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July 2007
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2007.07.05 16:02 "Re: 16-Bit-Per-Channel Lossless Compression", by Andrey Kiselev
On Thu, Jul 05, 2007 at 04:08:47PM +0100, Andy Cave wrote: > 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? Hmm, I tried $ gdal_translate -co "COMPRESS=ZIP" -co "PREDICTOR=2" -co "TILED=YES" -co "BLOCKXSIZE=48" -co "BLOCKYSIZE=128" -co "INTERLEAVE=PIXEL" IMG_2948.Flowers1.tif IMG_2948.Flowers1-zip2-tiled.tif ...and results are Original 60483984 ZIP, predictor 2, tiled 48269416 ZIP, predictor 2, tiled, separated 49714874 LZW, predictor 2, tiled 63307750 It seems you have encoder which is significally different from the libtiff one. Or you just made a mistake somewhere. Best regards, Andrey -- Andrey V. Kiselev ICQ# 26871517