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Author Topic: ETTR vs ISO  (Read 21668 times)
RFPhotography
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« Reply #60 on: May 25, 2013, 06:05:21 AM »
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Then I think you should include the rest of the quote...

This is important to understand for CCD and Exmor where the sensors are called ISOless, because you will not get any result from increasing ISO in camera than you can get in the RAW conversion.  In these cases, ISO for the photographer becomes the same as the sensor scientist...meaningless...except for the jpeg he sees in the LCD on the back of the camera.

Yes, I understand that.  But you miss my point.  I'll reiterate.  There are circumstances when screwing around processing images isn't an option.  In such circumstances raising the ISO to generate a 'normal' exposure is necessary.  In those circumstances ISO is part of exposure. 
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jrsforums
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« Reply #61 on: May 25, 2013, 08:25:24 AM »
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Yes, I understand that.  But you miss my point.  I'll reiterate.  There are circumstances when screwing around processing images isn't an option.  In such circumstances raising the ISO to generate a 'normal' exposure is necessary.  In those circumstances ISO is part of exposure. 

OK...didn't read that in your comment, as I thought it was implicit in the original statement, "For a photographer, the exposure net result includes the consideration of ISO", as well as Bill Janes post.
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bjanes
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« Reply #62 on: May 25, 2013, 10:38:54 AM »
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This entire ETTR, exposure, ISO, testing takes me back to the mid 1980's while at photo school. I think 2nd trimester, we had one of our first assignments shooting color (first trimester we only shot 4x5 B&W film, it could not be burned or dodged in the darkroom for any assignment). This new color assignment was to shoot 4x5 color neg, I think it was Kodak VPS II or something. Stated ISO 160 on the box. The subject had to be stationary and have an 18% gray card in the center filling up at least 20%. We were to shoot at the recommended ISO, then 1, 2 and 3 stops under and over. We processed all the film together. Then in the darkroom, we had to make prints whereby the gray card on the print matched the actual gray card. Once all 7 prints were mounted and viewed, the results were very surprising! The plus 1 and 2 stops were easily printable and both produced a better print quality than the "normal" ISO 160 image. The under exposed prints all suffered compared to the 'normal' exposure.

ISO 160 for VPS worked just fine! But rating it at ISO 80 (or 40) and treating the rest of the process the same produced a very visible and beneficial result! No Histograms. But we did expose to the right if you will.

Historical perspective is always helpful and many concepts learned earlier can be carried over into digital photography. However, the response of negative film and the digital sensor are quite different. Negative film has a toe on the H&D curve and exposures that do not place shadows above start of the toe will result in blank film base and all shadow detail will be lost. From my film days when using negative film, I had a sinking feeling when the shadows recorded as base density on an important shot that could not be recovered. Digital is linear and any shadow luminance will be recorded but any image detail may be lost in noise. The digital sensor response is linear without any shoulder and highlights will be clipped abruptly when the sensor saturates. Some highlight recovery may be possible with Bayer CFA sensors, since the red and blue channels may still have some detail, but the color information in the green channel that clips first (with daylight and most artificial illumination) will be lost.

The H&D curve has a shoulder that rolls off gradually and negative film is resistant to overexposure for this reason. With ETTR, one exposes for the highlights, placing then just short of clipping, and overall tonality can be brought back in post processing. What about negative film: the usual advice is to expose for the shadows and develop for the highlights, the exact opposite of digital.

Going back to your experiment with VPS the effect of exposure will depend on what you have surrounding your gray card. This is discussed in Ansel's The Negative, page 67 in my 1981 edition. For what he describes as a short-scale subject, one can place the important shadows on Zone III and the highlights will fall on Zone VI and less than the full range of tones will be exposed. This gives the option of placing the shadows higher and getting better shadow definition. Ansel states: "...Therefore, in the absence of compelling reason to give the additional one stop of exposure, use the Zone III placement of the shadow area; the resulting negative will have less grain and higher acutance since there is no 'wasted' density, and will still have full detail in the important areas." He then proceeds to talk about development and printing procedures to give the desired tonalities in the print and the handling of full scale subjects where there is less "exposure latitude".

This is the exact opposite of your findings with VPS, and we would call Ansel's exposure in this case as to the "Left". In his exposure scales, he placed Zone I to the left just as we do with histograms in the digital era. The concepts have not changed: one exposes to get optimal image quality, taking into account the characteristics of the medium.

Regards,

Bill
« Last Edit: May 25, 2013, 11:08:29 AM by bjanes » Logged
RFPhotography
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« Reply #63 on: May 25, 2013, 10:52:21 AM »
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OK...didn't read that in your comment, as I thought it was implicit in the original statement, "For a photographer, the exposure net result includes the consideration of ISO", as well as Bill Janes post.

I pay virtually no attention to anything Janes writes.  And yes, 'implicit'.  As in implied.  Which is what I said originally when I noted 'Emil hints at it'.  All I doing was trying to make it clearer. 
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bjanes
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« Reply #64 on: May 25, 2013, 10:53:08 AM »
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What's it doing to reduce the noise?

Good to know that at least some are agreeing that this process isn't increasing the photon count, I've been scratching my head trying to understand what the ISO on the Canon is doing to reduce the noise. Not implementing ETTR and setting the Canon to ISO 100 certainly doesn't produce the lowest noise in a capture. Why?

I can understand the argument that exposure is Aperture + Shutter but then ISO, at least in this case, plays a role. Do we need a separate acronym for Canon cameras whereby we increase ISO, don't adjust 'exposure' based on the increase and end up with less noise?

The answer for your Canon camera is discussed by Emil here in Figure 12a and the accompaning text:

"There are several ways to interpret this graph that are useful to keep in mind for making exposure choices. If one has the option to lower the ISO and the shutter speed (or widen the aperture), the highest S/N for the image is obtained by increasing the exposure, pushing the right end of the histogram right up to the upper edge of the range of exposure on the horizontal axis. This is the usual ETTR philosophy. Lowering the ISO one stop pushes the upper end of the dynamic range one stop to the right in absolute exposure, and pushing the histogram to the right climbs the rising S/N curve to better overall image quality.

If on the other hand, one is limited by the subject matter (freezing motion, depth of field requirements, etc) to a given maximum EV, then it makes sense to raise the ISO to pull the top end of the camera's dynamic range down to the top end of the histogram; this has little benefit at that upper end, since all the curves are on top of one another in that regime. Nevertheless it improves image quality by raising the S/N ratio on the shadow end of the curves."


In the latter case when one is limited by the subject matter, one gives the required exposure in terms of f/stop and shutter speed, and raises the ISO. In this case exposure (measured in lux-seconds) is fixed at the required level.

Bill
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bjanes
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« Reply #65 on: May 25, 2013, 11:01:49 AM »
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I pay virtually no attention to anything Janes writes.  And yes, 'implicit'.  As in implied.  Which is what I said originally when I noted 'Emil hints at it'.  All I doing was trying to make it clearer. 

I usually ignore your posts too, since any reasonable discussion with you is fruitless. You should brush up on basic definitions. Exposure is measured in lux seconds and is independent of the ISO. ISO (film speed on see Wikipedia) does affect our exposure decisions, since it describes how the sensor responds to exposure in terms of saturation.

Regards
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Jim Kasson
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« Reply #66 on: May 25, 2013, 11:05:26 AM »
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Digital is linear and any shadow luminance will be recorded but any image detail may be lost in noise. The digital sensor response is linear without any shoulder and highlights will be clipped abruptly when the sensor saturates. Some highlight recovery may be possible with Bayer CFA sensors, since the red and blue channels may still have some detail, but the color information in the green channel that clips first (with daylight and most artificial illumination) will be lost.

[snip]

The concepts have not changed: one exposes to get optimal image quality, taking into account the characteristics of the medium.

Well said, Bill -- as usual. Thanks.

There's something else that hasn't changed. Photographers can use knowledge of how their tools work to make better images, as you are proposing. They can also become fixated on technical minutia to a degree that it interferes with, or even prevents, making better images.

Jim

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« Reply #67 on: May 25, 2013, 11:27:58 AM »
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Historical perspective is always helpful and many concepts learned earlier can be carried over into digital photography.
That's why I posted it <g>. The point was that ideally, photographers test their processes. Digital doesn't change that a lick.

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However, the response of negative film and the digital sensor are quite different.
Of course it is (hence more reason to test). I'm well aware of H&D curves versus linear capture.

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Going back to your experiment with VPS the effect of exposure will depend on what you have surrounding your gray card.
I'm going back nearly 30 years but I don't recall that being an issue when this one class of 30-ish students presented their work. I can't recall any presented assignment where the decrease in of ISO 160 didn't produce better results.

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This is the exact opposite of your findings with VPS, and we would call Ansel's exposure in this case as to the "Left".
OK, but it doesn’t jive with the results from this class and I'm pretty sure, this assignment was given for years and years to other's. Maybe their results were different, I don't know. But again, the entire point was: test the process. Don't assume the ISO setting is ideal. Learn to expose for ideal (in this case) color neg. Digital doesn't change the need to understand and properly control exposure + development.
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Andrew Rodney
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RFPhotography
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« Reply #68 on: May 25, 2013, 11:35:17 AM »
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I usually ignore your posts too, since any reasonable discussion with you is fruitless. You should brush up on basic definitions. Exposure is measured in lux seconds and is independent of the ISO. ISO (film speed on see Wikipedia) does affect our exposure decisions, since it describes how the sensor responds to exposure in terms of saturation.

Regards

I feel exactly the same way and the rest of your statement is a perfect example of why. You are simply too caught up in the science and pedantry of dictionary definitions to make any discussion of practical photography possible.  To borrow fro Jim's blog essay, you spend too much time sharpening pencils.
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jrsforums
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« Reply #69 on: May 25, 2013, 11:43:20 AM »
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I feel exactly the same way and the rest of your statement is a perfect example of why. You are simply too caught up in the science and pedantry of dictionary definitions to make any discussion of practical photography possible.  To borrow fro Jim's blog essay, you spend too much time sharpening pencils.

Bob, in my opinion, understanding the definition of terms used....and by whom...is very important.  This is why I bothered to post the difference in how photographers use 'exposure' and how "sensor scientist" (the actual definition) use it.

If we do not all agree on the definition of the terms we are trying to discuss, we just talk past each other....which is what often happens on these forums.
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« Reply #70 on: May 25, 2013, 01:41:33 PM »
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Exposure is measured in lux seconds and is independent of the ISO. ISO (film speed on see Wikipedia) does affect our exposure decisions, since it describes how the sensor responds to exposure in terms of saturation.

That same page goes on to say:

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An appropriate exposure for a photograph is determined by the sensitivity of the medium used. For photographic film, sensitivity is referred to as film speed and is measured on a scale published by the International Organization for Standardization (ISO). Faster film, that is, film with a higher ISO rating, requires less exposure to make a good image

Again, maybe semantics, but the sentence above seems to link ISO and exposure together. Or as I said earlier, how can one expose properly, even within the ballpark without taking ISO into account?
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« Reply #71 on: May 25, 2013, 02:55:35 PM »
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Hi,

Getting back to the original question, ETTR is about utilizing the capability of the sensor. We want to have maximum exposure possible as this minimimises the noise in the image. Setting a higher ISO means underexposure, that is some of the capacity of the sensor is thrown away. What we really discuss is if it it better to underexpose at nomina ISO or set a higher ISO and let camera electronics play a few less or more dirty tricks.

Best regards
Erik

That same page goes on to say:

Again, maybe semantics, but the sentence above seems to link ISO and exposure together. Or as I said earlier, how can one expose properly, even within the ballpark without taking ISO into account?
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RFPhotography
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« Reply #72 on: May 25, 2013, 03:26:56 PM »
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Bob, in my opinion, understanding the definition of terms used....and by whom...is very important.  This is why I bothered to post the difference in how photographers use 'exposure' and how "sensor scientist" (the actual definition) use it.

If we do not all agree on the definition of the terms we are trying to discuss, we just talk past each other....which is what often happens on these forums.

I don't disagree.  However, it's also possible to get too caught up in the precision of dictionary definitions and in doing so give too short shrift to, let's call them, working definitions.  It's sort of like book learning vs practical experience.  Book knowledge is important but what many learn early on in their working lives is that what's in the books bears little resemblance to how things actually work.  Ask many lawyers, for example, and they'll tell you that what they learned in law school has little do do with the practice of law.
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bjanes
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« Reply #73 on: May 25, 2013, 03:36:49 PM »
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That same page goes on to say:

Again, maybe semantics, but the sentence above seems to link ISO and exposure together. Or as I said earlier, how can one expose properly, even within the ballpark without taking ISO into account?

I agree 100% that ISO must be taken into account since the ISO rating of the sensor determines how it responds to a given exposure (in lux seconds or a given shutter speed and aperture). That was what I was trying to convey to Bob Fisher in post 65 above, but he ignores me as well as generally accepted definitions. Without an ISO rating the light meter would be useless. The term "exposure" is used by some in a less restrive manner and to them merely taking the picture is an exposure.

I agree that testing is also absolutely necessary just as in Ansel's time. The ISO saturation standard allows 0.5 EV of headroom and if you are exposing to the right, you may not want to allow that. Those who use the camera histogram for exposure decisions must test to determine how much headroom it allows. For my Nikons it is about 0.5 EV. I don't shoot Phase One MF, but I understand that its sensors are rated to allow even more headroom.

Bill
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bjanes
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« Reply #74 on: May 25, 2013, 03:46:12 PM »
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Well said, Bill -- as usual. Thanks.

There's something else that hasn't changed. Photographers can use knowledge of how their tools work to make better images, as you are proposing. They can also become fixated on technical minutia to a degree that it interferes with, or even prevents, making better images.

Jim

Jim, masterfully stated, a compliment countered with constructive criticism. Too bad we sometimes do not have more in this vein on the forum. Sad

I hope I don't spend too much time sharpening my pencils. Smiley

Bill
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« Reply #75 on: May 25, 2013, 04:08:54 PM »
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Jim, masterfully stated, a compliment countered with constructive criticism.

Bill, I didn't mean it as any kind of criticism. I don't think that shoe fits you.

Jim
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jrsforums
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« Reply #76 on: May 25, 2013, 04:31:39 PM »
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I don't disagree.  However, it's also possible to get too caught up in the precision of dictionary definitions and in doing so give too short shrift to, let's call them, working definitions.  It's sort of like book learning vs practical experience.  Book knowledge is important but what many learn early on in their working lives is that what's in the books bears little resemblance to how things actually work.  Ask many lawyers, for example, and they'll tell you that what they learned in law school has little do do with the practice of law.

I think you totally missed my point or just choose to ignore it.

There is a difference between book learning (definitions) and practical experience (how you best apply what you learn).

However, you can not use practical learning to redefine terms.....unless you carefully ensure that you understand the (book) term and how you have modified it.  It does not allow you to reject the book learned definitions.

To use your analogy, if a lawyer is using case law, he would not state that it meant something that was not documented.  However, after stating what the case law "defined", he might state how it could be "interpreted" to mean something different...and used that way for the current case he was working on.

Back to what we have been talking about....if one person talks about exposure...and defines it not to include ISO...and the other talks about exposure...but believes it includes ISO...and they do not make sure about this when incuding it in there points, there will be confusion and much angst which would not happen if they carefully used the terms....as shown in this thread.
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John
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« Reply #77 on: May 25, 2013, 05:46:14 PM »
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I didn't miss your point, John nor did I choose to ignore it.  Look, forget anything I've said.  Clearly I have no credibility here and frankly, I don't care.  But another, highly regarded photographer, author and speaker participating in this thread also feels that ISO is part of exposure in some manner and in some circumstances.  So I'm not alone in my position.  I understand the dictionary definition.  I understand the technical points.   But from a practical, on the ground standpoint, ISO plays a part in determining exposure.  Even Emil 'intimates' that in the article of his that has been referenced several times; as you and I have both agreed.

You're saying the same thing I am with your legal analogy.  What's in the book is open to interpretation.  No different here.

I'm not rejecting the book learning.  Not by any means.  All I'm saying is that the book knowledge isn't always completely relevant in real world conditions.  That's the only point I'm making.  Test bench jockeys won't understand that.  Photographers will.  The 'angst' in this thread has, seemingly, been a result of the complete repudiation by some of the idea that, in some cases, 'exposure' will include ISO.  I think the people who support the idea that exposure 'can' include a consideration of ISO have been abundantly clear in their position.
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« Reply #78 on: May 25, 2013, 06:27:53 PM »
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We want to have maximum exposure possible as this minimimises the noise in the image.

Agreed!

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Setting a higher ISO means underexposure
Expect in the example I posted from the Canon <g>.

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What we really discuss is if it it better to underexpose at nomina ISO or set a higher ISO and let camera electronics play a few less or more dirty tricks.
Seems to depend on the camera and sensor. And takes us back to the need to test the process. I'm sure everyone in this conversations understands you'd treat a camera JPEG differently than a raw in terms of exposure. I would suspect we came to this understanding by testing ETTR while capturing a JPEG.

It does concern me that a Canon for example deals with ISO settings differently than other camera systems. But at due to some testing, I at least expect this and can say the advise that raising ISO always increases noise isn't always true.
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Andrew Rodney
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« Reply #79 on: May 25, 2013, 08:05:50 PM »
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I have to say that my interest in photographic matters leans strongly towards the practical application of the theory, which is why I frequently carry out my own tests on my own equipment, not necessarilly to prove or disprove the theoretical claims that are being made, but to find out how significant such claims for particular technical qualities may be in practice, and in what circumstances they may be of some advantage to my efforts in producing an image or print to my own satisfaction.

However, in order to make such tests one really has to understand clearly what it is one is testing, and therefore a precise definition of the fundamental concepts related to the features one is testing, is necessary.

I remember well the occasion when this phenomenon of improved image quality resulting from the use of an increased ISO first came to my attention. It was on the old Rob Galbraith photographic forum around the year 2005/6. A poster by the name of John Sheehy made a comment to the effect, "It is better to use an exposure at ISO 200 than ISO 100 because you get better shadow detail."

Now, being the sort of guy who refuses to accept anything that doesn't make sense, I chimed in and disputed his claim. How can an exposure at ISO 200 possibly be better than an exposure at ISO 100? At ISO 100 the sensor receives double the amount of light. SNR is bound to be better.

John quickly dispelled my confusion by explaining that he was referring to circumstances where the same exposure was used at both ISO settings. My misunderstanding was due to my conflating ISO settings with actual exposure, which is quite understandable because we always have to either deliberately choose a specific ISO everytime we take a shot, or allow the camera to automatically choose it for us.

In order to avoid such confusion, I think it is better to consider exposure as something which is determined only by F/stop, shutter speed, and that quality we often ignore, T/stop, which relates to the transmissive qualities of the glass in the lens.

The ISO setting is merely an instruction to the camera's internal processing electronics to process an exposure in a particular way.
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