[mapserver-users] ECW Image Quality

[Steve Lime]

Yup, MapServer does have an 8-bit output limitation. This is a function
of limitations within GD. A new version of GD has be available for
almost a year but is still in beta. I want to wait for the new GD API
and code to stabilize before heading into that mess. Hopefully soon.

Steve

Stephen Lime
Data & Applications Manager

Minnesota DNR
500 Lafayette Road
St. Paul, MN 55155
651-297-2937
>>> "brad" <brad at mapsolutions.com.au> 01/22/02 00:18 AM >>>

Rich,

I noticed this as well.  The reason for the poor quality is that GDAL
will
only return an 8 bit image for ECW.  I get this from the following
statement
"The current implementation reads any number of bands but returns only
as
eight bit image data" at the following URL.
http://www.remotesensing.org/gdal/frmt_ecw.html
Does MapServer itself have a limit to 8 bits for images other than ECW. 
I
have only tried ECW as this is the image format most commonly used by
us.

I also experienced the black image as I was zooming in close to the
photo.
I can't explain that, anyone else getting this ?  I am also getting an
error
that says:

-----------------
CGI Error
The specified CGI application misbehaved by not returning a complete set
of
HTTP headers. The headers it did return are:


abnormal program termination
-----------------

when I try using an ECW image that is large (671 MB).  It only happens
sometimes and if I look at the memory consumption on my machine it only
seems to happen when it gets to ~35MB usage for the mapserv.exe process.
 If
the memory consumed is less than this approximate value then there is
not a
problem displaying the image (albeit in 8 bit).

Hope this helps some.

Regards,

Brad Browne
GIS Application Specialist
Digital Mapping Solutions

Level 2, 2 Hardy Street
South Perth 6151
Ph: 08 9474 6311   Fax: 08 9474 6411
email: brad at mapsolutions.com.au
http://www.mapsolutions.com.au/



-----Original Message-----
From: owner-mapserver-users at lists.gis.umn.edu
[mailto:owner-mapserver-users at lists.gis.umn.edu]On Behalf Of Richard
Greenwood
Sent: Tuesday, 22 January 2002 11:24 AM
To: mapserver-users at lists.gis.umn.edu
Subject: [mapserver-users] ECW Image Quality


Hello listers,

I am displaying ecw color images in mapserver, but the color quality is
very poor. It looks like a palette
problem. The images look great in mapserver when displayed as a tiff,
and
the ecw images look great in the ecw viewer, but the ecw image displayed
via GDAL & mapserver look like paint-by-numbers.

Also, when I zoom in below I screen pixel == 1 image pixel, the ecw
image
goes to black.

Does anybody have any ideas?

Thanks,
Rich



Richard W. Greenwood, PLS
Greenwood Mapping, Inc.
Rich at GreenwoodMap.com
(307) 733-0203
http://www.GreenwoodMap.com