Calculating the Dynamic Range over the last set of plots, using a 12dB SNR threshold criteria, the following comparable DR figures are obtained:
When new FF sensors appear with such a performance, we can start to think about forgetting the need to shoot several times in HDR scenes.
Indeed, with these cameras there is no need to use an ISO over the base: one can simply increase exposure in the raw converter and not worry about ETTR. Of course, one should still give as much exposure as f/stop and shutter speed considerations permit.
Your noise floor of 12dB is more realistic for an estimate of photographic DR than the DXO floor of 0 dB. Your data seem consistent with the DXO data. One could determine the DR at a SNR of 12 dB from the full SNR data as Emil Martinec (http://www.luminous-landscape.com/forum/index.php?topic=42158.msg352373#msg352373) suggests, but the log scales are difficult to interpolate.
So...... should..... we... expect 13 stops DR for next generation FF? :) ;) :D ;D
Thanks for these results.
They are totally aligned with DxO and might, hopefully, open the door of a new era where LL finally accepts the reality: some manufacturers have really listened to us and have delivered these high DR cameras we were requesting... 2 years ago.
All we need to do is accept facts and pick our options. :)
Interesting. But you apparently did not question your results very carefully. Can you explain why for SNR does not fall at least 3dB per stop for the Pentax as one would expect based on nothing but photon noise?? This is a theoritical value and should show up if there hasn't been any manipulation of the data. Notice that the other bodies tend this way.
Interesting. But you apparently did not question your results very carefully. Can you explain why for SNR does not fall at least 3dB per stop for the Pentax as one would expect based on nothing but photon noise?? This is a theoritical value and should show up if there hasn't been any manipulation of the data. Notice that the other bodies tend this way.
Yes that is true, for exposure values close to saturation the samples seem to generate a slope even below the expected theoretical 3dB/EV. Surely it is not because any manipulation since it happens to me on all cameras I tested, so it must be something about the calculation of stdDev of noise.
In low exposure areas (the really interesting ones for DR calculation) the curves seem much closer to the expected theoretical model.
I asked Emil Martinec about possible explanations for this effect but reached no conclusion; will email him again.
When you are close to saturation, you will measure less variance because noise will lead to clipping.
e.g., consider image values in a nominal range of [0,1], where 1 represents the maximum representable value. Suppose the actual scene radiance is 0.99, and the noise fluctuation is 0.05. 0.99 + 0.05 is 1.04, but this will be clipped to 1.0. In other words, the recorded signal near 1 is no longer linear (due to the non-linearities introduced by clipping).
When you are close to saturation, you will measure less variance because noise will lead to clipping.
e.g., consider image values in a nominal range of [0,1], where 1 represents the maximum representable value. Suppose the actual scene radiance is 0.99, and the noise fluctuation is 0.05. 0.99 + 0.05 is 1.04, but this will be clipped to 1.0. In other words, the recorded signal near 1 is no longer linear (due to the non-linearities introduced by clipping).
Any visible flattening of the curve below 3dB/EV is likely caused by column gain variations, that lead to PRNU as Bill was mentioning.
Thanks Emil. Do you agree that in the areas where DR is calculated (typ. for a 12dB threshold criteria that means 8-11 stops from saturation), PRNU noise is negligible compared to photon+read noise? that would mean my DR calculations could be considered accurate.
Regards
... both the K-5 and D7000 ... have such a linear SNR curve that they are approaching the ideal of the ISO-less raw capture, where ISO can be relegated to metadata ...The idea that SLR A/D conversion has reached the level of recording all the useful signal range that photosites provide (simultaneously handling full well signals and giving quantization noise sufficiently below the noise floor of the analog signal from the photosites) is exciting: photographers can be freed of a lot of technical worries in setting up shots.
My plots after normalising provide 11,2 stops, but we must compare the DxO figure with the DR calculated on a per-pixel basis, i.e. before normalising to the Canon 5D. And this was 10,8 stops. So both measurements match quite well.
The above may not be 100% correct though. The Full SNR curves at DxO are pixel level curves (aka "screen") and have not been normalized to 8MP. So if I'm not mistaken, the DxO figure of 11.0 stops would compare to Guillermo's figure of 11.2 stops which still is a nice match.
A comparision ISO100 vs ISO1600 (same aperture/shutter) in a high dynamic range scene with the Pentax K5:
- In the highlights the 4 extra stops allow to properly capture the lamp area and view through the window at ISO100, not at ISO1600
- In the medium shadows, no SNR improvement for pushing ISO
- In the deep shadows, it seems read noise becomes important and a bit more noise can be seen in the ISO100 image. Also many pixels get clipped to 0 in the RAW file (perhaps the 14-bit RAW encoding was not enough here) producing darker areas lacking detail that displays better in the ISO1600 shot
If I had to choose, I would pick the ISO100. But we can see there are still some advantages in the very deep shadows for pushing ISO.
Regards
PS: RAW files to play
ISO100: http://dl.dropbox.com/u/136377/ISO100.DNG (http://dl.dropbox.com/u/136377/ISO100.DNG)
ISO1600: http://dl.dropbox.com/u/136377/ISO1600.DNG (http://dl.dropbox.com/u/136377/ISO1600.DNG)
HDR tone mapped scene:
(http://img256.imageshack.us/img256/8780/escenaa.jpg)
Is this tone mapped from a single ISO100 RAW file? If so, did you use special techniques (eg. processing one version for highlights, one for shadows, combining with Zero Noise), or just use curves in the RAW processor?
In any case, if this is from just 1 frame, wow. I hope they'll bring these sensors to MFT cameras soon.