How can I reduce chroma noise in RAW files while keeping some luminance grain in open-source software?
Asked 2/10/2019
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2 answers
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I’m processing Canon EOS 2000D RAW (.CR2) files and want a denoising result closer to the camera JPEG: very little chroma noise, some pleasant luminance noise left, and no “painted” look.
I tried blurring the A/B channels in Lab, but it was manual and reduced chroma resolution too much. In darktable, I also tried profiled denoise with a borrowed EOS 1300D noise profile. It removes chroma noise well, but it also smooths luminance noise too aggressively and can make high-ISO crops look painterly.
Is there an open-source workflow or setting that better suppresses color noise while letting me keep a controlled amount of luminance noise and detail?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
2 Answers
1
I have found a way to improve the denoising by switching to another open source software, RawTherapee 5.5. The denoising plug-in of RawTherapee doesn't create a painting-like appearance.
Here's the result:
I turned on the noise reduction, used its default L-a-b color space, used the default mode (Conservative) and default gamma (1.7). Then I set luminance noise reduction to approximately 50 and detail recovery to approximately 40. The chrominance method was "automatic global" (the default). I also turned on the median filter.
The noise reduction of RawTherapee does exactly what I want, i.e. removes the most annoying chroma noise automatically and lets me adjust the level of removed luma noise. As removing the luma noise removes details from the image, there's the detail recovery slider.
The problem with RawTherapee is that on my Windows 10 system with GIMP 2.10.8, RawTherapee prevents GIMP from starting due to a buggy plug-in! I removed the GIMP plug-in manually by deleting the directory containing the plug-in file, allowing GIMP to start normally. Then I use RawTherapee 5.5 by opening the software separately and exporting to 16-bit TIFF files. The TIFF format maintains the EXIF data, so if I create JPG using GIMP, EXIF data will be in the JPG. RawTherapee also allows directly storing to JPG, and supports cropping and resizing so it's possible to use it without GIMP.
The feature I miss from Darktable is the option to use profiled denoising, i.e. having an automatically generated preset for each ISO of each camera to contain the profiled noise information. However, you can create your own ISO presets manually and adjust the strength of noise reduction for each ISO speed of your camera.
Originally by user81735. Source · Licensed CC BY-SA 4.0
user81735
7y ago
0
Generated from our catalog & community — verify before relying on it.
A practical open-source solution is to use RawTherapee’s noise reduction rather than trying to force darktable to mimic the in-camera JPEG.
Based on the shared results, RawTherapee can better match your goal of:
- strongly reducing chroma noise
- leaving some luminance grain
- avoiding an overly painterly look
Suggested starting point from the community example:
- Noise Reduction: on
- Color space: default Lab
- Mode: Conservative
- Gamma: 1.7
- Luminance NR: about 50
- Detail Recovery: about 40
- Chrominance method: Automatic Global
- Median filter: on
The key idea is to treat chroma and luminance differently: remove color blotches aggressively, but use luminance reduction more moderately and compensate with detail recovery. That gives cleaner shadows while preserving a more natural texture.
If darktable’s profiled denoise is smoothing too much, the simplest answer is that another RAW converter may suit this specific look better. In this case, RawTherapee appears to provide the balance you want more easily.
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UniqueBot
AI7y ago
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