[mapserver-users] MS 6.0 beta6 and faulty image/png; mode=8bit output if source image has overviews

[Erik Gustafson]

> On Mon, Apr 18, 2011 at 10:18, Rahkonen Jukka <Jukka.Rahkonen at mmmtike.fi> wrote:
>> Hi,
>>
>> I am sometimes getting images with totally odd colours with MS 6.0 beta 6
>> (and the previous beta versions) with format image/png; mode=8bit.  I have
>> been doing some testing and I believe I can now reproduce the error.
>>
>> The error happens only if the raster image has overviews. If I delete or
>> rename the external .ovr file the 8bit png output is correct at any scales.
>> To be sure that there is nothing odd with the overview file I recreated it
>> with FWTools v. 2.4.2 by using a basic command
>> gdaladdo -r average -ro suomi1m.tif 2 4 8
>>
[snip]
>>
>> My conclusion is that exectly MS 6.0 version is creating at some scales
>> through ADD driver an 8 bit png output with messed up colours, but it
>> happens only if the source image has overviews.
>>
>> If someone is interested in having a look at this I can prepare and send my
>> mapfile and some imagery to play with.
>>
>> -Jukka Rahkonen-


Hello, I have a similar problem on vector data, possibly related.
The color problem appears when quantize is enabled and a large amount
if data is rendered. I can trigger the bug with mapfile below:

MAP
   OUTPUTFORMAT
       NAME "png"
       DRIVER "agg/png"
       FORMATOPTION QUANTIZE_FORCE=on
   END
   LAYER
       NAME corine
       DATA "corine"
       TYPE polygon
       CLASS
           NAME ALL2
           EXPRESSION ([area_ha] < 1000)
           STYLE
               COLOR 0 0 255
           END
       END
       CLASS
           NAME ALL
           EXPRESSION ([area_ha] < 1500)
           STYLE
               COLOR 255 0 0
           END
       END
       CLASS
           NAME ALL
#EXPRESSION ([area_ha] < 1500)
           STYLE
               COLOR 0 255 0
           END
       END
   END
END
~
To trigger the bug I need at least two classes with different colors.
If I use a single color or if I render only a subset of the data the
colors look good. I do not have a test case yet as the data used is
not free. I will try to create one but it might take a few days. Just
writing this to note that problem may not be related to the overviews
but the quantizing itself.

Another note: If I add and OUTLINECOLOR and WIDTH=1 in the style
definition the problem seems heal the bug, I guess thats because fewer
antialiasing colors are generated.

No problem with this mapfile on Mapserver 5.6.

 /Erik