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

[Ken Mankoff]

Newbie to Python here so please excuse dumb suggestions, but...

Must you use pure Python and PIL?

It seems PyLibTiff was written to solve something like this. 
https://code.google.com/p/pylibtiff/

Or you could perhaps load the TIFF with numpy which allows you to 
load just parts of the file, down-sample in segments, then combine.

Or just use 3rd party tools (I have used gdal with very large files, 
though none larger than my RAM).

   -k.


On Thu, 8 Sep 2011, 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
> L0F2, Adanac Drive, SOUTHAMPTON, United Kingdom, SO16 0AS
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