How is it that two different images, but same resolution, can have different storage size?

Question

How is it that two different images, but same resolution, can have different storage size?

In: Technology

Answer 1

Compression.

If an image is for instance pure white, you don’t need a huge file that goes:

pixel 1: white
pixel 2: white
…
pixel 1000000: white

You just write an image that effectively says:

pixels 1 to 1000000: white

In practice, compression gets a good deal more complicated than that, but that’s the basic principle. And of course it varies depends on content. For instance with the above scheme if each pixel was a different color, the compression would be ineffective.