Instantaneous manipulation of pixels shown on the screen

Question

I want to build an application where I can change display settings similar to what a TV does. So far, I could only come across manipulating screen brightness where we have a python library to do that task. However, I'd like to change screen sharpness, contrast and backlight as well for which I need to basically manipulate every pixel. Looping over every pixel on python is painfully slow as it is in C++. I'm guessing programming in Java would result in the same. But then how is a TV programmed so that it doesn't lose its smoothness? How is the brightness of any electronic device controlled internally if it's not manipulating the screen pixel by pixel? If it's written in a very primitive language is there no way to access it?