How can I calculate signal to noise ratio of a DSLR, using raw images?
Is it simply whole counts minus dark counts over dark counts?

  • 2
    Raw images of what?
    – mattdm
    Mar 8 '16 at 17:14
  • @mattdm For example a raw format image of a point source.
    – faf
    Mar 8 '16 at 17:29
  • Sorry, let me elaborate a little bit. Do you mean for arbitrary RAW images (like a random collection you've taken or from the Internet), or for that example in specific, or do you mean "given the ability to take RAW images as per any given instructions, what should I do?"
    – mattdm
    Mar 8 '16 at 17:37
  • @mattdm for that specific example, not any image as using a point source would be easier. Can I extract the pixel values from raw images taken from that point source and use it to calculate SNR?
    – faf
    Mar 8 '16 at 18:12

How can I calculate signal to noise ratio of a DSLR, using raw images?

You have a choice:

  • you can photograph an evenly lit surface (defocused so that no texture is preserved) and then open it with RawDigger (there are other programs possibly) which will display the statistics of the image. Rawdigger will also take care of black point. Another tool you could use is ImageJ
  • you can do the same but import the image to Photoshop, blur it manually and then create an image stack of the original and blurred images using the StdDev mode.
  • you can choose a very static scene, take a long series of images at base ISO, average them with image stacking tool to make them a reference image (with very small noise), and then compare the noisy image with reference using stacks in Photoshop (or, probably, something else too. GIMP or ImageJ might have something similar)

There is no way of computing SNR of an abstract image if you do not have a reference image without noise - because there is no strict way of distinguishing detail from noise.

More about definition and analysis of SNR:




  • I'd still like to emphasize that mentioned pages use only one possible definition of SNR, there might be more of them. Mar 9 '16 at 18:09

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