PIL-object to NumPy

[Roger Burnham]

On Tue, 4 May 1999 07:52:31 +0200, "Mads Andresen" <laura at post.cybercity.dk>
wrote:

>Hi,
>
>I'm using Python Image Library (PIL) and NumPy.
>
>I would like to open a image and make som imageprocessing on it. I would
>like to do the imageprocessing i NumPy, but I can't find out how to open af
>Image in NumPy??
>
>Q1: How do I open a image so I can use it with NumPy??
>
>Q2: If not(Q1) then: How do I convert a PIL-object to a NymPy-array???
>
>Mads Andresen, Odense, Denmark
>
>
Mads,

Heres a little demo I put together for a co-worker with the same questions:



import Image
import Numeric

def imageToArray(img, type=Numeric.UnsignedInt8):
    '''Given an 8bit Image object, return an Array object.
    '''
    arr = Numeric.array(img.tostring('raw', img.mode, 0, -1)).astype(type)
    arr.shape = img.size[1], img.size[0]
    return arr

def arrayToImage(arr, type='L'):
    '''Given an Array object, return an 8bit Image object.
    '''
    height, width = arr.shape
    img = Image.new(type, (width, height))
    img.fromstring(arr.tostring(), 'raw', type, 0, -1)
    return img

if __name__ == '__main__':
    import os
    import ImageChops
    
    os.chdir('C:/CRI/Bin/Test')

    # 8bit gray-scale
    # test img->arr->img
    img = Image.open('test_8bit.bmp')
    arr = imageToArray(img)
    testImg = arrayToImage(arr, 'L')
    diffImg = ImageChops.difference(img, testImg)
    for i in range(diffImg.size[0]):
        for j in range(diffImg.size[1]):
            val = diffImg.getpixel((i,j))
            if val:
                raise ValueError('Pixel %d,%d = %d, should be zero!'
                                 % (i,j,val))

    # test arr->img->arr
    def func(i,j):
        return (i*j + i + j) % 256
    arr = Numeric.fromfunction(func, (128, 256)).astype(Numeric.UnsignedInt8)
    img = arrayToImage(arr, 'L')
    testArr = imageToArray(img)
    diffArr = arr - testArr
    for i in range(diffArr.shape[0]):
        for j in range(diffArr.shape[1]):
            if diffArr[i,j]:
                raise ValueError('Element %d,%d = %d, should be zero!'
                                 % (i,j,diffArr[i,j]))
    

Cheers,

Roger Burnham   
Cambridge Research & Instrumentation   
rburnham at cri-inc.com   
http://www.cri-inc.com/   
http://starship.python.net/crew/roger/   
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