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Author Topic: DR, DxO, DSLR, MFDB, CMOS, CCD  (Read 17813 times)
BJL
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« Reply #100 on: July 13, 2010, 10:19:23 AM »
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Quote from: John R Smith
An issue here is the almost total lack of hard technical information from the manufacturers. Compare that with film, where you have highly detailed specification sheets from Kodak, Ilford and so on for all their emulsions, with characteristic curves and everything you need.
Kodak provides plenty of technical information for its sensors,
http://www.kodak.com/global/en/business/IS...l?pq-path=14425
Dalsa provides plenty of technical information for most of it sensors, but not the "exclusive" ones like the 60MP:
http://www.dalsa.com/sensors/Products/sensors.aspx
Sony provides specs for many of its smaller "digicam" sensors but not for its SLR sensors,
and Canon and Panasonic provide none, AFAIK.

There is a clear pattern: spec. sheets are provided for sensors being offered openly to any potential customer (customers being camera makers, not us camera buyers), but not for sensors used only in-house, or limited special somewhat exclusive relationships between sensor maker and camera maker.

With film the customers are photographers, so we are provided with all the specs.
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joofa
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« Reply #101 on: July 13, 2010, 10:43:04 AM »
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Quote from: ErikKaffehr
Let's assume that we have a uniform surface evenly illuminated that is imaged on say 100x100 pixels, that is a 10000 pixels. These 10000 pixels are independent in exposure. So we have 10000 exposures with average value of 20000 and assumed Stddev of 141. So Signal is 20000 , noise 141 and SNR = 141. Let's reduce exposure to 200, no we have noise about 14 from photo statistic but we need also to take readout noise into account.

If we assume readout noise to be 10 electrons and add noise in quadrature we get a noise level of 17 electrons so SNR would be 200/17 that is about 12.

Hi Erik,

One has to consider what the spatial array of 100x100 pixels is describing. For simplicity I shall only talk about shot noise. If we ignore some differences in pixels, then under reasonable illumination on a uniform surface the 100x100 array of pixels is considered to be describing the variation on any single pixel in this array. I.e., instead of acquiring 100x100=10,000 images and then picking a fixed pixel location and figuring out its standard deviation you just take one single image and consider that the spatial block of 100x100 pixels is describing more or less the equivalent variation you would have encountered temporally on a fixed pixel location in 10,000 images. So this experiment is a convenience for shot noise calculation and we can work with just one image instead of 10,000 by thinking of equivalence of spatial and temporal variations.

However, in a real, natural image (say of your dog or cat) you can't do this in this manner. Since, each of the 100x100 pixels is now sampled from a different underlying distribution because the input light as received by the sensor is no longer uniform as before. You can still of course compute mean and std.dev. and other statistics on this 100x100 array, but such statistics are not describing the shot noise on any single pixel any more in the usual sense.

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bjanes
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« Reply #102 on: July 13, 2010, 12:02:07 PM »
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Quote from: BartvanderWolf
Hi Bill,

I agree, it is tedious but one does learn a thing or two about one's specific camera body, and about rigid testing conditions and procedures. I did a similar analysis for my Canon 1Ds3 when there was no reliable info available. My conclusion was and engineering DR of 11.3, DxO recorded 11.22 on their body. The results are in enough of an agreement for me to trust the DxO data.

Bart,

I agree that doing one's own testing is a very worthwhile procedure for the reasons you cite. I certainly learned a lot from my own tests, which were in agreement with those of Peter Facey and DXO. Roger Clark's findings for the 1DMII are also in agreement with DXO, as are my previously posted calculations for the Hasselblad using the Kodak spec sheets and Roger's noise model. It seems that the ones who disagree with DXO are those who have not done their own rigorous tests but are relying on subjective impressions gained from merely looking at pictures.

What is your expert opinion on the conflicting reports with regard to the dynamic range of MFDBs? Factors rather than actual DR must be involved.

Regards,

Bill
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BartvanderWolf
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« Reply #103 on: July 13, 2010, 01:45:39 PM »
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Quote from: bjanes
What is your expert opinion on the conflicting reports with regard to the dynamic range of MFDBs? Factors rather than actual DR must be involved.

Hi Bill,

As I said earlier, DR is only a (small) factor in the explanation of the perceived dynamic range. One other factor of importance, IMHO, is differences in MTF due to sensor array dimensions. A larger sensor array will result in a larger magnification factor of a given FOV on the sensor. A larger magnification will mean that a different part of the MTF response curve is used, a part with potentially a significant higher response. That higher response will allow to discriminate microcontrast that may otherwise result in loss of discrimination due to veiling glare or other optical contributions to the system MTF.

Here's what I mean:


At the Nyquist frequency of a simulated smaller 'perfect' sensor, the MTF response is 56%. At that same resolution, due to larger magnification, a larger 'perfect' sensor will have 82% MTF response. That will allow for much more optical compromises before the same detail is drowning in the background detail. In addition the larger sensor array will have more resolution capability because output requires less magnification for same size output.

The complicating factors are of course things like the optical contributions, or rather detractions, from lenses and/or AA-filters. But also MTF killing factors like defocus and lack of DOF play a role. It makes it hard to demonstrate with cameras with different optical systems, that's why I isolated the sensor MTF because there are enough other factors to confuse an unambiguous analysis.

Hope that helps the discussion past the point of DR alone.

Cheers,
Bart
« Last Edit: July 13, 2010, 01:47:43 PM by BartvanderWolf » Logged
ErikKaffehr
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« Reply #104 on: July 13, 2010, 03:22:24 PM »
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Bart,

That would be consistent with Mark Dubovoy's comment on full texture. You mentioned it before, and I thought it was relevant.

Another think I'm considering is that we need to sharpen more because of the OLP filter. If sharpening is done without a gradient mask it would also amplify noise. Also small thing add up.

Best regards
Erik



Quote from: BartvanderWolf
Hi Bill,

As I said earlier, DR is only a (small) factor in the explanation of the perceived dynamic range. One other factor of importance, IMHO, is differences in MTF due to sensor array dimensions. A larger sensor array will result in a larger magnification factor of a given FOV on the sensor. A larger magnification will mean that a different part of the MTF response curve is used, a part with potentially a significant higher response. That higher response will allow to discriminate microcontrast that may otherwise result in loss of discrimination due to veiling glare or other optical contributions to the system MTF.

Here's what I mean:


At the Nyquist frequency of a simulated smaller 'perfect' sensor, the MTF response is 56%. At that same resolution, due to larger magnification, a larger 'perfect' sensor will have 82% MTF response. That will allow for much more optical compromises before the same detail is drowning in the background detail. In addition the larger sensor array will have more resolution capability because output requires less magnification for same size output.

The complicating factors are of course things like the optical contributions, or rather detractions, from lenses and/or AA-filters. But also MTF killing factors like defocus and lack of DOF play a role. It makes it hard to demonstrate with cameras with different optical systems, that's why I isolated the sensor MTF because there are enough other factors to confuse an unambiguous analysis.

Hope that helps the discussion past the point of DR alone.

Cheers,
Bart
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fredjeang
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« Reply #105 on: July 13, 2010, 03:48:29 PM »
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As I pointed, I'm normally allergic to curves and graphics, (exept when it comes to my incomes  )
But I think this thread is more and more interesting and I must say that valuable information is showing all the time.

Some explainations have already emerged and we are getting closer to understand the reasons of the OP questions.

That itself is a great accomplishment.

IMO, the reason why that has been possible here is that from the begining, instead of loading another war thread,
the attitude was: "ok, some experienced photographers are seeing something that contradict the measurements, why is so?"
This open mind to others views before condemning and the desire to understand are making this thread constructive.

I'm very happy to feel that and thanks again to Erik for his hability to conduct his "baby" (the thread),
and the great attitude of all the participant involved.
That really is an example of the high level of debate that Lu-La can have, independently of the divergences.
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ErikKaffehr
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« Reply #106 on: July 13, 2010, 04:36:33 PM »
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Hi,

I'm most thankful on both issues, and I also feel it has been a constructive discussion.

Best regards
Erik


Quote from: fredjeang
and the great attitude of all the participant involved.
That really is an example of the high level of debate that Lu-La can have, independently of the divergences.
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BartvanderWolf
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« Reply #107 on: July 13, 2010, 05:04:13 PM »
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Quote from: ErikKaffehr
That would be consistent with Mark Dubovoy's comment on full texture. You mentioned it before, and I thought it was relevant.

That's why I added a graph to illustrate.

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Another think I'm considering is that we need to sharpen more because of the OLP filter. If sharpening is done without a gradient mask it would also amplify noise. Also small thing add up.

Yes, it all adds up, although a good sharpening method can sharpen detail more than noise. In fact sharpening the output of an OLPF image sharpens quite well, without the more horrible low frequency aliasing-artifacts, while an unfiltered image can hardly be sharpened without exaggerating the aliasing artifacts. The shaded areas in my graph represent aliasing territory which folds back to the lower spatial frequencies. But then again, this only applies for in-focus high spatial frequencies. A larger sensor also means less DOF (or more diffraction when trying to get more DOF), and that's an effective MTF killer that could also require sharpening to compensate.

Things are not simple, we have to choose our compromises.

Cheers,
Bart
« Last Edit: July 13, 2010, 05:06:00 PM by BartvanderWolf » Logged
John R Smith
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« Reply #108 on: July 14, 2010, 03:14:40 AM »
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Quote from: BJL
Kodak provides plenty of technical information for its sensors,
Dalsa provides plenty of technical information for most of it sensors, but not the "exclusive" ones like the 60MP:
Sony provides specs for many of its smaller "digicam" sensors but not for its SLR sensors,
and Canon and Panasonic provide none, AFAIK.
With film the customers are photographers, so we are provided with all the specs.

Yes, true. But I was thinking only of MF at the time I posted, and what we don't have AFAIK is the specification for the sensor when it is implemented in a particular back (P-45 or HD-39, for example). I was assuming that the firmware, channel ampliifiers, signal processing path and so forth would vary between manufacturers, so that the response (and perhaps DR) of a Kodak KAV 39000 sensor might be different in a Phase, Hasselblad or Leaf back. But this is just speculation on my part.

There is an awful lot of highly technical stuff in this thread which I don't pretend to understand (and I never understood film chemistry either, I just used it) - fortunately one doesn't need to get that deep in order to take photographs. But others do need to understand it to make cameras, and write software, and it is a very good thing that there are people here who also have a grip on the technicalities so that manufacturers of cameras and software can be properly scrutinised and held to account.

From my own very set-of-the-pants subjective viewpoint - having shot film in all its forms since 1958, and for many years having done all my own B/W processing and E6 processing and B/W printing in 35mm, MF, and large format - I would say that my Hasselblad CFV-39 digital back has more DR than colour transparency film, about the same DR as B/W negative film, and perhaps a little less DR than colour negative film. Unfortunately I do not have a Nikon D3X to compare it with, but if anyone is offering . . .  

John
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« Reply #109 on: July 14, 2010, 04:06:07 AM »
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Hi,

Lloyd Chambers got a Leica S2 for testing yesterday (or so). He compares to the D3X. Unfortunately a pay site, but I'm interested in his writing so I find worth it.

Anyway, he says that although the AF on the Leica is correct under optimal conditions it doesn't work at all for his shooting. He has at least one sample showing advantage of S2 over D3X in sharpness but also DOF limitation.

Best regards
Erik


Quote from: BartvanderWolf
That's why I added a graph to illustrate.



Yes, it all adds up, although a good sharpening method can sharpen detail more than noise. In fact sharpening the output of an OLPF image sharpens quite well, without the more horrible low frequency aliasing-artifacts, while an unfiltered image can hardly be sharpened without exaggerating the aliasing artifacts. The shaded areas in my graph represent aliasing territory which folds back to the lower spatial frequencies. But then again, this only applies for in-focus high spatial frequencies. A larger sensor also means less DOF (or more diffraction when trying to get more DOF), and that's an effective MTF killer that could also require sharpening to compensate.

Things are not simple, we have to choose our compromises.

Cheers,
Bart
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BJL
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« Reply #110 on: July 14, 2010, 04:56:59 AM »
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Quote from: John R Smith
... what we don't have AFAIK is the specification for the sensor when it is implemented in a particular back (P-45 or HD-39, for example). I was assuming that the firmware, channel ampliifiers, signal processing path and so forth would vary between manufacturers, ...
True, but none of those is likely to produce a variation vaguely close to the alleged five or six stops, so sensor spec. sheets and third party test results for 35mm format DSLRs are easily accurate enough to answer the question that motivated this thread ...

... in the negative. None of the secondary factors raised in this debate looks likely to come close to supporting that five or six stop claim scientifically defensible. Probably the biggest factor causing a correction to per photosite DR values is the higher pixel count and related dithering when images are viewed at equal (apparent) size ... but that is only good for about a factor of at most sqrt(60/22)=1.65 in S/N ratio, about 0.7 of a stop, for the extreme case of 60MP vs 22MP.

Based on the impressive discussion in this thread so far, the best conclusion is that any genuinely perceived differences are related to
- sensor resolution
- lens resolution, and
- other lens quality factors like less damage to shadow regions by flare.
The latter two are likely to be exaggerated if comparisons are based on 35mm with zoom lenses vs MF with primes.

I have read that flare typically limits the DR of the image reaching the focal plane to something of order of 12 stops through lightening of shadow regions, though of course that depends on the pattern of lighting in the subject.
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bjanes
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« Reply #111 on: July 14, 2010, 07:37:24 AM »
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Quote from: BartvanderWolf
Hi Bill,

As I said earlier, DR is only a (small) factor in the explanation of the perceived dynamic range. One other factor of importance, IMHO, is differences in MTF due to sensor array dimensions. A larger sensor array will result in a larger magnification factor of a given FOV on the sensor. A larger magnification will mean that a different part of the MTF response curve is used, a part with potentially a significant higher response. That higher response will allow to discriminate microcontrast that may otherwise result in loss of discrimination due to veiling glare or other optical contributions to the system MTF.

Here's what I mean:
 

In his preliminary testing of the Leica S2, Digilloyd reports that the DR of the Leica (actually a tweener camera and not a full MFDB) seemed less than that of the D3x and that the latter camera handles high contrast better.

Regards,

Bill
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BartvanderWolf
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« Reply #112 on: July 14, 2010, 07:38:26 AM »
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Quote from: BJL
I have read that flare typically limits the DR of the image reaching the focal plane to something of order of 12 stops through lightening of shadow regions, though of course that depends on the pattern of lighting in the subject.

Indeed, see also http://luminous-landscape.com/forum/index.php?s=&showtopic=42158&view=findpost&p=352656.

Cheers,
Bart
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ejmartin
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« Reply #113 on: July 14, 2010, 08:59:38 AM »
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But microcontrast is not DR.  Why would an improvement in MTF affect DR?
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emil
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« Reply #114 on: July 14, 2010, 09:17:57 AM »
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Quote from: BartvanderWolf
As I said earlier, DR is only a (small) factor in the explanation of the perceived dynamic range. One other factor of importance, IMHO, is differences in MTF due to sensor array dimensions. A larger sensor array will result in a larger magnification factor of a given FOV on the sensor. A larger magnification will mean that a different part of the MTF response curve is used, a part with potentially a significant higher response. That higher response will allow to discriminate microcontrast that may otherwise result in loss of discrimination due to veiling glare or other optical contributions to the system MTF.

I'm not convinced that such factors are particularly significant to the perception of DR, Bart. It sounds as though you are making excuses for someone who doesn't know what DR is, or doesn't know what he's doing. On the other hand, perhaps it's me who doesn't understand the significance of DR.

I'd like to refer to those extraordinary results from DXO Mark that describe the D3X as having 1.33 stops greater DR than the P65+ (at the pixel level) and 0.68 stops greater DR when both images are downsampled to 8"x12" size for printing.

From the perspective of the practical photographer, this is what I think the results mean. Correct me if I'm wrong.

If I shoot a scene with a high SBR (subject brightness range) using the P65+ and the D3X, using the same focal length of lens with each camera but underexposing the D3X shot by 1 & 1/3rd stops, then both images should be perceived as having the same dynamic range.

Now it's true that the P65 shot will have a wider FoV because it has a bigger sensor and we used the same FL of lens in each case, but we're examining image quality at 100% on screen, not admiring the composition. As long as the full brightness range of the scene is represented in both shots, the different FoV is irrelevant to our purposes. The pixel pitch of the D3X is very close to that of the P65, so the 100% crops that are examined will be about the same size, which makes the comparison easier.

It may be the case that the P65+ shot will be perceived as being slightly crisper due to its lack of an AA filter, but such subtle effects should not change the perception of DR. Even if there's a mismatch of lenses and we use the most expensive Digitar lens with the P65 but an average Nikkor lens with the D3X, the better resolution in the P65 image would be apparent across the entire image and not confined to the shadows. The brain should be able to make allowances, realise that a better quality lens has been used for one of the images, and that the DR of both images is still the same.

In the comparison of images downsampled to 8"x12" size, I understand that equal FoV images would be the source, which perhaps creates a slight problem due to the different aspect ratio of the two cameras. Ignoring this slight mismatch, the DXO results are telling me when the D3X shot (underexposed just 2/3rds of a stop in this instance) and the P65+ shot fully exposed, are downsampled to 8"x12" at 300dpi, thus discarding some resolution from both images, but discarding more resolution from the P65+ image, both images will appear to have the same DR, and presumably the same resolution.

Have I got this right?

A high dynamic range capability in a camera allows for greater exposure latitude. I used to prefer shooting with negative film, rather than transparencies for that reason. I could underexpose one stop and still get acceptable shadows in situations where the subject had a wide brightness range. With slide film one had to be more precise and sometimes risk overexposure. It was widely accepted that B&W film had the highest DR, color negetive film next, and slide film a couple of stops lower.

The DR differences between these types of film was pretty obvious and didn't require endless debate. If camera A has a significantly high DR than camera B, then the shadows in camera A shots will be cleaner, more detailed and of higher quality.

If the DR differences are in the order of 4-6 stops, the cleaner and more detailed shadows from camera A would be so obvious they would smack you in the face. If the DR difference is in the order of 1/4 to 1/2 a stop, then. even with the best intentions, other factors may skew the result and it may not be perfectly clear which camera has the better DR.

Of course, you do have a point about the potential of the MTF of a lens to affect the perception of a camera's DR. This affect would be most obvious in the corners of the image where the MTF response of most lenses is worst. One could use this characteristic of lenses to demonstrate that an APS-C (cropped-format) camera has a higher DR than a FF 35mm.

This is how you would do it. Take a good 35mm format lens that has a reasonably flat MTF response to the corners and virtually no fall-off when used on the APS-C format. Take another FF lens of equivalent focal length for use with the 35mm format camera, but make sure it's a lens with significant MTF fall-off at the corners, as well as severe vignetting. Such a lens could still be impressively sharp in the centre.

Select a scene with a very high brightness range, but arrange the composition so that the shadows are all in the corners of the frame in both shots. Make sure you expose correctly, aiming for an accurate ETTR by bracketing in 1/3rd  stop increments.

Display 100% crops of the highlights and mid-tones of both image, demonstrating the superior tonality and resolution of the FF 35mm format and the fact that both shots have received a correct ETTR. Then display 100% crops of the shadows in the corners, lightening the shadows so that one can see clearly the better detail and lower noise in the APS-C shot.

This is an extreme example. I don't think many photographers would be hoodwinked by those results. However, the choice of F stop when comparing different format cameras can certainly skew the results against the smaller format, but I would think that resolution softness can be distinguished from noise.

If you want to exaggerate the resolution advantage of the DB in comparison with the FF 35mm format, then you would use wider apertures for a shallow DoF. For example, if we start with the premise that most lenses are sharpest at F5.6, then we choose F5.6 as the aperture used with the MF format.

In order to equalize DoF in both shots, we then have to use F4 (or even wider) with FF 35mm. But a 35mm lens at F4 is generally not at its sharpest. (Are we testing lenses here, or are we supposed to be testing camera sensor performance?)

If one is aware of such factors, then any serious comparison should include shots of the same scene taken at other apertures. In addition to pairing F5.6 with F4, we need to see F8 on the MFDB and F5.6 on the FF 35mm, or F11 on the MFDB and F8 on the FF 35mm.

I believe it's the case that MFDBs will generally produce noticeably sharper results than FF 35mm DSLRs when a shallow DoF is sought, even when the pixel count is the same. The smaller pixel pitch of the smaller format requires a higher MTF from the lens, not a lower MTF. The MTF at F4 is generally lower than it is at F5.6. However, the MTF is generally higher at F8 than at F11.
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BartvanderWolf
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« Reply #115 on: July 14, 2010, 09:28:03 AM »
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Quote from: ejmartin
But microcontrast is not DR.  Why would an improvement in MTF affect DR?

Hi Emil,

It wouldn't, because they are different things. However, it might explain what is incorrectly perceived as increased DR (even though it's actually a cumulation of different things). The partial explanation by a potentially boosted MTF does not only boost microcontrast, all spatial frequencies get a better start, but that is going to be reduced by several optical components/effects in actual practice.

Cheers,
Bart
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ErikKaffehr
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« Reply #116 on: July 14, 2010, 12:51:18 PM »
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Emil,

If you consider your image here: http://theory.uchicago.edu/~ejm/pix/20d/te...3noise-8bit.gif

How do you think it would be effected by increasing MTF? Text would be darker and have higher edge contrast?

If we increase sharpening, to compensate for OLP filtering how would that affect the image? If we do that indiscriminately I guess noise would go up?

Best regards
Erik


Quote from: ejmartin
But microcontrast is not DR.  Why would an improvement in MTF affect DR?
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BartvanderWolf
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« Reply #117 on: July 14, 2010, 06:38:31 PM »
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Quote from: Ray
I'm not convinced that such factors are particularly significant to the perception of DR, Bart. It sounds as though you are making excuses for someone who doesn't know what DR is, or doesn't know what he's doing. On the other hand, perhaps it's me who doesn't understand the significance of DR.

I'd like to refer to those extraordinary results from DXO Mark that describe the D3X as having 1.33 stops greater DR than the P65+ (at the pixel level) and 0.68 stops greater DR when both images are downsampled to 8"x12" size for printing.

Hi Ray,

I hope you're not misreading my intentions. My motivation is to understand why some people perceive a difference in image quality. The mere fact that they attribute it to a factor that demonstrably cannot explain their perception is of lesser importance (not everybody has the same technological insight).

Based on the measurements that I can personally verify (by rigorous testing), I have no problem accepting the DxOmark data as generally reliable (within reasonable per-sample variation limitations). As such, the DR alone cannot explain the perceived differences (unless those differences are grossly overstated). So, assuming the observations of 'some' difference in (presumably) shadow detail performance and/or highlight recovery capability are real (i.e. not just post-purchase-justification), the assumption of other contributing (because they could add up) factors playing a role seems valid.

Quote
From the perspective of the practical photographer, this is what I think the results mean. Correct me if I'm wrong.

If I shoot a scene with a high SBR (subject brightness range) using the P65+ and the D3X, using the same focal length of lens with each camera but underexposing the D3X shot by 1 & 1/3rd stops, then both images should be perceived as having the same dynamic range.

Well, assuming the same lens (not just the focal length, because design plays a role and we want to eliminate as many variables as possible), and the same sensor design (there are potentially major differences between CCD and CMOS designs, depending on the actual implementation and supporting electronics), one would expect similar results. However, there are already several variables. Whether they are relevant would need to be determined. Rigorous testing is not easy, one preferably only varies a single parameter to derive some level of relevance.

Quote
Now it's true that the P65 shot will have a wider FoV because it has a bigger sensor and we used the same FL of lens in each case, but we're examining image quality at 100% on screen, not admiring the composition. As long as the full brightness range of the scene is represented in both shots, the different FoV is irrelevant to our purposes. The pixel pitch of the D3X is very close to that of the P65, so the 100% crops that are examined will be about the same size, which makes the comparison easier.

Well, I'm not convinced that the difference in magnification factor does not lead a casual observer to make a wrong assumption. Human vision is not very good at objective quantification, we need direct and comparable scale samples side by side for a somewhat valid opinion.

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It may be the case that the P65+ shot will be perceived as being slightly crisper due to its lack of an AA filter, but such subtle effects should not change the perception of DR.

Well, there you have another subjective factor clouding the judgement. I'm not yet convinced that the effects are as subtle, QED.

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Even if there's a mismatch of lenses and we use the most expensive Digitar lens with the P65 but an average Nikkor lens with the D3X, the better resolution in the P65 image would be apparent across the entire image and not confined to the shadows. The brain should be able to make allowances, realise that a better quality lens has been used for one of the images, and that the DR of both images is still the same.

One can only hope, but I'm not optimistic.

Quote
In the comparison of images downsampled to 8"x12" size, I understand that equal FoV images would be the source, which perhaps creates a slight problem due to the different aspect ratio of the two cameras.

I tried to accomodate for that by using an aspect ratio indifferent metric in my graph by using the picture height (LW/PH) criterion, which disregards certain differences in aspect ratio, i.e. width. It was a deliberate part of my suggestion (always trying to eliminate variables).

Quote
Ignoring this slight mismatch, the DXO results are telling me when the D3X shot (underexposed just 2/3rds of a stop in this instance) and the P65+ shot fully exposed, are downsampled to 8"x12" at 300dpi, thus discarding some resolution from both images, but discarding more resolution from the P65+ image, both images will appear to have the same DR, and presumably the same resolution.

Have I got this right?

More or less, yup. There are considerations of the actual downsampling algorithm used, but I'm feeling generous tonight ;-) .

Quote
A high dynamic range capability in a camera allows for greater exposure latitude. I used to prefer shooting with negative film, rather than transparencies for that reason. I could underexpose one stop and still get acceptable shadows in situations where the subject had a wide brightness range. With slide film one had to be more precise and sometimes risk overexposure. It was widely accepted that B&W film had the highest DR, color negetive film next, and slide film a couple of stops lower.

The DR differences between these types of film was pretty obvious and didn't require endless debate. If camera A has a significantly high DR than camera B, then the shadows in camera A shots will be cleaner, more detailed and of higher quality.

Well, that depends on one's background. The debates, although more in the scientific community (where calibration of one's detectors plays a role), and the (somewhat) subjective preferences (yet an interesting stastistical basis) amongst professional photographers, were there.

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If the DR differences are in the order of 4-6 stops, the cleaner and more detailed shadows from camera A would be so obvious they would smack you in the face. If the DR difference is in the order of 1/4 to 1/2 a stop, then. even with the best intentions, other factors may skew the result and it may not be perfectly clear which camera has the better DR.

Which is what we are, at least I am, trying to dissect. Where does the disconnect (between observed and quantifiable) come from?

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Of course, you do have a point about the potential of the MTF of a lens to affect the perception of a camera's DR. This affect would be most obvious in the corners of the image where the MTF response of most lenses is worst. One could use this characteristic of lenses to demonstrate that an APS-C (cropped-format) camera has a higher DR than a FF 35mm.

Yes, I've read "How to Lie with Statistics" ;-(

Cheers,
Bart
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Ray
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« Reply #118 on: July 15, 2010, 10:10:52 AM »
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Quote from: BartvanderWolf
Which is what we are, at least I am, trying to dissect. Where does the disconnect (between observed and quantifiable) come from?

Hi Bart,
I don't think I've misconstrued your intentions here. Best of luck!   . This issue is particularly paradoxical when one takes into consideration that comparison that Michael made, at A3+ print size, using a P45+ and the 15mp Powershot G10.  If one looks at the DXO scores comparing those sensors at the normalised print size of  8"x12", the P45+ is way ahead with 1/4 the noise at 18% grey, 4.7 bits better color sensitivity and 2 bits better tonal range, yet at double the size of the DXO normalized print, experienced photographers were not able to distinguish any significant qualitative difference between the two prints, except the shallower DoF in one of the prints which was an indication that that was the print made from the P45 image.

If Michael had equalized the DoF in both shots, using F18 or F22 with the P45+ instead of F11, we might have had the even more amazing situation whereby the G10 print was confused as orininating from the P45 camera because it appeared slightly sharper.

It's because such differences can go unnoticed in a 'real world' print (as opposed to a print that is specifically designed to highlight such differences, such as a resolution line chart which highlights resolution differences), that I'm very skeptical that relatively small differences in 'effective' lens MTF performance, due to sensor size & pixel pitch, could have any significant bearing on the perception of DR.

When I first visited the DXO Mark site, I was a bit confused about the apparent conflict between SNR and dynamic range. We tend to associate a good SNR figure with a high DR, yet there are many examples of sensors having a worse DR but a better SNR on the DXO website. I presume this situation arises because DXO only measure SNR at 18% grey, which is a fairly light shade of grey, in the mid-tone range. I presume, if DXO were to measure SNR at significantly darker shades of grey, the SNR figures would correspond more closely with the DR figures, ie. a higher DR would tend to be associated with a higher SNR at the darker shade of grey. Is this correct?

Since DXO Mark don't provide results at larger, normalised print sizes, such as 23"x31" for the P65+ at 300 dpi, I can only speculate how the DR of an interpolated D3X image would compare, at this size.

Since the D3X image has a 1.33 stop DR advantage at the pixel level, and a 2/3rds stop advantage at the downsampled size of 8"x12", I think it would be reasonable to guess that at any larger, interpolated print size, the DR of the D3X print would not be worse than that of the P65+, or at least not perceptibly worse, because the resolution advantage of the P65+ image, in those darker shades of grey in the 11th and 12th stops, probably doesn't exist. It's been obliterated by noise.

If the resolution advantage in the darker shadows hasn't been recorded by the P65 sensor in the first instance, then it cannot magically materialize, however big the print size. Nor, I would imagine, could any slight advantage from an effectively higher MTF from the lens provide that additional detail in areas of the image that are swamped in noise.

However, I would of course expect to see higher resolution in the 23"x31" print from the P65, in the range from the lower mid-tones to the highlights. I would expect to see sharper eylashes and a slightly smoother, creamier complexion of the model's face. But I wouldn't expect to see a more detailed chihuahua, hiding in the dark, under the couch.

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joofa
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« Reply #119 on: July 15, 2010, 11:32:37 AM »
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Quote from: Ray
Since the D3X image has a 1.33 stop DR advantage at the pixel level, and a 2/3rds stop advantage at the downsampled size of 8"x12",

The downsampling algorithm has an effect on SNR improvement. For e.g., is it binning (box filter), or sinc, or lanczos, or something else. In general the implicit assumption has been that pixels are simply binned/averaged, derived from all those discussions on smaller/larger sensor SNR behavior. However, in practise, one would use binning seldomly for downsampling as more sophisticated methods are used. The good news is that it is possible to derive an analytical, closed form, solution to SNR improvement in a generalized downsampling operation that can cater to different methods, say lanczos downsampling.

But the point is not to go into detail of such a solution, but just to emphasize that quoting a figure such as '2/3rds stop advantage at the downsampled size of 8"x12"' without mentioning how the image was downsampled is not full piece of information.

Joofa
« Last Edit: July 15, 2010, 11:33:07 AM by joofa » Logged

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