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From: Andrey Kiselev <dron@ak4719.spb.edu>
Date: Thu, 5 Jul 2007 20:02:29 +0400
To: tiff@lists.maptools.org
Subject: Re: [Tiff] 16-Bit-Per-Channel Lossless Compression
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Status:   

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
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