[gdal-dev] gdal_translate compress is larger??

[Matt Wilkie]

I'm curious as to why I've not encountered this before as I use lzw 
compression all the time. Anyway, as always thanks for the education. :)

I've discovered that for my present project that jpeg-in-geotiff 
compression is good enough, which makes me happy because even with 
predictor=2 the space savings was only 10% or so.


matt wilkie
--------------------------------------------
Geomatics Analyst
Information Management and Technology
Yukon Department of Environment
10 Burns Road * Whitehorse, Yukon * Y1A 4Y9
867-667-8133 Tel * 867-393-7003 Fax
http://environmentyukon.gov.yk.ca/geomatics/
--------------------------------------------


> LZW compression packs a little dictionary at the front of each strip/tile
> with the table of patterns.  The size of an LZW compressed image can be
> noticably larger than an uncompressed image if the chunk size (strip/tile)
> is small so that this overhead becomes significant, and of course if the
> imagery is essentially uncompressable with LZW.
>
> Using larger strip/tile sizes can improve efficiency with LZW.
>
> Also, using -co PREDICTOR=2 can help with imagery that is smoothly
> varying as it compresses the differences from pixel to pixel instead of
> the absolute values, and these will tend to be small and have more
> patterns.
>
> Best regards,