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Author Topic: ETTR vs ISO  (Read 24980 times)
digitaldog
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« Reply #20 on: May 24, 2013, 12:13:45 PM »
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I agree...sorta.
I don't see anything but full agreement <g>. What part did I mess?

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Doing my own testing with RawDigger, I found, for the 5D3, that I could spot meter the highest significant highlight and then place it at +3 to +3.5 stops over metered.  This gave me an image exposed as far to the right as possible, without any channels clipped.
On my 5DMII using an incident meter, I was about 1.5+ stops but less than 2 stops before I clipped highlights (using the BableColor tile) with ACR/LR PV2010.
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Andrew Rodney
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BJL
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« Reply #21 on: May 24, 2013, 12:27:01 PM »
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But it's not obvious as I tried to illustrate with the Canon. A higher ISO produces less noise than a lower one (again, due to ETTR).
I think we agree, but with some extra complications for the special case of Canon's sensors: read on to my third bullet point. By "lowest viable ISO setting", I did not mean the camera's base ISO setting, but more like the lowest one that gives an acceptable combination of shutter speed and aperture when exposing "on meter".
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RFPhotography
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« Reply #22 on: May 24, 2013, 12:30:11 PM »
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It's only a problem when the photographer doesn’t understand the basics of exposure and the role it plays on other aspects of photography which I mentioned (ETTR that causes camera shake, undesired DOF etc). Otherwise ETTR is simply an attempt at producing the best quality data. In the old days, we could pop ISO 100 film OR ISO 800 film based on what we knew or thought we knew about exposing a scene. We used ISO 100 when we knew we wanted lower noise (grain) than ISO 800 and we had abundant light to produce the desired results (san's camera shake etc). IF you have enough light, why would you not setup the camera system to provide the most noise free image? Then you can go out and buy a plug-in that adds noise to look like film <g>.

I'm not denying that, Andrew nor am I arguing that point.  I'm simply stating that it's not, as some people believe, the only way to expose in all situations.  We're actually saying the same thing, just in a different way. 
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RFPhotography
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« Reply #23 on: May 24, 2013, 12:33:42 PM »
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But it's not obvious as I tried to illustrate with the Canon. A higher ISO produces less noise than a lower one (again, due to ETTR).


And that is a given with some cameras depending on how the sensor responds to changes in ISO.  With the so-called ISOless sensors the higher ISO and ETTR won't produce lower noise.  With some cameras, including some Canons it will - up to a point.  Where that point is will vary from camera to camera.  With the 5D it was about, if I recall, ISO 800.  With the newer 5D models it's a stop or so higher.
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digitaldog
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« Reply #24 on: May 24, 2013, 12:48:12 PM »
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And that is a given with some cameras depending on how the sensor responds to changes in ISO.  With the so-called ISOless sensors the higher ISO and ETTR won't produce lower noise.  With some cameras, including some Canons it will - up to a point.  Where that point is will vary from camera to camera.  With the 5D it was about, if I recall, ISO 800.  With the newer 5D models it's a stop or so higher.

Totally agree. The Canon's here are kind of unique. What I'm not fully understanding are the results and they differentiation between read noise and these settings versus exposure as defined by aperture/shutter to increase photon's which result in less noise. IOW, upping ISO on this Canon without adjust exposure lower results in less noise, this isn't ETTR? 
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Andrew Rodney
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« Reply #25 on: May 24, 2013, 12:56:14 PM »
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Totally agree. The Canon's here are kind of unique. What I'm not fully understanding are the results and they differentiation between read noise and these settings versus exposure as defined by aperture/shutter to increase photon's which result in less noise. IOW, upping ISO on this Canon without adjust exposure lower results in less noise, this isn't ETTR? 

I do not think it is....as the "classical" definition of ETTR is to increase the amount of photons captured, thus reduce SNR.  Increasing ISO does not increase the light (photons) captured.
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John
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« Reply #26 on: May 24, 2013, 12:59:48 PM »
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I do not think it is....as the "classical" definition of ETTR is to increase the amount of photons captured, thus reduce SNR.  Increasing ISO does not increase the light (photons) captured.

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?
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Andrew Rodney
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« Reply #27 on: May 24, 2013, 01:01:43 PM »
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In the case of the Canon used here...the real reason for increasing the ISO in this case is to reduce the read noise. Photon noise will be unchanged, since the number of photons collected is the same...

Bill


Bill...

With a camera such as the Canon, how do we know when it is beneficial to increase ISO to reduce noise?
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John
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« Reply #28 on: May 24, 2013, 01:04:45 PM »
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Totally agree. The Canon's here are kind of unique. What I'm not fully understanding are the results and they differentiation between read noise and these settings versus exposure as defined by aperture/shutter to increase photon's which result in less noise. IOW, upping ISO on this Canon without adjust exposure lower results in less noise, this isn't ETTR? 

But it sort of is.  At least in the context of the higher ISO.  If you shoot at ISO 100, f4 and 1/125 and that gives you a 'normal' exposure, then you switch to ISO 200 and shoot at the same aperture & shutter speed you're going to push the exposure 1 stop higher.  That's, essentially, what ETTR is doing.  Let's take it as a given for the moment that the 1 stop pushes the histogram to the right edge without clipping. 
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BartvanderWolf
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« Reply #29 on: May 24, 2013, 01:10:03 PM »
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Bill...

With a camera such as the Canon, how do we know when it is beneficial to increase ISO to reduce noise?


Hi John,

Jim Kasson devised an illustrative way to determine the maximum useful ISO setting, beyond which it is better to just underexpose and boost with the Raw converter's exposure setting.

See the attachment where I used a similar method to determine it for my camera.

Cheers,
Bart
« Last Edit: May 24, 2013, 01:17:31 PM by BartvanderWolf » Logged
digitaldog
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« Reply #30 on: May 24, 2013, 01:12:24 PM »
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But it sort of is.  At least in the context of the higher ISO.  If you shoot at ISO 100, f4 and 1/125 and that gives you a 'normal' exposure, then you switch to ISO 200 and shoot at the same aperture & shutter speed you're going to push the exposure 1 stop higher.  That's, essentially, what ETTR is doing.  Let's take it as a given for the moment that the 1 stop pushes the histogram to the right edge without clipping. 
What I initially thought too but now I'm more confused <g>.

My main purpose for the test I did and shown was to point out to those that write "Upping ISO always increases noise". Clearly that's not the case, at least with the Canon's.

IS the reduction I see in noise the result of ETTR or how Canon deals with this ISO (Read Noise)? IF our goal is to test ISO and exposure such we get the lowest noise, and altering ISO up provides less, is this or isn't this ETTR? Going back to film days, when I'd buy film in bricks, fill a refrigerator, run exposure, ISO and processing tests (with CC gel packs) to nail everything. I feel we need to do the same today with digital. It appears that with the Canon sensor, bringing ISO into the mix is necessary. Not fully sure why.
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Andrew Rodney
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« Reply #31 on: May 24, 2013, 01:17:06 PM »
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Hi John,

Jim Kasson devised an illustrative way to determine the maximum useful ISO setting, beyond which it is better to just underexpose and boost with the Raw converter's exposure setting.

Cheers,
Bart

Bart....

Jim did a great piece of work.  However, none of his testing included the Canons which have more of the ability to increase ISO.  Nor, if I remember correctly, a correlation to the DxoMark DR charts, which does seem to be valid.
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John
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« Reply #32 on: May 24, 2013, 01:19:14 PM »
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Jim did a great piece of work.  However, none of his testing included the Canons which have more of the ability to increase ISO.  Nor, if I remember correctly, a correlation to the DxoMark DR charts, which does seem to be valid.

John,

I just added a chart for my 1Ds3 to the earlier post, maybe that helps?

Cheers,
Bart
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RFPhotography
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« Reply #33 on: May 24, 2013, 01:20:54 PM »
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What I initially thought too but now I'm more confused <g>.

My main purpose for the test I did and shown was to point out to those that write "Upping ISO always increases noise". Clearly that's not the case, at least with the Canon's.

IS the reduction I see in noise the result of ETTR or how Canon deals with this ISO (Read Noise)? IF our goal is to test ISO and exposure such we get the lowest noise, and altering ISO up provides less, is this or isn't this ETTR? Going back to film days, when I'd buy film in bricks, fill a refrigerator, run exposure, ISO and processing tests (with CC gel packs) to nail everything. I feel we need to do the same today with digital. It appears that with the Canon sensor, bringing ISO into the mix is necessary. Not fully sure why.

It may be partly how Canon deals with noise.  There may be some sort of 'always on' noise reduction.  
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jrsforums
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« Reply #34 on: May 24, 2013, 01:24:41 PM »
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I don't see anything but full agreement <g>. What part did I mess?
On my 5DMII using an incident meter, I was about 1.5+ stops but less than 2 stops before I clipped highlights (using the BableColor tile) with ACR/LR PV2010.

The "sorta" was that with film many photogs had handheld incident or spot meters to support their testing and field work....today we often need to rely on what the cameras give us....which is why I mentioned what I d and Kasson's work.

With digital, I do not believe that an incident meter is key to optimizing exposure.  Middle grey is interesting; the significant highlight is what is most important as we want to get that properly placed without clipping.

 This is why I use the camera spot meter and Kasson used other methods to arrive at a histogram which mimic the Raw.

On Lightroom, as you know, 2010 and 2012 PV are significantly different on highlight clipping.  On 2012, a highlight above 96-97% will have at least one channel clipped and recovery applied.  this is why RawDigger was needed to calibrate the 5D3 readings...
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« Reply #35 on: May 24, 2013, 01:39:38 PM »
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The "sorta" was that with film many photogs had handheld incident or spot meters to support their testing and field work....today we often need to rely on what the cameras give us....which is why I mentioned what I d and Kasson's work.
IF they used such equipment in the past, why wouldn’t they do so today? Exposure is exposure. The only differences I see are: 1. We have an LCD to look at, which in this context is wrong. 2. We have linear encoded raw data which isn't like a JPEG or film which has a curve (film being H&D). So we treat this like a different kind of 'film' if you will.

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With digital, I do not believe that an incident meter is key to optimizing exposure.
 
The same is true for film. The differences are that an incident meter is less fooled than a reflective meter in an inexperienced users's hands. If they point that reflective meter at a white dog on snow and take what it tells them as a fact for proper exposure, they are in for a rude awaking. Not the case with the incident meter. But which ever you use, you have to use the tools properly. And no meter is useful until we decide on the ISO and that means we also have to put the processing (development) into the mix.

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Middle grey is interesting; the significant highlight is what is most important as we want to get that properly placed without clipping.
You can do this with either meter once you know how they behave and how your exposure and development behave.

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This is why I use the camera spot meter and Kasson used other methods to arrive at a histogram which mimic the Raw.
And if you point that at the white dog and understand it will inform you how to end up with a gray dog, then adjust, all is fine.

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On Lightroom, as you know, 2010 and 2012 PV are significantly different on highlight clipping.  On 2012, a highlight above 96-97% will have at least one channel clipped and recovery applied.  this is why RawDigger was needed to calibrate the 5D3 readings...
Yes but nothing brings back clipped data so you still need to figure out the limits here. In that context, this part of the test is somewhat raw processing agnostic. If you blow out all data at plus 2 stops over what the meter recommends, nothing will bring that back. Yet I agree that you can't separate the development further on, so again, we have to test the process, just as we did with film. That means finding the proper ISO, along with proper metering and development.
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Andrew Rodney
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jrsforums
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« Reply #36 on: May 24, 2013, 02:03:59 PM »
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IF they used such equipment in the past, why wouldn’t they do so today? Exposure is exposure. The only differences I see are: 1. We have an LCD to look at, which in this context is wrong. 2. We have linear encoded raw data which isn't like a JPEG or film which has a curve (film being H&D). So we treat this like a different kind of 'film' if you will.
 
The same is true for film. The differences are that an incident meter is less fooled than a reflective meter in an inexperienced users's hands. If they point that reflective meter at a white dog on snow and take what it tells them as a fact for proper exposure, they are in for a rude awaking. Not the case with the incident meter. But which ever you use, you have to use the tools properly. And no meter is useful until we decide on the ISO and that means we also have to put the processing (development) into the mix.
You can do this with either meter once you know how they behave and how your exposure and development behave.
And if you point that at the white dog and understand it will inform you how to end up with a gray dog, then adjust, all is fine.
Yes but nothing brings back clipped data so you still need to figure out the limits here. In that context, this part of the test is somewhat raw processing agnostic. If you blow out all data at plus 2 stops over what the meter recommends, nothing will bring that back. Yet I agree that you can't separate the development further on, so again, we have to test the process, just as we did with film. That means finding the proper ISO, along with proper metering and development.

First, there are a whole class of people, today, who never had all those tools...or want/need to carry them around if not necessary.  They need to understand how to use the tools they have available to them.

Second, I think you missed my point.  An incident reading will not help you find the significant highlight in a scene....and place it as far to the right as possible.  With testing, you can assume the range of the scene...or, if like you, you are really experienced, you can adjust the EC by knowing if bright tones are or are not present.

I agree that a wide reflective meter can be easily fooled.  However, I am talking about the spot meter, which is fairly narrow on a 5D3.

Reading the reflected light from the significant highlight with a spot meter places it (with knowledge and pretesting) in the right of the histogram....without any clipping (of significant tones).  All the other tones fall where they may.  No guessing on tonal values is needed.

This maximizes the dynamic range of the camera.  If the histogram shows shadows being clipped, the only choice is to bracket and blend.
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« Reply #37 on: May 24, 2013, 02:10:11 PM »
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Yes but nothing brings back clipped data so you still need to figure out the limits here. In that context, this part of the test is somewhat raw processing agnostic. If you blow out all data at plus 2 stops over what the meter recommends, nothing will bring that back. Yet I agree that you can't separate the development further on, so again, we have to test the process, just as we did with film. That means finding the proper ISO, along with proper metering and development.

We agree.

Just to be clear, this is why I mentioned "calibrating" with RawDigger.  The setting of for the 5D3 of about 3.5 stops over the spot reading of the significant highlight places that highlight at about 96%  in LR.  Above that is about 2 stops of potentially "recovered" highlights....which is nice, but will never have the texture and colors of the unrecovered highlights....a nice "buffer" to have, but not optimal to best image quality.
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« Reply #38 on: May 24, 2013, 02:10:27 PM »
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Yes. Exposure settings for aperture and shutter are identical, the only difference is the ISO setting. And the differences in the amount of noise is significant as one would expect with ETTR (optimal exposure for raw).

The exposures are the same, so how do you call the shot at higher ISO as optimal exposure for raw? To obtain the same exposure while varying the ISO, one would likely set the camera to expose manually, set the aperture and shutter speed, and then vary the ISO. If you are on auto exposure, increasing the ISO will result in reduced exposure and reduced number of photons collected.

I don't care about the Histogram! But what I see is a vast difference in noise whereby the ONLY setting change is ISO. So it's obviously affecting the degree of noise.

That is where confusion sets in. The appellation "ETTR" implies that the histogram is a determining factor and the histogram gives some indication of the number of photons collected only at base ISO. Certainly, at any ISO it is not wise to leave space at the right of the histogram is one is interested in the best SNR.

You saying increasing the ISO in this case is to reduce the read noise, this isn't also ETTR? Seems the number of photons collected should be the same since what he's calling exposure is fixed in both examples. The results however are clear in terms of the differences in noise and I understand that not all camera sensors respond as this Canon does.

I wouldn't call it exposure to the right, since the exposure is the same in both instances. However, this is all semantics and the important point it to obtain maximal image quality.

Bill
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digitaldog
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« Reply #39 on: May 24, 2013, 02:18:40 PM »
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First, there are a whole class of people, today, who never had all those tools...or want/need to carry them around if not necessary.  They need to understand how to use the tools they have available to them.
That's fine. But it doesn't dismiss the need for proper understanding of exposure and use of tools for producing proper exposure. Or they don't care, then neither do I <g>.

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Second, I think you missed my point.  An incident reading will not help you find the significant highlight in a scene....and place it as far to the right as possible. 

It will give you a very good indicator of scene exposure if the proper ISO is setup and one adjusts properly to produce ETTR. Yes, a reflective spot meter is useful to gauge where highlights specifically fall. Or for determining scene contrast. But you can use an incident meter for ETTR easily and this tool was the ONLY way to get a meter reading for the article I did where I wanted to shoot flash and figure out where I could pin white just below a very specular white. I couldn't use nor didn't need a reflective meter here.

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I agree that a wide reflective meter can be easily fooled.  However, I am talking about the spot meter, which is fairly narrow on a 5D3.
It's a useful tool, no question. Again, the user needs to understand what the tool is telling them, again this is exposure 101, it's been this way since meter's were invented I suspect.

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Reading the reflected light from the significant highlight with a spot meter places it (with knowledge and pretesting) in the right of the histogram....without any clipping (of significant tones).  All the other tones fall where they may.  No guessing on tonal values is needed.
What Histogram? The camera's is pretty much useless here if precision is your goal. Why even mess with a Histogram? One need to understand how their meter works I think we agree. We need to understand how the 'film' in your DSLR reacts too. We didn't have nor need histograms till very, very recently in the time frame of photography. We really don't need it today although if the camera gave us a raw histogram, that be useful to a point. It still has no idea about the processing part of this.
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Andrew Rodney
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