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<TITLE>Re: [ELGIS] Issue GDAL with JPEG-compressed TIFFS [SEC=UNCLASSIFIED]</TITLE>
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<FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:12pt'>Peter,<BR>
<BR>
We may want to look at the rationale of compressing a tiff via jpeg.<BR>
<BR>
The reason that many people use the tiff format is because that want a loss-less data format.<BR>
<BR>
When we introduce the jpeg compression, we introduce a ‘lossy’ compression algorithm that corrupts the source data.<BR>
<BR>
If you’re just after good compression and don’t care about losing some of the integrity of the data for performance and visualisation reasons, I’d suggest just compressing the data to a format that uses wavelet compression, e.g. Ecw or perhaps jpeg2000. I personally find ecw to be very good for this purpose.<BR>
<BR>
Bruce<BR>
<BR>
<BR>
On 3/02/12 10:23 PM, "Peter Hopfgartner" <<a href="peter.hopfgartner@r3-gis.com">peter.hopfgartner@r3-gis.com</a>> wrote:<BR>
<BR>
</SPAN></FONT><BLOCKQUOTE><FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:12pt'>I'm doing quite some experiments with GDAL and image compression these days<BR>
<BR>
I do have an issue with geotiff 1.3/gdal 1.8.1 on CentOS 6 with packages<BR>
from ELGIS. The story goes like this:<BR>
<BR>
I create tiffs with<BR>
<BR>
gdal_translate -of GTiff -co COMPRESS=JPEG -co JPEG_QUALITY=90<BR>
-co "TILED=YES" -co "BLOCKXSIZE=512" -co "BLOCKYSIZE=512" <infile><BR>
<outfile><BR>
<BR>
and then add overviews with (I do have to add the overlays in distinct<BR>
steps, otherwise gdaladdo aborts with an error message).<BR>
<BR>
gdaladdo --config COMPRESS_OVERVIEW JPEG --config INTERLEAVE_OVERVIEW<BR>
PIXEL --config JPEG_QUALITY_OVERVIEW 90 -r average <outfile> 3<BR>
gdaladdo --config COMPRESS_OVERVIEW JPEG --config INTERLEAVE_OVERVIEW<BR>
PIXEL --config JPEG_QUALITY_OVERVIEW 90 -r average <outfile> 9<BR>
gdaladdo --config COMPRESS_OVERVIEW JPEG --config INTERLEAVE_OVERVIEW<BR>
PIXEL --config JPEG_QUALITY_OVERVIEW 90 -r average <outfile> 27<BR>
gdaladdo --config COMPRESS_OVERVIEW JPEG --config INTERLEAVE_OVERVIEW<BR>
PIXEL --config JPEG_QUALITY_OVERVIEW 90 -r average <outfile> 81<BR>
<BR>
(Trying with power-of-2-steps gives the same result. If I drop all<BR>
options from gdaladdo: same result).<BR>
<BR>
I'll create a WMS service with MapServer 5.6.7 and do get a big red<BR>
square in the image. The square is "fixed" to the geografical position,<BR>
e.g. if I move the extend the square moves too. The square is situated<BR>
in the corner of the tiff file.<BR>
It appears only at some scales. If I change it very slightly, the square<BR>
remqins, if I change for more then approx 1%, it disappears.<BR>
<BR>
I've put the two images at<BR>
<BR>
<a href="http://www.r3-gis.com/gdal_issues/tiff_with_jpegcompression_and_overviews.jpeg">http://www.r3-gis.com/gdal_issues/tiff_with_jpegcompression_and_overviews.jpeg</a><BR>
and<BR>
<a href="http://www.r3-gis.com/gdal_issues/tiff_with_nocompression_and_overviews.jpeg">http://www.r3-gis.com/gdal_issues/tiff_with_nocompression_and_overviews.jpeg</a><BR>
.<BR>
<BR>
The problem disappears if I do not run gdaladdo on the images or when I<BR>
do not use Jpeg compression:<BR>
<BR>
gdal_translate -of GTiff -co "TILED=YES" -co "BLOCKXSIZE=512" -co<BR>
"BLOCKYSIZE=512" <origfile> <targetfile><BR>
<BR>
There are some hits for<BR>
<a href="http://www.google.com/search?client=ubuntu&channel=fs&q=mapserver+artefacts+in+raster+gdal&ie=utf-8&oe=utf-8">http://www.google.com/search?client=ubuntu&channel=fs&q=mapserver+artefacts+in+raster+gdal&ie=utf-8&oe=utf-8</a>,<BR>
but mostly related to older versions of GDAL and without resolution.<BR>
<BR>
<BR>
Thanks,<BR>
<BR>
Peter<BR>
<BR>
--<BR>
<BR>
Peter Hopfgartner<BR>
R3 GIS Srl - GmbH<BR>
www.r3-gis.com<BR>
<BR>
<BR>
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