Git diff help!

Here is the situation:
I git cloned a specific revision of a project to my machine, i made some changes to it, and now i want to generate a patch comparing with the same revision online, is this even possible with git or is there any other way to create a clean patch?
before you ask, i need to use “git diff” instead of “patch” because one of the changes i made is the addition of a binary to the cloned copy,( a PNG file to be exact), and “patch” does not handle binaries whereas “git diff” does if you add the “–binary” flag to the CLI.

PS: please give me complete syntax example, i don’t know anything about git i’m just starting to using it.