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Author Topic: The Optimum Digital Exposure  (Read 67200 times)

jjj

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Re: The Optimum Digital Exposure
« Reply #160 on: November 03, 2014, 06:03:02 pm »

I never said it is not simpler or easier, of course it is. I simply said camera digital noise is ugly, and if you like it is only because of a lack of good taste.
That's a pretentious and sneery thing thing to say to be honest. You are claiming your taste is superior because I like something you do not - that's a sad place to be.
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jjj

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Re: The Optimum Digital Exposure
« Reply #161 on: November 03, 2014, 06:05:32 pm »

It's all about context. As I'm pic-taking only for my own enjoyment your example has no relevance. If I were a pro, OTOH, I'd be doing everything I could to satisfy my clients…and that would include trying to anticipate their future wants & needs. But I'm not a pro and have zero interest in emulating that approach.

I'm not precious about my own photos. They remind me of experiences I've had & things I've seen but otherwise aren't that important in-and-of themselves. My favorites end up on a wall for awhile, then get replaced by others, which will in turn be replaced, etc. I get far more pleasure out of continually experimenting than from sticking with any particular photographing style, processing approach…or subject matter.
Seems like a very sensible approach to photography.
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Ray

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Re: The Optimum Digital Exposure
« Reply #162 on: November 03, 2014, 10:03:13 pm »

It's all about context. As I'm pic-taking only for my own enjoyment your example has no relevance. If I were a pro, OTOH, I'd be doing everything I could to satisfy my clients…and that would include trying to anticipate their future wants & needs. But I'm not a pro and have zero interest in emulating that approach.

I'm not precious about my own photos. They remind me of experiences I've had & things I've seen but otherwise aren't that important in-and-of themselves. My favorites end up on a wall for awhile, then get replaced by others, which will in turn be replaced, etc. I get far more pleasure out of continually experimenting than from sticking with any particular photographing style, processing approach…or subject matter.

-Dave-

Well, you'll have to forgive me for not realising this, Dave. You seems to be in a most unusual situation, from my perspective.

Whilst I also consider myself to be an amateur whose main motivation for engaging in photography is the creative pleasure I get from the taking and processing of the shots, as well as the pleasure I get from a sense of reliving past experiences when I view old shots that I've taken, sometimes many years later, I would not go so far as to claim that such enjoyment excludes other people's opinions and appreciation of my work, as your term 'only for my own enjoyment' implies.

Occasionally, I've sold prints in the past for a tidy sum, and occasionally I'll make a large print for a friend or neighbour, charging just the cost of the paper and ink. Sometimes I'll produce smaller prints for friends or relatives without charge, and quite often I'll entertain guests with a slide show of selected images on a large HDTV screen.

As an amateur, I consider myself to be my own client,and just as all clients can differ in their tastes and requirements, I, as my own client, accept that my tastes and requirements may gradually change over time. I frequently revisit old shots with new ideas for processing.

One of the great attractions of the DSLR for me, with its RAW image capability, is the concept that having a RAW file is like having an undeveloped film that can be developed again and again in as many different ways as one likes, without affecting the original undeveloped film. Imagine if Kodak had developed such a process before the digital age.   ;)

Experimenting with a noisy jpeg deliberately taken at an unecessarily high ISO, or severely underexposed, in order to compare how much crappier, or how different such an image appears, compared with a clean RAW file of the same scene deliberately processed to appear equally crappy, is fine as an experiment.

However, to exclude also taking a RAW image, or at least a correctly exposed ETTR of the same scene, seems very shortsighted to me, unless your motivation is to take an otherwise meaningless shot of no consequence, apart from its abstract nature of general crappiness.

For example, I would understand perfectly if someone wanted to exploit the banding problem of a Canon 5D by underexposing 10 stops at base ISO in order to produce a tapestry effect of coarsely woven threads.

The subject might be just a plain wall, in which case one might skip taking an ETTR shot, realising that without the extreme banding, the correctly exposed image would be just plain boring and that there would be almost no possibility of one ever wanting to produce a tack-sharp, noise-free image of such a boring subject, for any imaginable reason. Is that your concept here, Dave?  ;D

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Telecaster

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Re: The Optimum Digital Exposure
« Reply #163 on: November 03, 2014, 10:43:20 pm »

Whilst I also consider myself to be an amateur whose main motivation for engaging in photography is the creative pleasure I get from the taking and processing of the shots, as well as the pleasure I get from a sense of reliving past experiences when I view old shots that I've taken, sometimes many years later, I would not go so far as to claim that such enjoyment excludes other people's opinions and appreciation of my work, as your term 'only for my own enjoyment' implies.

You misread. I don't exclude anyone from enjoying photos I've taken. There are prints of mine at friends' homes and JPEGs on their gizmos. It pleases me when someone likes a photo I've taken. But I don't do the actual photography & editing with the intent of satisfying anyone other than myself. That's how I go about it. Other people have all sorts of different motivations and processes. These aren't challenges to anyone, just differences. Can you not accept this? Judging by your tone here the answer appears to be no.

And, as this is going nowhere fruitful or productive, that's all I have to say on the matter.

-Dave-
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Ray

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Re: The Optimum Digital Exposure
« Reply #164 on: November 04, 2014, 03:57:21 am »

Can you not accept this? Judging by your tone here the answer appears to be no.

I never accept what I consider to be poor advice. However, I have an open mind, which is why I'm prepared to consider and discuss alternative views.
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RogerW

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Re: The Optimum Digital Exposure
« Reply #165 on: November 04, 2014, 06:54:36 am »

To misquote the great Winston Churchill:

never in the field of digital photography has so much been posted to very little effect. 

If you don't want to use ETR, or Bob's OneZone, don't bother! 

As for me, I don't see any conflict between wanting to make creative, interesting photos and wanting to get the absolute most out of the equipment I've scrimped and saved to buy!

The ENT specialist I saw recently spent years learning the science and the result is that my ears are 100% better!
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jjj

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Re: The Optimum Digital Exposure
« Reply #166 on: November 04, 2014, 07:11:03 am »

To misquote the great Winston Churchill:

never in the field of digital photography has so much been posted to very little effect.
You obviously missed the thread with Ray's curious thoughts on perspective and lens then.  ;D
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dwswager

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Re: The Optimum Digital Exposure
« Reply #167 on: November 04, 2014, 02:38:47 pm »

John. You can't "overexpose" a sensor. Once the wells are full the photons fall on the floor. It's a brick wall.


If a sensor can't be overexposed, we could have cameras with infinite dynamic range and usable ISOs approaching zero!  Allah be praised!

In reality, sensors have both a lower threshold and upper saturation limit on how much photon energy can be converted to signal.  Below the lower threshold, signal is indistinguishable from the spurious noise.  Above the saturation limit, the signal generated basically tops out irregardless how much light hits it.

The fundamental issue is the way darker tones are expressed in a digital file as encoded in binary format.  Assuming an 8 bit channel, there are 8 different bits of data that can have values 1 or 0.  In a linear system then notice how little data is expressing the bottom tones and how little variation there is in the amount of data between them.  Add rounding errors from pushing and pulling the data around and pretty soon you have no data at all!

Linear Data
White  =  (2^8) 256,    100%
-1 stop = (2^7) 128,    50%
-2 stops = (2^6) 64,    25%
-3 stops = (2^5) 32,    12.5%
-4 stops = (2^4) 16,    6%
-5 stops = (2^3) 8,    3.1%
-6 stops = (2^2) 4,    1.56%
-7 stops = (2^1) 2,    0.78%
-8 stops = (2^0) 1,    0.39%
 
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Wayne Fox

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Re: The Optimum Digital Exposure
« Reply #168 on: November 04, 2014, 04:04:26 pm »

I'm a little late to the party here but I have read through most of the thread and I still have some questions regarding the article:

- What makes this article different from the normal ETTR article, including Michael's?  


Overall this article is a good summary, but I am a bit unclear what is new relative to the original ETTR concept?



After wading through the article again, and through this thread again, I must say these two comments sum it up for me as well ... I just don’t see any new ground from the article in regards to ETTR.  Even the concept of bracketing to insure a single correct ETTR exposure has been practiced by many for years.
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bjanes

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Re: The Optimum Digital Exposure
« Reply #169 on: November 04, 2014, 04:26:58 pm »

If a sensor can't be overexposed, we could have cameras with infinite dynamic range and usable ISOs approaching zero!  Allah be praised!

In reality, sensors have both a lower threshold and upper saturation limit on how much photon energy can be converted to signal.  Below the lower threshold, signal is indistinguishable from the spurious noise.  Above the saturation limit, the signal generated basically tops out irregardless how much light hits it.

The fundamental issue is the way darker tones are expressed in a digital file as encoded in binary format.  Assuming an 8 bit channel, there are 8 different bits of data that can have values 1 or 0.  In a linear system then notice how little data is expressing the bottom tones and how little variation there is in the amount of data between them.  Add rounding errors from pushing and pulling the data around and pretty soon you have no data at all!

Linear Data
White  =  (2^8) 256,    100%
-1 stop = (2^7) 128,    50%
-2 stops = (2^6) 64,    25%
-3 stops = (2^5) 32,    12.5%
-4 stops = (2^4) 16,    6%
-5 stops = (2^3) 8,    3.1%
-6 stops = (2^2) 4,    1.56%
-7 stops = (2^1) 2,    0.78%
-8 stops = (2^0) 1,    0.39%
 

That is a useful calculation for the encoding dynamic range of a linear space, where the DR in stops is equal to the number of bits used for the encoding. However, for a useful photographic DR, two factors are involved. The first is how much noise is acceptable in the darkest f/stop. A SNR of 10:1 is often used, but this is a judgement call. The second factor is how many levels are needed in the darkest f/stop to avoid posterization. Norman Koren has a useful table here. Look at the paragraph human vision and tonal levels. He requires 8 levels in the darkest f/stop. His table doesn't include values for a bit depth of 8. I recalculated the table for 8 bits and the 8 level cutoff is highlighted. With this criterion, the possible DR for 8, 10, 12, and 14 bits is 5, 7, 8, and 11 stops respectively.

For the DR of individual cameras, sensor data such as found on DXO are needed.

A bit of noise can dither the levels and reduce visible posterization as Emil discusses here.

Bill

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jmlphotography

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Re: The Optimum Digital Exposure
« Reply #170 on: November 04, 2014, 04:58:05 pm »

I'm confused.  How did I end up on DPReview?  (My reference is to the personal tone of some of the replies that I thought would not be acceptable here.)
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Herb

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Re:
« Reply #171 on: November 04, 2014, 05:33:42 pm »

... camera digital noise is ugly, and if you like it is only because of a lack of good taste.
Maybe digital noise 'was' always ugly, but that could soon be history. Have you see the noise from the Olympus OMD E-M5?

http://robinwong.blogspot.co.uk/2014/10/shoot-model-portrait.html

Most times I'd pass on ETTR to get that noise. Bad taste? Everyone can decide for themselves. But many users are happy about the grain-like effect and I expect all manufacturers are working to copy it.

A lot of things are being tweaked in software that didn't happen when Michael first wrote the article. Some smart guys think ETTR conflicts with such software tweaks:

http://chromasoft.blogspot.co.uk/2009/09/why-expose-to-right-is-just-plain-wrong.html

http://theonlinephotographer.typepad.com/the_online_photographer/2011/10/expose-to-the-right-is-a-bunch-of-bull.html
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Jim Kasson

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Re:
« Reply #172 on: November 04, 2014, 06:01:42 pm »


A lot of things are being tweaked in software that didn't happen when Michael first wrote the article. Some smart guys think ETTR conflicts with such software tweaks:

http://chromasoft.blogspot.co.uk/2009/09/why-expose-to-right-is-just-plain-wrong.html

This guy says this in the article linked to above: "But there is one situation where ETTR can help - when you're already at the lowest ISO setting you camera offers."  I don't think he really means that; I think he means at base ISO.

So, the way I think about it, he's saying that "real" ETTR works, but that you can't just crank up the ISO. Not a surprise.

Just for the record, I view "real" ETTR as minimizing photon noise. Moving the histogram to the right with the ISO control can mitigate things if you just can't get enough light on the sensor, but what you're doing there is managing read noise, because you've already decided what your exposure has to be.

If you don't think that ETTR is useful in modern cameras, and you can just throw away any improvements in photon noise because they're just so doggone good, you could save yourself some money and weight by using ETTR on a smaller sensor:

http://blog.kasson.com/?p=6871

Jim
« Last Edit: November 04, 2014, 06:03:27 pm by Jim Kasson »
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AlfSollund

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Re: The Optimum Digital Exposure
« Reply #173 on: November 05, 2014, 09:04:42 am »

Thanks a lot for sharing this. Most useful aproximation.

I assume by having a much larger, heavier camera (larger sendor) I can use ETTR and keep the advantage versus a smaller sensor  ;)? Example 2 steps advantage from Nikon D810 to m43. Still ignoring many things, among them lens quality, sensor technology, read noise lar, PRNU, diffraction, depth of field…
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williamchutton

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« Reply #174 on: November 05, 2014, 09:34:53 am »

This guy says this in the article linked to above: "But there is one situation where ETTR can help - when you're already at the lowest ISO setting you camera offers."  I don't think he really means that; I think he means at base ISO.

So, the way I think about it, he's saying that "real" ETTR works, but that you can't just crank up the ISO. Not a surprise.

Just for the record, I view "real" ETTR as minimizing photon noise. Moving the histogram to the right with the ISO control can mitigate things if you just can't get enough light on the sensor, but what you're doing there is managing read noise, because you've already decided what your exposure has to be.

If you don't think that ETTR is useful in modern cameras, and you can just throw away any improvements in photon noise because they're just so doggone good, you could save yourself some money and weight by using ETTR on a smaller sensor:

http://blog.kasson.com/?p=6871

Jim

How is it possible to alter photon noise?
How do you make improvements in photon noise?
Isn't the photon noise level a constant ratio in terms of the integer raw data?

Perhaps this Stanford Computer Optics article is incorrect or misleading?

http://www.stanfordcomputeroptics.com/technology/dynamic-range/photon-noise.html
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dwswager

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Re: The Optimum Digital Exposure
« Reply #175 on: November 05, 2014, 09:41:20 am »

That is a useful calculation for the encoding dynamic range of a linear space, where the DR in stops is equal to the number of bits used for the encoding. However, for a useful photographic DR, two factors are involved. The first is how much noise is acceptable in the darkest f/stop. A SNR of 10:1 is often used, but this is a judgement call. The second factor is how many levels are needed in the darkest f/stop to avoid posterization. Norman Koren has a useful table here. Look at the paragraph human vision and tonal levels. He requires 8 levels in the darkest f/stop. His table doesn't include values for a bit depth of 8. I recalculated the table for 8 bits and the 8 level cutoff is highlighted. With this criterion, the possible DR for 8, 10, 12, and 14 bits is 5, 7, 8, and 11 stops respectively.

For the DR of individual cameras, sensor data such as found on DXO are needed.

A bit of noise can dither the levels and reduce visible posterization as Emil discusses here.

Bill

Concur, but in all cases the darker tones are expressed with less data which is the point of ETTR: to move the darker tones up the scale which also helps with the S/N issue.  And, of course, because the sensor does not match our eye response, a gamma is applied.  

My point is there is no "optimal" exposure, at least in all cases.  A scene can contain DR less than, equal to or greater than that of our medium of capture.  If it is less than the DR of our medium, then yes, moving toward more exposure up to the saturation point of the sensor can result in better overall data capture.  But what of the other interesting cases.  What is optimal?

Can an a camera properly predict the saturation point of it's sensor based on the exposure meter data and other settings?  I don't know.  But that seems to be what we are asking for.  An exposure meter setting that set exposure to that 99.9% saturation point for the brightest pixel.  We will still have situations where the DR would be too large to capture.  Then a choice is required.
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bjanes

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Re: The Optimum Digital Exposure
« Reply #176 on: November 05, 2014, 10:40:22 am »

Concur, but in all cases the darker tones are expressed with less data which is the point of ETTR: to move the darker tones up the scale which also helps with the S/N issue.  And, of course, because the sensor does not match our eye response, a gamma is applied.  

My point is there is no "optimal" exposure, at least in all cases.  A scene can contain DR less than, equal to or greater than that of our medium of capture.  If it is less than the DR of our medium, then yes, moving toward more exposure up to the saturation point of the sensor can result in better overall data capture.  But what of the other interesting cases.  What is optimal?

Can an a camera properly predict the saturation point of it's sensor based on the exposure meter data and other settings?  I don't know.  But that seems to be what we are asking for.  An exposure meter setting that set exposure to that 99.9% saturation point for the brightest pixel.  We will still have situations where the DR would be too large to capture.  Then a choice is required.


Automatic ETTR exposure would be nice, but I favor giving the photographer the tools to take charge and set proper exposure manually. A raw histogram is often asked for, but is not forthcoming. Also, the widest color space available with most cameras is AdobeRGB, whose gamut is too narrow. To illustrate, here is an exposure of a red flower made according the the camera meter reading. The red channel appears severely blown on the camera histogram.



However, the raw histogram shows the red channel to lie nearly 2 EV below clipping.



Two factors are involved in the misleading camera histogram. The first is white balance. For daylight, the red multiplier is close to 2x. The raw channel can be intact before white balance but blown after WB. The other factor is that the color space of AdobeRGB can not contain the gamut of the flower. If the camera makers don't want to change their approach to give a raw histogram, they could at least offer ProPhotoRGB as a color space for the JPEG preview. To eliminate red channel clipping in the camera histogram required an exposure compensation of -1 2/3 EV.

Bill
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deejjjaaaa

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Re:
« Reply #177 on: November 05, 2014, 11:20:25 am »

How is it possible to alter photon noise?
mr Kasson naturally means not absolute reduction in photon noise, but reduction in S/N ratio, which naturally involves increase in absolute numbers, but reduction in ratio.
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Jim Kasson

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Re: The Optimum Digital Exposure
« Reply #178 on: November 05, 2014, 11:20:59 am »

Two factors are involved in the misleading camera histogram. The first is white balance. For daylight, the red multiplier is close to 2x. The raw channel can be intact before white balance but blown after WB.

Nice example, Bill. A custom WB can bring the in-camera histogram more into line (but not perfectly so) with the actual raw histogram, but then it becomes useless for judging color. You probably know that well, but it should be mentioned.

The other factor is that the color space of AdobeRGB can not contain the gamut of the flower. If the camera makers don't want to change their approach to give a raw histogram, they could at least offer ProPhotoRGB as a color space for the JPEG preview.

That's an interesting idea, but then we could have the opposite problem: the real raw histogram clipping while the PPRGB-derived histogram looks fine.

Jim

Jim Kasson

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« Reply #179 on: November 05, 2014, 11:31:58 am »

mr Kasson naturally means not absolute reduction in photon noise, but reduction in S/N ratio, which naturally involves increase in absolute numbers, but reduction in ratio.

Correct in every respect, except it's an increase in the SNR, which is I imagine what you meant to say..

Let me elaborate a bit. In a counterintuitive way, ETTR (real, ETTR, at base ISO) maximizes the photon noise, but maximizes the signal-to-noise ratio (SNR). How is that possible?

Photon noise varies as the square root of the exposure, exposure in this case being defined as number of photons per unit area impinging on the sensor. More light, more photon noise. Let's call the amount of photon noise sigma, and the light level mu.

SNR = mu / sigma.

Since sigma = sqrt(mu),

SNR = mu/sqrt(mu) = sqrt(mu)

So, every time we add a stop more light, the SNR goes up by 1.414; that's the square root of two.

That's the reason that ETTR (at base ISO) works.

Jim
« Last Edit: November 05, 2014, 11:34:57 am by Jim Kasson »
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