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

Started Apr 17, 2015 | Discussions thread
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bclaff Veteran Member • Posts: 8,544
Photographic Dynamic Range (PDR) is a More Useful Measure than the DxOMark Landscape Score
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I had been performing Photographic Dynamic Range (PDR) measurements for some time when DxOMark arrived on the scene with their Landscape Dynamic Range Score.
The methodologies are simlilar, and although the scores are on different scales, they correlated well. I preferred my PDR to the DxOMark Landscape Score but there was no compelling reason in the past to argue that one was preferred over the other.

However, with improved technology at the pixel level and higher pixel densities differences between the results are becoming more apparent.

The DxOMark criteria has the effect of pushing their result into the portion of the Photon Transfer Curve (PTC) which is near or below SNR = 1 (read noise).
In this region differences in the shape/slope of the foot of the PTC are lost. This results in DxOMark Landscape Scores that sometimes don't really fit. A prime recent example would be the DxOMark ranking the D7200 (a DX/APS-C sensor) ahead of numerous FX/Full Frame sensors such as the D750, D800, D800E, D600 and Sony A7R. (See below)

The PDR criteria operates in the PTC region well above SNR=1 (at least until we get 384Mp sensors!).
In this region the subtle interplay of read noise, other noise, small amounts of photon noise, slope due to Full Well Capacity (FWC), etc. is captured.
PDR has scaled better with shifting technology.

So now I do think that PDR is a better measure than the DxOMark Landscape Score.

As it happens, I can take DxOMark Signal to Noise Ratio (SNR) data and apply my PDR criteria to produce the dynamic range curves that DxOMark would get if they had applied my criteria rather than theirs. I never published these before, but now I think they have value.

I invite you to peruse the new interactive chart at my site: DxOMark Photographic Dynamic Range Chart

So we can have a concrete discussion about this matter consdier the following charts:

D7100 PTC dark corner

D7200 PTC dark corner

D610 PTC dark corner

D750 PTC dark corner

This data was all collected at the same time using the same technique. These are all 24Mp cameras so they normalize identically.
The axes are linear and cover the deep lower left corner of the PTC with signal from 0 to 14 and SNR from 0 to 6.

Note that the cameras with larger pixels and higher Full Well Capacities (FWC) have SNR values that improve more quickly as signal increases.
The blue diamond is the DxOMark unnormalized dynamic range and the red diamond is the DxOMark Landscape (normalized) Dynamic Range Score.
The green diamon is my Photographic Dynamic Range (PDR) measure.

The positions of the red diamonds are dictated exclusively by read noise.
The green diamonds are influenced by FWC (and to a lesser extent other factors).

From the charts you can see how great D7200 read noise causes DxOMark to rank the D7200 as better than the D610 and D750 (among others).
But it's also clear that the D610 and D750 have better SNR values and therefore better Image Quality (IQ) than the D7200 (and D7100).

To me it's very clear that PDR ranks the cameras more reasonably than DxOMark Landscape Score.

Respectfully,

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Nikon D600 Nikon D610 Nikon D7100 Nikon D7200 Nikon D750 Nikon D800 Nikon D800E
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