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POPixel manipulation with PIL.Image and ctypes
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copied!<p>I have a C function that does some pixel manipulation on a raw 2D array of 8 bit RGB values. I get the response in a <code>c_ubyte</code> array. My code looks roughly like this:</p> <pre><code>from ctypes import cdll, CDLL, Structure, byref, c_utype, c_uint # get a reference to the C shared library cdll.loadLibrary(path_to_my_c_lib) myclib = CDLL(path_to_my_c_lib) # define the ctypes version of the C image that would look something like: # struct img { # unsigned char data[MAX_IMAGE_SIZE]; # unsigned int width; # unsigned int height; # } class Img(Structure): _fiels_ = [ ('data', c_ubyte * MAX_IMAGE_SIZE), ('width', c_uint), ('height', c_uint), ] # create a blank image, all pixels are black img = Image() img.width = WIDTH img.height = HEIGHT # call the C function which would look like this: # void my_pixel_manipulation_function(struct img *) # and would now work its magic on the data myclib.my_pixel_manipulation_function(byref(img)) </code></pre> <p>At this point I'd like to use PIL to write the image to file. I currently use the following code to convert the byte data to image data:</p> <pre><code>from PIL import Image s = ''.join([chr(c) for c in img.data[:(img.width*img.height*3)]]) im = Image.fromstring('RGB', (img.width, img.height), s) # now I can... im.save(filename) </code></pre> <p>This works but seems awfully inefficient to me. It takes 125ms for a 592x336 image on a 2.2GHz Core i7. It seems rather silly to iterate over the entire array and do this ridiculous string join when Image could probably grab directly from the array.</p> <p>I tried looking for ways to cast the <code>c_ubyte</code> array to a string or maybe use <code>Image.frombuffer</code> instead of <code>Image.fromstring</code> but couldn't make this work.</p>

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