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<font face="Times New Roman, Times, serif">Thanks Trent, I tried it
out:<br>
<br>
original: 3.886.894.126b<br>
compressed DEFLATE: 266.046.034b<br>
compressed LZW: 372.085.756b<br>
compressed JPEG: 90.055.344b<br>
<br>
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.<br>
<br>
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.<br>
<br>
Thanks for all your suggestions, they made me see where the
problem lies. And a happy New Year to all.<br>
<br>
Jan<br>
<br>
</font>
<div class="moz-cite-prefix">On 12/27/2012 05:18 PM, Hare, Trent
wrote:<br>
</div>
<blockquote
cite="mid:CAB6t5t-tnvv71VaCSHwew0vFb30eXLrdyf2zHQ8FPcekv=2fGg@mail.gmail.com"
type="cite">
<meta http-equiv="Content-Type" content="text/html;
charset=ISO-8859-1">
Jan,
<div> 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".</div>
<div><br>
</div>
<div>Good luck,</div>
<div>Trent</div>
<div><br>
</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Thu, Dec 27, 2012 at 5:38 AM, Jan
Hartmann <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:j.l.h.hartmann@uva.nl" target="_blank">j.l.h.hartmann@uva.nl</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF"> <font face="Times
New Roman, Times, serif">Can anyone tell me wath is
happening here? I have a large three-band raster (3.8G)
looking like this:</font><br>
<br>
<font face="Times New Roman, Times, serif"><a
moz-do-not-send="true"
href="http://mapserver.sara.nl/map2a.png"
target="_blank">http://mapserver.sara.nl/map2a.png</a></font><br>
<br>
<font face="Times New Roman, Times, serif">I compress it
(from information from this list a few days ago) with:<br>
<br>
gdal_translate -co COMPRESS=JPEG -co PHOTOMETRIC=YCBCR
big.tif small.tif<br>
gdaladdo --config COMPRESS_OVERVIEW JPEG --config
PHOTOMETRIC_OVERVIEW YCBCR -ro -r gauss small.tif 2 4 8
16 32 64<br>
<br>
and get a file of 37M, which is nice. However, the map
has all kinds of rubbish at the borders. It looks like
this:<br>
<br>
<a moz-do-not-send="true"
href="http://mapserver.sara.nl/map2b.png"
target="_blank">http://mapserver.sara.nl/map2b.png</a><br>
<br>
The equivalent pictures of a small part of the map look
like this:<br>
<br>
<a moz-do-not-send="true"
href="http://mapserver.sara.nl/map1a.png"
target="_blank">http://mapserver.sara.nl/map1a.png</a><br>
<a moz-do-not-send="true"
href="http://mapserver.sara.nl/map1b.png"
target="_blank">http://mapserver.sara.nl/map1b.png</a>
<br>
<br>
Can anyone help me?<span class="HOEnZb"><font
color="#888888"><br>
<br>
Jan<br>
</font></span></font> </div>
<br>
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</blockquote>
</div>
<br>
</div>
</blockquote>
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