[mapserver-users] Rendering artefacts when serving raster via WMS

[John Westwood]

Hello

I have a problem with MapServer making a mess of some georegistered
raster map images when serving them as tiles via WMS. The images are not
reprojected on the fly, so this isn't the cause of the problem. The
source images are 24bit geotiff and the requesting format is jpeg or
png.

The maps are OS New Popular and they exhibited poor contrast so I
boosted the contrast and colours in Photoshop 7 using the auto color or
the auto contrast option.  Unfortunately, some of the sheets now exhibit
horrible artefacting or ghost images. Other maps in the set that have
been boosted do not have these problems. I attach two screenshots,
original.jpg and mapserver.jpg. These are portions of the original image
and the MapServer served image, respectively. Further examples of this
problem can be found via the map viewer on Historical Maps section of
the Vision of Britain website (www.visionofbritain.org.uk), check out
the New Popular maps in the vicinity of the Wirral.

I have tried various things to fix this, but to no avail. Things I have
tried:

Increasing the jpeg quality output
Using png instead of jpeg for the output
Using GDAL or AGG instead of GD

Here is the output format portion of my map file:

OUTPUTFORMAT
  NAME "jpg"
  DRIVER GD/JPEG
  IMAGEMODE RGB
  EXTENSION "jpg"
  MIMETYPE "image/jpg"
  FORMATOPTION "QUALITY=85"
END

OUTPUTFORMAT
  NAME "png"
  DRIVER GD/PNG
  IMAGEMODE RGB
  EXTENSION "png"
  MIMETYPE "image/png"
END

Does anybody have any ideas what the problem could be? I know it is
something to do with the fact that I boosted the images and MapServer
doesn't like them, but I would like to fix it. Suggestions greatly
appreciated.

Regards,

John Westwood

Great Britain GIS Project
Vision of Britain
www.visionofbritain.org.uk

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/mapserver-users/attachments/20110610/2d88a79b/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: original.jpg
Type: image/jpeg
Size: 215882 bytes
Desc: JPEG image
URL: <http://lists.osgeo.org/pipermail/mapserver-users/attachments/20110610/2d88a79b/attachment.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: mapserver.jpg
Type: image/jpeg
Size: 300595 bytes
Desc: JPEG image
URL: <http://lists.osgeo.org/pipermail/mapserver-users/attachments/20110610/2d88a79b/attachment-0001.jpg>