Discussion of 'Equivalence'

[simsurace]

Oops, now you are advocating making a loss of information something you questioned strongly earlier The path to travel surely is narrow.

I was only questioning it as a means to invalidate certain definitions.
If your output medium has a different dynamic range, you must do something.
But this does not mean that a worse sensor gets better just because you are evaluating it using an imperfect output medium. The output medium will only level out differences.
If you choose better and better output media, the differences will start to reappear. But they cannot exceed what was originally captured.

[David H. Hartman]

All of this theoretical stuff is of no use to me if it doesn't help me make a pleasing image.

Dave

[JohnMM]

However, this is an approximation and an example of erroneous math covered in DX Crop Mode Photographic Dynamic Range

OK, an approximation - but good enough for its purpose, and of the sort used by the "gang" on the DPR boards.

[JohnMM]

On other boards we distinguish "dynamic range" by calling pixel dynamic range Engineering Dynamic Range (EDR) rather than Photographic Dynamic Range (PDR).If you are referring to PDR you are very wrong; PDR is not based on EDR.

But doesn't the use of PDR imply use of your limit for the smallest signal and your method of normalisation using CoC. Here, rather arbitrarily, I've used the read noise for the lower signal limit and used all the pixels for normalisation. How might that be described? Joseph James sometimes uses the read noise and what he calls micropictures - one millionth of the total number of pixels.

[simsurace]

But doesn't the use of PDR imply use of your limit for the smallest signal and your method of normalisation using CoC. Here, rather arbitrarily, I've used the read noise for the lower signal limit and used all the pixels for normalisation. How might that be described? Joseph James sometimes uses the read noise and what he calls micropictures - one millionth of the total number of pixels.

My understanding was that while they are not based on each other, they are both based on the photon transfer curve. The cutoff point for EDR is a SNR of 1, for PDR it is a number that is computed based on the CoC, resulting in PDR being normalized to a photographic print size.

The value of your little calculation was to show another definition of dynamic range that exhibits a similar normalization.
My mind is not entirely clear on what the approximation in your calculation is, besides neglecting noise correlations. Perhaps Bill Claff can clarify his comment.

[Jack Dahlgren]

My understanding was that while they are not based on each other, they are both based on the photon transfer curve. The cutoff point for EDR is a SNR of 1, for PDR it is a number that is computed based on the CoC, resulting in PDR being normalized to a photographic print size.

The value of your little calculation was to show another definition of dynamic range that exhibits a similar normalization.
My mind is not entirely clear on what the approximation in your calculation is, besides neglecting noise correlations. Perhaps Bill Claff can clarify his comment.

My definition of Photographic Dynamic Range is a low endpoint with an SNR of 20 when adjusted for the appropriate Circle Of Confusion (COC) for the sensor - Bill Claff

The normalization to COC means this is just a question of magnification. Since the print does not use the entire dynamic range anyway, this normalization makes little sense. Dynamic range is important during capture and editing, it is not as important at the print stage so normalization to a viewing format size is interesting, but not particularly useful. Calling it photographic dynamic range is a stretch of the concept.

[Anthony]

Yes, but not from the point of view of information.  If you can, eventually, read the sign that says that the 12:45 train to Hogwarts leaves from Platform 9.75, you don't know any more because reading it was easier or more pleasant, or less because it was slower or more difficult.

Information is not such a simple concept.  At the margins, with imperfect eyesight, perceived information can change.  A 5 can look like an S.  One blinks, and it looks like a 5.  Or maybe one is looking at a digital representation of an image.  It may be "readable" but lots of interesting information may be missing.  Readable/not readable is not binary.  Unless one decides that the best readability technically available is what is meant by "readable".

[David H. Hartman]

...Dynamic range is important during capture and editing, it is not as important at the print stage so normalization to a viewing format size is interesting, but not particularly useful. Calling it photographic dynamic range is a stretch of the concept.

The dynamic range of a print is limited by how much light that print can reflect and how little light that print can reflect. The base of the print can cheat a little by having optical brighteners added so it glows under some light like your T-shirt that's been washed in Tide.

Dave Hartman who prefers ALL "Free and Clear" to Tide. 

Photographically speaking all the dynamic range in the **cosmos is useless unless you know how to ***shoe horn it into your limited display medium.

**I thought "cosmos" sounded more important than world.

***"shoe horn" here means compress to represent.

[simsurace]

The normalization to COC means this is just a question of magnification. Since the print does not use the entire dynamic range anyway, this normalization makes little sense. Dynamic range is important during capture and editing, it is not as important at the print stage so normalization to a viewing format size is interesting, but not particularly useful. Calling it photographic dynamic range is a stretch of the concept.

I agree with your first sentence. But the rest are blanket statements.

Why do think that the print having a lower dynamic range makes the concept useless? Let me make an example:

Let's say that your desired output medium has a dynamic range of 10 stops, and you compare two cameras with equal sensor size and number of pixels, but different per-pixel DR, e.g. 10 stops and 14 stops respectively. Now you shoot a scene that has some details that you would like to display that are 11 stops darker than the brightest part of the image (which determines your exposure). With the 10 stop DR sensor, the details will be buried in the sensor noise, while they are 3 stops above the noise floor for the higher-DR sensor. On your 10 stop output medium, you will be able to see the details if you prepare your high-DR capture suitably (i.e. by lifting the shadows*). Using the same processing on the low-DR capture, you will still not see anything but noise. So the DR definition is useful even though one sensor has a higher DR than your output medium.

*Of course, if you don't lift the shadows, you will not see anything on the output image. But why would you that? Just to prove that DR of the capture device is meaningless?

[bclaff]

My understanding was that while they are not based on each other, they are both based on the photon transfer curve.

Most dynamic range measures are not based on the Photon Transfer Curve (PTC) but simply on read noise at the pixel level.
My Photographic Dynamic Range (PDR) is based on a portion on the PTC in the region of interest.
Clearly this is what I think is appropriate, and although I don't want to argue it here; I think there's a good case for this approach.

.... Perhaps Bill Claff can clarify his comment.

Which part would you like clarified?

[simsurace]

Which part would you like clarified?

I'm wondering what other approximation (besides neglecting the correlation of read noise between photosites) is used in John's estimate of DR at the sensor level.

[bclaff]

...
My mind is not entirely clear on what the approximation in your calculation is, besides neglecting noise correlations. Perhaps Bill Claff can clarify his comment.

...
Which part would you like clarified?

I'm wondering what other approximation (besides neglecting the correlation of read noise between photosites) is used in John's estimate of DR at the sensor level.

OK, I get it; I think John would be a better source for that explanation than I.

[Les Olson]

*Of course, if you don't lift the shadows, you will not see anything on the output image. But why would you that?

Well, the obvious reason is that pictures with the shadows lifted one stop look hideous.  Another reason not to lift the shadows is that there is nothing wrong with them, and there need not be because there is no reason to accept your arbitrary condition that the exposure is set by the highlights.

Of course, you are perfectly entitled to disagree about the hideousness of lifted shadows, or the sacredness of highlights, but you are still basing your claim about the usefulness of knowing capture DR on an aesthetic judgement about the final image, which you previously said you weren't. 

[simsurace]

Well, the obvious reason is that pictures with the shadows lifted one stop look hideous.  Another reason not to lift the shadows is that there is nothing wrong with them, and there need not be because there is no reason to accept your arbitrary condition that the exposure is set by the highlights.

Of course, you are perfectly entitled to disagree about the hideousness of lifted shadows, or the sacredness of highlights, but you are still basing your claim about the usefulness of knowing capture DR on an aesthetic judgement about the final image, which you previously said you weren't.

It is distracting to always mix up aesthetic discussions with technical ones.

I did not talk about pleasingness. I did not say that the shadows have to be lifted in order to get a pleasing image.
The shadows have to be lifted to display the information at 11 stops below the highlight point because that was the brief for the image. By not displaying them on the output, you are not fulfilling the brief. The image can have pure documentation purposes and does not have to have any artistic value at all. Saying that the output medium only has 10 stops of dynamic range is no excuse for hiding the information that was supposed to be displayed.

Likewise for the highlights, the brief was that they cannot be clipped, and therefore they set the maximum exposure that can be set.

These are the conditions of my example. It is no use arguing the conditions, they were not up for debate.

The question is, how do you solve this photographic situation? It is a common one, e.g. when photographing interiors with windows.*

Another way to fullfill the brief is to light the dark parts of the image, or to do multiple exposures etc. But if for some reason you are forced to use one exposure and no additional lighting, then the example applies.

I know that lifting shadows too much can lead to unpleasing results, but that is subjective, and I'm not going to impose my subjective criteria on other people. But the point is that the information is there on the 14 stop DR capture, while it is totally buried in the noise in the 10 stop DR capture, and cannot be recovered with any kind of processing. This proves that capture DR that exceeds the output DR is useful.

* I have seen plenty of interior architectural photography with large dynamic range printed on paper, which has a much lower dynamic range. It can be done.

[Les Olson]

But the point is that the information is there on the 14 stop DR capture, while it is totally buried in the noise in the 10 stop DR capture, and cannot be recovered with any kind of processing. This proves that capture DR that exceeds the output DR is useful.

No, it proves you should always carry a flash.  Of course it is your fantasy and you can set the conditions however you like so using a flash is impossible?  So it proves that if you are photographing interiors with windows and you can't use a flash you should choose an overcast day.  Then you will modify the conditions again - the interior is in Dubai so overcast days are rare? - so as to preserve the conclusion.  The point is not that you can't modify the conditions endlessly, but that doing so is circular: the only reason to accept the conditions is that they are pre-conditions for the conclusion to be true.