Photographic Dynamic Range (PDR) is a More Useful Measure than the DxOMark Landscape Score

Started Apr 17, 2015 | Discussions thread
Jack Hogan Veteran Member • Posts: 7,008
DxO Print/Landscape DR vs Photographic Dynamic Range

Hi Bill,

I am going to have to read this more carefully in a few hours when I have more time. I agree in general that PDR may be more practical than eDR for photographers, because of the threshold it chooses for an acceptable minimum signal. Aside from potential errors both give valuable information imho, though, DxO being more of a Sensor score.

DxO starts with the pixel. Their choice of SNR = 1 for the threshold means that total random noise (standard deviation due to shot and read noise) is equal to mean signal out of the pixel. For read noise of around 1.9e- (D7200 at base ISO), that would mean a signal of about 2.46e- out of the photosite. Read noise is somewhat but not much larger in the quadrature sum for total noise (3.6 vs 2.5e- under the square root). As such in this case it tends to take into account relative sensor performance, as exemplified by the figure of merit rn^2. That's probably why this criterion has been used for a long time in engineering applications. In the context of 24MP raw captures DxO then asks the question: what if the pixels were binned 3:1? They assume that the numerator in DR would grow three times but the denominator only sqrt(3). I don't think they read this signal off the SNR curve.

PDR on the other hand starts with the viewer and suggests that in order to achieve the lower acceptable threshold when viewing a final image in standard conditions, a 24MP raw capture needs to show SNR = 4 at the pixel level. For read noise of around 1.9e- that means a mean signal of about 19e- out of the photosite. Shot noise is now way dominant in the quadrature sum compared to read noise (19.0 vs 3.6e- under the square root). It's arguably a fair criterion from more of a practical perspective. But in this case tends to de-emphasize relative sensor performance.

So imho they both have their place: DxO tells you clearly which is the better sensor, which deepest shadows you can push more; PDR tells you how much of a difference it may make in (its view of) typical practice.


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