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July 2007
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2007.07.05 16:56 "Re: 16-Bit-Per-Channel Lossless Compression", by Andy Cave
Hi Andrey, Sorry for wasting your time and others - my mistake. I had two different checkouts of s/w I was experimenting with. One was set to work with full RGB, the other was set to work just with R (and stripped out the GB), which I didn't realise. That's where I got 20M from. Andy. ----- Original Message ----- From: "Andrey Kiselev" <dron@ak4719.spb.edu> To: <tiff@lists.maptools.org> Sent: Thursday, July 05, 2007 5:02 PM Subject: Re: [Tiff] 16-Bit-Per-Channel Lossless Compression > 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 > _______________________________________________ > Tiff mailing list: Tiff@lists.maptools.org > http://lists.maptools.org/mailman/listinfo/tiff > http://www.remotesensing.org/libtiff/