[Tilecache] Where in TC code is metatile cutting?

[Guillaume Sueur]

Hi,

What about using image-magick
(http://www.assembla.com/wiki/show/pythonmagickwand) to crop the
MetaTile image ?

It's maybe worth a try.

Regards,

Guillaume

Le samedi 16 janvier 2010 à 15:52 -0800, Roger André a écrit :
> Ok, well after replicating the results Ivan got earlier, I'm not
> feeling as confident as I once was.  As Ivan found, the problem is
> that the palette information is being treated differently by PIL, than
> how MapServer generated it.  Below are 2 short snippets that show
> this:
> 
> MapServer palette output:
> -----------------
>     0: 0,0,0,0
>     1: 251,0,0,64
>     2: 250,0,0,54
>     3: 253,0,0,114
> 
> PIL output:
> -----------
>     0: 0,0,0,0
>     1: 251,0,0,255
>     2: 250,0,0,255
>     3: 253,0,0,255
> 
> The PIL image was created using these commnds:
> >>> import Image
> >>> image = Image.open('quant_on_mapserv.png')
> >>> assert image.mode == 'P'
> >>> transparency = image.info['transparency']
> >>> image.save('pil_test.png', transparency=transparency)
> 
> While the PIL-generated image looked just fine, all of the file size
> benefits of using the "QUANTIZE=on" MapServer option were lost.
> Athough a single-band, paletted image was produced, it was just as big
> as a 4-band RGBA image created directly in MapServer.
> 
> I still really don't like the idea of using a post-processing step to
> reduce the size of cached images, so I think there are 2 possible ways
> to approach the problem.  One is to not care at all about what format
> is being sent into TileCache, but to implement quantizing in PIL
> itself, maybe as a tilecache.cfg option.  (Note that I wasn't able to
> get quantizing to reduce image size in PIL, so maybe this isn't even
> possible.)  The other option is to have the binary string of image
> data read and processed by something other than PIL, something that
> can correctly replicate the image format MapServer produces.
> Initially I was thinking that GDAL could possibly do this.
> 
> Any thoughts on either of these options?
> 
> Roger
> --
> 
> 
> 
> On Fri, Jan 15, 2010 at 10:59 AM, Roger André <randre at gmail.com>
> wrote:
>         Ok, will let you know what I come up with. Am still testing
>         the TC code to see what it actually does with PIL.  I'm not
>         fully convinced that PIL cannot be made to correctly read the
>         palette info of the incoming metatile.  It appears this has
>         been explored already, but I need to convince myself
>         first.  ;)
>         --
>         
>         
>         
>         On Thu, Jan 14, 2010 at 12:10 AM, Guillaume Sueur
>         <no-reply at neogeo-online.net> wrote:
>                 I've also pointed out previously that PIL is generated
>                 default jpeg
>                 images, i.e. with 75 % compression. If the wms server
>                 itself sends 75%
>                 compressed images, that can give pretty ugly images,
>                 and make people
>                 wonder why the quality is different when using
>                 metatile or not. As this
>                 should be avoided I've suggested to use a 95 %
>                 compression (100 %
>                 doesn't even quantize, and produces fat images). Here
>                 is the diff on
>                 Layer.py :
>                 
>                 406a407,408
>                  >                 elif self.extension == 'jpeg':
>                  >                     subimage.save(
>                                        buffer,
>                                        self.extension,
>                                        quality=95,
>                                        optimize=True
>                                        )
>                 
>                 Regards,
>                 
>                 Guillaume
>                 
>                 
>                 Le jeudi 14 janvier 2010 à 08:09 +0100, Ivan Mincik a
>                 écrit :
>                 
>                 > On Thursday 14 January 2010, Roger André wrote:
>                 > > Hi All,
>                 > >
>                 > > I'd like to take a stab at fixing the problem
>                 TileCache has with cutting up
>                 > > 8-bit quantized metatiles.  I'm trying to find
>                 where in the code PIL is
>                 > > invoked to do this, but can't seem to put my
>                 finger on it.  Can someone
>                 > > save me a bit of time and tell me where I can find
>                 this?
>                 >
>                 > Hi Roger,
>                 > I am very happy that someone is trying to solve this
>                 (if we mean the same problem). I have spend lot of
>                 time trying to
>                 > fix this. By my opinion, it is PIL issue which can
>                 not be done without hacking PIL code.  You can find my
>                 post in PIL
>                 > mailinglist - with no help, but I am not very
>                 skilled programmer, more GIS person, so maybe You can
>                 make it easily.
>                 >
>                 > Here You can find my ticket with all info, code
>                 sample and test file.
>                 >
>                 http://hg.effbot.org/pil-2009-raclette/issue/8/corrupting-images-in-palette-mode
>                 >
>                 > Good luck and give us know about Your progress, even
>                 if not successfull.
>                 
>                 
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