JPEG2000

[Frank Warmerdam]

On 1/23/06, Stéphane RIFF <stephane.riff at cerene.fr> wrote:
> I get JPEG2000 to work with mapserver, but by using the JASPER driver
> because I can't get ECW SDK to compile
> on redhat RS4. (I saw on ECW distrib that they suggest gcc/g++ 3.4 or
> higher but I only have gcc/g++ 3.3.3 : maybe that's the problem)

Stephane,

JasPer would be a good solution for "screen sized" images
generally returned by WMS.

> To view the .JP2 file in mozilla/firefox/ie I have download the Morgan
> JPEG2000 plug-in on http://www.morgan-multimedia.com .
>
> Another question :
> Is it normal that my .jp2 files files are larger than my .png fies or do
> I missed some parameters ? (png ~ 400ko <-> jp2 ~ 700ko)

It depends alot on the nature of the image.  If there are
large areas of constant value then PNG will do very well.
Also, the jpeg2000 will generally be RGB while PNG may
be 8bit.

It looks like you can control the desired compression
rate for the Jasper based JPEG2000 driver by adding
a line like:

  FORMATOPTION "RATE=0.05"

The above should (I think) attempt 95% compression making
the result 0.05 times the size of the uncompressed data.

By the way, I have enabled JPEG2000 support on my South
American Landsat server from http://maps.gdal.org/
This is using the ECW SDK (an older FWTools).  The returned
results seem rather slow to me (2-3s results).  I imagine that is
due to the CPU time required to do the ECW compression which
I believe to be substantial.

Best regards,
--
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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