Posts: bclaff | Ugly Hedgehog

larryepage wrote:

...I'm still a little confused that the D500 shows up better than the D850 in crop format. Even though my experience has shown that images from the two cameras are pretty much indistinguishable in real life, I still would expect the D850 to come out at least a little bit ahead in a test environment given equal size sensors...

Your experience is consistent with the test results; ~1/3 stop difference would not normally be noticeable.

(Main Photography Discussion)

Why does cropping reduce dynamic range?

bleirer wrote:

That makes sense, so as Ysarex said, if one just took a crop out of a full frame sensor image without resizing there would be no impact?

Of course there would, whether you crop in camera or later the effect is the same, you still have to enlarge more to make the same image size.

(Main Photography Discussion)

Why does cropping reduce dynamic range?

bleirer wrote:

...
So why does cropping alone reduce dynamic range?

Photographic Dynamic Range (PDR) is normalized to a standard image size and viewing conditions.
The DX (APS-C) capture must be enlarge more than the FX (FF) one.
For some details see DX Crop Mode Photographic Dynamic Range

(Main Photography Discussion)

Sensors and dynamic range

PHRubin wrote:

As an ex Senior Staff Engineer (E.E.) I can say that 14 bits is the range of the A/D only. But in a camera there is much more that can limit the dynamic range of the system.

You may find the article Quantization Error in Practice interesting (heavy math).
You can get at least 1/2 stops more dynamic range out of an ADC that one might think; perhaps up to 0.8 stops.
So a 14-bit ADC can capture at least 14.5 stops and perhaps 14.8 stops of dynamic range.
There are cameras that push this boundary. One example is the Nikon D7200 with an EDR of 14.1

(Main Photography Discussion)

Sensors and dynamic range

Wallen wrote:

Do analogies need quantum details?
...

My point is that the discrete steps implies an integer value for the noise floor and leads to the incorrect assumption that, for example, a 14-bit ADC means 14 stops of dynamic range.

(Main Photography Discussion)

Sensors and dynamic range

Wallen wrote:

... The height of the stairs and the number of steps is a perfect explanation of the relationship between bit depth and dynamic range. How someone could see past that, I could not comprehend.
...

The imperfection in that analogy is that it implies that the values are solely integers (number of steps).
But in the real dynamic range situation you would need a fractional number of steps (for example 2.3) to represent the noise floor (read noise).
A crude example would be 16000 steps and 2.3 "steps" noise floor or log2(16000/2.3) = 12.8 EV dynamic range

(Main Photography Discussion)

Sensors and dynamic range

TriX wrote:

... I share your preference for the methodology of PhotonstoPhotos...

Thanks for that.
You realize I'm a bit biased in that regard; right?

(Main Photography Discussion)

Sensors and dynamic range

hjkarten wrote:

Hi TriX,
...

Aha! 1 EV = 1 bit!? = 6.02 dB
My search for that conversion drew a blank this morning.
If so, would that also mean that the Dynamic Range of the system can be directly expressed in bits. End of argument.
...
Harvey

So long as you are willing to use fractional bit values rather than whole numbers in which case you just saying EV another way (13.5 EV = 13.5 bits). It still is *not* the bit-depth of the ADC that establishes dynamic range only the upper limit.

(Main Photography Discussion)

Sensors and dynamic range

TriX wrote:

Yep, 1 EV = 1 bit = 6.02 dB. Question: why, for very low illuminance of the sensor, do you feel that shot noise doesn't contribute to the noise floor?

The noise floor is generally taken as read noise.
Read noise is noise that is present when there is no light.
If there is no light then there is no photon (shot) noise.
So the determination of EDR, pixel level dynamic range, has absolutely nothing to do with shot noise.

DxOMark print dynamic range is simply EDR that is normalized so it also has nothing to do with shot noise (which is one reason it's not that good a measure).

PhotonsToPhotos Photographic Dynamic Range (PDR) does take all forms of noise including shot noise into consideration. The low value in PDR is determined using a Signal to Noise Ratio (SNR) that takes (standard) final image size and viewing distance into consideration.

(Main Photography Discussion)

Sensors and dynamic range

hjkarten wrote:

... (WHEW! That was a long sentence.)
I would have no problem using dB, but habit might prompt me to think of dB in terms of shot noise at the low end and overflow at the high end, ... I can't do that calculation using EV values, and I would have to undergo all sorts of contortions to do that using dB. (I am not smart enough to even know how it can be done?)...

You may not know how to do it but dB and EV are entirely interchangeable; just like feet and meters.
For a rough estimate just divide dB by 6 to get EV.

Dynamic range is simply saturation for the high value and, in the case of a pixel, read noise for the low value.
It's not any more complicated than that (and has nothing to do with photon (shot) noise).

You can take this ratio of high / low and convert it to dB or EV.
Personally I think EV makes more sense in the context of photography.

This is dynamic range at the sensor data was represented by raw (linear) data.
It doesn't map easily to dynamic range in the (perceptual not linear) final output.

(Main Photography Discussion)

Sensors and dynamic range

hjkarten wrote:

I fully agree with you about the fallacy of believ... (show quote)

You are getting closer.
There is no conflating of dynamic range (EV) and bit-depth.
Bit-depth sets an upper limit on dynamic range. Dynamic range is *never* expressed as bit-depth.
FWIW, there are many sensor specification sheets PDFs available and you'll never see dynamic range listed as bit-depth, usually as dB.
You may be making an assumption that the chip manufacturer sets bit-depth to match required dynamic range.
That is not true. There are many 16-bit sensors that are well under 16 stops of dynamic range.
And I know of several 12-bit sensors that would have higher dynamic range if they had 14-bit ADCs.

Regards

(Main Photography Discussion)

Sensors and dynamic range

hjkarten wrote:

Hi Bill, (bclaff)
You're really pretty funny!
Would you be willing to entertain the remote possibility that you are incorrect? Under such circumstances, my first assumption is usually that I am wrong. I then spend as much time as necessary to read about the issue in question.
Regards,
Harvey

FWIW here's a well know article written by a world renounced string theorist:
Noise, Dynamic Range and Bit Depth in Digital SLRs by Emil Martinec

(Main Photography Discussion)

Sensors and dynamic range

hjkarten wrote:

Hi Bill, (bclaff)
You're really pretty funny!
Would you be willing to entertain the remote possibility that you are incorrect? Under such circumstances, my first assumption is usually that I am wrong. I then spend as much time as necessary to read about the issue in question.
Regards,
Harvey

This might be a cautionary tale for your experts.
Mastering one discipline doesn't necessarily make one qualified in another, even if it seems related.

Think about this.

Imagine that you put a 16-bit Analog to Digital Converter (ADC) in place of the 14-bit one on an existing sensor.

Would you magically get 2 stops more dynamic range? No !

You would simply have 2 extra bits of random information at the low end of each value.

Really, if it were that easy we'd have sensors with 16-bit, 20-bit ADCs, etc.

(Main Photography Discussion)

Sensors and dynamic range

hjkarten wrote:

As a followup to the discussion of the other day, ... (show quote)

Well, despite the credentials, that is really sad and wrong.

(Main Photography Discussion)

Sensors and dynamic range

hjkarten wrote:

... But then why did the author speak of "...more bits to describe a WIDER DYNAMIC RANGE..." The author introduces an ambiguity to the definition of dynamic range. ...

Perhaps the author was trying to say that bit-depth places an upper limit on dynamic range so you (may) need more bits to capture the higher dynamic range.