Will Michael revisit ETTR?

[mouse]

Well, I'll kick off with a few methods that have worked for me.

(2) Buy a new camera which has a linear noise and dynamic range response (on the graphs at DXO Mark) that reduces by one f stop (or EV) for every doubling of ISO, so that there is no fundamental image quality advantage to increasing ISO.

The Nikon D7000 and Pentax K5 are in this category. With such a camera, you have only one worry regarding ETTR, and that's inadvertent overexposure at base ISO.

Unfortunately, the review image with this method can look even worse than the first method, if you've been underexposing at base ISO instead of using a higher ISO. It may be so dark you can hardly see it at all and you may have to flatly refuse to show it to anyone in order to protect your reputation.

  It is not clear to me how this solution makes it easier to implement ettr.  Even with cameras which do not have a linear noise response to increasing ISO, boosting the ISO (as opposed to increasing the exposure) may diminish read noise but is never a correct solution to achieving proper ettr.  Using such a camera, you suggest that one need only  worry about inadvertent overexposure at base ISO; how does such a camera prevent inadvertent underexposure at base (or any other) ISO?   And finally, even if no one is looking over your shoulder, a very dark review image with any camera suggests that you are seriously underexposing or that your ISO is too low, or both.

[Ray]

It is not clear to me how this solution makes it easier to implement ettr.  Even with cameras which do not have a linear noise response to increasing ISO, boosting the ISO (as opposed to increasing the exposure) may diminish read noise but is never a correct solution to achieving proper ettr.  Using such a camera, you suggest that one need only  worry about inadvertent overexposure at base ISO; how does such a camera prevent inadvertent underexposure at base (or any other) ISO?   And finally, even if no one is looking over your shoulder, a very dark review image with any camera suggests that you are seriously underexposing or that your ISO is too low, or both.

It's always possible to make a mistake whatever the method used for achieving ETTR, even if one had a camera that presents a true RAW histogram. One could make a mistake thinking the camera was set to ISO 400 when in fact it was on ISO 100, or vice versa, simply because one was in a hurry to get the shot and not paying full attention.

I'm basically assuming that anyone who is so concerned about getting a really accurate ETTR, is likely to be using the camera in full manual mode, because getting an appropriate shutter speed and desired F stop is generally of more importance than getting a 'spot on' ETTR. At least it is for me.

If one accepts this as a reasonable premise, then an underexposure at base ISO would result only because the shutter speed selected for the conditions of the scene, to freeze subject movement and/or camera shake, were too fast in relation to the base ISO setting, but necessary regardless.

To use base ISO in these circumstances would be considered a mistake with certain models of cameras, such as all recent Canon DSLRs, because it's always better with such cameras, to raise ISO to achieve an ETTR in relation to that increase in ISO.

When thus raising ISO to avoid underexposure at base ISO, because of the image quality advantage of raising ISO, one still has the same ETTR problem of the possibility of blown highlights because of a slight miscalculation.

With cameras such as the D7000 and K5, there should be no such concern because an underexposure at base ISO provides the same fundamental image quality, as the same exposure with same settings of shutter speed and aperture, used at an oppropriately higher ISO. Got it?

[Peter_DL]

With cameras such as the D7000 and K5, there should be no such concern because an underexposure at base ISO provides the same fundamental image quality, as the same exposure with same settings of shutter speed and aperture, used at an oppropriately higher ISO. Got it?

Finally bought such camera which is supposed to represent latest sensor technology,
and my 'concerns' soon started to shift from ETTR to 'single shot HDR'.

Peter

--

[hjulenissen]

I see. In that case it's all just a 'strom in a tea cup' as far as I'm concerned. For a moment I thought there was a real possibility of extending the dynamic range of the camera, using UNIWB. Can't see what all the fuss is about.

The physical noise and clipping characteristics of the sensor can (of course) not be improved. But by helping you place the "signal" optimally compared to the (more or less) fixed noise and clipping point, you can get better DR using UniWB/ETTR/"insert good recording practice here" than not doing it. If e.g. 1 stop more DR is crucial to you, and worth the hazzle, I dont see the problem.

Automated exposure has some safeguards (probably for good reason), and in-camera histograms are flawed. By improving the feedback on signal level, you may buy yourself some DR headroom that otherwise would have to be bought in the for of a newer camera.

Of course, knowing the AE of your camera, its margins, and perhaps doing bracketing might in the end give similar results and less pain for some users?

-h

[Hans Kruse]

(2) Buy a new camera which has a linear noise and dynamic range response (on the graphs at DXO Mark) that reduces by one f stop (or EV) for every doubling of ISO, so that there is no fundamental image quality advantage to increasing ISO.

The Nikon D7000 and Pentax K5 are in this category. With such a camera, you have only one worry regarding ETTR, and that's inadvertent overexposure at base ISO.

I read the DxO curve as follows. There is a linear relationship between S/N and ISO. This means that exposing EV -2 at ISO 100 has the same noise as exposing EV 0 at ISO 400. In other words you can shoot at base ISO and increase exposure in post processing and get the same noise characteristics as if you had raised the ISO in the camera and exposed the same stops higher at a higher ISO with the risk of clipping highligts. However this is not the same noise as at base ISO!

Now as far as I would analyze this there are a couple of issues with this approach.

1) The noise will be higher when you underexpose and raise exposure in post processing just like if you shot a higher ISO. If you shoot landscape at is not a good idea from a noise perspective to underexpose by two stops relative to ETTR and the raise it by two stops in pp. Correctly exposed (ETTR) at base ISO will always give the lowest noise.

2) Underexposed images will loose gradations since there are fewer bits to represent the shadows. That's a reality of mathematics and nothing else. 14 bit RAW files helps on this, of course. Also deep shadows may not be so misrepresented with few gradations as they are deep shadows. But an extreme example of raising the exposure by 4 stops to go from ISO 100 to ISO 1600. The tonality will clearly be impacted as the shadows have now been lifted by 4 stops in pp. Btw. the max you can do in Lightroom and ACR without workarounds.

3) The DR is reduced by as many stops that the image is underexposed compared to perfect ETTR.

So just underexposing because it doesn't matter is simply not true. However these cameras with 14 stops of DR and a linear SN curve will do better than older ones when lifting shadows in a single exposure when lifting shadows. Like when you do a blend of multiple RAW conversions in e.g. Photomatix og you compact the DR in e.g. Lightroom using the tone curve or recovery and fill light combined with a suitable contrast curve (sort of like a tone mapping done in Lightroom). Alternatively using graduated filters and/or the brush to redistribute the light. In such cases a camera like the 1Ds mkIII can handle in my experience about a 2 stop lifting the shadows with no adverse effects. More than that you start seeing the extra noise and reduction of details when we compare to a clean ISO 100 shot of similar details.

[Guillermo Luijk]

2) Underexposed images will loose gradations since there are fewer bits to represent the shadows. That's a reality of mathematics and nothing else. 14 bit RAW files helps on this, of course. Also deep shadows may not be so misrepresented with few gradations as they are deep shadows. But an extreme example of raising the exposure by 4 stops to go from ISO 100 to ISO 1600. The tonality will clearly be impacted as the shadows have now been lifted by 4 stops in pp. Btw. the max you can do in Lightroom and ACR without workarounds.

Underexposing means losing gradations in the RAW histogram, but in practice you will _NOT SEE_ that loss because noise dithers posterization. You will not see even in the output histogram after RAW conversion since after demosaicing and output colour profiling, the 16-bit histogram gets full of levels everywhere. Just underexpose some RAW, lift the shadows, and look for posterization.

All this story about ETTR being helpful in having more tonal levels and prevent posterization always extends like a virus! (without anyone providing a single evidence of it).

ACR allows to lift exposure in the shadows (which is where the discusion about gradations and ETTR makes sense) by 7 stops: 4 stops through the Exposure slider + 3 stops by setting Brightness to +150.

[Hans Kruse]

So you agree with my points, except that you argue that the degradation in gradations will be hard to see.

As far as I'm aware the exposure slider and the brightness slider in Lightroom are not the same. Exposure sets the white point and brightness moves midtones without moving the white point. I think Schewe can comment on this.

[Guillermo Luijk]

So you agree with my points, except that you argue that the degradation in gradations will be hard to see.

As far as I'm aware the exposure slider and the brightness slider in Lightroom are not the same. Exposure sets the white point and brightness moves midtones without moving the white point. I think Schewe can comment on this.

No, I don't agree. It will not be hard to see, it is impossible to see the gradations, so talking about losing gradations is misleading because you can conclude that there is some advantage about gradations thanks to ETTR. I am ready to change my mind if you provide an example of those gradations.

Gradations become usually visible in areas with plain colours and very low noise, for example when converting skies to 8-bit JPEG. So paradoxically, ETTR will help in making banding appear in the highlight areas without textures. An ETTR'ed sky is more prone to banding than an underexposed sky.

The Brightness slider in ACR is the same as Exposure for the shadows, that means shadows can be lifted by 7 stops making both sliders work together. The straight lines are Exposure settings, the curves are Brightness. In the shadows they are the same; for instance Bright +50 will lift the shadows by 1EV:

[Hans Kruse]

You can look back to see what the other points were on 1) and 3). I take that you agree on these points.

[Guillermo Luijk]

You can look back to see what the other points were on 1) and 3). I take that you agree on these points.

I agree with 1 (noise is the one and only reason for ETTR), but disagree with 3.

Not all cameras loose 1 full stop of DR when underexposing by 1 stop, that depends on the dB/EV slope of the SNR response of the particular sensor. Canons typically have 6dB/EV in the shadows because they are read noise limited sensors, so a Canon will loose 1 full stop of DR for every 1 stop of underexposure. The late Pentax K5 and Nikon D7000 sensor however have softer slopes, closer to 3dB/EV for being rather photon noise limited sensors, so one of these cameras will only loose 0,5 stops of DR for every 1 stop of underexposure. The conclusion is that although ETTR is still very recommended on these late cameras to improve SNR, it is not so critical as in Canons.

The plots may me somewhat difficult to interpret, but they have the key to all this:



Regards

[Hans Kruse]

Thanks, so we agree on point no. 1 and no. 3 partially with the comments you made here. Now, how did you arrive at the curves you made in your last response?

[Guillermo Luijk]

Thanks, so we agree on point no. 1 and no. 3 partially with the comments you made here. Now, how did you arrive at the curves you made in your last response?

By measuring pairs (RAW exposure, SNR) and plotting them. I did it over patches of uniform colour, the procedure is explained here: NOISE AND DYNAMIC RANGE MEASUREMENT. CANON 5D vs 5D2 vs 7D vs PENTAX K5 (Spanish, hope the online translation suffices).

[Ray]

There is another very effective way of comparing an ETTR at, say, ISO 1600, with the same exposure at ISO 100, and that is to take the shots of the same real world, 'high DR' scene, and then compare results, after your best processing effort in your converter of choice.

[madmanchan]

A couple of notes:

- ETTR is about maximizing signal-to-noise.  That's all.  In-camera histograms and white balance settings don't help, because they don't reflect how the raw data is recorded.  It is true that photographers can try to use these tools to ETTR, but unfortunately these tools are misleading for this purpose, and can actually lead photographers down the wrong path (see the red flower example in Michael's article).

- ACR's Exposure and Brightness are essentially the same, except for the handling of highlights.  Exposure will hard-clip the highlights, whereas Brightness will not.  For example, if you push Exposure to +1, then anything that was in the top stop will get clipped off -- gone -- similar to digital exposure.  In contrast, if you push Brightness from +50 to +100, then anything that was in the top stop will get smoothly rolled off (instead of clipped off) -- similar to film.

[bjanes]

A couple of notes:

- ETTR is about maximizing signal-to-noise.  That's all. 

Halleluiah, we can finally put this myth about the number of levels in the highlights to rest. If Michal were to remove that concept from his otherwise fine post, I would be in complete agreement. My opinion may not carry much weight, but the opinions of experts like yourself and others do.

- ACR's Exposure and Brightness are essentially the same, except for the handling of highlights.  Exposure will hard-clip the highlights, whereas Brightness will not.  For example, if you push Exposure to +1, then anything that was in the top stop will get clipped off -- gone -- similar to digital exposure.  In contrast, if you push Brightness from +50 to +100, then anything that was in the top stop will get smoothly rolled off (instead of clipped off) -- similar to film.

An excellent point!

Regards,

Bill

[sandymc]

Halleluiah, we can finally put this myth about the number of levels in the highlights to rest.

Amen, brother

Sandy

[Hans Kruse]

A couple of notes:

- ETTR is about maximizing signal-to-noise.  That's all.  In-camera histograms and white balance settings don't help, because they don't reflect how the raw data is recorded.  It is true that photographers can try to use these tools to ETTR, but unfortunately these tools are misleading for this purpose, and can actually lead photographers down the wrong path (see the red flower example in Michael's article).

Yes, maximizing signal to noise. And underexposing many stops and raise in post will reduce levels. That's a fact, but how many we will see in a print is another question. Underexposing also reduces DR as mentioned although the number of stops depends on the camera.

- ACR's Exposure and Brightness are essentially the same, except for the handling of highlights.  Exposure will hard-clip the highlights, whereas Brightness will not.  For example, if you push Exposure to +1, then anything that was in the top stop will get clipped off -- gone -- similar to digital exposure.  In contrast, if you push Brightness from +50 to +100, then anything that was in the top stop will get smoothly rolled off (instead of clipped off) -- similar to film.

Exposure sets the white point and the black point and brigtness moves midtones between those points. So they are not the same.

[bjanes]

Exposure sets the white point and the black point and brigtness moves midtones between those points. So they are not the same.

Exposure sets the white point, and secondary changes may be seen in the black point. The black point is set by the blacks control. Obviously they are not exactly the same, or both controls would not be needed. If I were you, I would be careful about preaching to Eric Chan, since he is a senior engineer on the ACR team and he knows what he is talking about.

Regards,

Bill

[Guillermo Luijk]

underexposing many stops and raise in post will reduce levels. That's a fact, but how many we will see in a print is another question.

Probably Chuck Norris is the only one who will.

[Hans Kruse]

Exposure sets the white point, and secondary changes may be seen in the black point. The black point is set by the blacks control. Obviously they are not exactly the same, or both controls would not be needed. If I were you, I would be careful about preaching to Eric Chan, since he is a senior engineer on the ACR team and he knows what he is talking about.

Regards,

Bill

Yes, black point is set by the blacks slider, I'm sorry that fell out of my post. I'm not preaching to anybody I'm not aware of what position Mr. Chen has. I would certainly welcome an explanatory statement from him about the differences some more detail than posted here. I have used Lightroom and ACR quite a lot and it is obvious that exposure and brightness is not the same. I also have the videos from Schewe and Michael and they explain the differences between exposure and brightness in Lightroom. So if this is wrong or I'm wrong I would welcome being corrected