What is the purpose of the resolution property of images (when creating/editing)?

I want to check something I don't quite understand with the size/quality properties of an image.

OK, as much as I understand, the size of an image you create in Photoshop, for example, will determine what rectangular area of screen pixels it takes.

And the resolution determines what will be the area of the smallest editable element/block on this picture.

So, if I have an image 1024x1024 with 72 PPI:

• it will take 1024x1024 pixels on screen;


• but what area will an editable block will take - how do you calculate it?

Update:

What do I mean by the smallest editable block is the smallest area of the picture you can manipulate. I probably am deeply mistaken, but I think that if you set smaller PPI, you will not be able to edit every single pixel on the picture, but instead will be able to manipulate only bigger chunks of it. Is this correct?

And finally, the produced image, doesn't have a metadata (besides having single colour blocks with size x pixels^2) about the used resolution, right?

It will be awesome if someone answers this, thanks in advance!

Answer

I'll try a short-n-sweet answer:

What is the purpose of the resolution property of images (when creating/editing)?

The purpose of the PPI is to tell certain software what size the image should be when printed on a piece of paper. That is all. And most software doesn't care anyways.

A 100x100px image at 72dpi is the exact same image as 100x100px at 300dpi. The only difference is that certain software will print them at different sizes by default.

I believe you're getting confused because you are connecting PPI to 'interpolate' in PhotoShop's set up screens. In this situation, PPI is merely a calculation tool. And does confuse lots of people.