How to read the RGB value of a given pixel in Pyth

Question

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.

Answer 1

You can use pygame's surfarray module. This module has a 3d pixel array returning method called pixels3d(surface). I've shown usage below:

from pygame import surfarray, image, display
import pygame
import numpy #important to import

pygame.init()
image = image.load("myimagefile.jpg") #surface to render
resolution = (image.get_width(),image.get_height())
screen = display.set_mode(resolution) #create space for display
screen.blit(image, (0,0)) #superpose image on screen
display.flip()
surfarray.use_arraytype("numpy") #important!
screenpix = surfarray.pixels3d(image) #pixels in 3d array:
#[x][y][rgb]
for y in range(resolution[1]):
    for x in range(resolution[0]):
        for color in range(3):
            screenpix[x][y][color] += 128
            #reverting colors
screen.blit(surfarray.make_surface(screenpix), (0,0)) #superpose on screen
display.flip() #update display
while 1:
    print finished

I hope been helpful. Last word: screen is locked for lifetime of screenpix.

Answer 2

photo = Image.open('IN.jpg') #your image
photo = photo.convert('RGB')

width = photo.size[0] #define W and H
height = photo.size[1]

for y in range(0, height): #each pixel has coordinates
    row = ""
    for x in range(0, width):

        RGB = photo.getpixel((x,y))
        R,G,B = RGB  #now you can use the RGB value

Answer 3

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

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

Answer 4

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.

Answer 5

install PIL using the command "sudo apt-get install python-imaging" and run the following program. It will print RGB values of the image. If the image is large redirect the output to a file using '>' later open the file to see RGB values

import PIL
import Image
FILENAME='fn.gif' #image can be in gif jpeg or png format 
im=Image.open(FILENAME).convert('RGB')
pix=im.load()
w=im.size[0]
h=im.size[1]
for i in range(w):
  for j in range(h):
    print pix[i,j]

Answer 6

If you are looking to have three digits in the form of an RGB colour code, the following code should do just that.

i = Image.open(path)
pixels = i.load() # this is not a list, nor is it list()'able
width, height = i.size

all_pixels = []
for x in range(width):
    for y in range(height):
        cpixel = pixels[x, y]
        all_pixels.append(cpixel)

This may work for you.