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July 2002
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2002.07.23 22:50 "CCITT Group 4 assistence needed for HylaFAX", by Lee Howard
Hello. I know that this is perhaps off-topic, because it doesn't directly deal with libtiff, but it seems like the best place for me to find help on this... I'm needing some help with getting HylaFAX to support MMR-encoded (Group 4) faxes. I've got a nearly complete patch for HylaFAX which does this, but I've run into a couple of snags which are rooted in code incompatibility with the differences between Group 3 and Group 4 TIFF image data. As I'm not TIFF-savvy, I'm seeking for help on this. In HylaFAX's faxd/CopyQuality.c++ there is a rather large function, FaxModem::recvPageDLEData(), which (among other things) determines the number of lines received in the received TIFF image data by counting EOLs. This is obviously a flawed approach when dealing with MMR/Group 4 TIFF image data. Consequently HylaFAX ends up believing that it receives a zero-line TIFF image, and this is written into the TIFF tags. This EOL-counting mechanism may appear elsewhere in the code, also. In HylaFAX's faxd/TagLine.c++ there is yet another large function, FaxModem::imageTagLine(), which strips a few lines from the top of the image and replaces them with created lines which image the facsimile tagline information. It does this in accordance with Group 3 protocol (i.e., with EOLs) rather than Group 4. I'm wondering if there's anyone on this list who is familiar with CCITT Group 3 and Group 4 and would be willing to look at some HylaFAX code, correspond with me privately or with the hylafax-devel@hylafax.org list, and tolerate a fair amount of naievity on my part in order to get HylaFAX supporting MMR-encoded faxes. If so, please let me know. However, even if you don't have this kind of time, I wouldn't mind some general outlines on how these two procedures should be altered for Group 4 faxes (i.e., how to count lines and how to image a tagline on top of an existing image). Thanks. Lee Howard HylaFAX developer