PhotonsToPhotos PDR versus DxOMark Landscape Score and SNR 18%

Started Jan 4, 2021 | Discussions thread
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bclaff Forum Pro • Posts: 12,939
PhotonsToPhotos PDR versus DxOMark Landscape Score and SNR 18%
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This is a somewhat lengthy technical post prompted by a question here.

I'm posting in Open Talk rather than Photographic Science and Technology to reach a wider audience.

The single most useful chart showing sensor performance is a pixel level chart called the Photon Transfer Curve (PTC).
There are various flavors of the chart but the most common is a log-log  chart such as this one from PhotonsToPhotos :

Best viewed "original size"

I'm using the Canon EOS 80D since it was mentioned in the post prompting this thread.

The black curve is the PTC and the gray lines mark important regions which we won't cover in this post.

Here is an annotated PTC constructed from DxOMark data:

Best viewed "original size"

The black curve is substantially identical to that on the PhotonsToPhotos PTC.

First note the gray diagonal line labelled 'SNR=1'
This intersects the PTC at a particular point.
This point is in what is called the 'read noise regime' of the PTC.
Engineering Dynamic Range (EDR) is the distance from that point to the right-hand-side.
Because the x-axis is log2 it can be read off directly as 12.33 EV. (Red line)
DxOMark normalized this to an 8MP sensor, in this case by adding 0.84 EV
So the Landscape Score for this camera is 13.17 EV.

Now notice the vertical gray line labelled 'S=18%'
This intersects the PTC at a particular point.
This point is high in the 'photon noise regime' of the PTC not far below the 'PRNU regime'.
The blue diagonal line through this point is 6.1 EV (36.7 dB) which normalizes to 6.9 EV (41.8 dB).
These are the ISO 100 SNR18% values reported by DxOMark.

Rather than normalizing to 8Mp PhotonsToPhotos normalizes to a SNR value based on a standard final image size and viewing distance.
For this camera that SNR is 1.98
The gray diagonal line labelled 'SNR(PDR)' is at SNR 1.98
This intersects the PTC at a particular point.
This  point is at the high end of the 'read noise regime' quite close to the start of the 'photon noise regime'.
And the distance from that point to the right-hand-side is 10.06 EV.

A quick summary.
DxoMark Landscape Score and PhotonsToPhotos PDR are measures of dynamic range and relate to shadow performance.
DxOMark SNR 18% is well out of the shadows and technically relates most closely to Full Well Capacity (FWC).

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Bill ( Your trusted source for independent sensor data at PhotonsToPhotos )

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