The general problem is that Canon/Nikon (and most other) camera manufacturers do not provide RAW histograms in camera, the histograms is on the camera-generated JPEG even if you shoot RAW, and is affected by white balance setting etc so it may differ a lot from how the actual sensor's RGB channels are exposed. Making ETTR decisions from the camera histograms can lead to over-exposure or under-exposure depending on lighting conditions, certainly not very precise or safe.
Anyway, after doing these initial uniwb tests it seems to me that if you are going to practice ETTR and your camera cannot show RAW RGB histograms you really should consider using uniwb.
Is anyone else using universal white balance to make manual exposure decisions? It would be nice to hear some experiences from those that have used it for a while, if it indeed is safe or if you still come home with over-exposed / under-exposed pictures.
I tested this in indoor lighting with a Canon 7D and then I got about 1/3 stop clipping in the raw file of the green channel without any clip in the normal white balance RGB histogram (it showed that the red channel was about to clip, which it was not, and the green channel ok which was actually clipped), while uniwb presented the correct result. So this camera does not seem to be conservative as the Nikon D3. There are JPEG picture style settings to adjust though (I have default settings) that maybe will affect the result.
Those that shoot still life often practice ETTR, that is expose the sensor with as much light as possible without clipping highlight detail.
Having practiced this for a while I have been troubled by that it is so easy to mistakingly overexpose that a better practice may actually be to play it safe -- rather a bit noisier shadows than completely lost highlights.
How are you determining clipping in the raw channels? Are you using Rawnalize, DCRaw, or another program that looks directly at the channels? And how are you setting UniWB? Since UniWB should have a green multiplier of 1.0, I don't see how the regular and UniWB histograms for the green channel should be different, unless something else has changed. For tungsten lighting (approximately Illuminant A), the light contains more red and the red channel sensitivity will be closer to the green channel as shown in the shown DXO measurements. Still the green channel is most sensitive and should clip before the red unless the scene contains a lot of saturated red. Does your test target include saturated reds or does it have neutrals?
This is exactly the approach (http://theonlinephotographer.typepad.com/the_online_photographer/2011/10/expose-to-the-right-is-a-bunch-of-bull.html) Ctein takes on TOP, and is diametrically opposed to Michael's recent article (http://www.luminous-landscape.com/tutorials/optimizing_exposure.shtml) on the subject where he still appears to advocate ETTR despite its shortcomings with current camera histograms.
On topic, I found out that Olympus cameras have an ETTR setting (http://www.luminous-landscape.com/forum/index.php?topic=46071.0), but it has its shortcomings - mainly that it's a spot metering mode, and Guillermo Luijk's research down the thread shows it leaves too much headroom. I have not used it since, and prefer to take Ctein's approach.
This is exactly the approach (http://theonlinephotographer.typepad.com/the_online_photographer/2011/10/expose-to-the-right-is-a-bunch-of-bull.html) Ctein takes on TOP, and is diametrically opposed to Michael's recent article (http://www.luminous-landscape.com/tutorials/optimizing_exposure.shtml) on the subject where he still appears to advocate ETTR despite its shortcomings with current camera histograms.
Rather than systematically underexposing all one's images in order to prevent possibly blown highlights, the more prudent photographer would anticipate those situations where the camera histogram might not detect small important clipped highlights. For night scenes, bracketing gives the best chance of obtaining an optimal exposure.
This is exactly the approach (http://theonlinephotographer.typepad.com/the_online_photographer/2011/10/expose-to-the-right-is-a-bunch-of-bull.html) Ctein takes on TOP, and is diametrically opposed to Michael's recent article (http://www.luminous-landscape.com/tutorials/optimizing_exposure.shtml) on the subject where he still appears to advocate ETTR despite its shortcomings with current camera histograms.Why should these appear as opposite views? I'd thought that since advent of digital, everybody knows that clipping is to be avoided, and that it's taking for granted in Michael's article. The main difference is a tradeoff between noise and the risk of clipping.
On topic, I found out that Olympus cameras have an ETTR setting (http://www.luminous-landscape.com/forum/index.php?topic=46071.0), but it has its shortcomings - mainly that it's a spot metering mode, and Guillermo Luijk's research down the thread shows it leaves too much headroom. I have not used it since, and prefer to take Ctein's approach.I discovered it too (have an EPL1 since 2 weks), and even if it's not optimized for raw, I feel for now that it's the best guesstimate at hand when you have to shoot quickly.
Of course, it would be much more simple if manufacturers would give us the proper tools (http://www.luminous-landscape.com/forum/index.php?topic=33267), but as long as pigs don't fly ::) , is there a way to set a different exposition bias for spot metering (+3EV) and matrix metering (say 0EV) on Canon cameras that have spot metering?
Ctein is missing a couple key points with his article. BJanes brings up one of them.That is not how I understand the popular consensus of how "ETTR" should be interpreted, and it does not seem like a sensible approach.
Using ETTR, the exposure is pushed to the right such that no clipping occurs. None. Not 'unwanted clipping'. Not 'non-specular highlight clipping'. No clipping.
Also, for ETTR to be of any value the scene/subject contrast has to fit within the range of the sensor. The scene CTein was using as an illustration fails that aspect of ETTR.
Just because an interpretation is 'popular' doesn't make it right.No, but if a definition is both popular and sensible, I think that both make my case stronger. Of course, you may choose to provide arguments that it is not sensible, or that some expert thinks otherwise.
Well clearly you don't consider me an expert. ;DOn the internet, everyone is his/her own expert, so refering to oneself as an authority in discussions tends to be less than productive :-)
http://schewephoto.com/ETTR/index.htmlI think that this sentence is more or less in line with what I said:
Read and be educated.
So basically, someone agrees with you. I still think that it sounds counterproductive, and neither you nor Schewe (?) have provided arguments for why ETTR should _never_ be used together clipping highlights.
Huh?I was referring to this:
'why ETTR should _never_ be used together clipping highlights'
Not sure what you mean...
Using ETTR, the exposure is pushed to the right such that no clipping occurs. None. Not 'unwanted clipping'. Not 'non-specular highlight clipping'. No clipping.
...
for ETTR to be of any value the scene/subject contrast has to fit within the range of the sensor.
I am proposing that any given pixel will look better the closer to the sensor saturation point it is brought without actually clipping(given that artistic goals about scene movement, DOF etc actually allows some freedom in exposure). If possible, we would want all pixels to be just on the virge of saturation. Sadly, that is only possible if you take snaps of gray, uniform walls.
If the scene contrast is less than the dynamic range of the sensor, then you are leaving IQ on the table if you don't do ETTR...at what point do you consider 'clipping highlights' to be an issue?
I think the best way to explain how to expose digitally is that you should concentrate on the highlights, try to get them as close as saturation as possible in order to capture as many photons from the scene as possible for best signal-to-noise ratio in the whole picture, and if not possible to fit them without overexposure then decide what a suitable amount of overexposure is, but keep in mind what is lost is lost so do not overdo it, and that poor camera exposure evaluation tools can fool you, so play it safe and bracket if there is a difficult situation. Sounds pretty much as expose-to-the-right to me.Aaaamen, ite missa est, and all that sort of things as far as I am concerned. ;)
It's often even difficult to control specular highlights with HDR or other blending methods because it's sometimes difficult or impractical to bracket that many stops.And moreover, those specular haighlight themselves are often best rendered as pure white in a print, so clipping them is not that a problem. The trickier part is to render the "glow" around it, it's where having enough non-clipped data can make a huge difference.
If you actually think about it, the two go hand in hand. If a scene has specular highlights then it's not going to fit within the range of the sensor because those highlights are going to be several stops brighter than 'regular' light. It's often even difficult to control specular highlights with HDR or other blending methods because it's sometimes difficult or impractical to bracket that many stops.I dont see how any of that contradicts my initial statement. You seem to presuppose that all highlights must always be captured accurately. My point is that sometimes it makes sense to clip them. Sure the image wont fit within the range of the sensor. So what, if the image looks better as a result?
And if you don't know who Jeff is, then I'd suggest doing a bit of research because he knows a hell of a lot more than either of us likely ever will.I have seen good posts from Schewe. I try to evaluate statements based on their content, not so much on the author. On the bright side, that means that I am open for good arguments from you even though I don't know you.
No, I don't presuppose that all highlights must be captured properly. I understand that sometimes some highlights may be clipped. What I'm saying though is that if highlights are clipped then ETTR doesn't apply. 'Better' is a subjective term. What's better to you may not be to me and vice versa.Then we just have do agree that we disagree. I believe that you think that ETTR is about increasing exposure until the brightest pixels nearly saturate. I believe that ETTR is about increasing exposure until the brightest pixels that one care about nearly saturate. In all fairness, that difference is fairly minor in the big picture.
In all fairness, that difference is fairly minor in the big picture.
-h
For those new to uniwb, here's a link (for Canon cameras) http://www.guillermoluijk.com/tutorial/uniwb/index_en.htm
(in that case the sky would get clipped, no problem with that regarding the ETTR concept):
That's a matter of opinion.
You missed the point entirely.
This is why I think improved camera histograms don't address the issue at hand. I think it would be vastly preferable to have a visualization overlay on the image itself to show which pixels are clipped in the raw data.Rethinking to it (with the almost-ETTR feature of my new EPL1), I'd say you do need both to be efficient in the field : either the photo is underexposed, and then the histogram tells you by how much it is, or it is overexposed and the HL blinker tells you where it is blown.
This is why I think improved camera histograms don't address the issue at hand. I think it would be vastly preferable to have a visualization overlay on the image itself to show which pixels are clipped in the raw data.
If I had to choose, I would also prefer highlight clipping, but not so vastly as you suggest. At least not if there is not also an underexposure warning (certain number of stops below saturation). Otherwise you can be sure not to clip the highlights, but there will remain uncertainty about noise that can be expected when lifting the shadows.
In this sense, a dynamic histogram in EV divisions can even be more accurate and helpful than clip warnings. If this histogram let's you know visually the range of acceptable noise, it can be even user to do ETTL (Expose to the left = expose as low as possible right before having SNR below a threshold in the shadows) in critical shutter and/or DOF applications, where we want to expose as less as possible.
With this kind of histogram:
(http://www.guillermoluijk.com/misc/histogram.gif)
The RAW shooter just needs to make sure the histogram falls into the range between clipping and noise. Any exposure inside this range will be good enough regarding noise and highlight information.
Regards
Just to be clear, you all are talking about a live view image on the back LCD before the image is made, yes? And it would have to be calculated off some sort of raw (unprocessed light hitting the sensor) data, yes? Because I think pretty much all cameras have blinking highlight indicators available after capture calculated off JPEG data and the 'knob' in that case is the aperture value, shutter value or exp. comp. and retaking the shot (not always possible).
Otherwise you can be sure not to clip the highlights, but there will remain uncertainty about noise that can be expected when lifting the shadows.
But WB can impact colours/clipping so wouldn't it be better to have the preview include the WB?No : as long as the raw data is not clipped, recovery is dead easy (or almost so) in post. For me in LR, no math involved but some sliders tweaking (recovery+, exposure-/brightness+ eg).
Attached are two images. One taken with a WB of 10000 (read as 9100 in ACR), the other taken with a WB of 2500 (read as 2600 in ACR). The histograms are different and the clipping indicators are different. If WB doesn't affect a RAW exposure, what explains the difference between the two.
Not really that difficult to analyse. The small differences are pretty easily figured out.
You're right, it is not really that difficult. What happens is that in a linear scale the Histogram will "expand" or "contract" as you change exposure. In a logarithmic scale it would shift left or right (like in Guillermo's great animation), which I consider more intuitive.
Two raw images where the only difference is exposure will show the same Histogram shape at different locations.
in a linear scale the Histogram will "expand" or "contract" as you change exposure. In a logarithmic scale it would shift left or right (like in Guillermo's great animation), which I consider more intuitive.
If the raw channels are not clipped, but clipping occurs as you adjust WB, you could then adjust back with the exposure slider (or recovery) and you'll be working out from real raw data.
In a simplified way, WB multiplies the Red and Blue channels by numerical factors depending on the color temperature and tint. Exposure is a linear multiplication of a same number for all the channels
So, suppose that a specific WB multiplies the Red channel by 2 and the Blue channel by 1.5. Here you might end with clipped values in the red and blue channels because of this multiplication.
Then, adjusting the exposure by -1 f stop will multiply all channels by 0.5, now you get back to non-clipped values.
I guess it depends on what tool you're using, but I've found that Rawnalyze and Raw Therapee don't work that way. With both Rawnalyze and RT, if you reduce the exposure to -1 all the previously "blown" pixel become a lower value but they're all still the same...they're just not at 255 anymore. In RT, if I use highlight recovery, the same thing happens...except that the rest of the image remains unchanged.
The only thing that worked for me in RT is the Highlight Reconstruction tool. It seems to get rid of the obvious field of "blown but recovered" pixels.