Because JPEG2000 images inherently contain a pyramid of reduced
resolution images, the Kakadu Software demo application kdu_expand,
that is available for free for Win32, Mac OS X, Linux, Solaris,
provides a very fast way to create reduced resolution overview images.
For me, the kdu_expand -reduce operations typically take less than one
second. Greg
kdu_compress -v
This is Kakadu's "kdu_compress" application.
Compiled against the Kakadu core system, version v6.2.1.1
Current core system version is v6.2.1.1
kdu_compress -i 18stj940125.tif -o 18stj940125.jp2 Creversible=yes
kdu_expand -v
This is Kakadu's "kdu_expand" application.
Compiled against the Kakadu core system, version v6.2.1.1
Current core system version is v6.2.1.1
kdu_expand -i 18stj940125.jp2 -o 18stj940125_reduce1.tif -reduce 1
kdu_expand -i 18stj940125.jp2 -o 18stj940125_reduce2.tif -reduce 2
kdu_expand -i 18stj940125.jp2 -o 18stj940125_reduce3.tif -reduce 3
kdu_expand -i 18stj940125.jp2 -o 18stj940125_reduce4.tif -reduce 4
On Sep 30, 2009, at 7:52 AM, Even Rouault wrote:
As other drivers, the VRT driver is capable of using external
overviews
(normally in GeoTIFF format, but that's not required...), so here's
a possible
workaround, but that's probably not very practical to use unless you
use some
scripting to do it.
Let's suppose I've a file, test.tif, with a overview of factor 1/2
1) create the VRT : gdalbuildvrt test.vrt test.tif
2) copy test.vrt as test.vrt.ovr
3) edit test.vrt.ovr to divide by 2 the rasterXSize and rasterYSize
of the
<VRTDataset> element, as well as the values of the attributes xOff,
yOff, xSize,
ySize of each <DstRect> element
If you need overview of factor 1/4, copy test.vrt.ovr as
test.vrt.ovr.ovr and
repeat step 3)... A bit of cheating, but seems to work here.
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