[OSM-dev] NOT-saving empty Mapnik tiles

marqqs at gmx.eu marqqs at gmx.eu
Fri Aug 12 18:51:18 BST 2011


Hi Igor,

thank you, this link is very helpful!

> um, what is your definition of "empty" exactly? Is it "all pixels are 
> transparent"? Or is it "all pixels are of the same color"? Or is it "all 
> pixels are of color X"? I don't think there's an Image.is_empty() 
> because "empty" means different things to different people.

Sorry, my fault. :-)
I want to determine if an image has transparent pixels only. If yes I would like to dispose it because nobody could see it anyway.

Would save disk space - and inodes...


-------- Original-Nachricht --------
> Datum: Fri, 12 Aug 2011 19:36:28 +0200
> Von: Igor Podolskiy <igor.podolskiy at vwi-stuttgart.de>
> An: dev at openstreetmap.org, marqqs at gmx.eu
> Betreff: Re: [OSM-dev] NOT-saving empty Mapnik tiles

> Hi Markus,
> 
> > Is there a function like im.is_empty() ?
> um, what is your definition of "empty" exactly? Is it "all pixels are 
> transparent"? Or is it "all pixels are of the same color"? Or is it "all 
> pixels are of color X"? I don't think there's an Image.is_empty() 
> because "empty" means different things to different people.
> 
> There are different ways to do that depending on the definition. You can 
> loop over the image pixels with im.getdata() and check some property of 
> an image, or you might want to take a look on im.getcolors() dictionary 
> which tells you how often a color occurs in the image. There's PIL 
> documentation for all the Image methods here: [1].
> 
> If you have difficulties writing that down in Python, I'd be happy to 
> help - just drop me a line here.
> 
> Bye
> Igor
> 
> [1] http://www.pythonware.com/library/pil/handbook/image.htm



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