Nested for loops to access images

We can access the color information of certain columns of images in a similar way. We still have the 3X4 image saved as a 2D list our_image.

The RGB values of each pixel is as follows:

(0,0,0)   (0,80,0)   (0,160,0)   (0,240,0)
(120,0,0) (120,80,0) (120,160,0) (120,240,0)
(240,0,0) (240,80,0) (240,160,0) (240,240,0)

Using tricks we’ve learned so far, we can output each column by copy/pasting code:

for column in range(4):
    print(our_image[1][column])

for column in range(4):
    print(our_image[2][column])

which leads to

(120,0,0)
(120,80,0)
(120,160,0)
(120,240,0)
(240,0,0)
(240,80,0)
(240,160,0)
(240,240,0)

as we wanted. However, nested for loops can generate the same result with more concise code as follows:

for row in range(1,3):
    for column in range(4):
        print(our_image[row][column])

Here are the details of how the nested for loops printed the desired result.

• row is 1 at the initial iteration of the outer for loop

  • column is 0 at the initial iteration of the inner for loop

  • our_image[1][0] is printed

  • column is 1 at the next iteration of the inner for loop

  • our_image[1][1] is printed

  • column is 2 at the next iteration of the inner for loop

  • our_image[1][2] is printed

  • column is 3 at the next iteration of the inner for loop

  • our_image[1][3] is printed

• row is 2 at the next iteration of the outer for loop

  • column is 0 at the initial iteration of the inner for loop

  • our_image[2][0] is printed

  • column is 1 at the next iteration of the inner for loop

  • our_image[2][1] is printed

  • column is 2 at the next iteration of the inner for loop

  • our_image[2][2] is printed

  • column is 3 at the next iteration of the inner for loop

  • our_image[2][3] is printed

Similarly, we can print the information of the entire image!

for row in range(3):
    for column in range(4):
        print(our_image[row][column])

Here is the output.

(0,0,0)
(0,80,0)
(0,160,0)
(0,240,0)
(120,0,0)
(120,80,0)
(120,160,0)
(120,240,0)
(240,0,0)
(240,80,0)
(240,160,0)
(240,240,0)

You can be assured that the correct information is printed according to the RGB table of the image above.