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Menasseh Ben Israel

  File compression and file formats
 

|| biography || books || autographs || publications || OCR and Hebrew || description of the project and final report ||


A book opening, two pages from a Spanish Bible (call nr. 19F12) was scanned (Deskscan with HP Scanjet 3c) and resulted in BMP format, 2,8 Mb in size, 256 colours, 2000 x 1400 pixels.

GIF en JPG are commonly used on the world wide web. JPG consisting of 256 colours is, thanks to Huffman standard compression, a small file (994 KB) compared to the corresponding GIF (2,8 Mb).

Diminishing the size of the file can also be obtained by cutting the number of colours.
Two colours, black and white, does not work in the case of JPG: it remains 994 Kb. Here GIF has the best result: 110 Kb

994 Kb still is far too big for a webpage. Besides, pages of 110 Kb are not quickly paged through. Further compression makes them less eligible.
It was decided to diminish the pages from 2000 to 1000 pixels in width. Most books will remain legible, be it sometimes with some effort. Two colours will be sufficient.

A black and white image of a book opening in GIF format, 1000x700 pixels, is only 38 Kb.
The corresponding image in 256 colours JPG is 310 KB


From left to right: original size, b/w GIF 110 Kb
Reduced to half the size: b/w GIF, 38 KB; the same but consisting of 256 colours JPG, 310 Kb

The large, eligible version can be obtained by clicking the mouse.

       

Lightning Strike 2.6 converted the original (.BMP: 2,8 Mb and .JPG: 994 Kb) to .COD format with a size of 295 Kb and 256 colours.


Conclusion:
When the colour of the images is of no importance, b/w GIF is preferred. On the webpage a small illegible version can be presented because the interested layman can enlarge it by clicking the mouse.
Special viewers need not be installed.

If colour makes all the difference, the COD format is absolutely worth trying. How images are to be presented on a website using this technique of compression is a matter of further investigation. Any viewer, necessary to open the image, should be freeware. If not, then the choice is to the enduser: JPG and consequently a longer response time and perhaps less quality, or COD with zooming in facilities etc., but then a viewer has to be bought and installed.


Last revision: 25 February 1997