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

[thomas bonfort]

Jukka,
please create a ticket and attach your test case, I'll have a look.

thanks,
thomas

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
>
> I prepared also my own outputformat so I could compare the outputs from MS
> 6.0 and older MS 5.6.5 version. This is my outputformat which I have
> understood to mean just the same as the inbuild MS 6.0 outputformat
> "image/png; mode=8bit".
> OUTPUTFORMAT
>       NAME 'AGG_Q'
>       MIMETYPE "image/png"
>       DRIVER "AGG/PNG"
>       EXTENSION "png"
>       IMAGEMODE RGB
>       FORMATOPTION "QUANTIZE_FORCE=ON"
>       FORMATOPTION "QUANTIZE_DITHER=OFF"
>       FORMATOPTION "QUANTIZE_COLORS=256"
>   END
>
> With this outputformat the resulting map is correct with MS 5.6.5 at any
> scales even if the .ovr file is in use.
>
> 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-
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