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Author Topic: “Expose to the Right” & relation to ISO Invariance  (Read 93950 times)

AlterEgo

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #40 on: June 16, 2015, 10:39:02 pm »

However I am a bit curious about how that value got there and how it is used by the raw converters.
as it was noted it is hardcoded in ACR/LR code... other converters, if you are talking about NEF files, either do not have any hidden expo-corrections (like RPP for example) or deal with that by increasing brightness through some tone curves/commands in tone curve files (C1) or LUTs in whatever camera profiles they use or may be even have something like Adobe does... you need to test your specific converter by comparing with known tools that don't do anything hidden
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AlterEgo

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #41 on: June 16, 2015, 10:40:59 pm »

the dng profile editor
now with DCamProf from Torger this tools is simply obsolete for dcp profile creation, may be only useful as a visual profile editor...
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bernie west

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #42 on: June 17, 2015, 12:24:01 am »

Which demonstrates that not only the OP is getting confused by the wrong use of the ETTR concept.  :(

The ISO 100 shot received 8x less exposure than what the exposure meter recommended for ISO 800. And just because the Canon architecture uses pre- and post amplification,  there can be a benefit to increase the ISO setting if you deliberately underexpose (which is not ETTR), but not nearly as much as getting the benefit from correct exposure (=ETTR).

You can prove it to yourself by shooting the same shot with 8x as long an exposure time (which apparently does not clip this crop of the image you picked), and compare it with the ISO 800 shot which then received 8x less exposure and got amplified 8x after capture.

Nothing beats real signal in the form of Photons. That's what ETTR is about.

I'm sure others have already addressed this, but you contradict yourself here.  You say that the ISO100 image received 8x less exposure, therefore he doesn't understand ETTR.  But at the end here you say that ETTR is all about real signal in the form of photons.  Which is exactly what AR and I have said.  Your final pronouncement is correct.  The former is not.  Increasing ISO doesn't increase "real signal in the form of photons".
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mouse

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #43 on: June 17, 2015, 01:24:43 am »

I'm sure others have already addressed this, but you contradict yourself here.  You say that the ISO100 image received 8x less exposure, therefore he doesn't understand ETTR.  But at the end here you say that ETTR is all about real signal in the form of photons.  Which is exactly what AR and I have said.  Your final pronouncement is correct.  The former is not.  Increasing ISO doesn't increase "real signal in the form of photons".

First, I don't interpret Andrew's post as an example of ETTR.  The number of photons captured is the same in both images.  It is simply a demonstration of a situation where a predetermined aperture and shutter speed result in an underexposed image at base ISO.**   In such a case one has two options:
(1) Boost the ISO or
(2) Amplify the signal in post processing.
It is clear that, for the camera used for this demo, the first option results in a much less noisy image.

I think Bart's objection stems from the fact that Andrew's post could hardly be considered an example of how to employ ETTR, and I am guessing that AR himself would not describe it as such.  (However, I should hasten to add, I am not empowered to speak for either of these gentlemen.)

**In fact the image is underexposed at ANY ISO.  I do believe that, for the purpose of such discussions, one should confine the use of the term "exposure" to mean the amount of light (photons) reaching the sensor; thus influenced only by aperture and shutter speed.  ISO then is simply an (in-camera) electronic amplification of the signal generated by exposure.
« Last Edit: June 17, 2015, 01:29:14 am by mouse »
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bernie west

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #44 on: June 17, 2015, 03:22:46 am »

Andrew's post wasn't supposed to be an example of ETTR.  Anyone who thinks that needs to upgrade their reading firmware.  ;)
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Bart_van_der_Wolf

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #45 on: June 17, 2015, 04:14:30 am »

I'm sure others have already addressed this, but you contradict yourself here.  You say that the ISO100 image received 8x less exposure, ...

Hi Bernie,

The confusing part of the example is that both shots received the same exposure, check the exposure time and the shutterspeed. I said that it received 8x less exposure than the exposure meter would have suggested (if it had been metered at ISO 100), but it was instead exposed as if ISO 800 was used for metering.

That means that if we assume that the ISO 800 shot did not result in clipping (histogram moved to the right end without introduction of clipping), the ISO 100 shot therefore received 8x less exposure than an ETTR shot would have. Therefore it doesn't demonstrate ETTR. What it does demonstrate is something completely different, namely ISO variant behavior. That behavior is typical mainly for Canon cameras but not for most others, like Sony sensor based ones from Sony and Nikon.

Quote
But at the end here you say that ETTR is all about real signal in the form of photons.  Which is exactly what AR and I have said.  Your final pronouncement is correct.  The former is not.  Increasing ISO doesn't increase "real signal in the form of photons".

Indeed it doesn't, although increasing the ISO on the ISO variant Canon example does help to improve the S/N ratio of an underexposed non-ETTR shot. But I also said that using more photons for the exposure is always a better approach, provided that we have the luxury of absence of camera or subject motion that needs to be frozen with a short exposure time. When we must prioritize shutter speed to get the shot, we will not be using ETTR. ETTR is about optimizing signal quality, and collecting as many photons as possible without clipping important highlight detail is the best way. Base ISO will then allow to maximize the DR.

Cheers,
Bart
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Jack Hogan

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #46 on: June 17, 2015, 04:34:08 am »

Now I'm getting a bit confused, Jack.  ;)

Surely with all cameras, whether they are ISO invariant or not, one should attempt to apply ETTR at base ISO for best results, if the required shutter speed and aperture allow it.

Likewise, with all cameras, whether they are ISO invariant or not, one needs to apply the ETTR process regardless of  the ISO setting chosen, in order to get the best results, the best results being the lowest noise in shadows and mid-tones, without blowing wanted highlights.

For example, if I'm using a D7000 or D7200, which I would say are pretty close to being ISO invariant cameras, and I decide to use ISO 800, not only because I need a fast shutter speed, or because the light is not good, but also because I want to clearly see what I've shot on the camera's LCD screen, and/or share the images with others in the field, then I still need to apply the ETTR process at ISO 800 in order to achieve the lowest noise and the best review image.

In other words, any exposure which does not push the histogram to the right, whatever the chosen ISO, will result in more image noise.
Where's the confusion? The fact that one might not need to use a high ISO with an ISOless camera, if one doesn't feel the need to be able to clearly view the shots taken on the camera's LCD screen, does not mean that the ETTR principle does not apply if one does choose to raise ISO, rather than underexpose at base ISO.

However, that is not to deny that the ISOless camera has clear advantages. But that is a separate issue.

Well put Ray.  I would add that ETTRing an ISOless camera at base ISO the IQ maximizing photographer is guaranteed the best IQ possible from the capture.  Not necessarily so as ISO is raised.

Jack
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Bart_van_der_Wolf

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #47 on: June 17, 2015, 04:36:28 am »

Andrew's post wasn't supposed to be an example of ETTR.  Anyone who thinks that needs to upgrade their reading firmware.  ;)

Hi Bernie,

I interpreted Andrew's post as agreeing with you that at a higher ISO one can still use ETTR. That is what I disagree with, and that the example used an ISO variant camera was not what the OP seemed to ask.

At best, when you boost the ISO, the histogram is the result of amplifying the underexposed signal for a more normal looking thumbnail or OOC JPEG. It is not EXPOSING to the right (ETTR), but more post-exposure AMPLIFYING (the resulting histogram) to the right. There is a large difference in image quality.

Image quality can only be optimized by using more photons for the EXPOSURE, and to avoid clipping for the maximum possible exposure one needs to us the native ISO. Boosting ISO on an ISO invariant camera will normally just lead to underexposure, which will then be somewhat compensated by boosting the amplification during Raw conversion and postprocessing. The histogram that results is shifted to the right, but I do not consider that EXPOSING to the right.

Hope that clarifies what I intended to say.

Cheers,
Bart
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Bart_van_der_Wolf

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #48 on: June 17, 2015, 04:42:14 am »

In other words, any exposure which does not push the histogram to the right, whatever the chosen ISO, will result in more image noise.

Hi Ray,

I agree, with emphasis added to the word exposure. That's the gist of it, IMHO.

Cheers,
Bart
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bernie west

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #49 on: June 17, 2015, 04:43:04 am »

@Bart... No one is suggesting that bumping up ISO is an example of ETTR.  All that we are saying is that you can still employ ETTR (particularly in a non-ISOless sensor) away from base ISO.  Someone earlier (I think it might have been you) was asserting that you have to operate at base ISO to get the benefits of ETTR.  That's simply not true, as I and others have explained.  Andrew posted that example to show that increasing ISO doesn't necessarily result in a worse SNR as compared to doing it later in post processing.  This is related to what the OP was asking.
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Jack Hogan

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #50 on: June 17, 2015, 05:14:44 am »

Someone earlier (I think it might have been you) was asserting that you have to operate at base ISO to get the benefits of ETTR.  That's simply not true, as I and others have explained.  Andrew posted that example to show that increasing ISO doesn't necessarily result in a worse SNR as compared to doing it later in post processing.  This is related to what the OP was asking.

Bernie, if it was me I was misunderstood because I never said that one has to operate at base ISO to get the benefits of ETTR.  My first post said this instead, in the context of this thread's title, ISOless cameras:

Well, for maximum captured IQ you would ETTR at base ISO , if possible.

I am still asserting that :)  Of course if there are reasons why you cannot do that feel free to ETTR at a higher ISO with the same exposure.  Just be aware that with an ISOless camera it is less likely that you will capture the best IQ possible.

Jack
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spidermike

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #51 on: June 17, 2015, 05:17:19 am »

Some early digital cameras had a base ISO of 50. Now for nearly all DSLRs base ISO is ISO100, or even 160 or 200.
Does this mean it is impossible to practice ETTR with modern digital cameras?

 ::)
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bernie west

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #52 on: June 17, 2015, 05:53:02 am »

As an aside, ETTR is the gift of a story that keeps on giving!  It's years since this idea kicked off and it's still causing contention all these years later. :D
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Bart_van_der_Wolf

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #53 on: June 17, 2015, 06:49:49 am »

@Bart... No one is suggesting that bumping up ISO is an example of ETTR.  All that we are saying is that you can still employ ETTR (particularly in a non-ISOless sensor) away from base ISO.

Sorry, but now I'm becoming confused (speaking for myself again) about what you mean exactly, maybe we mean the same thing but are not saying it precisely enough? I (still) do not see how one can ETTR, away from base ISO. All that happens with an ISO boost in an ISO invariant camera is an amplification of the (resulting) histogram to the right, and that is also with a tonecurve/gamma applied. So we need to under-expose to avoid the histogram from climbing the right wall. If that's what you mean, then I understand, but I wouldn't call it "Expose to the right" but rather "Amplify to the right" after underexposure(!).

Cheers,
Bart
« Last Edit: June 17, 2015, 06:54:08 am by BartvanderWolf »
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bernie west

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #54 on: June 17, 2015, 09:07:32 am »

I can't really make it any simpler.  ETTR is about exposure - that is, amount of photons hitting the sensor.  What ISO you shoot at has zero affect on this.  Only your shutter speed and aperture affect exposure.  I think the reason you are getting confused is that you are assuming that an image taken at higher ISO will be clipped (i.e. the ADC will be fully saturated).  But that's clearly not necessarily the case, as we all know.  If there is leeway to increase exposure at ISO 800, then you can apply the principles of ETTR.  You can do it at ISO 4 billion if you want.  ISO has no effect on the principles of ETTR.  The only effect it has is that larger ISO's have reduced dynamic range, and may also saturate the ADC.
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Ray

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #55 on: June 17, 2015, 09:07:52 am »

If that's what you mean, then I understand, but I wouldn't call it "Expose to the right" but rather "Amplify to the right" after underexposure(!).

Cheers,
Bart

Now we're getting into semantics, Bart. The word 'right' in the phrase ETTR refers to the 'right' of the histogram. The histogram, as seen on the camera's LCD screen, does not distinguish between the different states of 'full-well highlights' (ETTR at base ISO) and the amplification of 'less-than-full-well highlights' resulting from ETTR at a higher-than-base ISO.

If one feels the need to distinguish between these two states with regard to optimum exposure, then one needs two different acronyms. ETTR at base ISO could become EFFWH (Expose For Full Well Highlights), and ETTR at higher-than-base ISO could become ATTR (Amplify To The Right).  ;D
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digitaldog

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #56 on: June 17, 2015, 09:25:28 am »

interpreted Andrew's post as agreeing with you that at a higher ISO one can still use ETTR. That is what I disagree with, and that the example used an ISO variant camera was not what the OP seemed to ask.
I'll post the facts, you Gentlemen can argue, discuss, come to conclusions.

I provided two captures.
Capture 1 was shot at ISO 100 with a f-stop and shutter recommendation from an Incident meter (Minolta Flash Meter III). It is what many would suggest is 'correct' exposure.
Capture 2 was shot at ISO 800 with the same settings as capture 1. Identical in every respect expect I changed the ISO setting from 100 to 800!
Capture 2 shows less noise than capture 1. This is a very magnified view of the image but it is clear that the capture with the higher ISO has less noise, better S/N.

I provided this example to dismiss two commonly heard urban legions. The first is higher ISO always produces more noise. That's clearly not the case here!
The other reason I posted was to dismiss the idea that ETTR must be conducted at base ISO. If that's true, explain the effect upon the noise at ISO 800.

Now you guys can argue, discuss and come to some conclusions in terms of semantics  about what Exposure means, what ETTR means, or the benefits expected from ETTR (I'll suggest the expected benefits are exactly what is seen in capture 2 and not capture 1 despite the external meter told me capture 1 was the 'correct exposure'.

Gentlemen, start your engines....
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Bart_van_der_Wolf

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #57 on: June 17, 2015, 09:43:49 am »

I can't really make it any simpler.  ETTR is about exposure - that is, amount of photons hitting the sensor.

Check.

Quote
What ISO you shoot at has zero affect on this.

Check.

Quote
Only your shutter speed and aperture affect exposure.

Check.

Quote
I think the reason you are getting confused is that you are assuming that an image taken at higher ISO will be clipped (i.e. the ADC will be fully saturated).

Well, there lies the rub. Try an ETTR at base ISO. Now boost the ISO, what happens?
We did 'expose to the right', and the histogram will be clipped at the right (because it was then amplified).

 
Quote
But that's clearly not necessarily the case, as we all know.

Not necessarily, but for that to not happen we must first underexpose. Calling that exposing to the right confuses (me), because you have to underexpose to get there, and its hurting image quality. What should have been done is reducing the ISO, i.e. the amplification, and retain optimal quality. Wasn't that the goal of ETTR, optimizing quality by exposure? Or is it just to fill out the histogram by changing the amplification? I'd say the former, you seem to say the latter.

Can we agree on that? Because if that's not what is confusing the real issue of quality, then what is?

Quote
If there is leeway to increase exposure at ISO 800, then you can apply the principles of ETTR.  You can do it at ISO 4 billion if you want.  ISO has no effect on the principles of ETTR.  The only effect it has is that larger ISO's have reduced dynamic range, and may also saturate the ADC.

Yes, because ISO has nothing to do with exposure as such, it's just like yanking the volume knob, but the band is not playing any louder nor is their music getting any better (if they don't play loud enough to begin with, people at the back won't be able to hear them, so then amplifying the volume would cure that, but band still isn't playing any louder). If it has nothing to do with exposure, then why call it Expose to the right?

Again, is that what we're dealing with? Although the exposure doesn't change, you call boosting the amplification by increasing the ISO an Exposure boost?

Cheers,
Bart
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Bart_van_der_Wolf

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #58 on: June 17, 2015, 10:16:00 am »

I'll post the facts, you Gentlemen can argue, discuss, come to conclusions.

I provided two captures.
Capture 1 was shot at ISO 100 with a f-stop and shutter recommendation from an Incident meter (Minolta Flash Meter III). It is what many would suggest is 'correct' exposure.
Capture 2 was shot at ISO 800 with the same settings as capture 1. Identical in every respect expect I changed the ISO setting from 100 to 800!
Capture 2 shows less noise than capture 1. This is a very magnified view of the image but it is clear that the capture with the higher ISO has less noise, better S/N.

Hi Andrew, thanks for taking the time to explain. Assuming these were Raw captures, the brightness of the converted ISO 800 shot should have been much brighter, so I assume that the brightness was made equal in Lightroom with a.o.  the Exposure slider. Is that correct?

Quote
I provided this example to dismiss two commonly heard urban legions. The first is higher ISO always produces more noise. That's clearly not the case here!

Correct, although the Canon is different than an ISO invariant sensor design.

Quote
The other reason I posted was to dismiss the idea that ETTR must be conducted at base ISO. If that's true, explain the effect upon the noise at ISO 800.

Sure. Since the actual exposure was identical, either the ISO 100 shot needs to be brightened (which will only show the shot-noise with a large percentage of read noise added), or the ISO 800 shot darkened. By increasing the ISO to 800, in the Canon specifically, there is an amplification added to the captured signal before reading it out. Amplifying the signal and then adding read noise is different from adding read noise and then amplifying that. The order of things matters, in Canons.

People like Jim Kasson have written computer applications to allow sensor simulatons that can be fed different pre- and post-amplification amounts. That could help to quantify the differences, but I'm not sure if he'd like to get caught up in this thread, and if he has the actual parameters needed for a Canon EOS 5D Mark III (he has done more simulations with Sony sensor models, like used in Sonys and Nikons).

So boosting the ISO in Canons (to something like ISO 800-1600 for different models) will improve/reduce the total noise that amplification plus read noise produces. That is particularly helpful for under-exposed shots, e.g. because a shorter exposure time was required to freeze motion. But again, this is not how ISO invariant (non-Canon) cameras respond.

So as useful the demonstration is, IMHO it's not about ETTR on ISO invariant cameras.

Cheers,
Bart
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bernie west

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Re: “Expose to the Right” & relation to ISO Invariance
« Reply #59 on: June 17, 2015, 10:19:14 am »

@Bart... Ok, I see the confusion, and it's probably my fault.  I've been talking about the concept of exposing to the rightest.  Not necessarily at the very rightmost point.  I went down that path as it more accurately represents the scenario of the OP.  Along the way I've carried that into a more specific discussion about ETTR.  But as you say, ETTR is more specifically about exposing right up to the clipping point.  So if you manage that at base ISO, then there is obviously nothing to be gained (and a lot to be lost) by raising ISO.

Apologies for the mixup.
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