Locating Position of Black Pixels from ImageGrab

Question

I am currently creating a PianoTiles AI, that has to locate all the black pixels from an ImageGrab. I have got all the positions of the Image Grab however I need to find out if there are black pixels in there and if so where they are so my AI can click them. Bellow I have put a snip-it of my code.

I have already had a look around the web but cant find anything. I think that the code goes something like this.

from PIL import ImageGrab, ImageOps    

class Coordinates:    
    lines = [    
    (520, 300, 525, 760),    
    (630, 300, 635, 760),    
    (740, 300, 745, 760),    
    (850, 300, 855, 760)]    
    restartcheck = (660, 590, 725, 645)    
    restartbtn = (695, 615)    


blackpixelpositions = []    

def findtiles():    
    for line in Coordinates.lines:  
        i = ImageGrab.grab(line)  
        for pixel in i.getdata():  
            #if pixel is black  
            # x, y = pixel position  
             blackpixelpositions.append((x,y))  

All I need is the above code to work and give me the black pixel positions.

Answer 1

You should try and avoid looping over images and using functions such as getpixel() to access each pixel as it is really slow - especially for large images if you are grabbing modern 4-5k screens.

It is generally better to convert your PIL image to a Numpy array and then use vectorised Numpy routines to process your images. So, in concrete terms, let's say you get a PIL image either by screen-grabbing or opening a file:

im = Image.open('someFile.png')

you can then make a Numpy array from the image like this:

n = np.array(im)

and search for black pixels like this:

blacks = np.where((n[:, :, 0:3] == [0,0,0]).all(2)))

which will give you an array of x coordinates and an array of y coordinates of the black pixels, eg you could do:

xcoords, ycoords = np.where((n[:, :, 0:3] == [0,0,0]).all(2))

Answer 2

You have an issue with i.getdata() that it flattens the data, ie you loose pixel coordinates (unless you keep track manually). so you will only know that there exists a black pixel, but not where. You can use getpixel instead:

def get_black_pixels(image):
    found = []
    width, height = image.size
    for y in range(height):
        for x in range(width):
            if all(map(lambda x: x < 20, image.getpixel((x,y)))):
                found.append((x,y))
    return found

The line:

all(map(lambda x: x < 20, image.getpixel((x,y))))

just checks that all values (r,g,b) is below 20, which you can change to some other threshold value.