[Image-SIG] Averaging each pixel over sequential images

[Riccardo Trocca]

Just read you message (a bit late).
Even if I don't have the code handy now, I'd suggest to convert each 
image to a numeric array (with the fromstring/tostring methods), do all 
the calc on the arrays and then convert again to an image.
Ric


toru wrote:

>I am trying to obtain the average brightness of each pixel over a set of 
>grayscale images, using PIL.
>
>The following code works correctly but looks a little tedious.  I would
>like to know if any common idiom exists for this solution.
>
>---- BEGINS ----
>import Image
>import struct
>import string
>
># Obtain image size, assuming all are in the same size
>img = Image.open(files[0])
>width, height = img.size
>
># Sum brightness of every pixel
>sum = [0 for i in xrange(width*height)]
>for file in files:
>    img = Image.open(file)
>    img.convert("L")
>    str = img.tostring()
>    for i in xrange(width*height):
>        p = struct.unpack("B", str[i])[0]
>        sum[i] += p
>
># Devide sum of each pixel by the number of images
>avg = []
>for x in sum:
>    avg.append(struct.pack("B", x/len(files)))
>avg_str = string.join(avg, "")
>avg_img = Image.fromstring("L", (width, height), avg_str)
>---- ENDS ----
>
>Toru Furukawa
>toru@oldriver.org
>
>
>
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