Fwd: Re: [MapProxy] more opacity questions

[DeDuikertjes]

Oliver,

Thank you. This is very informative.
Indeed the layer has transparency and areas that have to be semi 
transparent on blending.

Does this limitation of PIL mean that if the source wms serves images 
with transparency AND semi transparent features (and Mapproxy config 
does NOT have any transparency settings) the result of a multi-layer 
request will have these problems?

Can these PIL problems be mitigated by having the source WMS serve 
images on a white background and set mapproxy transparency color to white?

Marco
Op 8-1-2012 13:35, Oliver Tonnhofer schreef:
> Hi Marco,
>
> On 07.01.2012, at 20:27, DeDuikertjes wrote:
>> Here you can find some example images in different shades of black-opaque:
>>
>> http://178.63.74.185/hosting/demo/demo1.png
>> http://178.63.74.185/hosting/demo/demo2.png
>> http://178.63.74.185/hosting/demo/demo3.png
> So you have a layer that already has transparency and you want the filled areas to be semi-transparent. The image blending function of PIL does not support the alpha channel. The transparent areas in your image are blended over with your opacity value, but even if these areas are transparent they still have color value, and in your case they are either black or white.
>
> It should be possible to work around that with some image processing during the blending, but that would require more than just a single line patch…
>
>
> Regards,
> Oliver
>