“Expose to the Right” & relation to ISO Invariance

[rogoldboy]

Hello All:

I am fairly well versed with Histograms and ETTR.   

My basic understanding of ISO invariance is that you can have an exposure set with ISO 3200, or you can use the same shutter speed and aperture but reduce the ISO to 100 and then push it 5 stops in Camera RAW. Each image, made differently, will have roughly the same exposure value, with the +5 Camera RAW image exhibiting better noise qualities.

My question is “How does this then affect the use of ETTR?”

Thanks for any and all insight,

rogoldboy

[bernie west]

It depends on how the ISO gain is implemented in the camera.  As a really general principle, analogue gain via in-camera iso is going to be more accurate (i.e. better signal to noise ratio) than using post-processing digital gain.  But there's other variables that come into play.  I don't profess to understand it well (as I haven't bothered to look into it yet) but there is the concept of an ISO-less camera - or at the least a range of iso's that don't follow the above principle.  The others with more technical knowledge will post with the details.  As far as I understand it, some cameras with the Sony sensors - like the Nikon D800/810, Sony A, and some of the Pentax's have ISO-less performance.  That means, in the case of my camera the D810, that there is little to no benefit to raising ISO over about 800 ISO.  That is, you can get the same effect from a digital push as you can from in-camera ISO gain.  Why that is the case conceptually, I'd like to know.  It seems like a waste of opportunity to get a better SNR from analogue gain as opposed to digital gain.

[AlterEgo]

I am fairly well versed with Histograms and ETTR... then push it 5 stops in Camera RAW...

so are you aware about the difference between Process 2010 and Process 2013 when "pushing it" in "Camera RAW", right ?

[Dave Ellis]

Hello All:

I am fairly well versed with Histograms and ETTR.   

My basic understanding of ISO invariance is that you can have an exposure set with ISO 3200, or you can use the same shutter speed and aperture but reduce the ISO to 100 and then push it 5 stops in Camera RAW. Each image, made differently, will have roughly the same exposure value, with the +5 Camera RAW image exhibiting better noise qualities.

My question is “How does this then affect the use of ETTR?”

Thanks for any and all insight,

rogoldboy

As far as the term ISO-less is concerned, this is my understanding :-

Sensor Read noise can be introduced prior to the ISO amplifier or after the amplifier in the A/D converter circuitry. The noise introduced before the amp is amplified when the gain is increased as a result of an increase in ISO setting but the A/D noise is not.

With Canon sensors, it appears that at base ISO, A/D converter noise is a significant contributor to the total noise in the final digital signal. As ISO is increased, the noise introduced before the amplifier is increasingly amplified until at some point, it is the dominating contributor and the contribution from the A/D is insignificant. Once you reach this point, the sensor becomes virtually ISO-less as it makes little difference whether you increase the “exposure” digitally or in the amplifier. Before this point however, increasing gain digitally increases both sources of noise and hence is less effective than increasing ISO gain.

On the other hand, the latest Sony/Nikon sensors seem to have very little A/D noise (presumably because of the use of integrated column A/D’s.) So for these sensors, the noise introduced before the amplifier is always the dominant noise for any ISO. These cameras are therefore virtually ISO-less for the entire ISO range as it makes little difference whether the ‘exposure” is adjusted digitally or in the column amplifiers.

ETTR is really a separate issue and is more about making use of the full dynamic range of the camera. It may involve more exposure than is necessary for a given scene which in turn allows the exposure (and also the  noise) to be wound down in pp.

Dave

[spidermike]

My question is “How does this then affect the use of ETTR?”

Looking at ETTR as a principle for exposure, it doesn't.
ETTR is about pushing exposure as high as possible without actually clipping to maintain maximum amount of image information and this principle holds no matter what the ISO. As you increase the ISO you could argue that ETTR becomes even more important  because it would lead to less visible noise than if the histogram were more central.


What I suspect you meant to ask is 'given that ETTR is meant to maximise image information how does increasing ISO affect the information you collect with ETTR': higher ISO will always lead to smearing of detail and increase in noise even if it is not immediately visible at the chosen viewing size/medium.

[Jack Hogan]

My basic understanding of ISO invariance is that you can have an exposure set with ISO 3200, or you can use the same shutter speed and aperture but reduce the ISO to 100 and then push it 5 stops in Camera RAW. Each image, made differently, will have roughly the same exposure value, with the +5 Camera RAW image exhibiting better noise qualities.

My question is “How does this then affect the use of ETTR?”

Well, for maximum captured IQ you would ETTR at base ISO , if possible. You would simply maximize Exposure with the camera at base ISO based on your artistic constraints (say 1/400, f/2.8 for indoor sports, ensuring that no desirable highlights are clipped).  Then shoot away with abandon, forgetting about ISO.  Later correct for pleasing brightness during raw conversion.

The effects of the two approaches on IQ (ISO in-camera vs push in post) are shown here for a well designed (nearly) ISOless camera.

Jack

[Bart_van_der_Wolf]

ETTR is really a separate issue and is more about making use of the full dynamic range of the camera. It may involve more exposure than is necessary for a given scene which in turn allows the exposure (and also the  noise) to be wound down in pp.

Correct, ETTR is basically used at the camera's native ISO, i.e. the lowest ISO that thus allows a maximum of DR. The low ISO reduces the risk of clipping at the saturation point, and the optimal exposure level will be just shy of that clipping point, based on the lightest tones that need to have accurate texture and color. The shadows will then fall where they may, with as much exposure as possible without clipping whites. This typically produces the highest S/N ratio possible for all tones in a single exposure, and offers the best basis for post-processing (with the possible exception of hue twists introduced by some profiles when changing the Raw Conversion 'Exposure' control).

So to answer the OP's question, essentially ETTR is only used at native ISO. It's all about collecting as many photons as can possibly fit in the potential wells of the sensor, without saturating highlights that matter. Collecting more photons, results in lower shot noise (at all tonalities).

With boosted ISO one just has to avoid that the amplified signal doesn't clip important highlights, but DR will be reduced due to lack of photons.

Cheers,
Bart

[bernie west]

The principles still apply, though, at any ISO.  What matters is exposure (i.e. amount of light hitting the sensor).  So if you have the leeway, then a greater exposure is better than less exposure, whatever ISO you happen to select.  Or to put it another way, you can still employ the principles of ETTR away from base ISO, particularly so in cameras that don't have ISO-less like operation.

[digitaldog]

The principles still apply, though, at any ISO.  What matters is exposure (i.e. amount of light hitting the sensor).  So if you have the leeway, then a greater exposure is better than less exposure, whatever ISO you happen to select.  Or to put it another way, you can still employ the principles of ETTR away from base ISO, particularly so in cameras that don't have ISO-less like operation.

Exactly and as you pointed out first, in terms of ISO/ETTR, depends on the camera. Example of a Canon 5DMII:



ISO 100, more noise than ISO 800.

[bernie west]

Yeah, that's a marked difference.  I just wish I understood the technical aspects of why that no longer applies with some sensors.  Actually, on second thoughts, I don't really need to know.  I'm happy that there are a resourceful bunch of geeks here who keep us updated on what the best approach is to use for each camera/sensor. 

I remember a series of graphs that Guillermo posted years ago for the 5D that convinced me to skip ISO200 altogether, as it showed virtually no noise improvement over using ISO400.  It's all handy information.

[AlterEgo]

Yeah, that's a marked difference.  I just wish I understood the technical aspects of why that no longer applies with some sensors.  Actually, on second thoughts, I don't really need to know.  I'm happy that there are a resourceful bunch of geeks here who keep us updated on what the best approach is to use for each camera/sensor. 

I remember a series of graphs that Guillermo posted years ago for the 5D that convinced me to skip ISO200 altogether, as it showed virtually no noise improvement over using ISO400.  It's all handy information.

http://home.comcast.net/~nikond70/Charts/PDR.htm

[Jack Hogan]

Yeah, that's a marked difference.  I just wish I understood the technical aspects of why that no longer applies with some sensors.  Actually, on second thoughts, I don't really need to know.

Too late   A clumsy attempt at such an explanation.  In a nutshell: ISOless systems are able to store into the raw data (most) all the scene information collected by the sensor's photosites in one go.

Jack

[Bart_van_der_Wolf]

Exactly and as you pointed out first, in terms of ISO/ETTR, depends on the camera. Example of a Canon 5DMII:

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

ISO 100, more noise than ISO 800.

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.

So the comparison should have been between an ISO 100 shot optimally exposed (ETTR), compared to an underexposed shot boosted by ISO (which on Canons can benefit from cranking up the ISO, other cameras benefit less due to different architecture but may already be better at low noise underexposure).

Cheers,
Bart

[Jack Hogan]

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

Why would he be getting confused?  This thread and the original question are about ETTR on ISO invariant systems, per the pretty title.  The 5DMII is not ISO invariant as the relative images clearly show.

Jack

[Bart_van_der_Wolf]

Why would he be getting confused?  This thread and his question are about ETTR on ISO invariant systems, per the pretty clear title.

Hi Jack,

The confusion is clear when high (or not native) ISO is mentioned in the same sentence with ETTR. They are completely different things. High(er) ISO is all about underexposure, e.g. to achieve a shutterspeed that stops camera shake or subject motion that would have occured at an ETTR exposure level. ETTR on the other hand is all about not underexposing.

There is a reason that the Dynamic range of e.g. the 5D Mark III that Andrew used for a comparison is highest at native ISO, but you know better than most who have not done the math that more photons are hard to beat when signal to noise is concerned. Photon shot noise statistics (Poisson noise) produce a better increase of S/N with ETTR, than with underexposure and an ISO boost of the gain (as in Canons) or with a Raw converter's Exposure control. It's physics, which as usual is hard to beat (if at all possible in a single exposure).

Cheers,
Bart

[digitaldog]

Why would he be getting confused?  This thread and the original question are about ETTR on ISO invariant systems, per the pretty title.

Unlike Bart, I will not speak for the OP as he has. But I agree with you. The image and the results speak for themselves, Bart speaks for others. Enough said 

[Bart_van_der_Wolf]

Unlike Bart, I will not speak for the OP as he has. But I agree with you. The image and the results speak for themselves, Bart speaks for others. Enough said 

Correction, I speak for myself. If you disagree with my explanation of the effects of Photon shot noise statistics on image quality, feel free to proof me wrong, or ignore me. I'm fine with either.

Cheers,
Bart

[digitaldog]

Correction, I speak for myself.

This wasn't you:

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

Let's examine what the OP stated in his first post:

am fairly well versed with Histograms and ETTR.

Sure seems you're placing confusion upon him and speaking for more than yourself sir.

[spidermike]

I have seen many discussions on ETTR on many different sites and part of the problem is that people add their own twist on what it actually means. In his original 2003 article and the update in 2011, Michael Reichmann shows images shot at ISO200 and ISO 400 and does not even refer to base ISO yet now some people are claiming it is an important part of the definition.
I totally agree that if you are taking the trouble to ETTR to maximise informatoin then why not go the whole hog and use base ISO, but that is NOT the same as saying base ISO is a critical part of ETTR.

Interestingly, in this web page

http://photo.net/digital-darkroom-forum/00Vy86

Jeff Schewe contributes the following:

ETTR has NOTHING TO DO with the amount of levels in the shadows...it has nothing to do with the base ISO (vs altered ISO) is has EVERYTHING to do with the fact that more photons equals less perceptible noise (which means a better signal to noise ratio).
...
More photons=better noise

That's the basis of ETTR, has nothing to do with "shadow bits.

You should also test out the fact that HTTR can also actually benefit when "modest" increases of ISO are used...with today's cameras you can prolly go upwards of ISO 800 and STILL take advantage of ETTR if the scene contrast range is below the sensor...

[Bart_van_der_Wolf]

Sure seems you're placing confusion upon him and speaking for more than yourself sir.

I'm not a native English speaker, but I believe that "getting confused" is not the same as "he is confused", or "he is becoming confused" and certainly not the same as "he says he is confused". But feel free to correct my interpretation of the English language, I'm eager to learn.
Getting confused can IMHO mean that other people are (in my estimation) presenting confusing information (e.g. by only telling part of the story), which might lead to confusion. Not necessarily to the OP, but there are others reading these fora who would like to learn.

Cheers,
Bart