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Author Topic: 16-bit DSLR  (Read 61484 times)
EricV
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« Reply #80 on: December 06, 2007, 11:22:54 AM »
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Do you mind pointing out, where I posted 0 = 0 and 1 = 5 and 2 = 505? Or did you fail reading comprehension?
Panopeeper, this is getting ridiculous.  One last post and then I at least am done with this.

Let's go back to the basics.  Several of us claimed that a noiseless camera with a linear encoding scheme necessarily has dynamic range equal to the number of encoded values.  Going back to the ladder analogy, the height of the ladder divided by the step size is equal to the number of rungs.  (Is this a clear enough mathematical proof?)  We neglected to specify that the first rung of the ladder must be placed one step size above ground level.

You concocted a scheme which gets around this simple claim, by defining dynamic range as the height of the ladder divided by the height of the lowest rung above ground, then chopping off the bottom of the ladder so that the first rung is very close to the ground.  I will grudgingly admit that this ladder could still be called linear and that with this contorted definition of dynamic range, you have found a way around the proof.

Will you in turn admit that this extension of dynamic range is just a game to win an argument and has no practical application in photography?  The more you extend dynamic range this way, the fewer pixels get to participate in the extended dynamic range.  Your camere with infinite dynamic range and my camera with limited dynamic range take indistinguishable pictures.
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Jonathan Wienke
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« Reply #81 on: December 10, 2007, 01:57:52 PM »
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Do you mind pointing out, where I posted 0 = 0 and 1 = 5 and 2 = 505? Or did you fail reading comprehension?

Does this sound familiar?

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These are independent issues. I can start counting the photons with 10, then 510, 1010, 1510, etc. Then the dynamic range is 60000/10.

But I can start counting with photon 1, then 501, 1001, etc.

First increment of photon counter happens at 10, second at 510, or first counter increment at 1, second at 501, third at 1001, sounds pretty non-linear to me. "Linear" requires a reasonably fixed ratio between photons and ADU output values, which is not what you are describing in your December 4 quote. Clipping the black point (which is the net result of the process you describe) does not increase DR, it merely disguises noise by clipping it to black or near-black. The reduction of apparent noise is accompanied by a similar level of shadow detail loss.
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Panopeeper
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« Reply #82 on: December 10, 2007, 08:08:21 PM »
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First increment of photon counter happens at 10, second at 510, or first counter increment at 1, second at 501, third at 1001, sounds pretty non-linear to me

The increase is constant. That makes it linear, if the original values are linear.

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"Linear" requires a reasonably fixed ratio between photons and ADU output values

There are no photons and no ADU at the stage we are talking about (i.e. numerical representation). There are some measured, linear values, no matter how they have been arrived at. Now the question is, how they can be recorded.

I nowhere suggested to measure the light intensity differently from how it is measured now; "counting the photons" is only symbolic, as there is no such thing on the sensor, AFAIK. I am suggesting, that given a set of measured values, they can be recorded different ways, by varying the correlation between the measured and recorded values. (Note, that this correlation is not only not god-given, it is not fix even with the same camera.)

Furthermore, "0 = 0" is not correct. The measured/recorded value 0 represents all values under some limit. Likewise, 16383 (or whatever the clipping point is) represents all values above that as well. Therefor linearity does not include the two extreme values. In fact, non-linearity can include a range of values. This is the nature of the data, it has nothing to do with the numerical representation.

(Guillermo posted a raw file from the Nikon D3. I found, that the non-linearity of the green values streches from 15750 to 16060, while all red and all blue pixels clip "at once",  though red and blue not together.)
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Gabor
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