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- From: franti@polaris.utu.fi (Pasi Fr{nti)
- Subject: Re: bitmap compression
- Message-ID: <1992Nov6.143020.13682@polaris.utu.fi>
- Organization: University of Turku, Finland
- References: <Bx9C19.4r2@ccu.umanitoba.ca>
- Date: Fri, 6 Nov 92 14:30:20 GMT
- Lines: 44
-
- umfehr06@ccu.umanitoba.ca (John Fehr) writes:
-
- >I'm currently looking for compression algorithms to compress weather charts.
- >These charts contain about 95% white pixels, and 5% black pixels. I've
- >already thought of using GIF, but the files only shrink down to ~100k.
- >(Originally ~1meg uncompressed.) I've also thought of using arithmetic
- >coding. Does anyone have any suggestions as to other compression methods?
-
- I have tested several methods for a little bit similar A4-size image with
- 94,8% white pixels of total 2 miljon pixels (278kB).
-
- Method: Ratio (1:N) Speed (sec)
- ------- ----------- -----------
- PCX 3,76 ?
-
- GIF 7,05 ?
- CCITT G3-standard 7,23 22 (#)
- PKZIP -es 8,17 1 (*)
- Block Coding 8,89 4
-
- CCITT G4-standard 16,36 24 (#)
-
- BQ-coder 21,24 13
- Arithmetic Coding 21,86 64
- Q-coder 21,86 36
-
- (*) I used pkzip for the PCX-file.
- (#) Alchemy's TIFF-format was used.
-
- As you can see, it is a compromize of size and speed. All versions
- of arithmetic coding (BQ, A, Q) gave good result but they are also
- slower than for example Pkzip or Block coding. The arithmetic coders,
- especially Q-coder (BQ includes Q-coder) are complicated methods, so
- don't believe those who tell they are simple.
-
- What format your weather maps are? Can you possibly send me one or two
- files of them? I would like to use them as a test images also.
-
-
- ----------
- Pasi Fra"nti
- franti@utu.fi
-
-
-