This would seem a good range for 'average' sized jpg web pictures without noticably losing quality.
----------------------------- 4. jpg versus gif gifs are good for icons and small pics - these can be in 16 colours which makes very small files.
jpeg is a compression facility and does not do so well with 16 colour or small pics, unless compression number is increased. jpeg is really for compressing big pictures, lots of data, 24 bit colour.
With gif you do not get options for palette selection and compression levels that jpeg gives.
I use gifs for icons and small pics, jpeg for rest. ------------------------------
5.Black and white. For texts, scan textual material in B&W even if there are colour pics on page. Separately scan colour pics, in colour. Black and white is 1 bit not 8 bit - file sizes are much smaller than equivalent in colour.
I have received text scans in colour - usually black is grey rather than black. If 'ocr' software won't scan them because resolution is too low (and it usually is!), I do next best thing and convert pic to B&W. The process usually involves darkening colour image as much as possible, to increase blackness of characters.
Then convert to black and white using 'threshhold' control. This threshhold is just point at which analyser decides it is a 'black' pixel square, not 'white'.
The threshhold range is 0 t0 255, in range from 127 to 220 does trick, dependent on colour original, and allowable extra black 'dots' you get if value is set too high.
File sizes can reduce a text page from 100kb jpg to 20kb gif, just by going to b&w. Somehow I prefer gifs for black and white - I feel gifs are better suited to simpler jobs than jpeg.
Paul Hailey, email@example.com and site http://www.hailey,clara.net