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

Started Apr 17, 2015 | Discussions thread
OP bclaff Veteran Member • Posts: 8,680
Re: Photographic Dynamic Range (PDR) is a More Useful Measure than the DxOMark Landscape Score
1

Detail Man wrote:

bclaff wrote:

Just a couple of point ...

Regarding SNR = 20 see the other clarification.

Regarding E-M5 versus GH2 you intermix two concepts and make it incorrectly appear that the result has to do with FWC when it has entirely to do with read noise only.

In my procedure used in coming up with the information and graphics displayed in this post:

http://www.dpreview.com/forums/post/55668848

Before DxO published their E-M5 test results, any subsequent estimates of E-M5 FWC existed:

I took a small GH2 base-ISO deep shadow image-crop (recorded and posted by Rick'sAstro):

... from an area within this (larger) crop and pushed it in using RAW Therapee 4.x by +5.000 EV.

.

I took a small E-M5 base-ISO deep shadow image-crop (recorded and posted by Rick'sAstro, of the same scene, with the same lighting, using equal sensor-level Exposure):

... from an area within this (larger) crop and pushed it in using RAW Therapee 4.x by +5.345 EV - using a rationale that the E-M5 metering (when used) appeared to select an (approximately) 0.345 EV lower sensor-level Exposure level when presented with the same scene luminance.

My goal was to (roughly) simulate differences that appeared to exist between the two cameras when using the in-camera metering systems in both the E-M5 as well as the DMC-GH2.

The (approximate, "eyeballed only") SNR was estimated by me as being (around) 12 dB (equal to a linear factor of 4) in the above discussed case. I reported what I saw as a result.

Having an (albeit crude) look at GH2 and E-M5 dark-frame RAWs using RawDigger, the Read/Dark noise levels appeared to be fairly close in the value of their Standard Deviations.

.

Later (after DxOMark data was published), Sensorgen reported estimated E-M5 FWC as being 24959 e-, as compared to the DMC-GH2's 11835 e-, and estimated Read Noises of 6.5e-, and 6.0e-, for the E-M5 and the DMC-GH2, respectively. The difference between the (Sensorgen stated) photosite-pitches was a mere 100 nM (pretty close) - normalizing for photosite area would have only a small effect upon the above-stated Read Noise values.

I do not understand the meaning of your statement quoted above:

Regarding E-M5 versus GH2 you intermix two concepts and make it incorrectly appear that the result has to do with FWC when it has entirely to do with read noise only.

(Post DxOMark E-M5 data being published), I noticed that while the Sensorgen estimated Read Noise reported was nearly the same (thus, roughly comparable), the estimated FWCs were around twice as large in the E-M5 (relative to the DMC-GH2), and the (DxOMark published) base-ISO Dynamic Ranges were around 1 EV higher. That is all that I know ...

That's because sensorgen reports read noise in electrons, which came from read noise in DN and gain, and gain came from FWC / (ADC range).
The one stop difference in the Landscape score comes from the one stop difference in engineering dynamic range. Both are 12-bit ADCs and the read noises in DN are about 1.173 and 2.083 respectively.

I apologize for not recognizing any fundamental errors in my thinking (other than, perhaps, my attempts to simulate observed differences of in-camera metering systems by "pushing" the E-M5 deep shadow image-crops by +0.345 EV more). Could you possibly try to explain further ? Your statements above are not "sinking in" (my perhaps somewhat "thick head").

For simplicity I have snipped a lot to write this reply.

First, as they say, "what we have here is a failure to communicate". It probably runs both ways

I have had some interesting "chicken and egg" conversations in the past regarding gain and FWC.
My position is that gain comes first and FWC is a function of gain.
We can make that moot by sticking to DN and ignoring FWC.

So in DN, which is what we have in the raw data, the E-M5 read noise is 1.07 DN and the GH2 read noise is 2.08 DN for engineering dynamic ranges of 11.9 and 10.9 respectively.
This difference in engineering DR carries over to the DxOMark Landmark Scores of 12.3 and 11.3 respectively.

As we increase signal above read noise the higher gain of the E-M5 versus the GH2 would have an effect on the PDR; but in this case the distance is so small no effect is really seen.

I suppose it's a good time to point out that I'm not saying the DxOMark figures are always "wrong", particularly in a relative sense.
But I am saying it fails when read noise is very low and the conversion gain between two cameras being compared is very different.

Regards,

-- hide signature --
Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow