Hi all, I am working with images in python using PIL. I come from a MATLAB background so I am finding it to be sometimes frustrating to do things correctly and quickly.
Yup. That's the curse of changing toolsets.
All I need to do is load an image and store a list of pixel coordinates at which the alpha channel is set to 1. In Matlab this would be easy...Lets say we have a 2x2x4 array that represents the image. I would just type something like:
indices = find(im(:,:,3)==1);
then work with indices to get xy coords. Is there a similar way to accomplish the same thing in python and PIL without having a nested for loop and checking every pixel? I would appreciate advice. Thanks very much for your attention!
One way would be to use Numeric or numarray, which you will probably want anyway if you are doing Matlab-type stuff. If you are dealing with large images or are dealing with raw data on disk (as opposed to PNGs or GIFs), numarray might be best for you.
A mildly tested example:
import Numeric as N import Image
filename = 'heavy_1.gif'
img = Image.open(filename).convert('RGBA')
data = img.tostring()arr = N.fromstring(data, N.UInt8) arr.shape = (img.size[1], img.size[0], 4)
mask = (arr[:,:,3] == 255).flat
idx = N.indices(arr.shape[:2]) idx.shape = (2, len(mask))
pixels = N.compress(idx, mask) # for all i, arr[pixels[0,i], pixels[1,i], 3] == 255
I'm sure there's some code floating around that makes these kinds of operations simpler.
-- Robert Kern [EMAIL PROTECTED]
"In the fields of hell where the grass grows high Are the graves of dreams allowed to die." -- Richard Harter -- http://mail.python.org/mailman/listinfo/python-list
