Denoise Image
Denoise an image or video: smooth out grain, noise and JPEG blocking while edges stay sharp, using a bilateral filter. From a light touch to a painted look.
How does denoising keep edges sharp?
A plain blur averages every pixel with its neighbors, so noise goes away but so does every edge. This tool uses a bilateral filter instead. It still averages neighbors, but only those of a similar color, so the speckles in a dark sky blend together while the sky's edge against a roof doesn't blend into the roof.
Carlo Tomasi and Roberto Manduchi described the method in 1998, and it's still behind many noise reduction and skin smoothing features in photo apps.
Radius and Smoothing
Radius is how far the smoothing reaches, from 1 to 8 pixels, and it opens at 3. Smoothing is how different two colors may be and still get averaged, from 0 to 1. At the default 0.3 the filter takes out grain but stops at real detail.
Light touch uses Radius 2 and Smoothing 0.15, for a photo that's only a little noisy. Smooth skin goes to 5 and 0.4, softening pores and blemishes while eyes and hair keep their edges. Painted sets 8 and 0.8, which flattens everything into smooth areas of color, closer to an illustration than a photo.
What kind of noise can it remove?
Fine grain from a high ISO or a phone in low light comes out well, and so do the 8 by 8 pixel blocks of a heavily compressed JPEG, since both are small differences in otherwise flat areas. Large blotches of color noise are harder, because they're as big as the filter's reach. Raise Radius for those, and accept some softening.
If the result looks too smooth, as denoised photos often do, run Sharpen Image after it at a low Amount with some Threshold. That brings the edges back without bringing the noise back too.
Denoising video
The filter works on each frame alone. Noise in video changes from one frame to the next, so a still frame might look clean while the clip still shimmers a little. Raise Smoothing slightly beyond what a single frame needs, around 0.35 to 0.4, and the shimmer settles.