gdal question on no data.

[Frank Warmerdam]

Paul Moen wrote:
> Does anyone know how to take a tiff and apply jpeg compression without
> messing up the nodata areas?  For example, I have a tif with weather radar
> imagery in colors black is the nodata color.  I want to compress the tif
> using jpeg compression, but the compression causes some of the nodata colors
> to become something other than black.  Is there a way to tell gdal to
> consider the black areas no data and do not use them in the compression
> process? 
> 
> gdal_translate -a_srs "epsg:2266" -co "COMPRESS=JPEG" 40.tif 40n.tif

Paul,

No, I am not aware of any approach to doing this.  Generally speaking
preserving nodata regions via nodata values when using lossy compression
formats is a big pain, verging on impossible.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | President OSGF, http://osgeo.org