How to read the RGB value of a given pixel in Python?

If I open an image with open("image.jpg"), how can I get the RGB values of a pixel assuming I have the coordinates of the pixel?

Then, how can I do the reverse of this? Starting with a blank graphic, 'write' a pixel with a certain RGB value?

I would prefer if I didn't have to download any additional libraries.

Solution 1:

It's probably best to use the Python Image Library to do this which I'm afraid is a separate download.

The easiest way to do what you want is via the load() method on the Image object which returns a pixel access object which you can manipulate like an array:

from PIL import Image

im = Image.open('dead_parrot.jpg') # Can be many different formats.
pix = im.load()
print im.size  # Get the width and hight of the image for iterating over
print pix[x,y]  # Get the RGBA Value of the a pixel of an image
pix[x,y] = value  # Set the RGBA Value of the image (tuple)
im.save('alive_parrot.png')  # Save the modified pixels as .png

Alternatively, look at ImageDraw which gives a much richer API for creating images.

Solution 2:

Using Pillow (which works with Python 3.X as well as Python 2.7+), you can do the following:

from PIL import Image
im = Image.open('image.jpg', 'r')
width, height = im.size
pixel_values = list(im.getdata())

Now you have all pixel values. If it is RGB or another mode can be read by im.mode. Then you can get pixel (x, y) by:

pixel_values[width*y+x]

Alternatively, you can use Numpy and reshape the array:

>>> pixel_values = numpy.array(pixel_values).reshape((width, height, 3))
>>> x, y = 0, 1
>>> pixel_values[x][y]
[ 18  18  12]

A complete, simple to use solution is

# Third party modules
import numpy
from PIL import Image


def get_image(image_path):
    """Get a numpy array of an image so that one can access values[x][y]."""
    image = Image.open(image_path, "r")
    width, height = image.size
    pixel_values = list(image.getdata())
    if image.mode == "RGB":
        channels = 3
    elif image.mode == "L":
        channels = 1
    else:
        print("Unknown mode: %s" % image.mode)
        return None
    pixel_values = numpy.array(pixel_values).reshape((width, height, channels))
    return pixel_values


image = get_image("gradient.png")

print(image[0])
print(image.shape)

Smoke testing the code

You might be uncertain about the order of width / height / channel. For this reason I've created this gradient:

The image has a width of 100px and a height of 26px. It has a color gradient going from #ffaa00 (yellow) to #ffffff (white). The output is:

[[255 172   5]
 [255 172   5]
 [255 172   5]
 [255 171   5]
 [255 172   5]
 [255 172   5]
 [255 171   5]
 [255 171   5]
 [255 171   5]
 [255 172   5]
 [255 172   5]
 [255 171   5]
 [255 171   5]
 [255 172   5]
 [255 172   5]
 [255 172   5]
 [255 171   5]
 [255 172   5]
 [255 172   5]
 [255 171   5]
 [255 171   5]
 [255 172   4]
 [255 172   5]
 [255 171   5]
 [255 171   5]
 [255 172   5]]
(100, 26, 3)

Things to note:

• The shape is (width, height, channels)
• The image[0], hence the first row, has 26 triples of the same color

Solution 3:

PyPNG - lightweight PNG decoder/encoder

Although the question hints at JPG, I hope my answer will be useful to some people.

Here's how to read and write PNG pixels using PyPNG module:

import png, array

point = (2, 10) # coordinates of pixel to be painted red

reader = png.Reader(filename='image.png')
w, h, pixels, metadata = reader.read_flat()
pixel_byte_width = 4 if metadata['alpha'] else 3
pixel_position = point[0] + point[1] * w
new_pixel_value = (255, 0, 0, 0) if metadata['alpha'] else (255, 0, 0)
pixels[
  pixel_position * pixel_byte_width :
  (pixel_position + 1) * pixel_byte_width] = array.array('B', new_pixel_value)

output = open('image-with-red-dot.png', 'wb')
writer = png.Writer(w, h, **metadata)
writer.write_array(output, pixels)
output.close()

PyPNG is a single pure Python module less than 4000 lines long, including tests and comments.

PIL is a more comprehensive imaging library, but it's also significantly heavier.

Solution 4:

As Dave Webb said:

Here is my working code snippet printing the pixel colours from an image:

import os, sys
import Image

im = Image.open("image.jpg")
x = 3
y = 4

pix = im.load()
print pix[x,y]