Re: Roll File Formats
By Zoltán Jánosy
I'd add some more thoughts to my earlier letter.
> [ I think TIFF format with CCITT Group 3 compression is related to
> [ the current standard for facsimile transmission. It sounds like
> [ it's quite appropriate for the raster-scanned image, and it is a
> [ lossless compression scheme.
Yes, though it may not be optimal for rolls, since the Huffmann coder it uses was designed with scanned text files. Thus it is more optimal for short black and not too long white pixel blocks.
For rolls a simple run-length encoding (or something like LZ) would be good enough. It is also much easier to process a run-length encoded file (where only the length of the block of the same color is stored alternatingly) than a raw format. This feature of the CCITT Group 3 coding is extensively used in our roll processor.
> Has anyone tried viewing a long file
> [ like this with a graphics viewer/editor?
Yes I tried several programs without success. The problem is that all of them tried to load the whole file at once, and they ran out of memory. I began to write a buffered viewer but gave up because of the stupid memory management model of the PC. Now that there are flat model 32 bit compilers it should be much easier to write such a viewer. I may do it sometime. Run-length encoding comes handy here as well, since one image is about 10 MB (200 dpi b&w) but the coded image is only about 1-2 MB, which can be kept in memory all the time (decoding on the fly is much faster than loading from the disk).
Zoli
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= (Mr.) Zoltan Janosy <janosy@hit.bme.hu>
= Technical University of Budapest
= Department of Telecommunications
= Sztoczek u. 2. 308., H-1111 Budapest, Hungary
= Tel: +36-1-463-2093, Fax: +36-1-463-3266 |
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