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2007.07.05 15:08 "Re: 16-Bit-Per-Channel Lossless Compression", by Andy Cave
Actually, I used quite small tiles - not something I normally do. For 1 bit data, larger tiles are better (but then there's more repeatability). In this case I used tiles approx 40x128 and lzw'd it as a stream. Unless I made a mistake, it compresses to around 20M or thereabouts. That was RGB interleaved 16 bit data - no messing about splitting it or anything. I found that each tile compressed by around 50%+. I presume that was because the LZW code uses 9 or 10 bits for more data and also finds more repeated strings. Can you repeat your below test with BLOCKXSIZE=40 and BLOCKYSIZE=128? Best Regards, Andy. ----- Original Message ----- From: "Andrey Kiselev" <dron@ak4719.spb.edu> To: <tiff@lists.maptools.org> Sent: Thursday, July 05, 2007 1:57 PM Subject: Re: [Tiff] 16-Bit-Per-Channel Lossless Compression > On Thu, Jul 05, 2007 at 01:03:07PM +0100, Andy Cave wrote: >> I can easily do much better than that - 60:48. I can get ~21276876 >> (~20M) and with some more work I think I can get down to 15-20M. > > Really? But how? > >> Andrey - since you have tiffcp built, can you repeat your test, but >> produce tiled output? LZW and Flate. I think you'll find you get what > > Actually I did that --- without much success, so I have not listed these > results. The full results: > > Original 60483984 > ZIP, predictor 2 48095962 > ZIP, predictor 2, separated 49303374 > ZIP, predictor 2, tiled 47528554 > ZIP, predictor 2, tiled, separated 49347802 > > So we can get better results with tiling, but nothing serious. Band > separation doesn't help at all (though, I also thought that it should > help). Those, who want reproduce this tests should get the GDAL library > and use tool called gdal_translate, because tiffcp does not support band > separation for 16-bit images. The command line to get tiled separated > image is: > > $ gdal_translate -co "COMPRESS=ZIP" -co "PREDICTOR=2" -co "TILED=YES" -co > "BLOCKXSIZE=256" -co "INTERLEAVE=BAND" IMG_2948.Flowers1.tif > IMG_2948.Flowers1-zip2-tiled-sep.tif > > Best regards, > Andrey > > -- > Andrey V. Kiselev > ICQ# 26871517 > _______________________________________________ > Tiff mailing list: Tiff@lists.maptools.org > http://lists.maptools.org/mailman/listinfo/tiff > http://www.remotesensing.org/libtiff/