Use PiSKEL! (https://www.piskelapp.com
) You can make sizes up to 1000x1000 without lag, it's free, supports log-in with Google (no passwords :0), and it has really good tools. Even if it doesn't have tools like negative colors or resize certain parts, it's still really good for a free program! Give it a try! Here's some examples:
Random person out.