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

[thomas bonfort]

ok, I see where the issue is arising from: in 5.x you were using gd's
quantization algorithm, which to put it frankly, sucked badly (i.e.
note the duplicate entries in the color table which are a waste of
quality).
the current quantization algorithm is much higher quality, and thus
produces heavier images. If you want to return to something like GD,
try lowering the number of colors , e.g. QUANTIZE_COLORS=64 . Although
I'm not sure if by doing that the zlib compression will be able to
squeeze the final size down. As before, please post back your findings
if you try!

--
thomas

On Tue, Apr 19, 2011 at 10:44, Erik Gustafson <gustafson.erik at gmail.com> wrote:
> On Tue, Apr 19, 2011 at 10:27 AM, thomas bonfort
> <thomas.bonfort at gmail.com> wrote:
>> Erik,
>> the png compression that is applied is now configurable, and defaults
>> to "6". You can set it as it was by default in 5.6 for quantized
>> output with
>> FORMATOPTION "COMPRESSION=9"
>>
>> please post your image size after the change.
>>
>
> Mapserver 5.6: 74kb
> Mapserver 6, compression 1: 133kb
> Mapserver 6, compression 9: 129kb
>
> I'm on deep water now because I do not know much about the png-format.
> But, by looking at the output from gdalinfo the image from mapserver 5
> seems to have most colors set to rgba 255,255,255,255
>
>
> rio% gdalinfo out_v5.png|sed '1,/Color Table/d'|head -20
>    0: 255,255,255,255
>    1: 8,139,121,255
>    2: 255,255,255,255
>    3: 255,255,255,255
>    4: 5,202,56,255
>    5: 140,199,90,255
>    6: 255,255,255,255
>    7: 81,201,28,255
>    8: 207,135,90,255
>    9: 255,255,255,255
>   10: 255,255,255,255
>   11: 255,255,255,255
>   12: 140,138,170,255
>   13: 255,255,255,255
>   14: 95,95,132,255
>   15: 255,255,255,255
>   16: 255,255,255,255
>   17: 255,255,255,255
>   18: 255,255,255,255
>   19: 255,255,255,255
> rio% gdalinfo out_compression9_v6.png|sed '1,/Color Table/d'|head -20
>    0: 22,253,20,255
>    1: 6,253,6,255
>    2: 0,249,0,255
>    3: 6,253,10,255
>    4: 0,253,4,255
>    5: 16,253,18,255
>    6: 20,20,255,255
>    7: 6,253,8,255
>    8: 80,80,255,255
>    9: 96,94,253,255
>   10: 102,102,255,255
>   11: 0,239,16,255
>   12: 74,76,255,255
>   13: 64,64,255,255
>   14: 8,249,16,255
>   15: 161,255,161,255
>   16: 34,253,36,255
>   17: 26,26,255,255
>   18: 0,235,18,255
>   19: 0,245,10,255
>
>  /Erik
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