It is the principle of NL-means denoising: since an image is redundant, you use informations about shapes that are similar and are present at different scales i

It is the principle of NL-means denoising: since an image is redundant, you use informations about shapes that are similar and are present at different scales in the image to guess the shape of the zoomed version of the smallest ones by using the (more thorough) content of the bigger ones