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.hartm...@uva.nl
<mailto:j.l.h.hartm...@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
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