Luminous Landscape Forum
Equipment & Techniques => Digital Cameras & Shooting Techniques => Topic started by: EinstStein on November 05, 2015, 05:22:58 am
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Practically, is there IQ difference between a digital camera with 42MP x 12-bit dynamic range and one with 20MP x 14-bit dynamic range? Which one would be likely to be more useful?
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I am not sure that it is productive to specify dynamic range as "bits". Sure the raw file will use a number of bits per pixel and that will be an upper bound, but in practice, raw files seems to be limited to maximum unsaturated signal level (may well be less than the maximum integer value possible for N bits) and some noise floor >1/2 lsb.
42 is (obviously) more than 20. If you need large spatial precision and have sufficient light, 42 is probably the answer.
If you have a choice between (optimal) 20 MP 14-bit files and (optimal) 40 MP 13-bit files, the answer would perhaps be more clear cut, as the 40 MP file could always be filtered to produce something equivalent to a 20 MP 14-bit file.
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but in practice, raw files seems to be limited to maximum unsaturated signal level (may well be less than the maximum integer value possible for N bits) and some noise floor >1/2 lsb.
some people here allude that flare/glare/etc in lens to camera chamber to sensor assembly surface and layers on top of the silicon itself will limit that even more - so in fact you never get the engineering DR out there...
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some people here allude that flare/glare/etc in lens to camera chamber to sensor assembly surface and layers on top of the silicon itself will limit that even more - so in fact you never get the engineering DR out there...
Jim Kasson pointed to this paper in another discussion:
https://graphics.stanford.edu/papers/glare_removal/glare_removal.pdf
"Based on simulations, the Canon 20D can record nearly 20 stops of dynamic range using HDR imaging if only a point light source is present. If half of the field of view is covered by an extended source, then only 9 stops of dynamic range can be recorded by the 20D..."
It seems that flare can plausibly either restrict DR significantly or insignificantly, depending on the scene.
There is always the possibility that one is underexposing the shot (i.e. there are no bright parts in the scene to cause much flare). Brightness could be restored by upping the camera ISO or pushing a slider in you raw developer. I would still want the pushed image to look as good as possible.
-h
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Working with both 12bit and 14bit cameras I can tell you that I've never had to push my files so much as to notice issues. Under normal conditions, if you make the right exposure for the result you need/want, you won't feel limited either way.
Here are two pictures shot last weekend, one comes from a 16MP 14bit camera (D7000) and the other from a 10MP 12bit camera (D200). If you can tell which is which then you probably need a 14bit sensor because your eyes are too good! :P
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Just to mention something that apparently gets misinterpreted, 12 or 14 bit ADC conversions provide for more accurate smooth transitions and subtle color differences, not DR.
Dynamic range only depends on well depth and read noise, as a ratio. The read noise is a characteristic of all (supporting) electronics.
Cheers,
Bart
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Bit depth and MP are the maximun possible performance of two of th impotant imaging quality. The actual image is affected by noise and the interference.
Unless the vendor purposely lying, a sensor with more bits will perform better in terms of coloring or dynamic range, while a sensor with more MP will perform better in terms of resolution. assume all else are equal, such as same optical system, etc.
The question is, quantitatively, at these level, 42mp&12b vs. 20mp&14b, which one would be more practically preferred.
All the argument in this thread seems suggest no difference.
Of course, the judge must based on noncrappy, well exposed picture on sensible objects.
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Hi,
I would mostly go with a camera having 42 MP, especially as I have a camera with 42 MP and it gives stunning image quality. With the DR stuff, you either need it or you don't need it. Mostly you don't need it. AFAIK 42MP at 12-bit DR would correspond to about 12.5 EV when downsized to 20 MP.
There are quite a few situations where high DR is useful, but I still feel DR is a bit overrated. Twelve stops is sort of plenty.
Best regards
Erik
Practically, is there IQ difference between a digital camera with 42MP x 12-bit dynamic range and one with 20MP x 14-bit dynamic range? Which one would be likely to be more useful?
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Hi,
Your question in not possible to answer as all parameters are not known.
Anyway, high DR is essentially the same thing as clean shadows. So with a camera with higher DR you can pull out better shadow detail. At least as long as you expose optimally. But if you don't need that deep shadow detail the DR simply does not matter. Also, as pointed out on the thread, lens flare often limits DR anyway.
If you have high DR, you can opt your exposure to protect highlights, as you can still get good shadow detail. That will lower your image quality by increasing noise level. But again modern sensors are so good that noise is seldom an issue at low ISO numbers and small to moderate print sizes. If you print really large those pixels may be beneficial and you want to maximise your exposure to keep noise down.
So, depending on your exposure and scene illumination ratio DR may be beneficial for image quality.
This article discussed the issues in great detail: http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/
Best regards
Erik
Bit depth and MP are the maximun possible performance of two of th impotant imaging quality. The actual image is affected by noise and the interference.
Unless the vendor purposely lying, a sensor with more bits will perform better in terms of coloring or dynamic range, while a sensor with more MP will perform better in terms of resolution. assume all else are equal, such as same optical system, etc.
The question is, quantitatively, at these level, 42mp&12b vs. 20mp&14b, which one would be more practically preferred.
All the argument in this thread seems suggest no difference.
Of course, the judge must based on noncrappy, well exposed picture on sensible objects.
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You can (more than) make up for the resolution difference by shooting with a longer lens and stitching images. You can (more than) make up for the dynamic range difference by shooting multiple exposures and combining images. Excluding these options, the question is which is more important for your style of photography, resolution or shadow noise? If you do a lot of shooting in low light, if you find yourself using high ISO frequently, or if you lift dark shadows quite a bit in post processing and are bothered by noise, then pick the higher DR sensor. Otherwise pick the higher resolution sensor.
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Bit depth and MP are the maximun possible performance of two of th impotant imaging quality. The actual image is affected by noise and the interference.
Unless the vendor purposely lying, a sensor with more bits will perform better in terms of coloring or dynamic range
Providing a 16-bit file is not in any way "lying". But there is a distinct possibility that the same image-forming information could be stored in a 14-bit file. Thus using file size as an indicator of image quality is naiive in my view, especially as there are knowledgeable people out there who offers more relevant measures of image quality.
, while a sensor with more MP will perform better in terms of resolution. assume all else are equal, such as same optical system, etc.
The question is, quantitatively, at these level, 42mp&12b vs. 20mp&14b, which one would be more practically preferred.
If Eric Fossum is right and able to deliver, his single-bit sensor will provide more resolution and more DR than any current technology and mainly be limited by the physics of light.
-k
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Just to mention something that apparently gets misinterpreted, 12 or 14 bit ADC conversions provide for more accurate smooth transitions and subtle color differences, not DR.
Dynamic range only depends on well depth and read noise, as a ratio. The read noise is a characteristic of all (supporting) electronics.
Cheers,
Bart
+1
Dynamic Range is a ratio of analogue values expressed in logarithmic units (exposure stops in photography). To use the bit depth used in the digital processing of the image to describe Dynamic Range is meaningless and also confusing as some cameras have the option of recording the raw file in either 12 bits or 14 bits. But this has nothing to do with Dynamic Range, rather the precision of the processing. You can process a capture with a DR of 14 stops with a bit depth of 8 but you won't get the most out of it doing that.
Dave
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The dynamic range of a ADC (or DAC) is the ratio bentween the largest expressible value vs. the smallest expressible value. It's is that simple.
If a sensor/ADC is speced to capture 14bit bit depth, than it should make sure the (internal) noise figure is within the half bit range, unless the engineers or the marketing guys lie. Rarely happen for reputable.
Whether the signal it captures has that much of dynalic range is another issue.
Flare, interference, lens distortion, and optical system resolution etc., would affect the final captured image and will affect the effective usable dynamic range and resolution. Both MP and bit depth can suffer the deteriorating.
If you want to fool yourself, you are welcome.
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If you want to fool yourself, you are welcome.
What are you saying here? If you want to depend on specs like "16 bits" as a proxy for DR instead of directly measured DR, is it not you who are fooling yourself?
-h
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Dynamic Range is a ratio of analogue values expressed in logarithmic units (exposure stops in photography). To use the bit depth used in the digital processing of the image to describe Dynamic Range is meaningless and also confusing as some cameras have the option of recording the raw file in either 12 bits or 14 bits. But this has nothing to do with Dynamic Range, rather the precision of the processing. You can process a capture with a DR of 14 stops with a bit depth of 8 but you won't get the most out of it doing that.
What you say is not the case for a linearly encoded raw file, where the bit depth places an upper limit on the DR, which is equal in stops to the bit depth. If you are dealing with a gamma or log encoded file, then your statement is correct. However almost all digital cameras use linear encoding for the raw file.
Bill
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Hi,
DR is actually defined as full well capacity divided by readout noise. As pointed out by BJanes, the width of the ADC sets a limitation on the DR as long as linear representation is used. Sensor vendors sometimes specify the dynamic range of the chip, say for instance 76 dB. You can convert that 76 dB to EV by dividing by 6. So 76 dB -> 12.6 EV. DxO-mark measures DR for cameras and they came up with a DR 12.34 EV. Pretty close. The camera in question was the Leica M (typ 240). It is a 14-bit device, achieving 12.34 EV in DR.
Now, another device has been measured by DxO-mark, and it came in at 11.89 EV. That camera is a 16-bit device known as the Phase One IQ-180.
Which is the best camera regarding DR according DxO-mark? It is the Nikon D810 at 13.67 EV. It is a 14 bit device.
Now, of all these cameras the Phase One IQ-180 has the lowest DR, actually meaning it utilises 12 bits out of the 16 bits it is claimed to have. But, it has quite a lot of pixels. Now, if we make a small print, those pixels would be packed and yield a higher DR. This is simple math, and I don't go into that for now. DxO-mark does this calculation using a small 8MP print as a base, in this print mode we get:
Leica M (typ 240) 13.13 EV
Phase One IQ-180 13.56 EV
Nikon D810 14.76 EV
It seems that the Nikon can transfer more than 14 EV trough it's 14 bit data path, but this is not the case. It is a result of normalisation.
Let's check out Canon's latest creation, the 5DSR. In screen mode it reaches just 11.05EV, in spite of having a 14 bit data path. In the normalised mode it reaches 12.39 EV, a bit shy of the Leica M (typ 240).
Now, we may go up in ISO, somewhere around 1200 ISO the Canon is just as good in DR as the Nikon. At high ISO the signal of the sensor is amplified and noise in ADC is thus reduced.
Best regards
Erik
The dynamic range of a ADC (or DAC) is the ratio bentween the largest expressible value vs. the smallest expressible value. It's is that simple.
If a sensor/ADC is speced to capture 14bit bit depth, than it should make sure the (internal) noise figure is within the half bit range, unless the engineers or the marketing guys lie. Rarely happen for reputable.
Whether the signal it captures has that much of dynalic range is another issue.
Flare, interference, lens distortion, and optical system resolution etc., would affect the final captured image and will affect the effective usable dynamic range and resolution. Both MP and bit depth can suffer the deteriorating.
If you want to fool yourself, you are welcome.
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I think we are probably all on the same page here, just focusing on different aspects. The point I was trying to make is that DR should be referred to in stops not bit depth. The DR represents the widest possible useful range of light values that can be recorded by the camera. I agree that the bit depth used in the adc limits this range. So if the analogue part of the sensor has a dynamic range of say 13 stops, you should be using an adc bit depth of 14 rather than 12 to take full advantage of the sensor's dynamic range.
Dave
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Pretty much anything quoted in log-base-2 values can be given the unit of "bit". It's used very often as a unit of entropy, for example. So bits=stops and a preference one way or the other is really just aesthetic.
The fact that the data is then stored in 12, 14 or whatever bit-length memory locations is another matter.
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One of a digital camera vendor is desperately trying to release the firmware to fix this problem to boost the 12-bit bit-depth to 14-bit.
Now you can relax and stop defending for it for this short-come. I will be entertained to see you change your tone to swear how important the bit-depth is.
Whether the firmware can really fix the problem is yet to be seen. It won't be easy, since tbe original problem is not a firmware/software bug, it's the generic problem in the hardware.
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One of a digital camera vendor is desperately trying to release the firmware to fix this problem to boost the 12-bit bit-depth to 14-bit.
Now you can relax and stop defending for it for this short-come. I will be entertained to see you change your tone to swear how important the bit-depth is.
...
For a moment I thought that your original post was sincere, and my answers were attempts to contribute.
This last post makes me doubt that you really have any questions. I have nothing further to add.
-h
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The dynamic range of a ADC (or DAC) is the ratio bentween the largest expressible value vs. the smallest expressible value. It's is that simple.
Hello EinstStein,
All the definitions of DR I have seen with respect to imaging sensors refer to some variation of the ratio of maximum usable signal to minimum usable signal. Often the minimum usable signal is defined according to an application specific SNR, for instance the signal at which SNR = 1. DxOmark.com uses this latter definition. In some circles the minimum usable signal is considered to be equal to the read noise (i.e. the noise 'floor' introduced by the electronics). Some ADC designers use this rule to determine bit depth. On the other hand I have never seen a definition of DR based on 'expressible value'. Do you have a source for it? More information on DR for photographers here (http://www.strollswithmydog.com/engineering-dynamic-range-photography/).
Jack
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This thread has got me thinking about dynamic range, bit depth and noise and I decided to do a simple test with my D610 as follows.
I set up a fairly high dynamic range shot as shown in the first attachment and took the following variants as shown in the 100% crops.
1. ISO 100, 14 bit (DXOMark quotes dynamic range for ISO100 of 14.36 stops)
2. ISO 100 12 bit
3. ISO 800 14 bit (DXOMark quotes dynamic range for ISO 800 of 12.23 stops)
All crops were processed with the same settings in ACR ie Exposure +1, Highights -50, Shadows +100
These images indicate that there is very little difference in shadow noise between the 14 bit and 12 bit versions of the ISO 100 shots (14.36 EV).
The ISO 800 shot indicates considerably more noise than the ISO 100 shots corresponding to the lower dynamic range of 12.23 EV. This suggests to me that from a noise point of view, the 12 bit version of the ISO 100 shot does not show a reduction in dynamic range to 12 EV. Maybe I'm not looking at the whole picture though ?
Please note that the tests were not meant to investigate other issues such as posterisation.
Dave
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Hi Dave,
Thanks for making this experiment. Your findings are interesting, but I am quite a bit from drawing any conclusion yet.
Best regards
Erik
This thread has got me thinking about dynamic range, bit depth and noise and I decided to do a simple test with my D610 as follows.
I set up a fairly high dynamic range shot as shown in the first attachment and took the following variants as shown in the 100% crops.
1. ISO 100, 14 bit (DXOMark quotes dynamic range for ISO100 of 14.36 stops)
2. ISO 100 12 bit
3. ISO 800 14 bit (DXOMark quotes dynamic range for ISO 800 of 12.23 stops)
All crops were processed with the same settings in ACR ie Exposure +1, Highights -50, Shadows +100
These images indicate that there is very little difference in shadow noise between the 14 bit and 12 bit versions of the ISO 100 shots (14.36 EV).
The ISO 800 shot indicates considerably more noise than the ISO 100 shots corresponding to the lower dynamic range of 12.23 EV. This suggests to me that from a noise point of view, the 12 bit version of the ISO 100 shot does not show a reduction in dynamic range to 12 EV. Maybe I'm not looking at the whole picture though ?
Please note that the tests were not meant to investigate other issues such as posterisation.
Dave
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Hi Dave,
Thanks for making this experiment. Your findings are interesting, but I am quite a bit from drawing any conclusion yet.
Best regards
Erik
Look forward to hearing your thoughts Erik, and others too.
I am assuming that changing from 14 bit capture to 12 bit capture actually changes the bit depth of the adc. Even if this is not the case and the 12 bit is just down sampled from the 14 bit, similar considerations would apply I think.
Dave
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Hi Dave,
One consideration may be that your darks may be dominated by shot noise and not by readout noise and one reason for that may be lens flare.
Some knowledgeable authors say that lens flare limits practical DR to 11EV, I would guess it holds but I think I have demonstrated some cases when that assumption is not valid.
A different discussion, but I have not been able to observe any difference between Sony's compressed raw and uncompressed raw, except color shift in the darks in the raw compressed image. Noise levels were similar.
But, Jim Kasson did observe difference between 14-bit and 12-but samples on the Sony A7rII, but I think he was looking at much higher noise levels than you did. I'll try to dig up that article.
Best regards
Erik
Look forward to hearing your thoughts Erik, and others too.
I am assuming that changing from 14 bit capture to 12 bit capture actually changes the bit depth of the adc. Even if this is not the case and the 12 bit is just down sampled from the 14 bit, similar considerations would apply I think.
Dave
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Hi Dave,
One consideration may be that your darks may be dominated by shot noise and not by readout noise and one reason for that may be lens flare.
Best regards
Erik
Erik I had a look at the 14 bit ISO100 file in RawDigger. The darkest areas (between the wooden slats on the chair) have values around the 20-30 mark. I'm not sure I could calculate shot noise with confidence !!
Dave
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Erik I had a look at the 14 bit ISO100 file in RawDigger. The darkest areas (between the wooden slats on the chair) have values around the 20-30 mark. I'm not sure I could calculate shot noise with confidence !!
Dave
Assuming saturation at 16383 (may be less in practice), a raw value of 20 is 9.7 stops down from saturation. This is in the range that can be quantified at 12 bits. To see the advantage of 14 bits, you would have to have darker blacks. Correct?
Bill
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But, Jim Kasson did observe difference between 14-bit and 12-but samples on the Sony A7rII
wasn't that actually between 13 effective bits (with compressed raws, not with the recent totally uncompressed raws) vs 12 bit (where Sony drops to 12 bit in certain modes) ?
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Some knowledgeable authors say that lens flare limits practical DR to 11EV, I would guess it holds but I think I have demonstrated some cases when that assumption is not valid.
Hi Erik,
Veiling glare does limit DR. The extent of the limitation depends on the relative proportions of light and dark in the image. Here is a demonstration of an old test I did with the Nikon D3 using a Stouffer wedge. I took images with the wedge with the background masked off (on the right) and unmasked (left).
(https://bjanes.smugmug.com/Photography/Stouffer-Glare/i-2C572MK/0/O/small_comp.png)
I think I rendered to TIFFs using ACR with a linear tone curve (PV2010 with sliders on main tab zeroed) and here are the results.
(https://bjanes.smugmug.com/Photography/Stouffer-Glare/i-3RqzTQw/0/O/Glare_01_08.png)
And the DRs determined by Imatest.
(https://bjanes.smugmug.com/Photography/Stouffer-Glare/i-bHRtMjL/0/O/DR_Comp.png)
With the background masked off, I got 10.6 stops of DR. It would be interesting to repeat the test with the D800e or the A7Rii.
Bill
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Assuming saturation at 16383 (may be less practice), a raw value of 20 is 9.7 stops down from saturation. This is in the range that can be quantified at 12 bits. To see the advantage of 14 bits, you would have to have darker blacks. Correct?
Bill
Yes I think so Bill. I could repeat the test to try and get lower blacks but given the comments from you and Erik on veiling flare, that may be a waste of time. The tests on veiling flare you provide are interesting and yes it would be nice to see similar results for a D800.
Dave
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Hi,
Yes, I would not argue with that. But, the thing was that he has observed tangible benefits…
Best regards
Erik
wasn't that actually between 13 effective bits (with compressed raws, not with the recent totally uncompressed raws) vs 12 bit (where Sony drops to 12 bit in certain modes) ?
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Hi,
Yes, I would not argue with that. But, the thing was that he has observed tangible benefits…
Best regards
Erik
but what if tangible between 13 and 12 and tangible between 14 and 13 will yield a little more tangible between 14 and 12 (not talking about compression artefacts naturally) ? I think I saw somebody saying somewhere that totally uncompressed full 14bit also have some better (as in precise) black levels for RGGB channels in raw or something along those lines ...
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Hi Dave,
The best way to study the effects of 12-bit and 14-bit anologue to digital conversion is to check out the darks. Just shoot something like a bookshelf and underexpose 4-5 stops and pull the dark details by correcting exposure in post processing by 4-5 stops. That eliminates the flare factor.
Best regards
Erik
Yes I think so Bill. I could repeat the test to try and get lower blacks but given the comments from you and Erik on veiling flare, that may be a waste of time. The tests on veiling flare you provide are interesting and yes it would be nice to see similar results for a D800.
Dave
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Hi Dave,
The best way to study the effects of 12-bit and 14-bit anologue to digital conversion is to check out the darks. Just shoot something like a bookshelf and underexpose 4-5 stops and pull the dark details by correcting exposure in post processing by 4-5 stops. That eliminates the flare factor.
Best regards
Erik
Thanks Eric
I actually just did some more test shots this time with the lens cap on and a fast shutter speed to try and just record read noise. I'm currently analysing those with RawDigger but it might also be worth doing something like you suggest to get a better visual of the noise. I'll provide an update when I can.
Dave
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Thanks Eric
I actually just did some more test shots this time with the lens cap on and a fast shutter speed to try and just record read noise. I'm currently analysing those with RawDigger but it might also be worth doing something like you suggest to get a better visual of the noise. I'll provide an update when I can.
Dave
Here are the results of my latest tests. All three shots were taken with the lens cap on in a dark room with a fast shutter speed. The details of the three shots are
1. ISO 100, 14 bit capture
2. ISO 100, 12 bit capture
3. ISO 800, 14 bit capture
All shots have had exposure increased by 7 stops in pp as well as 100% shadow increase, purely so the noise is visible.
I did an analysis of the sample distributions from RawDigger to estimate Standard Deviation of the noise and hence Dynamic Range. Unlike Canon cameras, Nikon have no offset voltage applied to the black level. This means that negative values of noise voltage are all read as 0. I tried to adjust for this by assuming that the distribution of negative values was the same as the positive values and substituted some of the 0 values with these negative values.
The noise calculation for shot 1 (ISO 100) gave an estimated DR of just over 14 stops, which correlates well with the DXOMark results for this camera. The calcs for shot 3 (ISO 800) also gave good correlation around the 12 stop figure.
With shot 2 (ISO 100 with 12 bit), the only sample values were 0 and 1. This is because of the reduced bit depth which can't resolve this low noise figure reliably. This also shows up in the appearance of the shot.
However given the appearance of the images, these results indicate to me that changing from 14 bit to 12 bit for a camera with DR of around 14 doesn't really change the level of noise to any great extent (and hence there is little change to the DR based on the definition of DR= Sat level/Read Noise level.
I'd welcome further comments please.
Dave
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Hi Dave,
The best way to study the effects of 12-bit and 14-bit anologue to digital conversion is to check out the darks. Just shoot something like a bookshelf and underexpose 4-5 stops and pull the dark details by correcting exposure in post processing by 4-5 stops. That eliminates the flare factor.
Best regards
Erik
Erik,
The underexposed bookshelf method is a good method and easy to perform, and it allows to visualize the noise qualitatively. However, at times quantitive measurements are desired and the wedge with Imatest can do this.
However, does the underexposure eliminate the effect of flare? If the veiling glare of a lens is 0.5% (see Norman Koren (http://www.imatest.com/docs/veilingglare/)), the shadows are contaminated by 0.5% of the highlights regardless of exposure. When you bring up the shadows in the raw converter, the effect of the veiling glare is also magnified to the same extent as would occur with an exposure at a higher luminance. I'm not sure that this is the case, and what do you think?
Regards,
Bill
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Erik,
The underexposed bookshelf method is a good method and easy to perform, and it allows to visualize the noise qualitatively. However, at times quantitive measurements are desired and the wedge with Imatest can do this.
However, does the underexposure eliminate the effect of flare? If the veiling glare of a lens is 0.5% (see Norman Koren (http://www.imatest.com/docs/veilingglare/)), the shadows are contaminated by 0.5% of the highlights regardless of exposure. When you bring up the shadows in the raw converter, the effect of the veiling glare is also magnified to the same extent as would occur with an exposure at a higher luminance. I'm not sure that this is the case, and what do you think?
Hi Bill,
The veiling glare remains proportional (as a percentage of stray 'bright exposure' added) to the actual level of exposure (as a stepwedge example would show). So underexposing will only show less absolute glare (and shadow detail), but the same amount of relative glare. This of course assumes mo Raw processing prior to writing the Raw datafile.
The conceptual difficulty may be in the 'bright exposure' part, because as exposure becomes less, then the absolute amount of veiling glare also becomes less, unless it stems from a very bright lightsource that remains exceedingly bright/clipped. But otherwise, absolute veiling glare amount is reduced proportionally with exposure amount, as is the actual exposure amount, so their proportions stay the same.
The absolute/fixed amount of veiling glare just weighs heavier when it's added to little signal, that's why we lose Dynamic Range.
Cheers,
Bart
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I did an analysis of the sample distributions from RawDigger to estimate Standard Deviation of the noise and hence Dynamic Range. Unlike Canon cameras, Nikon have no offset voltage applied to the black level. This means that negative values of noise voltage are all read as 0. I tried to adjust for this by assuming that the distribution of negative values was the same as the positive values and substituted some of the 0 values with these negative values.
The noise calculation for shot 1 (ISO 100) gave an estimated DR of just over 14 stops, which correlates well with the DXOMark results for this camera. The calcs for shot 3 (ISO 800) also gave good correlation around the 12 stop figure.
I'd welcome further comments please.
Dave,
A better way to determine the read noise on Nikons is to use the optical black area of the raw file as Bill Claff (http://www.photonstophotos.net/GeneralTopics/Sensors_&_Raw/Sensor_Analysis_Primer/Read_Noise_-_Optical_Black.htm) describes.
Since you use Rawdigger, you can use it to gain access to the optical black area. In preferences check the masked pixels box and uncheck the 2x2 box. Then open the raw file and zoom to 1000% at the right edge of the image to show the masked pixels as shown here. The masked pixels are the 14 darker columns on the right.
(https://bjanes.smugmug.com/Photography/Black-Frame-Clippig/Black-Frame-Clipping/i-FgZxhXM/0/O/RN3.png)
You can select them by the numbers as shown.
(https://bjanes.smugmug.com/Photography/Black-Frame-Clippig/Black-Frame-Clipping/i-pB9gCHq/0/O/RN2.png)
You can then read the standard deviations showing the read noise, which is about 1.5 ADU for the green channels.
(https://bjanes.smugmug.com/Photography/Black-Frame-Clippig/Black-Frame-Clipping/i-hbFcgTC/0/O/RN1.png)
Hope this helps.
Bill
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Hi Bill,
Eliminates was the wrong word, reduces would be better. The idea was mostly that shooting a low contrast target and underexpose would show up possible differences in rendition.
Regarding the flare factor, if we have a bright part of the image, the size of that bright part plays a big role.
Shooting a Stouffer wedge gives good analytic info, but it is not very easy to shoot it well.
I have also noticed that real photographers often don't like things like numbers, graphs, things measurable, facts and so on. The best way to illustrate anything seems to be an 800x600 JPEG…
Best regards
Erik
Ps. Sorry for the rant…
Erik,
The underexposed bookshelf method is a good method and easy to perform, and it allows to visualize the noise qualitatively. However, at times quantitive measurements are desired and the wedge with Imatest can do this.
However, does the underexposure eliminate the effect of flare? If the veiling glare of a lens is 0.5% (see Norman Koren (http://www.imatest.com/docs/veilingglare/)), the shadows are contaminated by 0.5% of the highlights regardless of exposure. When you bring up the shadows in the raw converter, the effect of the veiling glare is also magnified to the same extent as would occur with an exposure at a higher luminance. I'm not sure that this is the case, and what do you think?
Regards,
Bill
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Dave,
A better way to determine the read noise on Nikons is to use the optical black area of the raw file as Bill Claff (http://www.photonstophotos.net/GeneralTopics/Sensors_&_Raw/Sensor_Analysis_Primer/Read_Noise_-_Optical_Black.htm) describes.
Since you use Rawdigger, you can use it to gain access to the optical black area. In preferences check the masked pixels box and uncheck the 2x2 box. Then open the raw file and zoom to 1000% at the right edge of the image to show the masked pixels as shown here. The masked pixels are the 14 darker columns on the right.
Bill many thanks for the reference and the advice on how to use RawDigger with the masked pixels. This is all most interesting.
I didn't realise that there must be a small "bias" voltage on the raw analogue values from the sensels and that these are zeroed out for the main data. Presumably these reference black pixels are used for the purpose of this zeroing.
I had a look at the method using these reference black pixels and it gave good correlation with the SD's I calculated for the images posted above. However this method should be more accurate and it is easy to use because you can just read the SD values directly from RawDigger.
There is always something new to learn in this game, but that's what makes it fun!
Dave
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Measurebation
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Measurebation
Hi,
So, that's your way of saying that you are not interested in finding out which shooting scenarios to use and which to avoid for a given task/assignment? You do not want to master the tools you use?
If so, then why read this thread?
Cheers,
Bart
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Hi,
So, that's your way of saying that you are not interested in finding out which shooting scenarios to use and which to avoid for a given task/assignment? You do not want to master the tools you use?
If so, then why read this thread?
Cheers,
Bart
I don't use these tools (er toys), I use an IQ180.
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Measurebation
I don't use these tools I use an IQ180.
That's nice. Your camera has 6 stops more DR than the Nikon D810--at least that is what the proponents of MFDB who don't believe in measuring have told us. :)
Bill
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Measurebation
I don't use these tools (er toys), I use an IQ180.
Crowing about one's IQ180 seems like a way of measuring one's self up. I found the discussion of dynamic range more useful.