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January 2005
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2005.01.03 14:25 "Re: tiff question - performance on large files", by Frank Warmerdam
On Sun, 2 Jan 2005 10:55:23 +0200, Natalya_Katz@amat.com wrote: > > I tried to use libtiff for win32 (I'm working on Windows 2000, VC 6). The > problem is the poor performance in case of very large files (for example, > appending 100 more gray images 64x64 to tiff file with 60000 images - all of > them are gray 64x64 takes about 15 minutes). I tried to use > TIFFWriteScanline or TIFFWriteRawStrip, I tried to open the file with "am" > flag for memory map files - nothing helped. > > The question is can I improve the performance significantly (I'm not talking > about 10-20%)? Can the misusage of libtiff be a reason of poor performance, > or oppositely it's a well-known problem on win 2000 platform? Natalya, I suspect the problem is due to the way libtiff just "walks" the list of images when doing various kinds of operations rather than maintaining a master in-memory list of all availalbe image directories. The current approach isn't really a problem with only a few images, but might well result in some quadratic performance problems when working with as many as 60000 appended images. If you could prepare a test mainline that internally generated 60000 images, and that demonstrated particularly bad performance then we might be able to look into the issue but I am not really interested in substantially changing libtiff for this use case which is very uncommon (in my world at least). You might find you need to do a few hacks on libtiff or be very careful in how you use it to get decent performance with so many appended images. It is also possible that if you images are very small that the problem is just the amount of overhead in how libtiff processes image directories. But without a working program to check it is hard to know what is hitting you. Best regards, -- ---------------------------------------+-------------------------------------- I set the clouds in motion - turn up | Frank Warmerdam, warmerdam@pobox.com light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush | Geospatial Programmer for Rent