How can I resize an image without using .resize() in python PIL

Question

I have the enlarge ratio provided, like two times in width, three times in height.

Here's my thought, I want to go through each pixel in the image, enlarge all of them by ratio and put them in a new created picture.

Answer 1

Well, your thought is the first step. There is some other steps. The most important step is interpolation.

For example, if you want to enlarge a image with 2 pixels in width, 2 pixels in height to 4 pixel in width and height. As your thought, you should let

new_img[0][0] = old_img[0][0]
new_img[2][0] = old_img[1][0]
new_img[0][2] = old_img[0][1]
new_img[2][2] = old_img[1][1]

But only 4 pixels' value are assigned, what is the value of the other 12 pixels? You have to provide an algorithm to interpolate.

You can find more information from Wikipedia.