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May 2006
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2006.05.07 01:13 "LW support?", by Arnaud Janc
Hi, I would like to read tiff linework (LW) images. But it doesn't work with libtiff. Is there any problem of patent which justify this lack of support? I saw two things to deal with: 1/ Compression Tag is define in tiff.h but the codec is not implemented tiff.h:#define COMPRESSION_IT8LW 32896 /* IT8 Linework RLE */ but there is nothing in tif_codec.c and nothing like "tif_lw.c" exists. Does anybody have an idea of the complexity to do such job? I know there are short run and long run to deal with in the compression and obviously some speed improvement to take care. 2/ COLORTABLE Once again the tag is define but nothing is implemented. tiff.h:#define TIFFTAG_IT8COLORTABLE 34022 /* LW colortable */ As far I can see the function "TIFFRGBAImageBegin" should read the tag and fill some tables (one per channel). Those tables are then use in function "makecmap" to fill a table "PALmap" from TIFFRGBAImage. The problem is that the structure is only define for RGB colormap (indexed tiff) so there is only 3 tables available instead of 4. A quick and dirty hack would be to simply use only the first one table to store data from TAG before filling "PALmap". We should then use PACK4 instead of PACK to fill it. For the moment that's all If anybody could give me some advice (or directly a working patch ;-) ) thanks in advance