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Author Topic: 16-bit DSLR  (Read 62858 times)
Jonathan Wienke
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« Reply #20 on: November 30, 2007, 12:10:49 AM »
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Perhaps it would be helpful to distinguish between linearly-encoded sensor image data (which does have a fairly fixed relationship between bit depth and maximum encodable DR) and other image encoding schemes with non-linear tone curves (HDR, ProPhoto, sRGB, etc), where the DR limit is flexible and limited only by the number of levels one wishes to devote per stop. Such encoding schemes do not have a fixed limit to the DR they can contain.
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digitaldog
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« Reply #21 on: November 30, 2007, 08:47:54 AM »
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Why would someone argue with this?
[a href=\"index.php?act=findpost&pid=157105\"][{POST_SNAPBACK}][/a]

See, what did I tell you? <G>
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Andrew Rodney
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« Reply #22 on: November 30, 2007, 08:50:16 AM »
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With the high Canadian dollar, this a consumer grade monitor (only US$45,000); however, only 1080pix high sucks, so I rather stick to the Samsung 24" 244T, contrast ratio 1000:1 (claimed).
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Well considering that IF your goal is imaging to print, and the best you'll get (again up to debate) is maybe 350:1 contrast ratio on paper, what's the big deal about a 1000:1 contrast ratio? You watching movies? Well displays designed for that use produce serious issues for those of us working with still imagery. The contrast ratio is about the least useful spec for displays I can think of. And the ambient light where the display resides makes a pretty huge difference. Keep the room dim, you don't need a huge range here.
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Andrew Rodney
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bjanes
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« Reply #23 on: November 30, 2007, 09:33:14 AM »
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There is an uncountable number of intensities within any given stop, which are not distinguishable from each other. The "stop" is only a point on that scale.

For example a monitor's dynamic range will not be measured in stops but in the ratio of intensity between the brightest and darkest levels. The contrast ratio of 1000:1 does not imply any number of required levels.
[a href=\"index.php?act=findpost&pid=157163\"][{POST_SNAPBACK}][/a]

With linear integer encoding and a limited bit depth, there are a finite number of intensities within any given f/stop, and your statement of an infinite number is incorrect.

The DR limitations we have been discussing for digital sensors are for linear capture, gamma = 1. The monitor space may have a gamma of 2.2 and coding is more efficient in the shadows. Still a certain number of bits are needed for that 1000:1 ratio, and 8 bits may not be sufficient. A contrast ration of 1000:1 is 3 orders of magnitude (log base 10). It could also be expressed in f/stops (log base 2), and 1000:1 is 9.97 f/stops.

Bill
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sojournerphoto
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« Reply #24 on: November 30, 2007, 11:47:34 AM »
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Data are starting to dribble out on the performance of the new Canon and Nikon sensors with 14 bit ADCs.

Emil Martinec, professor of physics at the University of Chicago, has published data for the Nikon D300 and Canon 40D. He uses the engineering definition of DR (dynamic range = raw saturation level divided by read noise). At base ISO both cameras have a DR of about 11.3 stops, and gain about 1/3 of a stop when going from 12 bit to 14 bit mode. It would appear that 12 bits would be sufficient for these cameras.

EJ Martin, also at the U of C, reported results for the Nikon D3. He found a DR of 11.7 f/stops. Since the D3 pixel size is considerably larger than that of the D300 or 40D, one would expect a better DR with the D3 if read noise is held to the same level, since DR = full well capacity/read noise.

These gains in DR are rather modest when compared with Roger Clark's prediction of a 2 stop gain for a properly implemented 14 bit camera as compared to 12 bits.
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I read some of Roger Clark's site the other day and I don't think he was claiming that moving from a 12 bit ADC to a 14 bit ADC would give 2 extra stops of dynamic range. He did suggest that the lower read noise possible with a 14bit (or 16 bit) device could benefit some current camera's, e.g. canon 5D and presumably Nikon D3 etc, giving a higher achievable dynamic range, but not a full 2 stops higher. Part of the issue is that the DR is limited by full well capcity and the noise floor, which the ADC contributes to. hence a 'quieter ADC' should improve the lowest readable levels.
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Guillermo Luijk
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« Reply #25 on: November 30, 2007, 01:10:56 PM »
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(...) He uses the engineering definition of DR (dynamic range = raw saturation level divided by read noise). At base ISO both cameras have a DR of about 11.3 stops, and gain about 1/3 of a stop when going from 12 bit to 14 bit mode. It would appear that 12 bits would be sufficient for these cameras.

Bill, it's nice to check in objective figures what one suspected.
Moreover, I would say that this DR figure in terms of Sat_Level/Read_Noise (11.7 f-stops) is too optimistic when compared to what it's usable in real photography.

I shot a high dynamic range scene with my Canon EOS 350D at ISO100 to make a subjective but valuable calculation of the DR:





The histogram shows the scene contained information along around 12 f-stops.

I developed it linear and plotted its distribution in f-stops:



Looking at the texture detail in each f-stop:



Beyond f-stop -7EV there is nothing but noise grain. We can conclude that 8 f-stops (0EV to -7EV) of usable dynamic range would be already quite optimistic for this camera. By repeating this test on the new 14-bit Mark III I don't think at all that bit depth will reveal as being determinant in defining the new achievable dynamic range; IMO still noise will set the low end of the DR and probably the influence of the 2 extra bits will be almost negligible for DR. Allowing 1 f-stop or 1.5 f-stops of improvement in noise for the new sensors (which is not a joke), we would estimate the final USABLE DR in around 9 or 9.5 f-stops, still recordable using a 12-bit linear A/D. The improvement would thus be thanks to noise optimisation, not to higher bit depth.


Panopeeper, bit depth doesn't guarantee achievable DR, but sets a physical limit to it if linear RAW encoding is used (and this is the case of most sensors, not Leica's M8 for instance). To have N bits of bit depth is not a sufficient condition, but a necessary condition to capture N f-stops of DR. And that assuming that the lower f-stops would be poorly represented, so actually you will need more than N bits for properly recording N f-stops of DR (remember we are talking about capture, not about image post process encoding).
A 12-bit RAW has the following levels for each f-stop:

    0EV: 2048 levels, 2048..4095
   -1EV: 1024 levels, 1024..2047
   -2EV: 512 levels, 512..1023
   -3EV: 256 levels, 256..511
   -4EV: 128 levels, 128..255
   -5EV: 64 levels, 64..127
   -6EV: 32 levels, 32..63
   -7EV: 16 levels, 16..31
  -8EV: 8 levels, 8..15
   -9EV: 4 levels, 4..7
   -10EV: 2 levels, 2..3
   -11EV: 1 level, 1


As you can see, the lowest f-stops have a strong lack of tonal variety. There is a direct link between a maximum achievable DR and the minimum number of bits required for it.
« Last Edit: November 30, 2007, 01:38:39 PM by GLuijk » Logged

bjanes
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« Reply #26 on: November 30, 2007, 05:03:37 PM »
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Bill, it's nice to check in objective figures what one suspected.
Moreover, I would say that this DR figure in terms of Sat_Level/Read_Noise (11.7 f-stops) is too optimistic when compared to what it's usable in real photography.

As you can see, the lowest f-stops have a strong lack of tonal variety. There is a direct link between a maximum achievable DR and the minimum number of bits required for it.
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Guillermo,

I used different methodology in [a href=\"http://luminous-landscape.com/forum/index.php?showtopic=21300&view=findpost&p=157253]another thread[/url] but arrived at similar conclusions. The engineering definition of DR is not that useful for routine photography and over estimates practical DR.

Bill
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DiaAzul
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« Reply #27 on: November 30, 2007, 05:22:55 PM »
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What does it take to make 16-bit DSLRs?  How much more would it cost?  What are the restrictions if any?

Most people do not need to go beyond 10/12 Mp captures but they do need/want better renditions of tones and gradations.  I think I would love to have a 16-bit Nikon D3xx.  I'm not technically familiar as to what needs to go into the making of such a camera.  Anyone better equipped can share their knowledge?
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Going back to your original question (not whether it is worth doing or not). You need a 16-bit analogue to digital converter. There are multiple design issues that make increasing the number of bits difficult and expensive. From memory these tend to be:

1/ Number of conversions that can be achieved per second - each time a new pixel is read from the array then it takes time for the signal to settle at the input to the Analogue to Digital Converter. This limits either the maximum number of pixels in the sensor array, the maximum number of frames per second or requires more ADCs in parallel which pushes up cost.

2/ The ADC needs a stable reference voltage or current against which to compare the incoming signal so that you produce the same digital output for the same analogue input. The more bits in the conversion the greater accuracy you need for the reference. NB this is a battery driven device, the reference needs to be constant irrespective of the actual battery voltage.

3/ Noise in the system becomes a limiting factor (even if there was a noise free source/sensor driving the ADC) there is still noise generated by the reference and also within the circuitry of the ADC itself. Eliminating this noise becomes harder the more bits of precision and the faster the conversion rate.

As with most things there already exist 16-bit plus ADCs and ADCs operating at higher frequencies. The problem is getting the combination of bits resolution, performance and acceptable price all at the same time.

[From a personal perspective I would welcome additional bit depth to provide greater colour accuracy in the darker parts of the image. For some of my images it is noticeable that there is a lack of colour information following post processing.]
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David Plummer    http://photo.tanzo.org/
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« Reply #28 on: November 30, 2007, 07:04:11 PM »
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With linear integer encoding and a limited bit depth, there are a finite number of intensities within any given f/stop, and your statement of an infinite number is incorrect

1. The concept of dynamic range has nothing to do with encoding.

2. As long as the individual photons can not be reliably counted, lightness remains an analog phenomenon for our purpose. As such, there is no fixed number of levels, there is no fixed spacing, there are no fixed locations of the levels.

3. Dynamic range is an arbitrary measurement of relative intensities. Even if one uses this measurement, it does not pose any requirements regarding the spacing and location of levels.

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The DR limitations we have been discussing for digital sensors are for linear capture, gamma = 1

The starting point was Bernard's

I am not saying that you can cover a 50 stops DR with 8 bits for practical applications

This did not relate to sensors, etc. but to DR per se.

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Still a certain number of bits are needed for that 1000:1 ratio, and 8 bits may not be sufficient

Not sufficient for what? For preventing posterisation? What about applications, which don't use continuous colors, like drawings, artificial coloring, like in astrophysics, etc?
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Gabor
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« Reply #29 on: November 30, 2007, 07:19:37 PM »
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bit depth doesn't guarantee achievable DR, but sets a physical limit to it if linear RAW encoding is used (and this is the case of most sensors, not Leica's M8 for instance). To have N bits of bit depth is not a sufficient condition, but a necessary condition to capture N f-stops of DR

You too are mixing up the concept of dynamic range with its measurement.

The meaning of "DR of ten stops" is, that the highest intensity is 1024 times higher than the lowest measurable intensity. It means nothing else. The unit of "f-stop' is not godgiven, it is arbitrary. You could measure it in decibel, or in 5%, or you could make uo your own measurement.

There is no basis to regard the measurement in stops as a basic characteristic of DR. What you are doing is something like

I measure the length in metri units, therefor the length of everything has to be expressable in meters or centimeters

However, if I measured the length in imperial unites, everything looks differently.
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Gabor
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« Reply #30 on: November 30, 2007, 08:09:07 PM »
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1. The concept of dynamic range has nothing to do with encoding.
You too are mixing up the concept of dynamic range with its measurement.

The meaning of "DR of ten stops" is, that the highest intensity is 1024 times higher than the lowest measurable intensity. It means nothing else. The unit of "f-stop' is not godgiven, it is arbitrary. You could measure it in decibel, or in 5%, or you could make uo your own measurement.

There is no basis to regard the measurement in stops as a basic characteristic of DR. What you are doing is something like

I measure the length in metri units, therefor the length of everything has to be expressable in meters or centimeters

However, if I measured the length in imperial unites, everything looks differently.
[a href=\"index.php?act=findpost&pid=157380\"][{POST_SNAPBACK}][/a]

I have to say, Panopeeper makes total sense to me. It seems again that those who keep going back to some specific articles that link dynamic range and bit depth are making the wrong assumption based on encoding. I'll keep an open mind but so far, everything seems to point to my original beliefs about the two being separate, and Panopeeper expresses why this is so. Dynamic range and bit depth are two separate spec's.
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Andrew Rodney
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John Sheehy
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« Reply #31 on: November 30, 2007, 08:17:11 PM »
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I have to say, Panopeeper makes total sense to me. It seems again that those who keep going back to some specific articles that link dynamic range and bit depth are making the wrong assumption based on encoding. I'll keep an open mind but so far, everything seems to point to my original beliefs about the two being separate, and Panopeeper expresses why this is so. Dynamic range and bit depth are two separate spec's.
[a href=\"index.php?act=findpost&pid=157389\"][{POST_SNAPBACK}][/a]

They are only separated by analog noise.  In the absence of analog noise, bit depth would strictly define possible DR.  16 linear bits would have *exactly* 4x the dynamic range of 14 linear bits, etc, regardless of what the standard was for minimum usable signal, as long as the standard was consistent.
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Henry Goh
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« Reply #32 on: November 30, 2007, 08:50:12 PM »
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Going back to your original question (not whether it is worth doing or not). You need a 16-bit analogue to digital converter. There are multiple design issues that make increasing the number of bits difficult and expensive. From memory these tend to be:

Thank you.  That looks like the technical limitations I was seeking to learn.
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Ray
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« Reply #33 on: November 30, 2007, 09:09:58 PM »
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They are only separated by analog noise.  In the absence of analog noise, bit depth would strictly define possible DR.  16 linear bits would have *exactly* 4x the dynamic range of 14 linear bits, etc, regardless of what the standard was for minimum usable signal, as long as the standard was consistent.
[a href=\"index.php?act=findpost&pid=157390\"][{POST_SNAPBACK}][/a]


I'm having trouble conceptualising the difference between these factors associated with DR. I can't think of anything clearer than the staircase analogy.

DR can be represented by the total height of a staircase. The higher the staircase, the greater the dynamic range.

However, the number of steps in that staircase will be determined by bit depth. 16 bit linear equates to a huge number of tiny steps. 8 bit linear equates to a relatively small number of very large steps. The height of the staircase (the dynamic range) can be the same in both cases and will be determined by sensor full-well capacity minus signal-obscuring noise. The ground is the noise and the first step in the staircase is the darkest, usable signal value above the noise floor.

Any flaws in that analogy?
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wildlightphoto
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« Reply #34 on: November 30, 2007, 09:46:31 PM »
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The Leica DMR back for the R8 and R9 is a 16 bit camera.  It has excellent dynamic range and gradation and can retain much more shadow detail than a 12- or 14-bit camera.  Those who have used both the DMR and 5D (for example) in RAW mode overwhelmingly prefer the DMR's image quality.
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Panopeeper
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« Reply #35 on: November 30, 2007, 09:59:21 PM »
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In the absence of analog noise, bit depth would strictly define possible DR.  16 linear bits would have *exactly* 4x the dynamic range of 14 linear bits, etc

With linear encoding, the proportions between bit depths reflect the proportions between the dynamic ranges, like in the above example. However, this does not define the magnitude of the DR; that depends on the scale.
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Gabor
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« Reply #36 on: November 30, 2007, 10:10:44 PM »
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With linear encoding, the proportions between bit depths reflect the proportions between the dynamic ranges, like in the above example. However, this does not define the magnitude of the DR; that depends on the scale.
[a href=\"index.php?act=findpost&pid=157402\"][{POST_SNAPBACK}][/a]

DR is a relative metric, not an absolute.  Scale is totally irrelevant to DR.
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Ray
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« Reply #37 on: November 30, 2007, 11:43:01 PM »
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DR is a relative metric, not an absolute.  Scale is totally irrelevant to DR.
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I don't see how this can be true. The smallest possible step in a dynamic range is limited by the effect of a single photon. If photodetectors on sensors could actually count photons, which I believe they can't, but lets assume that they can without any interference from noise of any description, then the dynamic range is determined by the maximum number of photons that a sensor can 'process' during any exposure.

This maximum is determined by the size of the sensor, all else being equal, or if you like, the size of individual photodetectors, all else being equal.

In this sense, size or scale is very relevant to DR.

In practice, you have to either subtract or cancel all sources of noise from this maximum signal capacity of the sensor in order to determine a useful DR.

If DR is not 'scale' dependent as you suggest then you could claim, if it were possible to design a completely noise free tiny sensor containing say 100 photodiodes just 1 micron in diameter, that such a tiny sensor could have the same dynamic range as, say a 5D or P45+.

This would be clearly ridiculous. Reductio absurdum!
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Panopeeper
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« Reply #38 on: November 30, 2007, 11:53:21 PM »
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DR is a relative metric, not an absolute

That's right. However, the numerical representation does not have to follow that one-to-one.

Example: if the DR is only one stop and the values are stored in 256 levels, then the highest value is 256 times as high as the lowest value - but that represents only twice the lightness.

Likewise, the numerical values from 0 to 7 can represent leves of a dynamic range of 1000:1.
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Gabor
Ray
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« Reply #39 on: November 30, 2007, 11:56:44 PM »
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That's right. However, the numerical representation does not have to follow that one-to-one.

Example: if the DR is only one stop and the values are stored in 256 levels, then the highest value is 256 times as high as the lowest value - but that represents only twice the lightness.

Likewise, the numerical values from 0 to 7 can represent leves of a dynamic range of 1000:1.
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Exactly! So you agree with my staircase analogy, Panopeeper?
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