Illustration of the forward and backward diffusion processes used in 21cmPSDenoiser. The forward process adds noise to a mean 21 cm 2D PS sampled from the data distribution (leftmost panel), transforming it into a pre-defined Gaussian prior distribution (rightmost panel). This allows us to then write the reverse process that allows us to sample the Gaussian prior and generate a mean 2D PS, conditioned on the input realisation of the 2D PS.