How to Efficiently Convert PIL Images to NumPy Arrays for Pixel Manipulation and Back?

Converting PIL Images to NumPy Arrays for Efficient Pixel Manipulation

Question: How can you convert a PIL Image into a NumPy array for faster pixel-wise transformations without encountering issues during the conversion back to a PIL Image?

Answer:

The process involves two steps:

Converting PIL Image to NumPy Array

To convert a PIL Image to a NumPy array, you can use this code as an example:

pic = Image.open("foo.jpg")
pix = numpy.array(pic.getdata()).reshape(pic.size[0], pic.size[1], 3)

Converting NumPy Array Back to PIL Image

Using pic.putdata():

If pic.putdata() is not behaving as expected when attempting to load the modified array back into the PIL Image, check that you are providing the data in a format that putdata() accepts. It expects a sequence of tuples, so you may need to convert the array to this format, as shown below:

data = list(tuple(pixel) for pixel in pix)
pic.putdata(data)

Using PIL 1.1.6 :

As of PIL 1.1.6, you can use the following simplified approach for converting between images and NumPy arrays:

pix = numpy.array(pic)

This will result in a 3-dimensional array with rows, columns, and RGB values.

Final Steps:

After making modifications to the array, you can use either pic.putdata(pix) or Image.fromarray(pix) to create a new PIL Image.

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