Programmatically change image resolution

Question

I have calculated that if I want my generated image to be A4 size @ 600dpi for print purpose, it needs to be 7016x4961px @ 72dpi. So, I generate it programmatically, then test

Answer 1

If you have generated your image 7016 x 4961 px, it is already A4 at 600 dpi. So you don't need to resize it, you just have to set resolution information in file.

You can do it with PIL:

from PIL import Image

im = Image.open("test.png")
im.save("test-600.png", dpi=(600,600))