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January 1997
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1997.01.31 16:13 "Re: write subset", by Gary Burgess
Rainer wrote: > > 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). I don't see this as being the only possible approach. TIFF is a suitable format for large files mainly because of its strip/tile organization. With libtiff it's a snap to handle these files an appropriate piece at a time. > Greetings Rainer > PS: Does anyone know about image processing tools that work on > files and not in main memory? I don't see how image processing can avoid using main memory to at least some extent. I think the standard approach is to use a tiled version of the image. The only thing to watch out for is to properly handle tile boundaries so as not to introduce visual artifacts. Gary --------------------------------------------------------------------------- Gary Burgess gburgess@zgs.com Zeh Graphic Systems, Inc. (281) 589 7757