What is the best way to make a big picture?

Question

Unity

I use a picture (like a map) on the entire screen of a smartphone, after clicking on some area, this area increases to become full screen, the original picture is enlarged by 2-10 times (depending on the area), naturally this I have a large picture and weighs 8-15Mb, while this is a sketch and a more detailed picture is needed ...
So the question became - how best to make it, photoshop and make png? (will weigh a lot)
Maybe in a blender? (I haven’t really worked in it yet, I don’t know what will happen)
Or how and in what way is it better to do what was planned?

For example, there is a person on the whole screen, we press on the hand and it approaches the whole screen, while it becomes transparent and you can already see the arteries of the vein, etc., so 2 pictures are the same in volume and weight, well, at least for me so now...

Tell me which way to dig...

Ps - I chose the section correctly, this object is used in my game on unity, so maybe a different approach is needed...

Answer 1

Make a grid of images, at the beginning of the cell approximation, replace the cell with a more detailed one.
That is, you need to have two sets of images, from normal and detailed.
The format is not important. It is important not to store the detailed ones in memory, when you click to load, replace, and then zoom in on the camera.