CODEWITHSUNDEEP
pythonarraysimage-processingpython-imaging-librarygrayscale
Sachin Titus
Sachin Titus

Reputation: 2339

Converting image to greyscale outputs wrong result

 def desaturate_image(self, image):
    desatimage = Image.new(image.mode, image.size)
    pixellist = []
    print(len(pixellist))
    for x in range(image.size[0]):
        for y in range(image.size[1]):
            r, g, b = image.getpixel((x, y))
            greyvalue = (r+g+b)/3
            greypixel = (int(round(greyvalue)), int(round(greyvalue)), int(round(greyvalue)))
            pixellist.append(greypixel)
    print(pixellist)
    desatimage.putdata(pixellist)
    return desatimage

I'm writing a python method to convert the image passed as parameter to greyscale. The result I get is though, not right. Here's the input and output. Where is it wrong?

enter image description here

enter image description here

Upvotes: 1

Views: 130

Answers (1)

miradulo
miradulo

Reputation: 29690

You are iterating over the pixels with the wrong dimension first - Pillow images are column-major order. So you want

...
for y in range(image.size[1]):
    for x in range(image.size[0]):
...

such that your pixel list stores the pixels column-wise.

This gives you

enter image description here

Of course, you could just use the .convert method to get a greyscale representation more easily, which uses the transform mentioned in the docs. 

image.convert('L')

As abarnert mentioned below, this gives you an image actually in greyscale mode ('L') as opposed to your current answer that keeps the image in RGB mode ('RGB') with triply repeated data.

Upvotes: 2

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