[gdal-dev] Compression artifacts

[Jan Hartmann]

Thanks Trent, I tried it out:

original:                          3.886.894.126b
compressed DEFLATE:    266.046.034b
compressed LZW:             372.085.756b
compressed JPEG:             90.055.344b

Although DEFLATE and LZW give very good results, JPEG compression is so 
much better that I need to go for it. The base raster is the cadastral 
map of Amsterdam in 1832 with a resolution of 30 cm. This is only the 
low-resolution scan, the base scan has a resolution of 15 cm, slightly 
better than Google Satellite. We are trying to set things up for the 
whole of the Netherlands, and with this sort of precision even a small 
country generates an awful lot of raster scans, and needs unbelievable 
amounts of processing, even with the Cloud system we have available now.

That means, I'll have to clip the maps. It can be done as Dmitry 
suggested (gdalwarp -cutline), or alternatively using gdal-rasterize. I 
do have the bounding polygons. It can also be done with nearblack, as 
Even suggested. I guess the last method will take somewhat more time, as 
the area of the map has to be computed.

Thanks for all your suggestions, they made me see where the problem 
lies. And a happy New Year to all.

Jan

On 12/27/2012 05:18 PM, Hare, Trent wrote:
> Jan,
>    Jpeg is a lossy compression and thus the collar will not be 
> maintained perfectly as black (or 0). You will not get as much 
> compression, but you can try a lossless method like LZW or Packbits. 
> If you are getting close to the 4GB limit you might need to add "-co 
> bigtiff=if_safer".
>
> Good luck,
> Trent
>
>
>
> On Thu, Dec 27, 2012 at 5:38 AM, Jan Hartmann <j.l.h.hartmann at uva.nl 
> <mailto:j.l.h.hartmann at uva.nl>> wrote:
>
>     Can anyone tell me wath is happening here? I have a large
>     three-band raster (3.8G) looking like this:
>
>     http://mapserver.sara.nl/map2a.png
>
>     I compress it (from information from this list a few days ago) with:
>
>     gdal_translate -co COMPRESS=JPEG -co PHOTOMETRIC=YCBCR big.tif
>     small.tif
>     gdaladdo --config COMPRESS_OVERVIEW JPEG --config
>     PHOTOMETRIC_OVERVIEW YCBCR -ro -r gauss small.tif 2 4 8 16 32 64
>
>     and get a file of 37M, which is nice. However, the map has all
>     kinds of rubbish at the borders. It looks like this:
>
>     http://mapserver.sara.nl/map2b.png
>
>     The equivalent pictures of a small part of the map look like this:
>
>     http://mapserver.sara.nl/map1a.png
>     http://mapserver.sara.nl/map1b.png
>
>     Can anyone help me?
>
>     Jan
>
>     _______________________________________________
>     gdal-dev mailing list
>     gdal-dev at lists.osgeo.org <mailto:gdal-dev at lists.osgeo.org>
>     http://lists.osgeo.org/mailman/listinfo/gdal-dev
>
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/gdal-dev/attachments/20121227/7ca1477a/attachment-0001.html>