Creating a copy of an image

We can use nested for loops to help us create copies of 2D lists. The idea is to create an empty list and add each element into this newly created list. Referring to the code below, we want to make a copy of img which is a 2×22 times 22×2 image. We first created a new list called copy_img and used a nested for loop to add each element into this new list. The outer for loop will iterate through the indices of the row. Within this outer for loop, we have created a new empty list called row which will be used to store the copied values from that particular row in img. Then we have an inner for loop that will iterate through the indices of the column. Within this inner for loop, we append the element at that particular row and column to the row list. Once this inner for loop finishes, we have successfully copied that particular row in img, img[row_idx], to row. We then append row to copy_img and continue to copy the next row until we have finished copying all rows.

Our piece of code prints out the following. Notice that img and copy_img contain the same elements in the 2D lists. However, they have separate id’s, recall from previous modules that separate ids indicate two references that point to separate objects. This means img and copy_img contain references that point to separate objects. (The id numbers printed when you run the code may vary.)

img = [[(0, 0, 0), (255, 255, 255)], [(255, 255, 255), (0, 0, 0)]]
copy_img = [[(0, 0, 0), (255, 255, 255)], [(255, 255, 255), (0, 0, 0)]]
id of img = 229476360
id of copy_img = 229755752