What is Noise Schedule?

The image changes from noisy to clean. Do you wonder if the noise predictor not working well in the initial steps? 

Actually, this is only partly true. The real reason is we try to get to an expected noise at each sampling step. This is called the noise schedule. Below is an example.

A noise schedule for 15 sampling steps.

The noise schedule is something we define. We can choose to subtract the same amount of noise at each step. Or we can subtract more in the beginning, like above. The sampler subtracts just enough noise in each step to reach the expected noise in the next step. That’s what you see in the step-by-step image. 

Image at each sampling step.