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Author Topic: “Expose to the right” vs “JPEG Histogram to the right”  (Read 27987 times)

bjanes

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #80 on: March 24, 2018, 10:25:51 pm »

But Ray, you should know by now that you will not impress me with DXO's "total engineering dynamic range" graphs, with an unknown number of a camera's lowest stops having uselessly low SNR, and that number of "junk stops" of DR unlikely to be the same for all cameras. Are there any good up-to-date photographic dynamic range graphs for recent cameras, from Bill Claff or Jim Kasson or other sources?

If you don't want to use 0 dB as the floor for DR calculations as per DXO, you can use their full SNR plots to calculate the DR for other noise floors as discussed here.

Regards,

Bill
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Ray

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #81 on: March 25, 2018, 07:34:47 am »

If you don't want to use 0 dB as the floor for DR calculations as per DXO, you can use their full SNR plots to calculate the DR for other noise floors as discussed here.

Regards,

Bill

Thanks for that reminder, Bill. This is all 'deja vue' for me. I've been a bit puzzled as to why I couldn't find the full SNR plots for the cameras I've been comparing. I wondered if DXOMark had discontinued the provision of such graphs.

However, after a bit of inquiry on the internet, I was reminded that the full SNR plots are not available from the 'camera comparison' page. One has to do a search for the specific camera measurements, where an additional heading of 'Full SNR' is included.

BJL should be ecstatic to discover this.  ;D
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BJL

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“Expose to the right” etc.: interpreting DXOMark's full SNR curves
« Reply #82 on: March 25, 2018, 05:05:50 pm »

If you don't want to use 0 dB as the floor for DR calculations as per DXO, you can use their full SNR plots to calculate the DR for other noise floors as discussed here.
Thanks Bill! This does look like the core information, as used by Bill Claff and others to estimate "photographically useful dynamic range". (Once you mentioned it, I had guessed that it would show only in the single camera measurements, not the camera comparisons [too many curves!], but then discovered that it is also only available in the "desktop" version of the site, not on phones.)

On one hand, at what I find interesting SNR levels, from 12dB [SNR of 8:1] up, the results are close to what one would expect from shot noise alone: about one more stop for the D850 than for the EM1MkII at their lowest ISO settings (ones with minimum gain, so sending full wells to about maximum raw level rather than clipping.) It does seem that at "equal total exposure" [see note], so with suitably higher EI with the larger sensor, the advantage goes slightly the other way—but care is required due to the different pixel counts and the different gain levels used at the same ISO setting.

My raw observations, not yet carefully analyzed, are that
1) At 12dB [SNR 4:1] and rising, the EM1MkII is increasingly "better" (curves to the left) at equal ISO settings.
2) At 24B [SNR 16:1] the curves are offset by about one stop on the ISO speed settings scale: curves at a given ISO speed setting on the D850 roughly match those for the EM1MkII at twice the ISO speed setting.
3) On the other hand, at 6dB [SNR 2:1] and below, the D850 is about one stop better, and a bit more than one stop way down at 0dB [SNR 1:1].

Note: "Equal total exposure" meaning equal amount of light delivered to the sensor, as when both DOF and exposure time are equal.
« Last Edit: March 25, 2018, 07:06:05 pm by BJL »
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ErikKaffehr

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #83 on: March 25, 2018, 06:40:26 pm »

That would not work. Incident light metering ignores highlights.

Best regards
Erik






Use an incident light meter?


Kent in SD
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Ray

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Re: “Expose to the right” etc.: interpreting DXOMark's full SNR curves
« Reply #84 on: March 25, 2018, 10:52:25 pm »

Thanks Bill! This does look like the core information, as used by Bill Claff and others to estimate "photographically useful dynamic range". (Once you mentioned it, I had guessed that it would show only in the single camera measurements, not the camera comparisons [too many curves!], but then discovered that it is also only available in the "desktop" version of the site, not on phones.)

On one hand, at what I find interesting SNR levels, from 12dB [SNR of 8:1] up, the results are close to what one would expect from shot noise alone: about one more stop for the D850 than for the EM1MkII at their lowest ISO settings (ones with minimum gain, so sending full wells to about maximum raw level rather than clipping.) It does seem that at "equal total exposure" [see note], so with suitably higher EI with the larger sensor, the advantage goes slightly the other way—but care is required due to the different pixel counts and the different gain levels used at the same ISO setting.

My raw observations, not yet carefully analyzed, are that
1) At 12dB [SNR 4:1] and rising, the EM1MkII is increasingly "better" (curves to the left) at equal ISO settings.
2) At 24B [SNR 16:1] the curves are offset by about one stop on the ISO speed settings scale: curves at a given ISO speed setting on the D850 roughly match those for the EM1MkII at twice the ISO speed setting.
3) On the other hand, at 6dB [SNR 2:1] and below, the D850 is about one stop better, and a bit more than one stop way down at 0dB [SNR 1:1].

Note: "Equal total exposure" meaning equal amount of light delivered to the sensor, as when both DOF and exposure time are equal.

In case anyone is confused, I'd like to emphasise the point that these 'Full SNR' graphs relate to the pixel, not the full frame of the sensor. It might be more revealing if DXO were to provide the Full SNR plots for the entire sensor, normalized to the usual 8mp..

Another point that should be emphasized, which Emil Martinec also made, is that Photographic DR is a very subjective definition that can vary wildly from individual to individual, and also be influenced by the display size of the image, whether print or screen.

The engineering definition that DXO uses, is at least objective and consistent. If Camera A has 14 EV of DR, and Camera B has 12 EV of DR, then it's reasonable to presume that both cameras will produce unacceptable shadows at their DR limits.

However, it's also reasonable to presume that the shadows in a shot from Camera A, at 12 EV of DR, will be noticeably better than the shadows in the same shot from Camera B at it's engineering limit of 12EV.

The attached image of graphs comparing the Full SNR of the D850 with the E-M1 MkII, the D850 at the top, shows that the SNR of the D850 pixel is generally better. However, it's not clear where the SNR 18% level lies on the graph.

Interestingly, at maximum exposure, ie. full well capacity, the D850 pixel has about 5dB better SNR. At 1% on the Logarithmic scale, which represents reasonably deep shadows, it has about 4dB better SNR. This just goes to show how limited the SNR 18% plot is.

When one extrapolates all the values on the Full SNR graphs to full frame values, with approximately 4x the number of photons reaching the D850 sensor, the noise advantages of the D850 are apparent across the entire range, from the deepest shadows to the brightest highlights.

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BJL

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Re: “Expose to the right” etc.: interpreting DXOMark's full SNR curves
« Reply #85 on: March 26, 2018, 10:26:11 pm »

Another point that should be emphasized, which Emil Martinec also made, is that Photographic DR is a very subjective definition that can vary wildly from individual to individual, and also be influenced by the display size of the image, whether print or screen.
You make that sound like a bad thing! But apart from the gratuitous pejorative "wildly", what you and Emil are saying is that Photographic dynamic range is a measure adapted to be relevant to the actual needs of a particular photographer and particular intended uses. To me, that is far more useful than a consistent but in itself irrelevant measure based on a SNR lower than could be of any direct practical use for assessing image quality. That is the usual sorry end when one attempts to reduce a complex reality to a single number. (For worse examples, see DXOMark's single number scores for "portrait", "landscape", "sports", and even overall scores for "sensor" and "lens".) That is why more useful assessments of a tool as complicated as a camera need a healthy range of measurements from which practical conclusions can be derived according to actual practical needs — like those complete SNR curves. It is like understanding and using MTF curves vs a single "bragging rights" number for "resolution" or "sharpness".

If you crave a number to use in comparisons that is consistent and clearly defined, one can choose a particular standardized PDR, as Bill Claff does. I would go for something like a low end where pixel level SNR = 5:1. Using SNR = 1:1 is equal arbitrary relevant to photographic needs.
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kirkt

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BJL

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #87 on: March 27, 2018, 10:12:28 pm »

Just in time:

https://www.fastrawviewer.com/blog/determining-practical-dynamic-range

Kirk

Quite a lot to think about there. Maybe — in the spirit of Bill Claff's choice of standardized print size and viewing distance and Ray's desire for something similar in the form of DR after downsampling to 8MP — there is an informative curve of "usable DR vs resolution", or "resolution at various levels of scene brightness". At one extreme, even an image file with SNR<=1 per pixel might be salvageable by sufficient downsampling. In fact, that is sort of what we do with traditional black and white film, where the raw signal is all 0's and 1's, because each silver halide grain is either exposed or not, but there are many billions of "chemical pixels".
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Ray

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #88 on: March 28, 2018, 10:25:17 am »

Quite a lot to think about there. Maybe — in the spirit of Bill Claff's choice of standardized print size and viewing distance and Ray's desire for something similar in the form of DR after downsampling to 8MP — there is an informative curve of "usable DR vs resolution", or "resolution at various levels of scene brightness". At one extreme, even an image file with SNR<=1 per pixel might be salvageable by sufficient downsampling. In fact, that is sort of what we do with traditional black and white film, where the raw signal is all 0's and 1's, because each silver halide grain is either exposed or not, but there are many billions of "chemical pixels".

Photographic Dynamic Range is what you decide through your own tests in relation to particular circumstances which can vary. The print size will also have some bearing on the amount of shadow noise and detail which is acceptable. Noise can be significantly reduced if one is prepared to sacrifice detail, which is less of a concern on the smaller print.

When I bought the Nikon D7000 to replace my Canon 50D, the main attraction was its high DR, almost 2.5EV better than the 50D at base ISO. Shortly after taking delivery of the D7000, I made a thorough comparison of the DR capability of both cameras by taking a serious of shots of the same target in the same lighting conditions, starting with an ETTR shot with both cameras, then reducing exposure successively, one stop at a time, with each camera until I reached  13 &2/3rds stops of underexposure, the DR limit of the D7000.

At the different DR limits of both cameras, the images were similarly degraded, but some detail was still discernible. At 13 stops underexposure on the 50D, no detail at all was discernible. It was all pure noise.

However, at 11 stops underexposure, the D7000 image was acceptable, but not the 50D image because it was at its DR limit. At 9 stops underexposure, the 50D was acceptable for shadows, but the D7000 was significantly better and more detailed.

In other words, the PDR of the D7000 was about 11.5 EV and the PDR of the 50D about 9 EV, which corresponds with the DXO engineering DR differences of about 2.5 EV. At 8 stops underexposure, the D7000 had an insignificant edge, and at 7 stops underexposure there was no discernible difference.

The issues as I see them, are:
(1) How to determine the PDR of your camera? Do you just accept someone elses view, or do you take the trouble to do your own testing?
(2) How do you determine the DR (or SBR) of the scene you are about to shoot?

I've already described the first process, so what about the second process? If you have plenty of time to organize everything in a studio, then no problem. However, if you are taking numerous shots of various scenes as you travel, there needs to be a quick and reliable process.

The quickest process is to simply automatically bracket all exposure, which is what I used to do when using the older Canon DSLRs. However, bracketing most shots fills up you memory card faster and involves a lot more processing time for those shooting in RAW mode.

With my Nikon cameras, it has become apparent that by far the majority of my shots do not require bracketing if I take the trouble to find the optimum ETTR exposure.

If I do get the impression that a particular scene might exceed the PDR capabilities of my camera, then it takes me a little more time than it takes to get a ETTR shot, because a mathematical calculation is required.
Using a single focusing square, and camera in manual exposure mode, I simply move the focusing square to the brightest part of the image and adjust exposure with my thumb on a wheel untill the meter in the viewfinder is at the far right where the + sign changes into an arrow head. That is the correct exposure for an ETTR shot, which I've determined through my own tests. No calculations are required, except if the shutter speed is too slow for a hand-held shot, in which case I'll raise the ISO and readjust the exposure.

If I think the lighting in the shadows, in another part of the composition, might be inadequate for PDR quality, I'll simply move the focusing square to those shadows and reduce the shutter speed, with thumb on wheel, till the camera's meter moves to the extreme right, as though I'm taking an ETTR shot of the shadows.

I then have to do a mathematical calculation to convert the differences in shutter speeds into numbers of stops or EVs. Alternatively, as I move the exposure adjustment wheel, I could count the number of clicks involved before the exposure meter reaches the far right. If the cameras is set for 1/2 a stop exposure increments, then I could divide the number of clicks, or changes in exposure, by 2 to get the difference in EV range between the highlights and the shadows. However, the D810 allows for 1 stop changes in exposure, which would make it even easier.

If the difference between the two ETTR readings, one for the brightest highlights, and one for the deepest shadows which have meaningful detail, is greater than my calculated PDR for my camera, say 11 stops, then I need to bracket exposure.

However, even if one has gained a general PDR rating for one's camera through one's own testing, this rating can change according to circumstances. A good example would be the photographing of the amazing ruins at Angkor Wat. In a particular scene there might be an amazing and detailed engraving in the stone, in the deepest shadows. After using my method to check the lighting conditions in those shadows, one might find that the shadows are in fact within the PDR range of one's camera. On the other hand, because the content of the shadows is so interesting, one might decide to bracket exposure in order to get the maximum quality and detail in those shadows.

This is the one major reason why I prefer the higher DR of the Nikon cameras. There are far fewer occasions when these sorts of time-consuming difficulties arise. Most of the time I can simply take an ETTR shot and be confident that the shadows will be okay, at base ISO and/or a couple of ISO stops above.
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bjanes

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #89 on: March 28, 2018, 12:00:50 pm »

This is the one major reason why I prefer the higher DR of the Nikon cameras. There are far fewer occasions when these sorts of time-consuming difficulties arise. Most of the time I can simply take an ETTR shot and be confident that the shadows will be okay, at base ISO and/or a couple of ISO stops above.

I agree that with the latest Nikon sensors (and many others) DR is often not a limiting factor. I also find that bracketing is seldom necessary with my D850 if one uses proper ETTR exposure at base ISO. If one has to increase the ISO, jumping directly to ISO 400 makes sense because this is where the Aptina dr-pix kicks in. See Here.

At ISOs over 400 one can protect the highlights by shooting dark and increasing exposure in post. To obtain a decent LCD preview, I shoot dark only by one or two stops.

Regards,

Bill
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Ray

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #90 on: March 28, 2018, 08:37:45 pm »

I agree that with the latest Nikon sensors (and many others) DR is often not a limiting factor. I also find that bracketing is seldom necessary with my D850 if one uses proper ETTR exposure at base ISO. If one has to increase the ISO, jumping directly to ISO 400 makes sense because this is where the Aptina dr-pix kicks in. See Here.

At ISOs over 400 one can protect the highlights by shooting dark and increasing exposure in post. To obtain a decent LCD preview, I shoot dark only by one or two stops.

Regards,

Bill

Yes. From ISO 400 onward the D850 appears to be essentially ISO-invariant, according to the DXO graph, although the accumulation of very insignificant degrees of DR loss for each stop of underexposure, instead of using the same exposure at the appropriately higher ISO, does eventually lead to a noticeable effect, according to the DXO DR graph.

For example, if one were to underexpose by 7 stops at ISO 400, instead of raising ISO to 51,200, one would lose 0.5EV of DR, which is at the threshold of significance.

Perhaps you could test this, Bill, to confirm the accuracy of DXOMark's results, and determine whether that claimed improvement of 0.5EV is noticeable. I don't have a D850 yet. My D810 is still functioning well, despite my having dropped it from a shopping trolley onto a concrete slab some time ago, which produced an open gash in the corner of the camera, which I've plugged up with glue so that dust and water will not get in.
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BJL

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I also find that bracketing is seldom necessary with my D850 if one uses proper ETTR exposure at base ISO.

And I find that ETTR exposure at base ISO is seldom necessary with proper bracketing!

More seriously, thanks Bill for the confirmation that with the latest sensor technology, settings beyond about ISO 400 and analog gain beyond that level are mostly for convenience (making in-camera reviews, live view previews and default JPEG conversions look roughly right, for example) rather than being of much importance to image quality.
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BobShaw

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #92 on: April 23, 2018, 07:05:44 pm »

One wonders how Ansel Adams managed to take a photo without access to a computer and this 5 pages of priceless information?
In the good old days you took a guess or measured it.
Now I put the camera on manual, point the camera at the sky or brightest part of the shot, adjust until the pointer is against the right hand stop but not blinking. Then shoot once and move on. (:-)
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EricV

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #93 on: April 23, 2018, 08:34:58 pm »

Ansel Adams's technique was the complete opposite of "taking a guess".  The Zone System requires careful light meter measurements of multiple points in the scene, coupled with detailed knowledge of the response characteristics of film and developer.  Modern digital sensors have greatly simplified the process of getting an acceptable exposure, and there is no longer a development process, as digital sensors have linear response curves.  The creative part of image processing is now in what Adams called printing, and what we call post-processing and printing.
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digitaldog

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #94 on: April 23, 2018, 09:27:38 pm »

Ansel Adams's technique was the complete opposite of "taking a guess".  The Zone System requires careful light meter measurements of multiple points in the scene, coupled with detailed knowledge of the response characteristics of film and developer.
Yes! And we can and should do the same with digital (raw capture).
Quote
Modern digital sensors have greatly simplified the process of getting an acceptable exposure, and there is no longer a development process, as digital sensors have linear response curves.  The creative part of image processing is now in what Adams called printing, and what we call post-processing and printing.
There still is development; the raw processor. But you're absolutely correct if and when we view a raw Histogram. When doing so, no development and where we really should examine exposure san's development.
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BobShaw

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #95 on: April 23, 2018, 10:03:53 pm »

Ansel Adams's technique was the complete opposite of "taking a guess".
Not that I said Ansel was guessing but that depends what you mean by a guess. If he did make a guess then it was a very good guess because he was a very good photographer. I am not sure that he had an exposure meter in his plate camera or that he come up with the Zone System before the time of his earliest works. The Zone System was documented as a teaching aid for other photographers in about 1940. He did not need to bracket because he had skill and only about 12 shots available for the day anyway.

The point was that if you don't capture within acceptable limits then there is no amount of post production creativity that will fix it.
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Eric Myrvaagnes

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #96 on: April 23, 2018, 10:48:40 pm »

Minor White once described a photography outing with Ansel and Edward Weston. At Ansel's insistence, Edward was using a light meter.
Edward's technique, according to Minor, was to wave the meter around, then glare at it and mutter "It's wrong!"
Then he proceeded to set the exposure his eye told him was correct.

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digitaldog

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #97 on: April 23, 2018, 11:09:31 pm »

Minor White once described a photography outing with Ansel and Edward Weston. At Ansel's insistence, Edward was using a light meter.
Edward's technique, according to Minor, was to wave the meter around, then glare at it and mutter "It's wrong!"
Then he proceeded to set the exposure his eye told him was correct.
But was it?
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Eric Myrvaagnes

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #98 on: April 24, 2018, 08:31:05 am »

But was it?
Judging from the many of his prints that I've seen, I'd say it was. It was certainly more reliable than my eye.
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Bart_van_der_Wolf

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #99 on: April 24, 2018, 08:40:53 am »

Judging from the many of his prints that I've seen, I'd say it was.

Maybe thanks to extensive "Post-processing" during development and printing?

I've manipulated images myself during my wet darkroom days, both during the film development process, by using the temperature of my fingers, and easier (because it's easier to see what's happening) by dodging and burning during the exposure of the print and again using my fingers.

Cheers,
Bart
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