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Expose to the right (ETTR) or underexpose?


Muizen

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Thanks.

How about for the M9: ETTR but constrained by not blowing highlights

 

Best, K-H.

 

With a Canon 5DII, the ability to render information from shadows is very difficult, so ETTR is well suited, almost a necessity.

 

Another issue is getting the right exposure with the M9 depends on the quality of lighting.

 

Agree with both here. With the 5DII I will actively ETTR even when running and gunning. With the M9 I'm aware of the limited highlight recovery and will protect higher tone areas that are important to me. What this means in practice is that I just meter "normally" for the M9 nearly all the time. When I am obviously faced with a predominantly middle toned scene I may bump it up a bit to gain the extra signal but that's very rare to be honest.

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Whether ETTR is a good idea or not depends on the sensor in question.

 

For the M9 the answer is that it is not. On the contrary, the M9 has far more latitude in the shadows than in the highlights..

 

No, ETTR refers to exposing to the right, before blowing the highlights. One needs to know his/her camera and histogram reading to do this effectively. The M9 hasn't turned digital logic on its head (as I wrote earlier regarding the M8); most of the pixel info still resides in the higher zones.

 

And again, that doesn't mean ETTR is right for everyone or for every scene, but the logic still holds, even for the M9. It's a matter of good execution. That's why I carry a pocket meter for tricky light; otherwise I know my camera and its limitations (M8.2 for me).

 

Jeff

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No, ETTR refers to exposing to the right, before blowing the highlights. One needs to know his/her camera and histogram reading to do this effectively. The M9 hasn't turned digital logic on its head (as I wrote earlier regarding the M8); most of the pixel info still resides in the higher zones.

 

And again, that doesn't mean ETTR is right for everyone or for every scene, but the logic still holds, even for the M9. It's a matter of good execution. That's why I carry a pocket meter for tricky light; otherwise I know my camera and its limitations (M8.2 for me).

 

Jeff

 

Of course the logic is the same but it's still not a good idea due to

1) ETTR makes in practice relatively little difference

2) The M8/M9 have limited headroom in the highlights so you risk blowing them beyond recovery.

 

 

In essence chances are that you'll do more damage than good. On a Canon 5DII for instance on the other hand you have a lot of latitude in the highlights and very little in the shadows (including the infamous noise banding at low ISO) so ETTR can be useful. It has however more to do where the mid point of the latitude span is rather than because of the linear nature of camera sensors.

 

If you are well within the dynamic range of the camera AND have sufficient light to use low ISO then by all means ETTR to your heart's content. However very often having light enough for low ISO and the scene having limited dynamic range are mutually exclusive. So it's not a generally good principle when the camera output has limited capability of highlight recovery.

 

May I re-phrase the question from the other side:

 

Does the M8/M9 tolerate ETTR better or worse than other cameras?

 

Worse because you are at higher risk of blowing the highlights beyond recovery.

Edited by denoir
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By the way, we actually know what Leica thinks of ETTR: not much. From the M9 manual (p.128):

 

Optimum reproduction quality is achieved with the ISO 160 setting. Higher sensitivities result in an increasing amount of “picture noise”. This effect can be compared to the “graining” that occurs with highly sensitive films. The Pull 80 setting has the same brightness as an ISO sensitivity of ISO 80. However, pictures taken with this setting have a lower contrast range.when Using this sensitivity setting, you should always make sure that important parts of the picture are not overexposed.

 

Using PULL ISO 80 instead of ISO 160 is ETTR. It's still actually ISO 160, just overexposed and then pulled back a stop in software. Given what Leica says in the manual and that Auto-ISO doesn't include 80 and that they've called it "Pull ISO 80" rather than "ISO 80" we can pretty much conclude that they don't think ETTR is a good idea. And they also warn you that if you use it you can forget about recovering any blown highlights.

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I have very limited experience but it seems to me that ETTR depends very much on the scene and the camera. The pic below was taken with my M9 and overexposed two stops compared to M9 metering (just resized jpeg). The same scene with the X1 was impossible not to blow out highlights, I could not get a good exposure even when underexposing a lot.

 

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In my experience with the M9, underexposing by half a stop yields perfect results. As Luka noted earlier, you can even get good results when underexposing by more than 1 stop.

 

On the other hand, even a slight overexposure (except when this is needed) will ruin most evenly lit scenes.

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IMHO (after 52 years in photography) there are no magic formulas to substitute for your own judgment and experience with any particular scene shot with a particular piece of gear and a particular post processing routine. You have to decide which parts of the scene are important to you. Of course there has to be a starting point, and after my own experimentation with my M9, I have concluded that the starting point for me is what the camera suggests (Leica isn't ignorant after all about their equipment) with zero exposure compensation. After the camera suggests an exposure, that marvelous subjective data processing system between your ears has to be applied to decide where to meter or whether to adjust the exposure. Adopting ETTR is just a way to start differently but it is where you end up that counts. My advice is go out and make a lot of exposures so you understand what the camera is doing and how it behaves before you adopt any rules.

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With a mathematical model of the M9, much can be taken out of the guesswork.

 

The accurate model that I have, contains all existing kinds of noise, Photon Noise, Sensor noise, A/D Noise, Photo response non uniform etc. giving a reliable picture of the Signal to Noise of the complete camera.

I have calculated the noise of the two combinations ISO 160/320 and ISO 800/1600, in both cases the lower ISO value with “normal” exposure and the higher ISO value with +1 stop ETTR.

First the graphical representation of both combinations, where yellow is the higher and magenta is the lower ISO value of the two.

 

On the horizontal axis, 13 is the highest or lightest level, just before overexposure.

Going to the left is decreasing the luminance.

On the vertical axis is the Signal to Noise in stops.

Zero means that the signal is just as strong as the noise, and 6 means that the signal is 2exp6 = 64 times stronger as the noise.

 

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The graphs are roughly showing that the S/N is the same for all luminance values when the higher ISO value is exposed with +1 stop ETTR.

For instance the yellow dot at Luminance 7 has the same S/N as the Magenta dot at Luminance 6, and so on.

But the graphs are not accurate enough to show the exact difference.

So here are the S/N values at the Luminance levels 12 –7 for ISO 160, compared to S/N at the Luminance levels 13-8 ( +1 stop ETTR ) for ISO 320.

 

 

At lower Luminance levels (darker area’s) there is an absolute insignificant S/N advantage of 0,05 stops in favor of ISO 320 with +1 stop ETTR. At the higher Luminance levels (lighter area’s) there is no difference at all.

 

Now for ISO 800 and ISO 1600.

 

 

Although the S/N in absolute value is worse than at ISO 160/320, the relative value between S/N at ISO 800 is exactly the same as the S/N value at ISO 1600 with 1 stop ETTR. There is simply no difference.

 

When just looking at noise, the conclusion is:

Instead of shifting the exposure +1 stop ETTR, one can just as well go one Stop down in ISO without overexposure. This is true for low as well as high ISO values, and it is true over the whole range from light to dark.

 

According to Sandy, there is a negative effect of ETTR on color reproduction. ETTR should therefore be avoided.

 

Hans

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Hans, the model you have could you elaborate a bit? What relations does it describe and on what data is it built? You don't specify wavelengths or factors such as operating temperature - are they included?

 

Hi Luka.

 

It was a hell of a job to isolate and calculate the magnitude of all individual noise types.

How this was done is described in detail over here:

 

Noise, Dynamic Range and Bit Depth in Digital SLRs

 

All measurements have been made on the unprocessed DNG file where R,G and B are still untouched by demosaicing.

Although R,G and B can differ in magnitude, the S/N couples for many different exposure values all fitted on exactly on the same curve for R,G and B. That is why the model is color independant.

The only thing that was not regarded was the temperature. All my measurements have been done at room temp.

 

Hans

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Using PULL ISO 80 instead of ISO 160 is ETTR.

Actually it has nothing to do with ETTR whatsoever.

 

Given what Leica says in the manual and that Auto-ISO doesn't include 80 and that they've called it "Pull ISO 80" rather than "ISO 80" we can pretty much conclude that they don't think ETTR is a good idea.

We cannot since their statements cannot be construed as being about ETTR, much less as advocating against it. (Leica calls it “Pull ISO 80“ because that’s what it is – a sensitivity setting below the sensor’s native sensitivity. They could have called all the ISO levels > 160 “Push ISO” if they wanted to since the sensor has just one true ISO specification.)

 

And they also warn you that if you use it you can forget about recovering any blown highlights.

If you are blowing highlights you are not correctly exposing to the right. ETTR means to move the histogram as far to the right as possible without blowing highlights. But of course you can only move to the right as long as there is any room to shift the histogram about. If the scene contrast is high, exposing for the highlights would result in an apparently underexposed image that needs some boost to shadows and mid tones to be applied in the raw converter.

 

The traditional way would be to expose for a middle gray like a gray card, assuming that as long as you get the mid tones correct, highlights and shadows will care for themselves. With digital photography that isn’t true anymore; for high contrast situations this is a recipe for blowing out highlights. Thus the advice to expose for the highlights and leave it to the raw conversion process to care for the shadows and mid tones.

Edited by mjh
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When just looking at noise, the conclusion is:

Instead of shifting the exposure +1 stop ETTR, one can just as well go one Stop down in ISO without overexposure. This is true for low as well as high ISO values, and it is true over the whole range from light to dark.

 

Hans' results are fully consistent with the results of my testing on this - see the first blog post referred to above.

 

Sandy

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Actually it has nothing to do with ETTR whatsoever.

 

Michael,

 

Sorry, but I'd have to disagree with you on that. Admittedly, ETTR means different thing to different people, but I'd argue that synthesizing a lower ISO than the camera has, such as Leica are doing here, is one of the very situations where ETTR is genuinely useful. Nikon's active D-lighting is another example of ETTR, broadly defined. Nikon can make it work because the "ETTR" offset gets handled automatically by Capture NX.

 

Regards,

 

Sandy

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Admittedly, ETTR means different thing to different people, but I'd argue that synthesizing a lower ISO than the camera has, such as Leica are doing here, is one of the very situations where ETTR is genuinely useful.

No actual disagreement here I think. My disagreement was with the statement that “Using PULL ISO 80 instead of ISO 160 is ETTR” when of course it isn’t. That the reduced dynamic range at this setting emphasizes the need to expose for the highlights goes without saying.

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My disagreement was with the statement that “Using PULL ISO 80 instead of ISO 160 is ETTR” when of course it isn’t.

 

Of course it is ETTR. The camera overexposes by one stop and pulls it back in the software. It's the text book example of ETTR. There couldn't be a more obvious one and the general agreement is that it is actually the only useful example of ETTR. Well, general agreement among people who understand what ETTR is. :rolleyes:

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