Question

I am new to python and would like to be pointed in the next direction. I am using PIL. Done a fair bit of research, and I’m still stuck!

I need to get the rgb of each pixel starting at 0,0 and going along each row all the way down the y coordinate. Its a bmp and only black and white, but I only want python to print pixels which are between 10,10,10 and 0,0,0. Could someone offer me some wisdom?

Answer 1

If you’re sure that r==g==b for all pixels, then this should work:

from PIL import Image

im = Image.open("g.bmp")       # The input image. Should be greyscale
out = open("out.txt", "wb")    # The output.

data = im.getdata()            # This will create a generator that yields
                               # the value of the rbg values consecutively. If
                               # g.bmp is a 2x2 image of four rgb(12, 12, 12) pixels, 
                               # list(data) should be 
                               # [(12,12,12), (12,12,12), (12,12,12), (12,12,12)]

for i in data:                   # Here we iterate through the pixels.
    if i[0] < 10:                # If r==b==g, we only really 
                                 # need one pixel (i[0] or "r")

        out.write(str(i[0])+" ") # if the pixel is valid, we'll write the value. So for
                                 # rgb(4, 4, 4), we'll output the string "4"
    else:
        out.write("X ")          # Otherwise, it does not meet the requirements, so
                                 # we'll output "X"

If it is NOT guaranteed that r==g==b for some reason, adjust the conditions as necessary. If you want an average of 10, for example, you could change the condition to something like

if sum(i) <= 30: # Equivalent to sum(i)/float(len(i)) <= 10 if we know the length is 3

Also note that for greyscale-format files (as opposed to greyscale images in a color file format) im.getdata() will return simply the grey level as a single value. So for a 2×2 image of rgb(15, 15, 15), list(data) will output [4, 4, 4, 4] instead of [(4, 4, 4), (4, 4, 4), (4, 4, 4), (4, 4, 4)]. In this case, when analyzing, refer just to i instead of i[0]