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April 2006
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2006.04.11 09:54 "Re: application supplied JPEGTables", by Gerben Vos
Joris wrote: > Meanwhile, why are you refering to a pseudo tag? Would it not > suit these needs, if the actual JpegTables tag can be set, > and when next LibJpeg is used to compress, in this case, the > application supplied tables that are set in this tag are used? Yes, that could also be an idea. But I suppose you will either have to a) parse the tables out from the tag yourself, or b) create a temporary libjpeg decompression object to do that parsing, and then copy the tables into the libjpeg compression object. Neither seems very elegant to me. But I'm not going to implement this, and I'm not very much into the libtiff internals when it comes to JPEG compression, so your ideas are probably worth more than mine. > > However, maybe for your application at this moment it would be easier > > to do the JPEG compression yourself, and then use the raw strip/tile > > writing functions? > > You can do that, because the tables inside the strip/tile are > supposed to overwrite the tables inside the JpegTables tag, > if there are tables in both. Well you' d have to not write a JpegTables tag in that case of course, or construct your own (doesn't libtiff support writing a raw JpegTables tag?). Gerben.