Will Michael revisit ETTR?

[ejmartin]

Indeed it is. But Emil's point, as I understood it, was that noise would prevent any advantage of an increase in the number of levels beyond 12 bit, and that 14 bits served no purpose other than a possible slight increase in the accuracy of the conversion.

Perhaps it would be clearer to state, if the DR of the camera is no greater than 12 stops, then more levels that 12 bits afford, is of little use.

However if the camera has a DR of more than 12 stops, then more than 12 bits is of use.

If one wishes to engage in pixel peeping, 14 bits does provided a pixel-peeping  IQ  advantage in the 11th and 12th stops, with the D7k. However, I doubt that would be the case with lesser cameras, DR-wise.

Noise will effectively dither, when the noise is sufficiently large relative to the quantization step.  If you expose to mostly only populate the 13th and 14th bit of data, and then truncate as you have to 12 bits, then of course it's going to look like garbage.

[Bart_van_der_Wolf]

I developed a RAW file from the Pentax K5 (same sensor as D7000), emulating a 12-bit RAW file (by decimating the RAW data from 14-bit to 12-bit prior to RAW development), and posterization began to show up:
[...]
However, doing the same test on Canon 40D's RAW files, there was no loss of IQ using 12-bit. That camera is noisy enough to make 14 bits unnecesary.

Hi Guillermo,

When you say unnecessary, I wonder if that is true under all circumstances. Maybe 'hardly necessary' is closer to the truth? Have you for instance tried averaging, say 4 or 16, different exposures (as is routinely done in astophotography) and then analyse the resulting noise level? If there is truely no benefit for, or information in, the 13th and 14th bit then you would be correct and both would have identical noise levels and posterization ...

Cheers,
Bart

[Ray]

However, doing the same test on Canon 40D's RAW files, there was no loss of IQ using 12-bit. That camera is noisy enough to make 14 bits unnecesary.

I suspect that would be true. I tried similar tests with my D700 whilst my D7k was in for repair, and was very surprised to find virtually no image quality difference in the 11th stop, between 12 bit and 14 bit, except for a slight additional graininess in the 12 bit image, almost like the difference between an ISO 200 film and an ISO 400 film, but not as great.

I admit I was expecting to see a greater difference.

However, the D7k is a different kettle of fish. Not only is that slightly greater graininess apparent in the 12 bit shots, in the 11th and 12th stops also, but there seems to be an unavoidable clipping of the blacks in 12 bit mode. Such clipping is not apparent in the 14 bit shots with the D7k.

It goes without saying that I've applied no sharpening nor noise reduction in the following ACR conversions. Tone curve is linear, blacks zero and contrast either 0 or -50, depending on the image.

[Ray]

Noise will effectively dither, when the noise is sufficiently large relative to the quantization step.  If you expose to mostly only populate the 13th and 14th bit of data, and then truncate as you have to 12 bits, then of course it's going to look like garbage.

Emil,
I admit those images I've presented, that are extremely underexposed, look like garbage.

The issue for me is, do the 12 bit images look even more like garbage than the 14 bit images?

In a real scene with a correct exposure, only the deepest shadows would look like a crop of my underexposed shots, after selecting and raising such shadows in the real scene, in order to see the detail.

I believe my methodology is sound. However, I agree with you that ETTR is mainly about SNR and little about the number of levels, considering that most cameras probably provide an excess of levels in relation to the noise floor.

[lenelg]

Back in the 1960´s, when I was a wee lad, audiophiles were the serious nerds, competing to build a better sound system. The really serious ones did not bother to listen to their systems. Instead they connected an oscilloscope to the output of their latest amplifier, and sat entranced by the pureness of the waveforms displayed on their little green screens.

This discussion seems dangerously close to veering in that direction. Or as Yogi Berra put it: "It´s déjá vu all over again!"

[ejmartin]

Back in the 1960´s, when I was a wee lad, audiophiles were the serious nerds, competing to build a better sound system. The really serious ones did not bother to listen to their systems. Instead they connected an oscilloscope to the output of their latest amplifier, and sat entranced by the pureness of the waveforms displayed on their little green screens.

This discussion seems dangerously close to veering in that direction. Or as Yogi Berra put it: "It´s déjá vu all over again!"

Ooh, great idea!  I'll have to get an oscilloscope right away...   

[Eric Myrvaagnes]

Back in the 1960´s, when I was a wee lad, audiophiles were the serious nerds, competing to build a better sound system. The really serious ones did not bother to listen to their systems. Instead they connected an oscilloscope to the output of their latest amplifier, and sat entranced by the pureness of the waveforms displayed on their little green screens.

This discussion seems dangerously close to veering in that direction. Or as Yogi Berra put it: "It´s déjá vu all over again!"

I think I still have an ancient oscilloscope in my basement somewhere. If any of you geeks want to come and get it, you can have it. Of course you might have to hunt up some new tubes (yes, tubes) for it.

[stamper]

Back in the 1960´s, when I was a wee lad, audiophiles were the serious nerds, competing to build a better sound system. The really serious ones did not bother to listen to their systems. Instead they connected an oscilloscope to the output of their latest amplifier, and sat entranced by the pureness of the waveforms displayed on their little green screens.

This discussion seems dangerously close to veering in that direction. Or as Yogi Berra put it: "It´s déjá vu all over again!"

I am surprised that the.....you don't have to read it .....reply hasn't surfaced. At the end of the day we don't but we do read it to see if something practical has been posted. Alas no.

[kwalsh]

When you say unnecessary, I wonder if that is true under all circumstances. Maybe 'hardly necessary' is closer to the truth? Have you for instance tried averaging, say 4 or 16, different exposures (as is routinely done in astophotography) and then analyse the resulting noise level? If there is truely no benefit for, or information in, the 13th and 14th bit then you would be correct and both would have identical noise levels and posterization ...

Averaging isn't the correct operation.  Accumulating is.  Summing four 12-bit files gives you 14-bits of information and increases your SNR by one bit (so you could round to 13-bits without loss).  Summing sixteen 12-bit files gives you 18-bits of information and increases your SNR by two bits (round to 14).

You are correct that once you accumulate or average a number of 12-bit files you may get to the point that 12-bits is no longer sufficient to keep the quantization noise sufficiently low.  But this doesn't imply that 12-bits was insufficient in the individual files.  If read noise was stronger than quantization noise in the individual files at 12-bits then additional bits in the individual files won't help you later on.  Where you need the extra bits is after you combine the files, not before.

Ken

[Ray]

Back in the 1960´s, when I was a wee lad, audiophiles were the serious nerds, competing to build a better sound system. The really serious ones did not bother to listen to their systems. Instead they connected an oscilloscope to the output of their latest amplifier, and sat entranced by the pureness of the waveforms displayed on their little green screens.

This discussion seems dangerously close to veering in that direction. Or as Yogi Berra put it: "It´s déjá vu all over again!"

There's something wrong with this analogy. We're not using our ears to assess visual matters here. Audio is a hearing thing. Photography is a visual thing. Judging audio quality with one's eyes would be as silly as judging photographic technical quality with one's ears.

The issue of 12 bit versus 14 bit A/D conversion, in cameras, is interesting because it does seem that for many models of cameras 12 bits are sufficient, and 14 bits may be mostly an advertising gimmick.

The D7000 is probably the only camera I own where 14 bits are useful. I didn't know that until I carried out the above tests.

[Bart_van_der_Wolf]

Averaging isn't the correct operation.  Accumulating is.

Hi Ken,

Adding values will make the result brighter until the result is clipped by the (often) integer math word length. In the end you need to scale down (=divide by the number of images taken, AKA averaging) to get the original brightness (but with lower noise and thus more accurate). One can opt for addition, and subsequent division by less than the number of images, but that also increases the brightness of the resulting image, with potential clipping.

Summing four 12-bit files gives you 14-bits of information [...]

Unless the images were ETTR exposures with the MSB filled, or when the 12 bit images were not scaled properly on the MSB when promoting to more bits. Not scaling 12-bit input properly when converting to 14-bit or 16-bit equals a division, hence averaging takes place. It would also require an exact number of 2, 4, 8, 16 images to get the orginal brightness, which is an unnecessary restriction (15 images are almost as useful as 16, especially when the brightness doesn't drop by more than 6%).

Cheers,
Bart

[kwalsh]

Adding values will make the result brighter until the result is clipped by the (often) integer math word length. In the end you need to scale down (=divide by the number of images taken, AKA averaging) to get the original brightness (but with lower noise and thus more accurate). One can opt for addition, and subsequent division by less than the number of images, but that also increases the brightness of the resulting image, with potential clipping.

If you have a primitive image processing chain this is true.  Black and white points are arbitrary and 64-bit integers are supported in most real processing applications (or in some 52-bits if they prefer floating point) so the reality is there is never any reason to divide or average in image processing.  But yes, if you want to get back to something that will fit in an original RAW file bit depth to then pass through something like LR then you need to worry about getting back to the original integer range through division.  The point still holds though, more bits in the individual capture images is irrelevant, bits in the combined output image is what matters.  Forcing oneself back into the original RAW bit depth from a combination of multiple exposures can lead to quantization noise being higher than averaged read noise.  This is why averaging is suboptimal compared to accumulation.

Unless the images were ETTR exposures with the MSB filled, or when the 12 bit images were not scaled properly on the MSB when promoting to more bits. Not scaling 12-bit input properly when converting to 14-bit or 16-bit equals a division, hence averaging takes place. It would also require an exact number of 2, 4, 8, 16 images to get the orginal brightness, which is an unnecessary restriction (15 images are almost as useful as 16, especially when the brightness doesn't drop by more than 6%).

Again, I was just using a simple example.  The proper solution is to not round or truncate but instead just add and change your white point (and possibly black point depending on the ADC bias).  In such a manner an arbitrary number of images can be handled.  Again, to get back to a "standard" processing flow you'll be forced to average which is suboptimal.

Happy shooting!

Ken

EDIT: Part of that was confusing.  Obviously dividing and averaging in double precision floating point would be just fine.  When I said averaging was suboptimal compared to accumulation and white point adjustment I was referring to integer operations.

[joofa]

I am surprised that the.....you don't have to read it .....reply hasn't surfaced.

May be the technical crowd also realizes that the discussion on ETTR is becoming a bit futile 

[Ray]

Talk about obsession!!!   

[stamper]

Quote

EDIT: Part of that was confusing.  Obviously dividing and averaging in double precision floating point would be just fine.  When I said averaging was suboptimal compared to accumulation and white point adjustment I was referring to integer operations.

unquote

I think it is now obvious that each of the obsessives are now taking the mickey with each other?

[Jack Hogan]

Referring to the RAW files of my DR tests for the D7000, I see that the last shot in the series, beginning with a 4 secs exposure, was taken at 1/8000th exposure, which represents the 16th stop.

Surprisingly, there's still some broad detail visible through the noise. At least one can read the heading.

Hi Ray,

I recently came across this old thread and would be interested in taking a look at the NEFs (in particular DSC0037, 52, 58 and any other you may think relevant).  Any chance I could trouble you to share them (dropbox, skydrive, google drive)?  I have PM'd you my email address.

Thanks,
Jack

[Ray]

Hi Ray,

I recently came across this old thread and would be interested in taking a look at the NEFs (in particular DSC0037, 52, 58 and any other you may think relevant).  Any chance I could trouble you to share them (dropbox, skydrive, google drive)?  I have PM'd you my email address.

Thanks,
Jack

Hi Jack,
I'll have a look for them. I'm in the process of reorganizing my images so it shouldn't take too long.

Regards