CODEWITHSUNDEEP
pythonimagepython-imaging-library
dsv_dsv
dsv_dsv

Reputation: 59

Python - gray scale formula with PIL

I want to make greyscale image by my own code. 

from PIL import Image

path = "people.jpg"

img = Image.open(path)
img = img.convert("LA")
img.save("new_image.png")

So I change img.convert() for my own formula. But it does not work.

from PIL import Image

path = "people.jpg"

img = Image.open(path)
rgb = img.convert("RGB")
width,height = rgb.size

for x in range(width):
    for y in range(height):
        red,green,blue = rgb.getpixel((x,y))
        value = red * 299/1000 + green * 587/1000 + blue * 114/1000
        value = int(value)
        rgb.putpixel((x,y),value)


rgb.save("new.png")

Any idea what is wrong? The new image is with red backgroud.

Upvotes: 3

Views: 7529

Answers (2)

dpdwilson
dpdwilson

Reputation: 1007

As martineau mentioned, rgb is initialized as an RGB (tri-band) image, so it is expecting RGB values. You want grayscale, which only requires a single band. You have two options here:

  1. Follow martineau's advice and simply swap out rgb.putpixel((x,y),value) for rgb.putpixel((x, y), (value, value, value)). This will give it the proper three color values.
  2. Create a new grayscale image using Image.new('L',...) before putting the pixels into it.

Here's how you might implement option 2 (note that I'm using Python 2.7):

from PIL import Image

path = "people.jpg"

img = Image.open(path)
width, height = rgb.size
gray = Image.new('L', (width, height))

for x in xrange(width):
    for y in xrange(height):
        r, g, b = img.getpixel((x, y))
        value = r * 299.0/1000 + g * 587.0/1000 + b * 114.0/1000
        value = int(value)
        gray.putpixel((x, y), value)

gray.save("new.png")

Also, if speed is a concern, consider using putdata() instead of putpixel(). (That's beside the point, so I won't belabor it.)

Upvotes: 3

kanatti
kanatti

Reputation: 785

Greyscale image will be having a tuple of two values for each pixel - (luminosity value, 255). Creating a new greyscale image and putting values to each pixel will work.

greyim=Image.new("LA",(width,height))

for x in range(width):
    for y in range(height):
        red,green,blue = rgb.getpixel((x,y))
        value = red * 299/1000 + green * 587/1000 + blue * 114/1000
        greyim.putpixel((x,y),(value,255))

Upvotes: 0

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