D5 - ETTR?

[Les Olson]

Photon shot noise is one area where ETTR will help in a very predictable fashion. Could you elaborate why you think that this is not the case?

Low ISO noise in monochrome areas - say, a blue sky - is not photon noise.  It arises from other channels - in the blue sky case, mostly the red channel - which are under-exposed and noisy.  Increasing the exposure has minimal effect because there is still no red in the sky so the red channel is still under-exposed and noisy. 

[Valerie S.]

Thanks for all of the replies and information. I'll shoot as is unless the situation calls for it.

[simsurace]

One reason not to use ETTR is if you want the  file to be usable with minimal or no adjustments in post.

Yes, I agree but this has nothing to do with flare.

[JohnMM]

Low ISO noise in monochrome areas - say, a blue sky - is not photon noise.  It arises from other channels - in the blue sky case, mostly the red channel - which are under-exposed and noisy.  Increasing the exposure has minimal effect because there is still no red in the sky so the red channel is still under-exposed and noisy.

So if the red channel noise is NOT photon noise how would you describe it ?

[simsurace]

If you set your exposure so flare is seven stops below FWC, and then say, "I will ETTR" and increase flare to six stops below FWC the darkest pixel in the image, that in a flare free image was black, is one stop brighter.  The maximum dynamic range has, therefore, been reduced by one stop.

Yes, it is clear that increasing exposure has the potential of clipping any highlights that are already near full well. But that does not change in the presence of flare.

So, I still don't see how flare can affect the decision when to use ETTR or not.

If you are not using ETTR in the scenario you describe, it is because you do not want to clip highlights and not because there is any flare.
ETTR is really meant to push the data that the photographer finds relevant to the picture as far to the right as possible. If you do not want to clip more than what is already clipped, there is no point in further increasing exposure. Flare or not, I do not see how that matters.

[David H. Hartman]

Not only can ETTR push data out the top it squishes data together in the shoulder of the image. Instead try shooting with the Neutral or Flat PC. Clip only specular highlights. Put punch back into the image using an "S" curve using the Master Lightness feature of LHC.

Dave

If not using Nikon software use a preset that gives you an NEF conversion without putting and "S" curve into the conversion. Do that under your control in LCH (Lightness, Chroma, Hue).

[Frank Fremerey]

Friday night physicists chat room!

[simsurace]

Not only can ETTR push data out the top it squishes data together in the shoulder of the image. Instead try shooting with the Neutral or Flat PC. Clip only specular highlights. Put punch back into the image using an "S" curve using the Master Lightness feature of LHC.

Dave

If not using Nikon software use a preset that gives you an NEF conversion without putting and "S" curve into the conversion. Do that under your control in LCH (Lightness, Chroma, Hue).

I try to think of the raw conversion as something that is separate from the collection of data. When using ETTR in the field, I usually also make an image with the "right exposure" i.e. that would yield the desired brightness with standard raw conversion settings. Then I can import both the ETTR and the regularly exposed image into, say, ACR and adjust the ETTR image to match the brightness of the regularly exposed one.* I will use the exposure slider to do so, and I have found the scale on the exposure slider to match the actual exposure pretty closely, i.e. if the ETTR was two stops above the regularly exposed image, I can set the exposure slider at -2 stops in the ETTR image and have a pretty close match in overall brightness, but also the histograms are pretty similar. The ETTR image will have an extra two stops better shadow details. One can also do the same with curves, but I find the curve interface to be quite difficult to master and it will take me more time to find a suitable curve. The difficulty arises because of the nonlinear transformation from linear raw levels to RGB levels. Applying the transformations on raw levels would make this task much easier. I am not sure what exactly the exposure slider in ACR does, but it is not far from a linear scaling on the raw levels from what I can infer.

* The added benefit of taking a normal exposure is that if I botched and blew some important highlights in using ETTR (which is quite likely given the fact that the camera does not show you what exactly has been clipped), I can always recover them from the normal exposure or just use the normal exposure and suck up the inferior shadows.

[Les Olson]

So if the red channel noise is NOT photon noise how would you describe it ?

Sorry for the delay - I have been away. 

Yes, it starts out as ordinary photon noise, but the question is why it is obvious in the final image.  That is because (1) the red channel is not silent, as ideally it would be when blue light falls on the sensor, because the spectral responses of the channels are not perfectly separated, and (2) noise is imported from the red channel during raw processing.  The effect of the second point is that channel noise is different for different raw converters.  http://www.libraw.org/articles/channel-noise-and-raw-converters.html has examples. 

[David H. Hartman]

Did ETTR ever really work or were people fooling themselves with the standard curves applied by the camera maker. For example the it may look like one has blown the highlights with a Nikon when using the Standard Picture Control but one may well find there is more useful highlight information when using the Neutral or Flat PC. Some negative exposure compensation may help. Then one puts a bit of punch back into the mid tones with an "S" curve in LCH's master brightness.

I've always considered ETTR to be dicey at best and frequently a detriment to the photo to gain a bit lower noise in the shadows. With my D2H I could loose the shadows and blow the highlights and all at the same time. The D300s was a huge relief for me.

With negative film one would expose for the shadows (Zone I) and develop from the highlights. With roll films one would develop the roll at N-1. With digital one should expose for the highlights and develop RAW files for the shadows.

Maybe I'm missing something. Maybe it was a Canon thing. I don't know. I don't see ETTR as useful with either my D300s or D800.

Dave

[pluton]

Did ETTR ever really work or were people fooling themselves with the standard curves applied by the camera maker.
....

Maybe I'm missing something. Maybe it was a Canon thing. I don't know. I don't see ETTR as useful with either my D300s or D800.

Dave

David, I think you are on to something by bringing in the historical angle.  Digital raw imaging systems used to be much more limited in tonal range than they are now.  I recently fooled around processing (in ACR/LR) a Canon raw shot from an APSC Canon Digital Rebel camera, circa 2005.  The tonal capture range in the raw file was extremely narrow by today's standards. No matter how much you played with the raw file, it still looked like a jpeg from a budget point and shoot JPEG camera.  Coincidentally, the photographer who, in my early days of digital(2006), preached ETTR was a Canon user.

[simsurace]

Did ETTR ever really work or were people fooling themselves with the standard curves applied by the camera maker. For example the it may look like one has blown the highlights with a Nikon when using the Standard Picture Control but one may well find there is more useful highlight information when using the Neutral or Flat PC. Some negative exposure compensation may help. Then one puts a bit of punch back into the mid tones with an "S" curve in LCH's master brightness.

When you can recover anything, you haven't fully blown it. You might have blown one channel which allows context-sensitive highlight recovery by guessing what the color was and filling in the missing information. You think you have blown something because the clipping warnings are based on the color space you use to convert your file. You will observe than upon changing color space, the clipping areas change. Your clipping also depends on white balance, to confuse matters further.

If you want to experiment with ETTR, the first thing IMO is to get a program that shows you raw levels and histograms so you can see how far you can go until genuinely blowing channels. You will find that in many normal exposures of low dynamic range scenes your top 2 or more stops are really left unused by the camera (if going by the exposure meter). Of course this is the correct way of exposing if developing the file with standard settings should produce the correct brightness, but it is certainly a very sub-optimal way of collecting data about the scene. By pushing the data to the right (not by increasing ISO of course, but by having more exposure!), you can definitely get a much cleaner picture, particularly if your processing of the image involves expanding the data to get high contrast.

This is not something that applies only to Canon and not to Nikon. Sure, sensors are different and if you can get away without using ETTR on your camera -- good for you! But the fundamental principles do not depend on the brand of sensor.

[David H. Hartman]

If you want to experiment with ETTR, the first thing IMO is to get a program that shows you raw levels and histograms so you can see how far you can go until genuinely blowing channels.

OK, I'll bite: what program for Nikon's NEF(s)?

Dave

[Bjørn Rørslett]

I believe RAWDigger is what you should be looking for. Not freeware, though. Andrea B. uses this program a lot, you might PM her about it.

[David H. Hartman]

Thanks!