Why does noise become visible when I brighten and saturate a RAW file in post-processing?
Asked 6/19/2017
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2 answers
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I'm editing RAW files in RawTherapee and notice that after increasing exposure, contrast, and saturation, the final image shows much more visible noise, especially in darker areas like the sky. It doesn't seem obvious in the unedited file, but it becomes prominent in the JPEG export after processing.
What causes this? Is the editing creating noise, or just revealing and amplifying noise that was already in the RAW data? What adjustments tend to make noise worse, and what can be done in-camera or in post to reduce the problem?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
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The noise is present in the original file.
What you have done with your choice of settings is amplified it. Noise is mostly present in dark areas but you have basically applied gain to those areas and hence to noise noise.
All channels have noise but the blue and red channels have more noise since they are formed using fewer photosites. In your processing, it is clear that you increased its level beyond anything resembling reality. Keep it down. A friend said processing is like applying make-up: A little goes a long way but too much looks trashy.
To reduce this issue, you need to improve the exposure right in-camera which will allows you to get better output since you will not to apply go much gain. The simplest and on of the most effectives is to Exposure-To-The-Right (ETTR) as described in the linked answer on mine.
Originally by user1620. Source · Licensed CC BY-SA 4.0
user1620
9y ago
0
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The edits aren’t creating new noise so much as making existing noise more visible.
RAW data always contains some noise, especially in darker areas. When you raise exposure/brightness in post, you’re effectively adding gain to the shadows, which boosts both the image detail and the noise. Increasing saturation can also make color (chrominance) noise stand out more, and some corrections such as vignetting/peripheral illumination correction can brighten dark corners and reveal more noise there.
A RAW file also has no single “original look” until it’s processed, so it’s normal for noise to appear differently depending on your settings.
To reduce the problem:
- Expose better in-camera so you don’t need as much brightening later.
- Avoid pushing shadows, contrast, and saturation too far.
- Use noise reduction in your RAW processor.
- If appropriate, use an ETTR-style exposure approach to capture more signal without clipping highlights.
JPEGs may seem cleaner because the camera already applies processing and noise reduction. RAW usually gives better flexibility, but it also makes underlying noise easier to see when heavily edited.
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AI9y ago
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