AGG, paletted image and transparency (Mapserver 5.0 beta 5)

[Gilles Bassière]

Flavio Hendry wrote:
> Hi Gilles
>
> Did you try TRANSPARENCY alpha (on LAYER level).
>   

I did but it doesn't change anything. According to 
http://mapserver.gis.umn.edu/docs/howto/agg-rendering-specifics :

"All rendering is now done antialiased by default. All ANTIALIAS 
keywords are now ignored, as well as TRANSPARENCY ALPHA. Pixmaps and 
fonts are now all drawn respecting the image's internal alpha channel 
(unless a backgroundcolor is specified)."

Without the TRANSPARENCY ALPHA, I don't know how to get this "image's 
internal alpha channel" to work as I want

Regards,
Gilles

> Mit freundlichem Gruss / Best Regards
> Flavio Hendry
>
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>
> -----Original Message-----
> From: Gilles Bassière <gilles.bassiere at MAKINA-CORPUS.COM>
> To: MAPSERVER-USERS at LISTS.UMN.EDU
> Date: Thu, 30 Aug 2007 16:44:41 +0200
> Subject: [UMN_MAPSERVER-USERS] AGG, paletted image and transparency
> (Mapserver 5.0 beta 5)
>
>   
>> Hi List,
>>
>> I run Mapserver 5.0 beta5 as a WMS server and have some troubles with
>> background transparency :(
>>
>> In a first attempt, I just replaced my GD OUTPUTFORMAT definition by:
>>
>> OUTPUTFORMAT
>>    NAME             "png"
>>    DRIVER           "AGG/PNG"
>>    MIMETYPE         "image/png"
>>    IMAGEMODE        "rgba"
>>    EXTENSION        "png"
>>    FORMATOPTION     "transparent=on"
>>    # TileCache can't use meta-tiling on interlaced PNG files...
>>    FORMATOPTION     "interlace=off"
>> END
>>
>> Changed my config to have my OpenLayers pointing directly at
>> Mapserver 
>> 5.0, launch my browser and... Wow, it looks great !!!
>>
>> Then, I tried some optimization and I added to my OUTPUTFORMAT
>> element 
>> (as seen in "AGG rendering specifics" howto) :
>>    FORMATOPTION     "quantize_force=on"
>>    FORMATOPTION     "quantize_dither=off"
>>    FORMATOPTION     "quantize_colors=256"
>>
>> Well, the line work is still beautiful but I now have 2 problems :
>> 1) I lost background transparency. My tiles appear with a white 
>> background, I tried to change IMAGECOLOR from 255 255 255 to -1 -1
>> -1, 
>> also to remove this element but it doesn't change anything.
>> 2) Fonts and symbols looks very crappy, they are mixed black and
>> white 
>> where they should be filled with black with a white outline.
>>
>> On a random tile, the image size fall from 102KB down to 25KB. Such 
>> ratio is not representative at all since it's not an average and it's
>> only about vector data but still, quantize option seems very
>> interesting 
>> and I don't want to give up because of transparency problems.
>>
>> Trying to solve the first problem, I found a workaround for the
>> second. 
>> When I set the TRANSPARENT parameter of the WMS request to 'false'
>> (or 
>> any value different of 'true'), then fonts and symbols are displayed 
>> normally. It could have been ok if TRANSPARENT was not an optional 
>> parameter... The map should looks good in the default case.
>>
>> Does someone could give more explanation about the quantize option, 
>> especially regarding transparency management ?
>>
>> If possible, a broader answer about the FORMATOPTION element would
>> help 
>> a lot. Indeed, it seems like most optimizations are possible through 
>> output format tuning. Unfortunately, I have not been able to find any
>> reference document on this...
>>
>> Regards,
>>
>> -- 
>> Gilles Bassiere
>> MAKINA CORPUS
>> 30 rue des Jeuneurs
>> FR-75011 PARIS
>> http://www.makina-corpus.com
>>     


-- 
Gilles Bassiere
MAKINA CORPUS
30 rue des Jeuneurs
FR-75011 PARIS
http://www.makina-corpus.com