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I have read recently about how even RAW images can have DNR and sharpening applied and I'm wondering, is this something some particular camera manufacturers are known to do or it's a universal thing ??

For people asking how a RAW file can have DNR applied:

"The “Star Eater” problem is a form of software spatial filtering designed to reduce noise in photos, particularly hot pixels. Unfortunately, the rather rudimentary filtering algorithm that Sony is using easily mistakes sharp pinpoint stars for noise, nearly deleting them from the image or greatly reducing their brightness. The result is an astrophoto with less stars and the appearance of diminished resolution. Sony a7RII, a7SII and a7RIII cameras exhibit this problem for all exposure times longer than 3.2″. Furthermore, the “Star Eater” issue affects RAW images (whether uncompressed or not) and cannot be disabled by any means. There are no user selectable settings that will prevent these cameras from eating stars."

https://www.lonelyspeck.com/sony-star-eater-and-how-to-fix-it/

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    \$\begingroup\$ I think you've misunderstood what a RAW file is & what must be done before you can even view it at all. \$\endgroup\$
    – Tetsujin
    Commented May 4, 2023 at 16:27
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    \$\begingroup\$ Can you provide the source of "even RAW images can have DNR and sharpening applied"? \$\endgroup\$ Commented May 4, 2023 at 16:34
  • \$\begingroup\$ @RomeoNinov lonelyspeck.com/sony-star-eater-and-how-to-fix-it - "The 'Star Eater' problem is a form of software spatial filtering designed to reduce noise in photos, particularly hot pixels. Unfortunately, the rather rudimentary filtering algorithm that Sony is using easily mistakes sharp pinpoint stars for noise, nearly deleting them from the image or greatly reducing their brightness. The result is an astrophoto with less stars and the appearance of diminished resolution." \$\endgroup\$ Commented May 4, 2023 at 20:22
  • \$\begingroup\$ @RomeoNinov "Sony a7RII, a7SII and a7RIII cameras exhibit this problem for all exposure times longer than 3.2″. Furthermore, the “Star Eater” issue affects RAW images (whether uncompressed or not) and cannot be disabled by any means. There are no user selectable settings that will prevent these cameras from eating stars." \$\endgroup\$ Commented May 4, 2023 at 20:25
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    \$\begingroup\$ All NR is not digital noise reduction. Analog signaling (of many types, including audio and video) can also have nose reduction applied via various limiters. The charges accumulated by each photosite of a digital camera sensor are analog until converted to digital information by the analog-to-digital converter (ADC), \$\endgroup\$
    – Michael C
    Commented May 5, 2023 at 15:00

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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):

enter image description here

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:

enter image description here

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.

enter image description here

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RAW files are the least processed data a camera makes available as a file.

All cameras process data as it is written to a file. For instance by adding EXIF fields.

But they also add information about the filter array so that colors may be consistently interpreted and amplify (or attenuate) analog voltages to create different ISO behaviors…and of course quantize those voltages to create digital values for digital processing.

Hardware hot pixel mapping essentially is a form of error correction. Like all engineering it is a series of tradeoffs.

Maybe an analogy is a RAW file is like a piece of lumber. Although a 2x4 isn’t a tree, it is still wood and generally more useful than a tree for ordinary tasks that involve wood.

Sure there are edge cases where hot pixel correction is not what someone wants just as there are times when a tree is the solution to a wood need.

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    \$\begingroup\$ "Least processed" does not equal "not processed". This includes pixel data, not just ancillary fields like EXIF. \$\endgroup\$ Commented May 11, 2023 at 2:21
  • \$\begingroup\$ @MarkRansom That is why I said “least processed”…although practically speaking the processing that happens is what distinguishes arbitrary voltages from data. \$\endgroup\$ Commented May 11, 2023 at 4:52

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