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For some photographers it is important to receive unadulterated raw files which have not been pre-processed by the camera. For example, Nikon is known to apply denoising algorithms on sensor data before producing raw files. This is a big problem for some applications, such as astrophotography.

Is there any way to know what pre-processing a particular camera might be doing to its sensor data?

  • See photo.stackexchange.com/questions/77983/… as pretty much every camera does some degree of processing. – nwcs Aug 19 '17 at 23:12
  • @nwcs that one answers what can be done, but not how you can tell. I've always been suspicious of the claims of de-noising in RAW, unless it's simply to compensate the black level and gain of each individual pixel. – Mark Ransom Nov 6 '17 at 23:48
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Is there any way to know what pre-processing a particular camera might be doing to its sensor data?

You could ask the manufacturer of the particular camera. If they are nice they will tell you (although I'm not aware of any publicly available lists).

If they are even more nice they may offer an option to turn any pre-processing off for raw data, although you may not want all of that and keep some calibrations (like brightness corrections?).

The chance is pretty low though because this is usually only built-in for scientific grade cameras.

An alternative would be to try to detect this pre-processing steps in the raw data by a standardized test experiment. You could take images of an array of point-like light sources of variable brightness and if the single images remain smooth independent of the brightness you know that some denoising has been applied (because the SNR of real raw data usually increases with lower brightness). This could also be used to compare different cameras and select the one with the best performance and the lowest amount of pre-processing (might be a trade-off though).

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Is there any way to know what pre-processing a particular camera might be doing to its sensor data?

You can assume that most manufacturers apply some Secret Sauce® to their raw and JPEGs - that means that if you don't want to do extra work just skip to the end.

Searching for an answer led me to the dcraw website where it says: "... use dcraw.c as the documentation that camera makers refuse to provide" and goes on to say that if your camera isn't amongst the several hundred supported ones "... I need a photo of a Wolf Faust, ColorChecker, CMP, or other calibrated color chart.".

Those links are an interesting read but the last leads to CMP's webpage: Raw RGB levels and their interpretation, which recommends RawDigger.

RawDigger is also mentioned on our site here: https://photo.stackexchange.com/a/50715/37074 , in a question about accessing pure raw data. RawDigger has a "Profile Edition" which claims is useful for: "Advance Study of Sensor and Lens - creating of sensor calibration data, linearization data, or device data for color profiling, including Flat Field normalization" and can create ICC Color Profiles. It has a fully functional 30-day trial.

So with some test charts and a 'raw file analyzer' you can test your camera and with expertise know what pre-processing is being done in-camera.


For Astrophotography, and to avoid the need to analyze a camera not designed for extreme accuracy, you might consider an Astrophotography Camera such as the Atik 414EX cooled CCD camera (designed to eliminate noise, and not use any secret-sauce) or something more user friendly like the Canon EOS 60Da or Nikon D810a with a specialized IR cut filter and no optical low-pass filter.

Why wreck the light before it hits your sensor and then worry about pre-processing of the raw data?

Use this link to search for more info about pre-processing raw camera Astrophotography.

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