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January 1997
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1997.01.31 07:51 "Re: write subset", by Rainer Wiesenfarth
Kyriakos Georgiou wrote: > > Thomas Loecherbach <thomasl@hjw.com> writes: > > > [...] > > [...] > > > > > A similar problem: can I open a file for read/write (I don't want to > > append a new tiff directory) and read/write scanlines ? > > > > Open it for read, read the whole thing, close it, modify whatever > scanlines you want, reopen it for write, write it, close it. > (by the way, reading/writing strips TIFFReadEncodedStrip etc. is faster.) Why do the members of this list always assume that an image would fit completely in main memory? What if you use images with a minimum size of 70MB (grayscale) or 210MB (RGB) (like we do)? The limit of TIFF images is given by the 32-Bit offsets used. This allows images of at least 2GB in size. It is a bad approach to copy the whole file when applying changes. If you want to update this kind of images, you have to 'program around' libtiff. In case you use uncompressed images, you can modify images by getting the TIFF fields StripOffsets or TileOffsets and do the reading/writing by hand. This approach is not very handy, but - as far as I know - the only solution when you want to use libtiff. BTW, I would be very happy if Sam would introduce random access to libtiff. But I also know that this is not that easy (simply think of compressed images). Greetings Rainer PS: Does anyone know about image processing tools that work on files and not in main memory? > > Kiriakos -- | This mail came from: | Rainer Wiesenfarth Tel: +49 7364 203321 | c/o Carl Zeiss, Div. Phm-A Fax: +49 7364 202829 | 73446 Oberkochen e-mail: Wiesenfarth@zeiss.de | Germany