Expose to the right (ETTR) or underexpose?

[thighslapper]

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Well yet again .... that was an interesting read.....

 

A long discussion about achieving the impossible.....

 

There are many situations where you are never going to win...... pulling up shadow detail only works to a degree and toning down highlights produces odd effects....

 

The M9 is ideally suited for HDR and a custom pre-set can produce 3 or 5 shot combos....

 

....and no, the images DONT have to look like garish comic book illustrations ....

 

This is a 5 shot hand held HDR with a WATE on 18mm, starting at 1/6 sec and combined with Oloneo Photoengine..... straight with no manipulation.... took me all of 2 minutes... Could possibly have the shadows brought up a bit more ... but this captures the overcast conditions and looks more natural to me....

 

No doubt this comment will get me panned by the Leica purists, but hey, photography should be fun

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Edited August 16, 2011 by thighslapper

[jaapv]

I can probably be classed as a Leica purist - and I fail to see why I should slam good darkroom technique.

This is a very nice example of the advantages of the digital workflow.

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[pgk]

From a sensor perspective, does ETTR help? Yes and no.

 

It largely depends on the scene histogram distribution, photographic goals and noise / tonality concerns. If a scene has large shadow areas, one might be better off exploiting this technique (without blowing out the highlights). If the scene is uniformly distributed, then there is very little to achieve by ETTR.

I liked your full post explanation but for me this part sums up very well what I have found in practice. 'Correct' exposure depends on what you are trying to achieve and there is no absolute rule which covers all situations.

[ho_co]

Perhaps "ETTR" is the digital mantra just as "Zone System" was the analog one?

 

IOW, any handle is a good one if it helps to get a better grip on 'right exposure.'

[SJP]

First time posting<snip>There is no free lunch.

Respect and welcome, great entry:)

 

I am not sure if I understand ETTR (or even want to;)) but your posting was an example of clarity.

[john_newell]

It largely depends on the scene histogram distribution, photographic goals and noise / tonality concerns. If a scene has large shadow areas, one might be better off exploiting this technique (without blowing out the highlights). If the scene is uniformly distributed, then there is very little to achieve by ETTR.

 

*snip*

 

There is no free lunch.

 

My short version would be: nihil novum sub sole - remember the lessons you learned (and some of us had to continually re-learn ) about exposure in film days. Know your recording media, know your meter, know your scene.

[henning]

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Yes- but some kittens must be murdered:eek:

 

One of the problems in this discussion is that the word highlight covers two things.

1. it is meant as the lightest part of the image we would wish to show some detail.

2. it is meant as specular highlight which is supposed to show no detail.

 

If we interpret ETTR (please, no exact definitions and theoretical nit-picking , I know the whole story...)

as the exposure which just preserves highlights #1 and pushes highlights #2 off the histogram to the right we will have pulled as much of the shadows above the noise floor and have the fullest contrast range as possible in our file. The histogram will show this.

If the essence of the photograph is to get all detail in the shadows, highlights #1 will sadly have to go as well, only to be saved by bracketing and HDR techniques.

 

This is the best summation of the ETTR discussions I've seen.

 

Getting a camera to automate this completely is impossible at current levels of technology. As with many other technical aspects of photography, as soon as we automate something we are sure to make some shots impossible.

 

Under medium and low contrast conditions an 'Auto ETTR' system could work quite well, but that is largely what multi-pattern metering tries to do right now. You just have to be able to over ride it easily when your intent or the contrast range don't fit with the automation, which we can do right now with exposure compensation or manual mode. So my take is that the LuLa article is a bit of a red herring with respect to this point. And please, please, please spare me voice control!

Edited August 16, 2011 by henning

[t024484]

First time posting on this forum

Welcome to the forum

 

There are a number of misconceptions in your posting that I will try to anwer.

your data is showing that the M9 is shot noise limited (i.e. the noise is pretty much caused by the arrival rate of the photons itself, and the sensor circuitry adds very little noise if any, at least for a good part of the ISO / gain range). All good cameras behave in a narrow band when it comes to this..

Shot noise only plays a role in the 6 most brightest luminance stops, but even there other types of noise are contributing as well. At the highest luminance level noise is completely dominated by Photo response non uniformity. But on ETTR all this has no relevance.

Take for instance, your favorite M9. The ADC (analog-digital converter - the block which is responsible for digitizing pixel output) output is 14 bit for the M9, which means this block is capable of breaking down a pixel output into 16384 levels (or tones), and assume that the ADC assigns these codes in a monotonic fashion with 0 for the purest black and 16383 for the purest white.

The m9 has an 14 bit a/d, but the dynamic range of the sensor is only 12 bit, and only at ISO 160. For each doubling of the ISO value this dynamic range is halved or 1 bit less.

But no screen or printed output is capable of displaying 12 stops and that is why we can correct for exposure because, depending on ISO, (large) parts of the available information are 'unused'.

Now take a scene where all the tones in the histogram are uniformly distributed (i.e. all these 16384 levels occur at least once). If you underexpose this scene, what happens is that some of the levels between 8191 and 16383 (I used half of the full range as an example) get incorrectly shifted towards the lower half of the full range.

Not just some of the levels, but all of them.

Now if one were to map an underexposed scene (generally involves stretching both the ends of the captured histogram),

If an underexposed scene is corrected for exposure, the whole histogram goes to the right. Stretching occurs when increasing contrast.

RAW converters / camera processors have limited information (especially at the high end), and this information needs to be mapped to the higher end of the histogram. ie we are asking to create information out of thin air.

All the information is there, it is just shifted to the right, multipied with an exposure correction factor. No interpolation no guesswork.

The histogram can be shifted, but it is like adding more light to a certain part of the histogram. If one is not careful, subtle shifts in tonality are lost.

not certain parts are shifted, but everything will be shifted keeping all ratios intact.

RAW converters / onboard processing has come a long way in this regards. And the reverse is not the case with an over exposed histogram, because it involves redistributing already existing data to lower values, and setting the corresponding black level

Some sensors try to allocate extra information at the ends of the tonal range.

Through this simple shifting of bits around, color tonality gets affected.

This all happens not to be the case.

 

Hans

[algrove]

Perhaps a stupid question about the M9 histogram, but I'm new to this.

 

After recording an image, at first you get a certain histogram. Is this the JPG image/histogram? Then after several seconds you get a second histogram showing sometimes very different data. What is generating this second histogram?

 

I assume when members talk histogram they are referring to the second histogram. If not how do you get back the first histogram before the M9 automatically displays the second histogram?

[BerndReini]

You can generally do whatever you want. In film days, people would expose in a way that would give them the best negative for printing. Overexposing a negative to make it denser was really not something that real master photographers recommended. If you spot meter and get exactly the exposure you want to create the intended mood for the scene, it is better than to expose to the right - even though that might give you better SN ratio and luminous shadows. If you don't want those luminous shadows, it is better to get your mid-tones exactly where you want them to be.

 

I usually want as much range as I can get out of a scene, so I do tend to expose to the right a lot, but that this has to be done with caution. Nothing worse than digital sunburn, I.e. When skin starts to be overexposed and takes on all kinds of funky colors, or even burns out to an ugly torn off white triangle. With negative, that gradual roll-off looks nice. It is unfortunately an area where digital still suffers. When it's gone, it's gone, and the image is lost. So expose to the right, yes, but be careful with it.

[40mm f/2]

I find the M9 tends to slight underexposure (I have set my camera mostly to +1/3 exposure compensation). To make ETTR working one must know at which exposure value one reaches highlight saturation. The M9's LCD display is not very accurate. The histogram on the camera often does not show well the highlights. A narrow bar next to the right edge is often not visible. May be a better warning function like a red bar could be implemented through a software upgrade.

[douglasf13]

I simple point to remind everyone is that exposure in digital is simply how much light hits the sensor as a result of your aperture and shutter speed. ISO is simply the amount of gain applied after the fact, and it is not a part of exposure. When you have cameras with linear DR, like the M9, most MFDBs, newer Sony CMOS sensors, etc., pushing exposure in your raw converter may yield as good or better results than raising ISO in camera.

 

This is why, as Sandy mentioned, ETTR only makes sense at base ISO, because that is when you're only focused on how much light is hitting the sensor. Raising ISO is not part of the solution.

[kdriceman]

I simple point to remind everyone is that exposure in digital is simply how much light hits the sensor as a result of your aperture and shutter speed. ISO is simply the amount of gain applied after the fact, and it is not a part of exposure. When you have cameras with linear DR, like the M9, most MFDBs, newer Sony CMOS sensors, etc., pushing exposure in your raw converter may yield as good or better results than raising ISO in camera.

 

This is why, as Sandy mentioned, ETTR only makes sense at base ISO, because that is when you're only focused on how much light is hitting the sensor. Raising ISO is not part of the solution.

 

I understand this, but my question is, what is the difference in the actual M9 files of two images of the same scene taken at, say, 1/125s, f/1.4, ISO 160 vs 1/125s, f/1.4 ISO 2500 respectively? ( i.e. I have compared these two files in Lightroom and can find very little difference in IQ between the ISO 160 with a +4 stop exposure adjustment and the ISO 2500 file). Does the M9 actually write a raw file with different data or does it write the same data and include the ISO information in a header or somewhere in the file that tells the raw processor the ISO value and thus the appropriate settings with which to display the file. Or, more simply put, is the M9 actually applying the gain - on sensor - for a raw file. I know for OOC jpeg and for the display image/histogram, the gain must be applied somewhere in camera.

[mjh]

The additional gain is applied to the voltages read out from the sensor and is thus reflected in the raw data. But this ain’t necessarily so. Cameras such as the Fuji X100 stop applying additional gain above ISO 1600 so the raw images taken at ISO 1600, 3200, and 6400 could contain the exact same image data, differing only in the meta data. In practice the image data would usually differ since the ISO setting informs the camera of how the image should be exposed. An ISO 6400 image taken would appear two stops darker than an ISO 1600 image until the raw converter has applied the required correction.

 

The main point of the ISO setting is to control automatic exposure. With an ISO setting above the sensor’s base sensitivity the camera may also apply an additional amplification to the analog sensor signals before these are digitized, multiply the digitized values, or both, but theoretically it could refrain from doing either, leaving it to the raw converter to adjust for the ISO setting. If and when such an approach is worthwhile depends on how much the various sources of noise are contributing to the total noise. Since the CMOS sensor of the M looks like being one of those where a conservative approach to amplification could be beneficial, it will be interesting to see which strategy Leica is pursuing.

[anupmc]

...Since the CMOS sensor of the M looks like being one of those where a conservative approach to amplification could be beneficial, it will be interesting to see which strategy Leica is pursuing.

 

Doesn't support for correlated double sampling on the CMOSIS sensor suggest a more traditional amplification approach? (Albeit it doesn't exclude the use of post/meta data).

[mjh]

Doesn't support for correlated double sampling on the CMOSIS sensor suggest a more traditional amplification approach?

Correlated double sampling is just state of the art for reducing the fixed pattern noise CMOS sensors are prone to.

[MarkP]

... but hey, photography should be fun

 

Agreed

 

Oh, and congratulations on post #1000

[Photoskeptic]

I'm a little late to party on this as I've been away. However, my opinion is that for my purposes ETTR doesn't work because most new sensors have a lot of latitude in the shadow end and not much on the bright one. A lesson I learned years ago was that if you blow the highlights the image is garbage. The best explanation I have read was on The Online Photographer (TOP) in a column by Ctein and he mostly stated (and proved well enough for me) that ETTR is just wrong. I routinely underexpose by 1/3 or 2/3 of a stop irregardless of make of camera.

[mjh]

However, my opinion is that for my purposes ETTR doesn't work because most new sensors have a lot of latitude in the shadow end and not much on the bright one.

Expose to the right doesn’t mean you should expose beyond the right. Just get as far right as you dare without blowing the highlights.

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Hallo,

Look here: Leica M

[douglasf13]

I understand this, but my question is, what is the difference in the actual M9 files of two images of the same scene taken at, say, 1/125s, f/1.4, ISO 160 vs 1/125s, f/1.4 ISO 2500 respectively? ( i.e. I have compared these two files in Lightroom and can find very little difference in IQ between the ISO 160 with a +4 stop exposure adjustment and the ISO 2500 file). Does the M9 actually write a raw file with different data or does it write the same data and include the ISO information in a header or somewhere in the file that tells the raw processor the ISO value and thus the appropriate settings with which to display the file. Or, more simply put, is the M9 actually applying the gain - on sensor - for a raw file. I know for OOC jpeg and for the display image/histogram, the gain must be applied somewhere in camera.

 

It is highly dependent on the raw converter that you use. From what I've seen, LR doesn't quite measure up to boosting ISO in camera, but RPP does.