Do camera makers apply noise reduction or sharpening to RAW files?
Asked 5/4/2023
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2 answers
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I’ve read that some cameras can still alter RAW data with things like noise reduction or other preprocessing. For example, Sony’s "star eater" issue in some long-exposure astrophotography modes appears to suppress small stars even in RAW files. Is this kind of processing common across camera brands, from smartphones to DSLRs and mirrorless cameras, or is it more of an exception? Also, is sharpening ever applied to RAW, or is the main concern limited to things like hot-pixel mapping and noise filtering?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
3y ago
2 Answers
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Some camera do, some don't. There is no rule, but in general noise reduction is not applied to RAW files. I think cleaning up RAWs is the exception.
If you are interested in checking whether a camera does noise filtering, you can try to obtain a raw file shot in complete darkness (lens cap on) and do 2D Fourier transform of the pixel values, as explained here. Star-eating is mentioned also here.
This is a 2D Fourier of an image with Gaussian blur, see the "vignetting" (not in a traditional sense):
It appears that the Z50 does some preprocessing anyway, see here, so the issue is not always that easy and related only to noise filtering. In particular, it appears that Nikon "calibrates" the response of the sensor to get more consistent colours between units, which is done by prescaling of the sensor output and which results in empty gaps in the red and blue channels:
You can also check noise graphs obtained by someone else, see for example Z50 which talks about noise filtering at 10 000 ISO. Graphs can be found also on Photons to photos.
Originally by user27445. Source · Licensed CC BY-SA 4.0
user27445
3y ago
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Generated from our catalog & community — verify before relying on it.
RAW files are usually the least-processed image data a camera provides, but they are not always completely untouched sensor dumps.
Based on the answers, there is no universal rule: some cameras do apply limited preprocessing to RAW, while many do little or none beyond necessary capture steps. In general, strong noise reduction on RAW is the exception rather than the norm.
What can affect RAW includes:
- hot-pixel mapping / correction
- sensor calibration or response normalization
- ISO-related analog amplification and digitization
- metadata and color filter array information
These are still forms of processing, even if they’re not the same as JPEG-style image enhancement.
Sharpening is generally not expected in RAW in the usual sense. The bigger concern is selective filtering or correction that changes fine detail, such as the Sony "star eater" behavior in certain long exposures.
So the practical answer is: RAW is minimally processed, not unprocessed. Some cameras/brands/modes may alter RAW data, but it’s not something you should assume every camera does in the same way. If this matters for your use case—especially astrophotography—check camera-specific testing rather than relying on the word RAW alone.
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