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January 2009
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2009.01.12 01:19 "Libtiff compression ratios", by <myopicwatchmaker@gmail.com>
Hi All, As part of my doctoral thesis work, I produce two and a half terapixels of grayscale images a month. As you might imagine, I am eager to minimize the storage requirements for this data. Libtiff's support for deflate compression has served me quite well up until this point. Recently I noticed that with identical compression settings, Adobe Photoshop CS2 achieves significantly higher compression ratios than my libtiff code--producing files that are almost 40% smaller in many cases. A typical example: I have a 30,000x6500pixel 8-bit grayscale image which, uncompressed occupies 174Mb on disk. Libtiff's deflate algorithm compresses this down to a 66Mb file, where Photoshop produces a 48Mb file. I save my images in ~8Mb strips, which appears to be the optimum for zip compression. Does anyone know why libtiff might fail to match Photoshop's compression rates? Are there any paramters in libtiff or libzip that might allow optimization for humungous images? Thanks for any input. Nick