Gradients in photographs or video rarely have a perfect linear progression like you can generate in an image editor. (Sensor noise and other natural phenomena)

Gradients in photographs or video rarely have a perfect linear progression like you can generate in an image editor. (Sensor noise and other natural phenomena) There basically already is some natural dithering. If your software is not dithering extremely gradual gradients that's the problem. Still in that case if you wanting to dither you gradient you better be working in a higher precision format. Anyways, please notice I said: "8 bits is enough (generally)". There is a reason I said generally, I did not say always. -Edit- Although, lossy compression may effectively linearize gradients from video or photographs. Consider an extremely simple example: A compression algorithm that detects/fits to a gradual gradients to much smaller delta encoding. Such as increase the channel value by 1 every pixel for a 100 pixels. While this might be rather simple example. It's obvious to see how that would remove noise and make that section of an image highly linear.