[mapserver-dev] Paletted PNG and Quantization

[Christy Nieman]

Perfect Thomas, thanks for clarifying.  I'll do something about the 
documentation.

Christy

On 04/13/2012 02:21 PM, thomas bonfort wrote:
> If you don't add QUANTIZE_COLORS, only the colors given in the palette
> will be used. If you add it, then a png file with that number of
> colors will be created, and QUANTIZE_COLOR-num_palette_entries will be
> added to the final palette, computed from the image data.
> If the docs need updating to reflect this, please submit a doc ticket
> or even better a pull request with the updated explanations.
>
> cheers,
> thomas
>
> On Fri, Apr 13, 2012 at 20:09, Christy Nieman<cnieman at dmsolutions.ca>  wrote:
>> Steve W,
>>
>> I'm using AGG/PNG, but, I also tried with CAIRO/PNG and got the same
>> results.
>>
>> I used to just have to specify a palette file and PALETTE_FORCE=TRUE, but
>> now to get the same functionality, I need to also have QUANTIZE_COLORS=<a
>> value>.
>>
>> I think this changed with MS 6.0, and I was wondering if this is a bug in
>> the code (i.e. I shouldn't have to have QUANTIZE_COLORS specified), or if it
>> is an error in the documentation (i.e. the docs should say that along with
>> PALETTE and PALETTE_FORCE you need QUANTIZE_COLORS).
>>
>> Christy
>>
>>
>> On 04/13/2012 01:25 PM, Stephen Woodbridge wrote:
>>> I have used it with tile generation and it performs quite well at avoiding
>>> the color shifts between tiles, but setting a palette does a better job. I
>>> have not tried an explicit palette in a while but I do not maintain a tile
>>> cache here.
>>>
>>> Given it a try. Also try my output block and swap you explicit palette and
>>> see if the quality issues are resovled. You did post your whole output block
>>> so I'm not sure if there were other thing affecting the quality, like using
>>> driver GD/PNG vs AGG/PNG.
>>>
>>> -Steve W
>>>
>>> On 4/13/2012 1:06 PM, Christy Nieman wrote:
>>>> Thanks for the reply, SteveW.
>>>>
>>>> How does this perform with for creating tiled maps? The reason I use a
>>>> palette is to make sure colours of features are the same between tiles.
>>>>
>>>> Christy
>>>>
>>>> On 04/13/2012 12:45 PM, Stephen Woodbridge wrote:
>>>>> Christy,
>>>>>
>>>>> You might try this:
>>>>>
>>>>> OUTPUTFORMAT
>>>>> NAME "agg_qn"
>>>>> DRIVER "AGG/PNG"
>>>>> EXTENSION "png"
>>>>> MIMETYPE "image/png"
>>>>> IMAGEMODE RGB
>>>>> FORMATOPTION "INTERLACE=false"
>>>>> FORMATOPTION "QUANTIZE_NEW=ON"
>>>>> FORMATOPTION "QUANTIZE_FORCE=ON"
>>>>> FORMATOPTION "QUANTIZE_DITHER=OFF"
>>>>> FORMATOPTION "QUANTIZE_COLORS=256"
>>>>> #TRANSPARENT ON
>>>>> #FORMATOPTION "TRANSPARENT=ON"
>>>>> END
>>>>>
>>>>> You can replace FORMATOPTION "QUANTIZE_NEW=ON" with your two lines
>>>>> below I think.
>>>>>
>>>>> -Steve W
>>>>>
>>>>> On 4/13/2012 11:22 AM, Christy Nieman wrote:
>>>>>> Hi all,
>>>>>>
>>>>>> Just wanted to make sure that I'm doing this right before filing a bug:
>>>>>>
>>>>>> With MapServer 6.0.2 and master, I wanted to have an 8-bit PNG with the
>>>>>> colours defined by a palette. In previous versions of MapServer, all I
>>>>>> had to do was put
>>>>>>
>>>>>> FORMATOPTION "PALETTE_FORCE=TRUE"
>>>>>> FORMATOPTION
>>>>>>
>>>>>> "PALETTE=/mnt/data1/mapsherpa_v3_demo_data/map/map_overlay/templates/palette_rgba.txt"
>>>>>>
>>>>>>
>>>>>> in the OUTPUTFORMAT. When I did this in MapServer>= 6, I got a very
>>>>>> ugly output (looked like there was hardly any anti-aliasing happening).
>>>>>> Looking in mapimageio.c around line 422, I discovered that I needed to
>>>>>> also have FORMATOPTION "QUANTIZE_COLORS=<a number greater than 0>" in
>>>>>> the OUTPUTFORMAT or no quantization would happen to add the required
>>>>>> colours for anti-aliasing.
>>>>>>
>>>>>> The documentation for the AGG/PNG driver explicitely says that
>>>>>> “PALETTE_FORCE=on” is used to reduce image depth with a predefined
>>>>>> palette. This option is incompatible with the previous quantization
>>>>>> options. But this would seem to no longer be true.
>>>>>>
>>>>>> Is this a documentation error, or a problem in the mapimageio.c code?
>>>>>>
>>>>>> Thanks,
>>>>>> Christy
>>>>>> --
>>>>>> Christy Nieman
>>>>>> GIS Technician
>>>>>> DM Solutions Group, Inc.
>>>>>> Email: cnieman at dmsolutions.ca<mailto:cnieman at dmsolutions.ca>
>>>>>> Web: http://dmsolutions.ca
>>>>>>
>>>>>>
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