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 Author Topic: dynamic range  (Read 44186 times)
Mike W
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 « on: September 29, 2007, 07:59:14 AM » Reply

I'm sure this topic has passed many times.
So this topic is redundant, but it will only be short-lived :-)

Here goes:

Most current digital backs have a dynamic range of 12 f-stops.

Current DSLRs promote a 14bit-A/D conversion, MFDB are in the 16bit range.
My understanding is that this bit-talk referes to color depth, so my question is:

How many f-stops can a DSLR handle? And why are they more limited than MFDB's?

Authors note: This topic is in no way a do-I-really-need-a-25k-digital-back-when-I-can-buy-a-5k-canikon? So please, don't go where I didn't :-)

thanks

Mike
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digitaldog
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Dynamic range and bit depth are two different spec's. Higher bit depth doesn't equate higher dynamic range.

Dynamic range is the range from highlighted to shadow. Bit depth is the number of steps. Think of dynamic range as a staircase of a fixed height and bit depth as the number of steps in that staircase.
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Andrew Rodney
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thsinar
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or in other words, "bit depth" describes the number of grey shades = tonal values (steps) available/possible for each colour channel. Therefore, for a given dynamic range (exposure latitude) you can have more or less tonal values (grey shades) going from white to black, depending on the bit depth of the digital device (256 for 8 bit; 1024 for 10 bit; 4096 for 12 bit; 16384 for 14 bit; 65536 for 16 bit).

Thierry

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Dynamic range and bit depth are two different spec's. Higher bit depth doesn't equate higher dynamic range.

Dynamic range is the range from highlighted to shadow. Bit depth is the number of steps. Think of dynamic range as a staircase of a fixed height and bit depth as the number of steps in that staircase.
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Thierry Hagenauer
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Mike W
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Ok, everything so far seems to be as I expected. So long story short -> what kind of dynamic range (expressed in f-stops) can you get out of a dslr?

I'm curious about this since all (or most) MFDB brands state 12 f-stop dynamic range in their product descriptions, but dslr-brands don't.

regards

Mike
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alba63
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So long story short -> what kind of dynamic range (expressed in f-stops) can you get out of a dslr?

Hi, DSLRs range from 6,5 or 7 (like Nikon D2x) up to 8,5 - 9 for the better ones (Canon 1ds II and a bit less for Canon 5d), an exception are the Fuji S3 and S5 pro which have a dual pixel approach with one set of (smaller) extra pixels placed between the regular pixels only for the highlights.

I had the S3 and it works, it just comes at a price: RAW files are huge (double as large as normal) and slow down the camera while not holding that much of detail (actually little more than 6MP). But after getting my Canon 5d I was dissapointed to see again how easily highlights are brutally burned out.

I am also curious to know what the reasons are why MF backs can theoretically achieve higher DR. It cannot be pixel size alone, as the more recent backs with resoluton more than 30MP don't have larger photosites than certain DSLRs.

Has anyone actually really measured real life DR or the backs?

I think that DR is the future of DSLR progress. Pixel count will probably top out at 18-20 for 35mm sensors, but DR is far from ideal.

Bernie
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TechTalk
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Quote
I'm sure this topic has passed many times.
So this topic is redundant, but it will only be short-lived :-)

Here goes:

Most current digital backs have a dynamic range of 12 f-stops.

Current DSLRs promote a 14bit-A/D conversion, MFDB are in the 16bit range.
My understanding is that this bit-talk referes to color depth, so my question is:

How many f-stops can a DSLR handle? And why are they more limited than MFDB's?

Authors note: This topic is in no way a do-I-really-need-a-25k-digital-back-when-I-can-buy-a-5k-canikon? So please, don't go where I didn't :-)

thanks

Mike
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An interesting and somewhat complex set of questions. Your first question "How many f-stops can a DSLR handle?" is difficult to answer because dynamic range is a moving target on any digital sensor, camera or back. It changes based on a number of factors. It can be influenced by ambient temperature, cooling capability, exposure time and package electronics–among other factors.

For instance, for every 6.3°C increase in sensor temperature of the Kodak 39mp sensor the dark current noise will double and decrease dynamic range by about one stop.

The measure for dynamic range is not the bit-depth of the A/D converter. The A/D converter can not replace dynamic range that the analog sensor (CCD or CMOS) is unable to capture. Knowing the bit-depth of the A/D converter does not tell you the dynamic range of the capture device.

Also, the specification given by manufacturers of "f-stops of dynamic range" is not standardized. It is based on the maker's standard for a given set of conditions.

The measure of dynamic range is signal-to-noise ratio at a specific temperature. As mentioned above, increases or decreases in sensor temperature have a dramatic effect on dynamic range (signal/noise ratio). So, depending on a host of variables, the dynamic range varies.
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jsch
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Best,
Johannes
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etrump
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I recently switched from a Canon 5D (excellent camera) to a P30+ on a Mamiya 645AFDII.

I was not sure if the DR claims were real or just hype.  According to the specs the DB should have 2-3 stops more dynamic range than the 5D.

After using the back for a few months I am still amazed at the increase in dynamic range.  I have found both shadow and highlights to have more accurate detail.  For example, if I have shadow areas on the 5D that need to be lightened you will see noticeable noise.  With the P30+ there is  less noise and more detail in those shadows.

Imagine you are shooting landscapes where you would normally use a 2 stop ND grad filter or take two exposures and layer them.  With 2-3 stops extra range, simply forget about it and shoot.

Combine the DR with no AA filter, better optics, higher resolution and greater bit depth and the difference can be dramatic even for 16x20 prints.

8 bit jpeg: 256 levels
12 bit raw: 4096
14 bit raw: 16384
16 bit raw: 65536

I also switched from a Canon 1DmkII at 12 bits to the 1DmkIII at 14 bits.  The difference with just a 2 bit increase (4X) makes substantial improvements in image quality.  Multiply that difference by 16 when comparing 12 bit to 16 bit images.  More levels means cleaner grads and more realistic detail.  Makes the announced Canon 1Ds MK III look very interesting and will split the advantages of high end DB image quality.
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bjanes
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Quote
Dynamic range and bit depth are two different spec's. Higher bit depth doesn't equate higher dynamic range.

Dynamic range is the range from highlighted to shadow. Bit depth is the number of steps. Think of dynamic range as a staircase of a fixed height and bit depth as the number of steps in that staircase.
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That analogy (which comes from Bruce Fraser's writings, and perhaps from other sources) is often quoted, but I don't think that it is entirely true when referring to modern digital cameras. This is discussed in this [a href=\"http://luminous-landscape.com/forum/index.php?showtopic=19935]Link[/url]. Higher bit depth does not guarantee increased dynamic range, but is necessary for it. With linear encoding 12 bits can encode 12 f/stops and 14 bit encoding can give two additional stops. The extra two bits can decrease quantization noise.

Bill
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digitaldog
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That analogy (which comes from Bruce Fraser's writings, and perhaps from other sources) is often quoted...

I think I'll take credit for that analogy if I can. I dug up a slide of a presentation I did back in January 1999 (note how crude it is visually <g>). I have Bruce's Real World Photoshop 3 (1996) signed by him (the first of many books he signed for me), page 298 has a great paragraph on dynamic range and dMax, but nothing about stair cases. Even earlier in my old book collection is Real World Scanning and Halftone by David Blanter and Steve Roth (that goes back to 1993!). Page 107 also has a very good discussion of this topic and they point out, as they should that "not all 8-bit and 24 bit scanners can capture the same amount of information", and discuss the fudge factors in measuring dynamic range due to noise issues (where to begin?).
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Andrew Rodney
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DiaAzul
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I think I'll take credit for that analogy if I can.
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Possibly in the context of photography, but in the general context of electronics and analogue to digital conversion it has been around for a long time.
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David Plummer    http://photo.tanzo.org/
Gary Ferguson
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I use a digital back alongside a DSLR, I'm sceptical about the claims for significantly greater latitude from digital backs. Maybe a half or two-thirds of a stop, but I've never seen the evidence for much beyond that.

I may be wrong here, but I seem to recall that Phase One base their 12 stop claim on the latitude up to the blooming point (ie where light spills over into adjacent pixels), if so then it isn't latitude as I or most photographers would understand it, and it may explain why I don't see the roughly four stop advantage over DSLR's that their claim implies.
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digitaldog
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Possibly in the context of photography....
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I'll take anything I can get <g>
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Andrew Rodney
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John Sheehy
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I also switched from a Canon 1DmkII at 12 bits to the 1DmkIII at 14 bits.  The difference with just a 2 bit increase (4X) makes substantial improvements in image quality.  Multiply that difference by 16 when comparing 12 bit to 16 bit images.  More levels means cleaner grads and more realistic detail.[a href=\"index.php?act=findpost&pid=143201\"][{POST_SNAPBACK}][/a]

More levels can not be appreciated unless the blackframe noise is below about 1.25 ADU.  Any time the noise is above 1.25 ADU, the number of levels used is excessive.  1Dmk3 ISO 100 RAWs do not suffer any loss of DR by dropping the 2 extra bits.  If you are getting better results from the mk3 at ISO 100, it is probably for some other reason than the two extra bits of noise, like a converter being forced to use two more bits of precision (which it could have done with 12 bit data), or different defaults used by the converter for the camera.  At higher ISOs, the mk3 has up to 1/2 stop more DR, but this does not require the 2 extra bits.
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Ray
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Dynamic range is the range from highlighted to shadow. Bit depth is the number of steps. Think of dynamic range as a staircase of a fixed height and bit depth as the number of steps in that staircase.
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This does not clarify the issue for me, Andrew. I can appreciate that bit depth could be analagous to the number of steps of fixed height, but dymanic range as it is usually expressed (in terms of number of f stops) is more like a staircase with each step being twice the height of the previous step.

If we could have a dynamic range consisting of steps of equal height we could increase DR dramatically. Those steps at the top are too steep to climb   .
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thsinar
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isn't it rather those steps at the bottom which are to narrow to step on?

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Those steps at the top are too steep to climb   .
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Thierry Hagenauer
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isn't it rather those steps at the bottom which are to narrow to step on?

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Or is it both at top and bottom that is critical? Whereas with lower bit depth top and bottom would render as white and black without distinguishable details, the larger bit depth allows detail to be rendered in these regions due to the more steps of the ladder there.

I am not sure, but... does this make us perceive it as greater DR, while it is actually not? Is this what has been a key difference between MFDBs and DSLRs?

How will as example files from a 1Ds Mk 3 compare to those from an equivalent MP MFDB?

Much thanks.

Regards
Anders
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bjanes
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More levels can not be appreciated unless the blackframe noise is below about 1.25 ADU.  Any time the noise is above 1.25 ADU, the number of levels used is excessive.  1Dmk3 ISO 100 RAWs do not suffer any loss of DR by dropping the 2 extra bits.  If you are getting better results from the mk3 at ISO 100, it is probably for some other reason than the two extra bits of noise, like a converter being forced to use two more bits of precision (which it could have done with 12 bit data), or different defaults used by the converter for the camera.  At higher ISOs, the mk3 has up to 1/2 stop more DR, but this does not require the 2 extra bits.
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John, do you have data on the 1DMIII or is this merely conjecture? From [a href=\"http://www.clarkvision.com/imagedetail/digital.sensor.performance.summary/]Roger Clark's[/url] analysis of the noise characteristics of the 1DMII, there is reason to believe that a 14 bit ADC would improve the DR of that camera at low ISO. The black frame noise at ISO 100 (this is for very short exposures and is not to be confused with thermal noise present with long exposures of many seconds or minutes) is strongly influenced by the ADC noise. The SNR of an ideal ADC is related to bit depth, as explained here. The SNR of an ideal ADC is 6.02N+1.76 decibels (db), where N is the bit depth of the device. For a 14 bit ADC the ideal SNR is 86 db and it is 74 db for a 12 bit ADC.

Look at Roger's figure 8a. At high ISO the bit depth of the ADC has little effect on noise, since read noise of the sensor predominates. However, at ISO 100 ADC noise predominates and a high quality ADC with more bit depth would reduce this noise. Of course other components in the imaging chain affect DR and merely sticking a 14 bit ADC in the chain may not improve performance.

Bill
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Bernd B.
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For me DR is the most important thing in the whole MFBD discussion. The abrupt way a DSLR (in my case 5D) goes from a defined area to a blown out area is the most disturbing and unaesthetic point in digital photography for my work. As long as a subject is in controlled light, there are little problems, but a reflex or a bit backlight might destroy the whole atmosphere of a photo. My three or four year old back behaves much better (film-like) here and is definitely worth the effort. If Canon and Nikon came along with sensors capturing the same DR I would probably drop the MF thing for a faster and more comfortable working.
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Tim Gray
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