Le vendredi 14 octobre 2016 09:45:38, Neumann, Andreas a écrit : > Hi, > > I have a question on TIFF compression alternatives. > > My data of concern is 8bit gray value. Lots of white pixel (>95%), the > rest is black pixels (content) and some gray pixels because of > antialiasing. > > I would like to compress to save some storage, but I need a good > performance. What is the recommended compression that is fast on > decompression? > > I tried DEFLATE, but it is rather slow to decompress. Would LZW or > PACKBITS be preferred in this situation? How about LZMA? I would like to > avoid non-compressed data, because I use SSD storage for performance > reasons.
My findings on a 37614 x 18816 8 bit image (a scan of a text page) that should be similar to what you describe. Decompression time is the result of the second run of "time gdalinfo - checksum" (so you can consider that I/O is cached by the OS and you measure essentially CPU time. storage is spinning disk) No tiling: Size Compression Decompression time 707895750 out_nocompression.tif 9.3 s 11239972 out_deflate.tif 10.8 s 17749306 out_lzw.tif 10.5 s 12337710 out_lzma.tif 12.6 s 36201320 out_packbits.tif 9.9 s Tiling: Size Compression Decompression time 8813833 out_deflate_tiled.tif 11.1 s 14614121 out_lzw_tiled.tif 11.0 s 8479238 out_lzma_tiled.tif 13.0 s 37018470 out_packbits_tiled.tif 10.2 s Note: in the tiling case, the gdalinfo -checksum benchmark might not be ideal as it proceeds line by line (and not block by block), thus there's a lot of copying between cached blocks and output buffer that is done. So I've done time gdal_translate XXX.tif /vsimem/out.tif -q : deflate tiled: 2.5 s lzw tiled: 2.3 s packbits tiled: 1.5 s lzma tiled: 4.5 s Times for non tiled files are essentially the same. Note: if you use tiling and you have whole tiles that are at white value, if you use GDAL trunk, set the SPARSE_OK=YES creation option and set the nodata value to 255, then those tiles will be entirely omitted from the compressed file. This might save a few extra bytes, and also some decompression time. gdal_translate out_nocompression.tif out_packbits_tiled.tif -co tiled=yes -co compress=packbits gdal_translate out_nocompression.tif out_packbits_tiled_sparse.tif -co tiled=yes -a_nodata 255 -co compress=packbits -co sparse_ok=yes 37018470 out_packbits_tiled.tif 30409074 out_packbits_tiled_sparse.tif time gdal_translate out_packbits_tiled_sparse.tif /vsimem/out.tif -q: 1.3 s Even -- Spatialys - Geospatial professional services http://www.spatialys.com _______________________________________________ gdal-dev mailing list email@example.com http://lists.osgeo.org/mailman/listinfo/gdal-dev