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

Started Apr 17, 2015 | Discussions thread
Horshack Veteran Member • Posts: 7,922
Re: Clarification - Read Noise and Engineering Dynamic Range

bclaff wrote:

However, normalized read noise is not photographically relevant; and the DxOMark Landscape Use Case score is supposed to be a photographic use case.

Read noise is not relevant to whose photography specifically? The problem with randomly selecting an SNR cutoff for DR and calling it relevant is that it's only relevant to some and not others. And even for the group it is generally relevant for it may not be relevant for all of their photographic scenarios.

It's the same problem with using any composite metric to convey an overall IQ score, which is why I think both PDR and DxO's Landscape number aren't very useful as a one-size-fits-all metric. Since no composite score can convey IQ I think the best solution is to provide the raw data points, explain how those data points apply to specific shooting situations and then let individuals decide which sensor is better for their shooting scenarios.

Btw, DxO themselves sort of agree with you and think the SNR cutoff should be higher than 1:1. They believe it should be 10:1 [20db], source and quotes:

"The problem, Guichard said, is that the technical measurement of dynamic range is based on a signal-to-noise measurement that's not useful in practice. With that formula, "the dynamic range of film is eight stops more than any sensor on the planet," he said. However, "this threshold doesn't make sense. We have to define another threshold more related to a minimal quality acceptance threshold."

"DxO Labs has studied whether film really does have a better dynamic range than digital cameras. When based on measurements with a signal-to-noise ratio of 0 decibels, Kodak's Portra 160NC film (shown with the green line) has a wider range than the Nikon D3X camera (the green arrow-tipped line is longer than the black one). However, DxO argues that it's more practical to use a signal-to-noise ratio of 20dB, at which point the Nikon outdoes the film. (Nikon's newer D800 camera also outdoes the D3X in terms of dynamic range.)"

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