Don’t we all wish we didn’t have to worry about noise in our images? With modern cameras and their ever improving quality on high ISO, noise is becoming less and less an issue. But then again our demands increase. We always want to stretch the limits of the impossible with ultra sharp images of the Milky Way, freezing the motion of a bird’s wings in the low evening sun or the athletes in a dimly lit gymnasium.
Also, not everyone can afford the newest full frame cameras with the best ISO performance, but we still want our images clean and free of these coloured speckles that seem to ruin all too many images.
Then we have to turn to our software’s noise reduction tools. My favourite RAW developer, Darktable, has several tricks up its sleeve. There are a total of four modules dedicated to noise reduction, and also the equalizer, which can do its magic on many frequency based challenges, including noise.
Works by blurring the RAW image data a little bit very early in the pipeline, before demosaicing. Don’t rely only on this one, as it is easy to do loose much detail. Just use it as a start to get a bit less noise for the other tools.
This one is based on noise profiles made by the Darktable developers and community. For every supported camera there are profiles for every whole ISO step (100, 200, 400 etc). These are selected automatically based on the image’s EXIF data. This method works best when there is a certain amount of detail in the image, as it tends to be a bit blotchy on large, smooth surfaces.
Denoise (bilateral filter)
Very good on large areas with little detail, but at the same time preserves sharp edges. Intensity can be set individually for each of the red, green and blue channel.
Denoise (non-local means)
As the Darktable manual says: “This module reduces noise in your image but preserves structures. This is accomplished by averaging each pixel with some surrounding pixels in the image. The weight of such a pixel in the averaging process depends on the similarity of its neighborhood with the neighborhood of the one pixel to be denoised. A patch with a certain size is used to measure that similarity.”
Noise reduction in the Equalizer module works by smoothing out high frequencies with low intensity. As is the nature of the equalizer, you choose the frequencies yourself.
For a deeper explanation of Darktable’s noise reduction capabilities, watch the video below:
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