Signal to noise ratio (SNR) for the Pentax K-x. Full measurement for various luminosities and ISO 100 at color temperature 2900°K. Measurement similiar to dxomark.com. The dotted lines indicate the slope for pure photon shot noise.
This graph is meant to study the "bump" at about luminosity 2% in the ISO 100 curve of the full SNR graph (previous image). The full 12 EV test chart is compiled from two parts: one exposed normally, another underexposed by 5 stops.
The current plot is a reexamination of both parts, now separately evaluated. There indeed is a discontinuous step (by +1.8 dB) when going from the normal to the -5EV curve which I cannot currently explain. The flattening of the brightest parts looks the same and could indeed be due to imperfect bright print patches. This would imply an underestimation of the "bump" by another 1.7 dB leading to a possible overall overestimation of SNR by +3.5 dB in the dark part.
Even taking this correction into account though, the current plot still confirms an extrapolated 0 dB SNR point at 0.01% luminosity leading to the same claim of 13.6 EV print-normalized dynamic range. Therefore, the conclusions made are not altered by this detail examination.