[Image-SIG] What is the best way to anti-alias a very large resolution image in PIL

Kevin Cazabon kevin at cazabon.com
Tue Sep 13 21:48:40 CEST 2011

I just found an article that Fredrik wrote based on a discussion we had on memory limits back in 1999.  Using the .tile attribute and doing your work in chunks is one sure-fire way of getting there, although it'll take some effort.  I hope this helps!



On Sep 8, 2011, at 7:07 AM, Craig Coleman (C) wrote:

> Hi,
> I have a really thorny problem.
> I need to downsample a raster map that is 23622x23622 pixels to 7874x7874 pixels using the ANTIALIAS filter.
> I have the following Python code:
> >>> import Image 
> >>> img = Image.open(r"C:\temp\24bit_nd.tif") 
> >>> nimg = img.resize((7874,7874),Image.ANTIALIAS)
> As soon as the resize method is called, python crashes instantly.  I presume this is a memory allocation issue.
> Is there another way of performing anti-aliasing on such a large image (its 2.7GB uncompressed although I'm using LZW for storage).
> I have tried converting the file to 8bit with a palette and this successfully downsamples but the ANTIALIAS is not performed.  What am I doing wrong?
> Craig Coleman 
> Technical Lead
> Information Systems, Ordnance Survey
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