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Author Topic: Thom Hogan's interesting points regarding DxOMark scoring and the future  (Read 12173 times)

Fine_Art

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Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #40 on: November 14, 2014, 01:05:29 pm »

Hi Erik,
Dynamic range requirements depend entirely on what you shoot, not just a bit.  ;)

The camera tries to mimic what the eye sees. Unfortunately, the camera is limited by a fixed aperture for every single shot, whereas the iris of the eye will automatically adjust the diameter of the eye's pupil (aperture) to accommodate changes in brightness.

Some of these adjustments in pupil size take place almost instantaneously, as for example when we peruse a landscape scene and shift our attention from the bright sky to the moss-covered roots of a fig tree which is in the shade, to the right of the composition we are about to photograph.

If the eye's aperture, after its adjustment to see the detail in the bright sky, could not instantaneously widen when we shift our gaze to the tree roots in the shade, we wouldn't be able to see any detail in the shade, just like a camera with a low dynamic range.

Sometime the adjustments in pupil size take a while, as for example when walking from bright light into a dark room such as a cinema theatre. If one were to combine the 2 situations of almost instantaneous adjustment of pupil size when perusing the average contrasty scene, and the slower adjustment required when moving to a darkened area, the total dynamic range of human vision would be in the order of 30 stops.

However, for general scenes with high contrast, such as the scene in one's living room combined with the view of the sky and landscape through the window, the eye can accommodate about 20 stops of dynamic range without any noticeable delay in pupil adjustment, which is much better than even a modern Nikon DSLR can manage with a single shot.  ;)

I'm with you Ray, IMO the whole avoid harsh mid-day contrast that washes out your images is due to the lack of DR in the artificial imaging system. You go out in the day things look normal. You take a picture of it, it looks terrible. That is the camera to screen system failing to represent what our eyes see.
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Ray

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Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #41 on: November 14, 2014, 08:34:26 pm »

You are right that the human eye has an immense dynamic range: the inter-scene range is well over 40 f-stops. However, it only achieves a small portion of that range through pupil size variation. The range of the pupil is from about f/2 to about f/8, or about 4 stops.

Jim

Yes, my post is misleading. I gave the impression that the eye's adaption to changes in brightness and contrast is due only to changes in pupil diameter. The rods and cones also undergo a change in sensitivity to accommodate more extreme changes in brightness, and that process takes more time.

Nevertheless, if one views a contrasty scene that is clearly outside of the DR capability of a single shot from the best camera, such as an indoor scene which includes a view of a landscape and sky on a sunny day, as seen through the windows of a room, then the eye has no trouble making almost instantaneous adjustments when the gaze is redirected from the brightest cloud in the sky to the darkest corner in the room. There is no sense of impenetrable blackness or noise in those shadows.

Also, I imagine (but I'm no expert here) that in addition to the 'almost instantaneous' change in pupil diameter, in the situation described above, there will occur some additional adaption of the cones, over a period of just a few seconds, that will add to the effect of that 4 stop change from F8 to F2.
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Ray

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Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #42 on: November 14, 2014, 08:40:19 pm »

Regarding my statement that DR is overrated is more based on experience

Of course. I understand, Erik. We all have different experiences and different interests in different types of subjects. If you try taking shots in a Rainforest in sunny Australia, or in the ruins at Angkor Wat in Cambodia on a sunny day, you might be dissatisfied with the quality of detail in the shadows if you don't take multiple shots for merging to HDR, or use fill flash where practical, and/or if you don't have a high-DR camera.

I also rarely bother to use HDR now that I have a Nikon DSLR. My concern about the DR limitations of DSLRs was greatest when I was using Canon equipment. I used the 5D a lot, my first full-frame DSLR. It was my favourite camera at the time, although shadow noise could be an eyesore.

It's interesting to now compare the DR values of the Canon 5D and the Nikon D800E, on the DXOMark site. At base ISO the D800E has whopping 3.2 stops better DR, at equal print size. Even at the pixel level, the DR of the D800E is 2 & 1/2 stops better.

I recall when I first moved from the U.K to Australia I was struck by the increased brightness of the light. It was very noticeable. In England the sun rarely shines. Who needs a high-DR camera in the U.K. or Northern Europe!  ;)  Any Canon DSLR should be perfectly adequate.  ;)

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allegretto

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Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #43 on: November 14, 2014, 10:11:17 pm »

Retinal ganglion cells/Optic radiations and indeed the Occipital Cortical cells also join in the business of exposure. It' a System we can't even totally map. But one day it seems likely that a 30-40 stop DR may be achievable in a camera. Funny that some think the tehnolpg is near-plateau.

Just need more breakthroughs...



Yes, my post is misleading. I gave the impression that the eye's adaption to changes in brightness and contrast is due only to changes in pupil diameter. The rods and cones also undergo a change in sensitivity to accommodate more extreme changes in brightness, and that process takes more time.

Nevertheless, if one views a contrasty scene that is clearly outside of the DR capability of a single shot from the best camera, such as an indoor scene which includes a view of a landscape and sky on a sunny day, as seen through the windows of a room, then the eye has no trouble making almost instantaneous adjustments when the gaze is redirected from the brightest cloud in the sky to the darkest corner in the room. There is no sense of impenetrable blackness or noise in those shadows.

Also, I imagine (but I'm no expert here) that in addition to the 'almost instantaneous' change in pupil diameter, in the situation described above, there will occur some additional adaption of the cones, over a period of just a few seconds, that will add to the effect of that 4 stop change from F8 to F2.

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Ed B

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Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #44 on: November 14, 2014, 11:18:34 pm »

I'm with you Ray, IMO the whole avoid harsh mid-day contrast that washes out your images is due to the lack of DR in the artificial imaging system. You go out in the day things look normal. You take a picture of it, it looks terrible. That is the camera to screen system failing to represent what our eyes see.

I don't agree with this. Harsh mid day sun is flat and has no depth. It's the same as using a flash on camera as opposed to off camera. 30 stops of DR isn't going to make an on camera flash look good.
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ErikKaffehr

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Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #45 on: November 15, 2014, 01:10:19 am »

Hi,

I don't think that the photons are there… Todays sensors are close natural limits.

To get much further I would say that ND filters are needed over half of the pixels or variable exposure time for groups of pixels.

Best regards
Erik

Retinal ganglion cells/Optic radiations and indeed the Occipital Cortical cells also join in the business of exposure. It' a System we can't even totally map. But one day it seems likely that a 30-40 stop DR may be achievable in a camera. Funny that some think the tehnolpg is near-plateau.

Just need more breakthroughs...



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Erik Kaffehr
 

shadowblade

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Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #46 on: November 15, 2014, 01:11:55 am »

I don't agree with this. Harsh mid day sun is flat and has no depth. It's the same as using a flash on camera as opposed to off camera. 30 stops of DR isn't going to make an on camera flash look good.

Depends where you are and what time of the year it is.

At the right time of the year, mid-day sun is perfectly acceptable in polar and near-polar regions. At other times, so is midnight sun...
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shadowblade

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Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #47 on: November 15, 2014, 01:15:42 am »

Hi,

I don't think that the photons are there… Todays sensors are close natural limits.

To get much further I would say that ND filters are needed over half of the pixels or variable exposure time for groups of pixels.

Best regards
Erik


The photons are there. You just need to expose for long enough so that even the darkest areas receive enough photons to show detail above the noise floor. Brighter areas, obviously, will receive more photons.

The challenge, then, is to have enough well capacity that the highlights don't blow out (i.e. The wells don't fill up) before the shadows receive enough light to show detail. In other words, the challenge is to engineer for brighter highlights, not darker shadows.
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ErikKaffehr

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Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #48 on: November 15, 2014, 03:07:26 am »

Hi,

Theere are two problems with your way of reasoning:

1) There is no noise floor, really. Readout noise is so low that shadow noise is dominated by photon flux variations.

2) The exposure is limited by FWC (Full Well Capacity). If full well capacity is exceeded clipping will result.

It is possible to make pixels larger, and that would increase the possible dynamic range of each pixel, but we would have less pixels so the effect on highlights would be nil, but large pixels give marginally lower shadow noise.

Adding ND filters on half of the pixels or using two different exposures on different pixel groups could expand dynamic range greatly. That would be HDR within a single exposure. Fuji has done it in different variations.

I guess that single exposure HDR is not what the market is asking for.

One real problem with HDR exposures is that they need to be downmapped (tone mapped) to something that can be seen in print or screen, doing that in a harmonious way is no easy feat. Think grungy HDRs. Obviously, it can be done in a nice way, but still it's a complex issue with pitfalls.

Best regards
Erik





The photons are there. You just need to expose for long enough so that even the darkest areas receive enough photons to show detail above the noise floor. Brighter areas, obviously, will receive more photons.

The challenge, then, is to have enough well capacity that the highlights don't blow out (i.e. The wells don't fill up) before the shadows receive enough light to show detail. In other words, the challenge is to engineer for brighter highlights, not darker shadows.
« Last Edit: November 15, 2014, 03:40:46 am by ErikKaffehr »
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Erik Kaffehr
 

shadowblade

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Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #49 on: November 15, 2014, 03:45:21 am »

Hi,

Theere are two problems with your way of reasoning:

1) There is no noise floor. Readout noise is so low that shadow noise is dominated by photo flux variations.

That's exactly what I'm saying. You need to expose for long enough that there is detail in the shadows above the random noise generated by photon flux. I never said anything about read noise.

Quote
2) The exposure is limited by FWC (Full Well Capacity). If full well capacity is exceeded clipping will result.

Again, that's exactly what I'm saying, and is the main challenge in increasing DR.

You need to ensure that the wells don't reach capacity before sufficient shadow detail is recorded.

Therefore, the problem is in the highlights rather than the shadows. You can take care of shadow detail by exposing for long enough. But the wells need to have enough capacity that the highlights don't blow out in the time it takes to collect the shadow detail. And every 1-stop increase in dynamic range requires a doubling of the well capacity.

Perhaps the solution isn't in an expose-then-readout system as is used now, but in a continuous readout system, whereby the sensor is continuously read while the exposure is happening. Exposure could continue until sufficient detail is recorded in the shadows above the photon noise; the continuous readout would mean that the numbers from the highlights would simply keep adding up, rather than reaching the limit and being capped there. But that would require different sensor and readout architecture.

Quote
It is possible to make pixels larger, and that would increase the possible dynamic range of each pixel, but we would have less pixels so the effect on highlights would be nil, but large pixels give marginally lower shadow noise.

Adding ND filters on half of the pixels or using two different exposures on different pixel groups could expand dynamic range greatly. That would be HDR within a single exposure. Fuji has done it in different variations.

I guess that single exposure HDR is not what the market is asking for.

Or multiple exposures (either with continuous shooting or by shooting a video file) with the frames averaged. Photon shot noise would be averaged out, revealing shadow details that were previously hidden in the noise. And the highlights wouldn't be blown out, since each single exposure would be short enough for the wells not to reach capacity.

Quote
One real problem with HDR exposures is that they need to be downmapped (tone mapped) to something that can be seen in print or screen, doing that in a harmonious way is no easy feat. Think grungy HDRs. Obviously, it can be done in a nice way, but still it's a complex issue with pitfalls.

Every image needs to be tonemapped, HDR or not. Without anything to tell you what recorded luminance equals what brightness and colour in the output, it's just a meaningless list of numbers in a file. It's just that single-exposure images already have pre-made tone-mapping curves via RAW conversion software, while curves for HDR images need to be made manually - and, in the hands of the inexperienced, can be made very badly.
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jduncan

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Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #50 on: November 15, 2014, 12:09:59 pm »

it's worth a read

http://www.dslrbodies.com/newsviews/do-you-believe-in-dxomark.html

At the end he makes some really interesting comments, ones I happen to agree with

"I guess to end this discussion, I should probably suggest what we Nikon users want to see on the DxOMark tests for the next Nikon. We’ve got it pretty good at the moment, after all. Incremental movement of the dynamic range chart upward would always be welcome, but I think we’re now very close to the point where we want to see something entirely different. We really want to see base dynamic range unbound (e.g. the two-shot type DR that the Apple iPhone 6 is doing, and which Sony’s latest patents all hint at). Beyond that, we want to see flattening of the dynamic range slope as ISO is boosted (less of a hit per doubling of ISO).

Simply put, we’re deep ending into small, incremental gains that aren’t pushing us very much further above the “good enough” bar. What we need is to push that bar far forward again, and that’s going to take another sensor generation/design, I think. Until then, you can all anguish over small differences in DxOMark measurements, but I’d be surprised that those show up anywhere near as clearly in your images. "


Frankly  I don't see anything new on his comments. Some people are lazy, and most reporters are. I have been advocating to use the measurements tab here and on getdpi  for both lenses and sensors for a long time.
He can say anything he wants about "Nikon is client" and "perhaps" Canon is not, but the true is that DXO numbers that show that the D4 vs the D3s for low light were a complicated story, or that the D750 super low light capabilities (against the D610) were software jpg stuff. The numbers also show that even the 6d has better dynamic range than the Nikons above iso 1600.

People should read and if someone takes a bad decision because they were too lazy to do a few  clicks on a dynamic interface before making a massive investment they get what they deserve. They can also ask on the forums and someone will tell them how to use  DxO data.

Overall I am glad that T.H post this, maybe now some people will stop the laziness (if this become something all the cool guys do).

In the other hand, it is important to underscore the importance of DxO testing. Before them we were listening to camera brand affiliated experts saying that the dynamic range of CCD base backs was 4 stops (8 vs 12, some times 8 vs 14) better than the best DSLR, even after the release of the D800.
T.H conclusions are very interesting too, the "what we should ask from Sony /Nikon is very valuable.

In a final note, I aside from the conspiracy, I the article is very good, and I know that as a columnist sometimes he has to stress the evident to help the community do better.

Best regards

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Fine_Art

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Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #51 on: November 15, 2014, 03:52:41 pm »

I don't agree with this. Harsh mid day sun is flat and has no depth. It's the same as using a flash on camera as opposed to off camera. 30 stops of DR isn't going to make an on camera flash look good.

Lets consider it some more. With high sun you get the direct full black body spectrum plus off angle refracted light from the surrounding sky, which is mostly blue. So you are right that many textures get filled in with this blue light. The sun near the horizon has very direct yellow angle rays.

To my eye, strong overhead sun gives high contrast that the eye can manage. Overcast is washed out, mild looking. Sun near the horizon lets you work with the textures to make a certain look.

To the camera, it might interpolate the blue from overhead sun as fill, never thought about it before. What I see in many images is shadows go to black or the sky is blown. Overcast the camera loves. You crank the contrast in post bringing out lots of detail. Sun at the horizon again lets you define a look based on the direction of light.

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