Pages: 1 [2] 3   Go Down

Author Topic: Thom Hogan's interesting points regarding DxOMark scoring and the future  (Read 12156 times)

Jim Kasson

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2370
    • The Last Word
Re:
« Reply #20 on: November 12, 2014, 10:40:37 am »

So are you averaging dark frames? I don't know theory and math but I guess the result would be the same more or less. For shorter exposures it might be practical. Dark + bias frames might be used only because it is impractical to grab so many long exposure darks.

That's right. I haven't finished the testing, but I think I can use the same averaged image at shutter speeds from 1/60 to 1/8000 sec -- the handholding range -- on the D810.

http://blog.kasson.com/?p=7936

The technique doesn't work on the alpha 7S -- not at all at ISO 100, and very weakly at ISO 3200. It appears that there isn't much fixed pattern noise at those shutter speeds with that camera.

http://blog.kasson.com/?p=7971

Jim

Jim Kasson

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2370
    • The Last Word
Re:
« Reply #21 on: November 12, 2014, 10:43:06 am »

And you also put a lens cap on, fastest shutter speed and grab a series of bias frames. 20+ or 256 in your case. These are averaged together and are used to calibrate all of the other types of frames, basically to remove read pattern noise.

Right. You never know how many frames you need until you do the averaging. When the standard deviation of the averaged image stops dropping, you've got enough.

Jim

dwswager

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 1375
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #22 on: November 12, 2014, 01:37:58 pm »

Thom refers to "pragmatic dynamic range," which I guess takes into account his preferred software and workflow. He also mentions exposure blending and notes the 7Dii & D7100 can yield essentially identical results DR-wise via this method. IOW, in scenes exceeding the single-exposure DR of both cameras it doesn't matter which one you use.

-Dave-

But doesn't 'blending exposures' defeat the high fps and great action camera selling point for the 7DmkII?  That is basically why you are paying $850 more for it in the 1st place.  Obviously, the logic would have to be "you get a high speed action camera though with somewhat lower quality output, and when you are shooting other subjects you can use exposure blending to achieve dynamic range."

Logged

ErikKaffehr

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 11311
    • Echophoto
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #23 on: November 12, 2014, 02:48:11 pm »

Hi,

My take is that dynamic range is a bit overrated. It depends a bit what you shoot. Personally, I am a low ISO shooter and I feel having good DR is an advantage. Would I shoot high ISO, DR may be less important to me.

But, high DR stuff also works well at high ISO, as high DR is essentially the same a clean signal processing.

If a photographer doesn't use base ISO, the DR advantage disappear and other properties play a greater role.

Best regards
Erik

But doesn't 'blending exposures' defeat the high fps and great action camera selling point for the 7DmkII?  That is basically why you are paying $850 more for it in the 1st place.  Obviously, the logic would have to be "you get a high speed action camera though with somewhat lower quality output, and when you are shooting other subjects you can use exposure blending to achieve dynamic range."


Logged
Erik Kaffehr
 

Telecaster

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 3686
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #24 on: November 12, 2014, 03:34:19 pm »

But doesn't 'blending exposures' defeat the high fps and great action camera selling point for the 7DmkII? That is basically why you are paying $850 more for it in the 1st place.

Are you talking real-world photography or what's theoretically achievable? From what I've seen specs-wise I doubt there'll be much real-world difference in image quality between the two. If you're gonna blend multiple exposures with one you'll probably do it with the other too. (Note that I have no interest in owning or using either camera. I'm merely curious about what Canikon is currently up to.)

-Dave-
Logged

dwswager

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 1375
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #25 on: November 12, 2014, 07:09:34 pm »

Are you talking real-world photography or what's theoretically achievable? From what I've seen specs-wise I doubt there'll be much real-world difference in image quality between the two. If you're gonna blend multiple exposures with one you'll probably do it with the other too. (Note that I have no interest in owning or using either camera. I'm merely curious about what Canikon is currently up to.)

-Dave-

First, I'm talking real world as you can get cleaner images from having extra dynamic range.  And yes, if you are blending multiple exposures, then you can overcome this handicap.

But let us make sure we understand the data.  Below are the 3 Dynamic Range versus ISO curves Hogan cites.  His original point was to debunk the notion that both the D300s and 7DmkII scored equivalently as the '70' overall rating indicated without regards to how the camera might be used.  But it's a silly comparison between a discontinued 5 year old technology and a just release camera.

The other 2 graphs are much more relevant.  The middle compares the 7DmkII to the current Nikon D7100 that is 1.5 years older and $850 cheaper ans shows the D7100 has 1.5 stops more DR at base ISO and never under preforms the 7DmkII at any ISO.  The bottom graph, to me is much more ominous.  It shows that 5 years of development has yielded only a 1 stop gain in DR from ISO 1000 and up! 
Logged

allegretto

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 660
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #26 on: November 12, 2014, 11:37:48 pm »

First, I'm talking real world as you can get cleaner images from having extra dynamic range.  And yes, if you are blending multiple exposures, then you can overcome this handicap.

But let us make sure we understand the data.  Below are the 3 Dynamic Range versus ISO curves Hogan cites.  His original point was to debunk the notion that both the D300s and 7DmkII scored equivalently as the '70' overall rating indicated without regards to how the camera might be used.  But it's a silly comparison between a discontinued 5 year old technology and a just release camera.

The other 2 graphs are much more relevant.  The middle compares the 7DmkII to the current Nikon D7100 that is 1.5 years older and $850 cheaper ans shows the D7100 has 1.5 stops more DR at base ISO and never under preforms the 7DmkII at any ISO.  The bottom graph, to me is much more ominous.  It shows that 5 years of development has yielded only a 1 stop gain in DR from ISO 1000 and up! 


well you're correct of course. Sensorgen says the same thing. 7100 is a good two stops better in DR than the 7D II at base ISO bu they tighten up above 1600 and are very close at 6400

But a camera System is the sum of many parts. Now I don't know since I did own a 7100 but never a 7D II but the 7100 wasn't very video friendly. The 7D II appears to be a better companion for such matters. Both great crop sensor cameras. If we dissect out the sensors the Nikon appears to have some advantage. But in the real Real World it probably will come down to usage and which lenses are on your shelf.

Time will tell... maybe the 7D II will be "nailed to the shelf" and Canon will have to unveil the Rabbit in their hat earlier than they wanted to...
Logged

dwswager

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 1375
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #27 on: November 13, 2014, 09:48:16 am »

But a camera System is the sum of many parts. Now I don't know since I did own a 7100 but never a 7D II but the 7100 wasn't very video friendly. The 7D II appears to be a better companion for such matters. Both great crop sensor cameras. If we dissect out the sensors the Nikon appears to have some advantage. But in the real Real World it probably will come down to usage and which lenses are on your shelf.

Agreed.  No camera ranking system is meant to have you go pick the highest rated that you can afford and call it a day.  As an Amatuer and a generalist shooting everything from sports to studio portraits, I just find the 7DmkII very uncompelling against the D7100.  10fps is nothing to sneeze at, but I just don't need it to capture baseball, soccer, golf and other "action" areas I have experience in shooting.  I've never had a super fast camera and have had to learn to execute without it.  If I won a super duper wildlife photo trip, I would probably beg, borrow or steal a super fast camera because I lack the knowledge and experience in that area to shoot it well with a slow camera.

Time will tell... maybe the 7D II will be "nailed to the shelf" and Canon will have to unveil the Rabbit in their hat earlier than they wanted to...

The million dollar question on everyone's mind is "Does Canon have something in the hat worth pulling and when will they finally pull it?" To date, they haven't shown any indication they 1) have something to compete with the Sony sensors or 2) are willing to go outside to get it.   I would have thought the 7DmkII would have been a good time, especially if the Rumored D9300 (24MP, DX, Expeed4b, 8fps (10fps w/ grip), D810 like body) materializes. 
Logged

Fine_Art

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 1172
Re:
« Reply #28 on: November 13, 2014, 03:25:01 pm »

Yes exactly. One dark frame actually increase noise but removes unwanted signal. A program like deep sky stacker will work with stacks of different frames. I'm certainly no expert but a typical scenario would be you have 20 (or more) light frames of your deep sky object, then during the night you also grab some 20 dark frames with the same duration, then you take (next day perhaps) some flat field images to remove vignetting. And you also put a lens cap on, fastest shutter speed and grab a series of bias frames. 20+ or 256 in your case. These are averaged together and are used to calibrate all of the other types of frames, basically to remove read pattern noise. Then you end up with master dark and flat field images that you can reuse with different light frames. More serious astrophotographers will keep a library of master darks for different sensor temperatures.

So are you averaging dark frames? I don't know theory and math but I guess the result would be the same more or less. For shorter exposures it might be practical. Dark + bias frames might be used only because it is impractical to grab so many long exposure darks.

Raw Therapee lets you use dark frame and flat frame RAW on other RAWs. No bias frames yet.

The translation for others that may not be familiar with astro lingo, is you can store the noise and imperfections of your camera to be subtracted from all your future images. That is impressive in a raw converter.
Logged

BernardLanguillier

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 13890
    • http://www.flickr.com/photos/bernardlanguillier/sets/
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #29 on: November 13, 2014, 03:43:33 pm »

The million dollar question on everyone's mind is "Does Canon have something in the hat worth pulling and when will they finally pull it?" To date, they haven't shown any indication they 1) have something to compete with the Sony sensors or 2) are willing to go outside to get it.   I would have thought the 7DmkII would have been a good time, especially if the Rumored D9300 (24MP, DX, Expeed4b, 8fps (10fps w/ grip), D810 like body) materializes.  

Thom has recently confirmed that Nikon had moved their Expeed range to ARM based processors. I wonder if that means that they have the possibility to parallelize processing?

That would limit the high speed challenge to sensor readout, shutter speed and battery life only. ;)

Cheers,
Bernard

bjanes

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 3387
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #30 on: November 13, 2014, 03:49:52 pm »

If your metric of dynamic range is the ratio of full-scale to the average signal level that produces a signal-to-noise ratio of around 10 or so, which happens to be mine, without a radical change to the design of the sensor, there's not much progress to be made here. If he's talking about engineering dynamic range, which is read-noise limited, I do think we can expect some improvement in the near future. The Sony Alpha 7S changes the conversion gain as you go from ISO 1600 to 2000, dramatically lowering the read noise. Designs that offer more granular adjustments to conversion gain might do what he wishes for.

Jim

One can use the DXO Full SNR graphs to calculate the DR for any desired nose floor as described by Emil Martinec. I downloaded the graphs for the Canon 7D MII and Nikon D7100 and calculated the DR for Jim's 10:1 SNR (20 dB) for base ISO of 100 and for ISO 1600. The DRs for SNR 1:1 (0 dB) as used by DXO are also calculated for verification of the methodology, and the values agree with the reported DXO DR at base ISO of 11.11 stops and 12.92 stops for the Canon and Nikon respectively.

At Jim's 10:1 floor, the Nikon has somewhat better DR at base ISO (8.04 stops vs 7.28 stops), but the DRs at ISO 1600 are very close, 4.35 stops and 4.51 stops respectively for the Canon and Nikon.

Bill

 
« Last Edit: November 13, 2014, 04:01:42 pm by bjanes »
Logged

Jim Kasson

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2370
    • The Last Word
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #31 on: November 13, 2014, 04:19:41 pm »

One can use the DXO Full SNR graphs to calculate the DR for any desired nose floor as described by Emil Martinec. I downloaded the graphs for the Canon 7D MII and Nikon D7100 and calculated the DR for Jim's 10:1 SNR (20 dB) for base ISO of 100 and for ISO 1600. The DRs for SNR 1:1 (0 dB) as used by DXO are also calculated for verification of the methodology, and the values agree with the reported DXO DR at base ISO of 11.11 stops and 12.92 stops for the Canon and Nikon respectively.

At Jim's 10:1 floor, the Nikon has somewhat better DR at base ISO (8.04 stops vs 7.28 stops), but the DRs at ISO 1600 are very close, 4.35 stops and 4.51 stops respectively for the Canon and Nikon.

Bill, I don't look at the DxO numbers myself. Does DxO say how they get from a ratio to dB? 10*log10(ratio) vs 20*log10(ratio). I'd agree with you that electrons linearly convert to voltage and therefore it ought to be the latter, but it would be good to make sure.

Good work on the DR calcs.

Jim
« Last Edit: November 13, 2014, 06:29:53 pm by Jim Kasson »
Logged

Ray

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 10332
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #32 on: November 13, 2014, 06:27:39 pm »

My take is that dynamic range is a bit overrated. It depends a bit what you shoot. Erik

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.  ;)
Logged

Jim Kasson

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2370
    • The Last Word
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #33 on: November 13, 2014, 06:37:36 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.  ;)

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

allegretto

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 660
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #34 on: November 13, 2014, 06:40:26 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

THIS

It's the 15 (or so)Teraflop computer between your ears and the intra-cellular biochem of the eye's system that does the heavy lifting under the broader DR of the real world...
Logged

bjanes

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 3387
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #35 on: November 13, 2014, 07:04:46 pm »

Bill, I don't look at the DxO numbers myself. Does DxO say how they get from a ratio to dB? 10*log10(ratio) vs 20*log10(ratio). I'd agree with you that electrons linearly convert to voltage and therefore it ought to be the latter, but it would be good to make sure.

Good work on the DR calcs.

Jim

Jim,

They use 20*log10 as outlined here.

I'm not an engineer, but understand that 20*log10 is for power and 10*log10 is for voltage. Perhaps you can explain the difference to us.

Bill
Logged

ErikKaffehr

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 11311
    • Echophoto
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #36 on: November 13, 2014, 07:29:03 pm »

Hi,

I would say that human vision is complex.

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

  • I shoot mostly landscape
  • Very few of my 75000 images have issues with DR
  • On most occasions I shot HDR I could make an equivalent image from a single ETTR exposure
  • Even the camera most limited in DR I am using, the P45+, is doing just fine in most situations
  • When I got my Sony Alpha 99 SLT, giving almost 2EV gain in DR over my Sony Alpha 900, it took me three months to find a case where I could find an advantage in DR, and that was duping a extremely high contrast Velvia slide in a "totally" dark room. A Velvia slide can have a density range of about 13 steps, I think

But there are some other points.

  • The DR that DxO reports is at SNR=1, and it is essentially readout noise. I think it is quite relevant for black areas.
  • But areas affected by low light will be dominated by photon statistics.
  • Read noise on modern sensors is close physical limits, I think. FWC is not growing fast (I would think). So I expect delopment to slow down

I would certainly suggest that Canon is lagging in the DR/shadow noise area, specially at low ISO-s, but low ISO work is probably not what the majority of their buyers does. Most buyers may not even shoot raw, expose ETTR or even use a tripod.

Best regards
Erik
« Last Edit: November 13, 2014, 08:38:50 pm by ErikKaffehr »
Logged
Erik Kaffehr
 

ErikKaffehr

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 11311
    • Echophoto
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #37 on: November 13, 2014, 07:33:50 pm »

Never noticed…

You may take it as a compliment.

Best regards
Erik


Jim,

They use 20*log10 as outlined here.

I'm not an engineer, but understand that 20*log10 is for power and 10*log10 is for voltage. Perhaps you can explain the difference to us.

Bill
Logged
Erik Kaffehr
 

Jim Kasson

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2370
    • The Last Word
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #38 on: November 13, 2014, 07:46:05 pm »

They use 20*log10 as outlined here.

That's good.


I'm not an engineer, but understand that 20*log10 is for power and 10*log10 is for voltage. Perhaps you can explain the difference to us.

It's the other way 'round, actually. The idea is to make dB's related to power and dB's related to voltage match if a resistive load doesn't change. dB's started out as a power measurement; 10 dBs meant 10 times as much power. Then people wanted to measure voltage that way. If you increase the voltage into a resistive load by a factor of 10, you get 10 times the current and 100 times the power. Since the log10 of 100 is 2 and the log10 of 10 is 1, people figured that you could multiply the log10 of a voltage ratio by 20, and get the same power ratio as if you'd multiplied the log of the power ratio by 10.

Try it: let's start with one volt into one ohm. That means one amp, and thus one watt. Now raise the voltage by 20 dB. Since it's voltage, it takes 10 times the voltage to get the voltage up by 20 dB. (20*log10(10) = 20) Now we've got 10 volts, 10 amps, and 100 watts. Go back to the beginning, and raise the power by 20 dB. We have to go from 1 watt to 100 watts to do that. (10*log10(100) = 20)

Jim
« Last Edit: November 13, 2014, 07:48:24 pm by Jim Kasson »
Logged

bjanes

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 3387
Re: Thom Hogan's interesting points regarding DxOMark scoring and the future
« Reply #39 on: November 14, 2014, 07:58:38 am »

That's good.


It's the other way 'round, actually. The idea is to make dB's related to power and dB's related to voltage match if a resistive load doesn't change. dB's started out as a power measurement; 10 dBs meant 10 times as much power. Then people wanted to measure voltage that way. If you increase the voltage into a resistive load by a factor of 10, you get 10 times the current and 100 times the power. Since the log10 of 100 is 2 and the log10 of 10 is 1, people figured that you could multiply the log10 of a voltage ratio by 20, and get the same power ratio as if you'd multiplied the log of the power ratio by 10.

Try it: let's start with one volt into one ohm. That means one amp, and thus one watt. Now raise the voltage by 20 dB. Since it's voltage, it takes 10 times the voltage to get the voltage up by 20 dB. (20*log10(10) = 20) Now we've got 10 volts, 10 amps, and 100 watts. Go back to the beginning, and raise the power by 20 dB. We have to go from 1 watt to 100 watts to do that. (10*log10(100) = 20)

Jim

Jim,

Thanks for the correction and physics lesson. Things make more sense now, and i can see the advantages of megavoltage transmission lines, but that takes us away from our photography discussion.

Bill
Logged
Pages: 1 [2] 3   Go Up