Hi Even, Thank you for your detailed reply.
I should have added that my concern is mainly about random access to parts of the images - for QGIS server and QGIS Desktop. I have internal pyramids. I am not so sure if it is tiled or not. Does gdalinfo reveal whether the TIFF was created with "TILED=YES"? So from your analysis it looks like lzma is the slowest, but overall, the differences aren't that huge. I don't know how random access to parts of the image changes the game a bit, compared to your analysis where you examine the decompression of the whole image - right? Thanks, Andreas On 2016-10-14 12:09, Even Rouault wrote: > 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
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