Thanks for this suggestion
Does PhotonstoPhotos have a page for SNR vs. luminosity? Is not luminosity another term for Dynamic Range? I looked at the DXOMark site but any analyses are too well hidden to excavate. I also recall this thread here in 2017, just as the D850 had been measured: in which Bill Claff's underscored his explicit methodology he uses to measure sensors
https://nikongear.net/revival/index.php?topic=6649.msg107054#msg107054
Luminosity refers to the luminous power of the light source. That wasn't quite a good choice of word from me, as what I meant is really the pixel brightness in the image or the number of detected photons for each photosite. I'll try to give a more precise explanation. SNR of the signal from each photosite is dependent on how many photons are detected (leading to photon shot noise n_ph = sqrt(eta*N), where eta is the quantum efficiency and N is the number of photons), the thermal and other sources of noise. As the photon shot noise depends on the quantum efficiency and the other noise sources depend on the quality of the analog-to-digital conversion and electronics, different sensors have different SNR vs. number of detected photons. This can be measured for R, G, and B photosites.
DXOMark do publish "Full SNR" graphs; for some reason I'm not able to see them in the mobile version, only when viewing their site in a desktop browser. However, without the numerical data these are not easy to utilize. The comparison between the full SNR across camera models is not directly featured. I'm not sure if it is possible to extract the full SNR data from the site in numerical form. They use "gray value" in the X axis of the full SNR graphs, I'm not sure how they calculate the gray value from R, G, and B.
The protocol they use and the parameters are explained here:
https://www.dxomark.com/dxomark-camera-sensor-testing-protocol-and-scores/https://www.dxomark.com/glossary/color-depth/What they do present in an easy-to-compare way are the following:
- SNR for 18% gray (this represents the signal-to-noise ratio of midtones)
- Engineering dynamic range (which is the (log) difference between maximum luminosity that doesn't introduce clipping and the luminosity at which the SNR equals 1)
- Tonal range (essentially the log number of distinct gray tones that can be distinguished from noise)
- Color sensitivity (log number of distinct color values that can be distinguished from noise)
Basically, SNR for 18% tells us how good the SNR is for midtones, dynamic range tells us how wide a range of tones (in terms of image luminance value, I wasn't quite able to see how dxomark calculate this from R, G, and B SNR graphs, is there visually perceived sensitivity weighting of the colors?) can be separated from noise, and it reflects mainly the quality of the deepest shadows or how deep those are. Tonal range tells us how many different gray values can be distinguished from noise and this is dependent on the whole SNR curve. Color sensitivity tells us how many different colors can be separated from noise, again it is dependent on the whole SNR data.
A lot of online discussion revolves around dynamic range but I believe all of these parameters are important to characterise sensor image quality. Dynamic range is imporatant if one photographs a very contrasty scene, such as one where the sun is in the photograph and foreground objects are in shadow or if one underexposes the main subject heavily and requires brightening of the subject in post-processing. In such cases the sensor dynamic range can be, and is, important. However, in a normally-exposed image which doesn't need shadow-lifting, the other image quality parameters can tell us more about the differences in image quality. I guess photographing contrasty scenes is very common and is perceived as a limitation of photography vs. how the human eye and brain see scenes (processing a lot!), and thus the dynamic range gets talked about a lot.