Luminous Landscape Forum
Site & Board Matters => About This Site => Topic started by: bjanes on June 03, 2008, 09:02:03 pm
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Mark Segal's post on noise is a valuable contribution for those interested in noise in digital images since it contains actual photographic comparisons and complements the more theoretical post by Emil Martinec.
One point that I would like to make is that ACR's histograms are a poor indication of the raw data, since ACR uses a baseline exposure offset of +0.5 EV for the D3 and with default settings the highlights will appear clipped when they are intact in the actual raw file. I would recommend Rawanalyze to look at the actual raw histogram.
Here is the raw histogram of a Stouffer stepwedge exposed so the highlights are just shot of clipping as shown with Rawnanalyze:
(http://bjanes.smugmug.com/photos/306816807_tVzJt-O.png)
And here is what it looks like in ACR with default settings. The top two steps (each is 0.1 EV) appear clipped:
(http://bjanes.smugmug.com/photos/306816817_j8Fk9-O.png)
One needs to use -0.6 EV of negative exposure compensation to place the highlights just short of clipping:
(http://bjanes.smugmug.com/photos/306816833_sP4tG-O.png)
I would like to ask Mark if his D3 shots are really properly exposed according to ETTR.
Bill
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Mark Segal's post on noise is a valuable contribution for those interested in noise in digital images since it contains actual photographic comparisons and complements the more theoretical post by Emil Martinec.
One point that I would like to make is that ACR's histograms are a poor indication of the raw data, since ACR uses a baseline exposure offset of +0.5 EV for the D3 and with default settings the highlights will appear clipped when they are intact in the actual raw file. I would recommend Rawanalyze to look at the actual raw histogram.
Here is the raw histogram of a Stouffer stepwedge exposed so the highlights are just shot of clipping as shown with Rawnanalyze:
And here is what it looks like in ACR with default settings. The top two steps (each is 0.1 EV) appear clipped:
One needs to use -0.6 EV of negative exposure compensation to place the highlights just short of clipping:
I would like to ask Mark if his D3 shots are really properly exposed according to ETTR.
Bill
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Hi Bill,
Many thanks for reading and commenting. Appreciated. Some points:
First - something went wrong with the links to your illustrations - the first two started as the same image in Camera Raw 4.4., then as I was writing, the first two sorted out correctly. Weird.
Second, in the 3rd illustration is there any reason why you would prefer to reduce exposure rather than increase recovery to rescue the blown highlights?
Third, I like your idea of seeing these histograms in more than one raw converter. That could help shed light on the role of the converter in exposure rendition.
Fourth, the kind of histogram you get in the raw converter of course depends on what the user decides to be the ACR defaults. I notice you have Brightness and Contrast set on the usual ACR defaults we download the program with. Perhaps in the defaults you are using there is also a moderate S in the Point Curve. These things can cause some highlight clipping when the highlights are very close to the edge in the raw file. I turn all that stuff off to zero in the basic tab and set the tone curves to Linear. Then I see things as they are without any "pumping-up" in the raw converter. It's what I like to think of as a "Greenfield" starting point. Then I build up. So with that background I can turn to your question: were the D3 shots properly exposed as ETTR?
The answer is a qualified YES, in the sense that when we made the D3 shots, on the camera's LCD screen the histograms looked bang-on ETTR, except for minor clipping of specular highlights. Downloaded into ACR with the settings at the flat defaults I discussed just above (and in footnote 6 in the article), lo and behold there was clipping of the brightest portion of the sky, which we did NOT see in the camera LCD. However, using ACR's Recovery function, the blueness of the sky got perfectly recovered. So I would say the D3 shots were ETTR+a bit.
I think perhaps one lesson of experience from doing this work is the usefulness of experimenting to select in-camera JPEG settings and raw converter default settings that will best produce similar histograms of the raw file in both places - should limit unpleasant surprises.
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Bill,
Further to the above, interesting that Rawanalyze shows the same kind of result we expected given what the histogram looked like in the camera LCD - no clipping. But then one wonders what Rawanalyse would do with Canon raw images? Do you think it has a generally more accurate fix on the raw data, or is this an anomoly affecting the treatment of the D3?
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Hi Bill,
Many thanks for reading and commenting. Appreciated. Some points:
First - something went wrong with the links to your illustrations - the first two started as the same image in Camera Raw 4.4., then as I was writing, the first two sorted out correctly. Weird.
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I hit the wrong key and made my post prematurely, before I had refinished writing it. I then had to go back and edit it and had some trouble posting the images. So you were viewing my post as I was editing it. Sorry for the confusion.
Second, in the 3rd illustration is there any reason why you would prefer to reduce exposure rather than increase recovery to rescue the blown highlights?
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I used the exposure control since it is linear and moves the entire scale down by 0.5 EV whereas recovery is nonlinear and affects mainly the highlights and would not give the desired result.
Fourth, the kind of histogram you get in the raw converter of course depends on what the user decides to be the ACR defaults. I notice you have Brightness and Contrast set on the usual ACR defaults we download the program with. Perhaps in the defaults you are using there is also a moderate S in the Point Curve. These things can cause some highlight clipping when the highlights are very close to the edge in the raw file. I turn all that stuff off to zero in the basic tab and set the tone curves to Linear. Then I see things as they are without any "pumping-up" in the raw converter. It's what I like to think of as a "Greenfield" starting point. Then I build up. So with that background I can turn to your question: were the D3 shots properly exposed as ETTR?
The answer is a qualified YES, in the sense that when we made the D3 shots, on the camera's LCD screen the histograms looked bang-on ETTR, except for minor clipping of specular highlights. Downloaded into ACR with the settings at the flat defaults I discussed just above (and in footnote 6 in the article), lo and behold there was clipping of the brightest portion of the sky, which we did NOT see in the camera LCD. However, using ACR's Recovery function, the blueness of the sky got perfectly recovered. So I would say the D3 shots were ETTR+a bit.
I think perhaps one lesson of experience from doing this work is the usefulness of experimenting to select in-camera JPEG settings and raw converter default settings that will best produce similar histograms of the raw file in both places - should limit unpleasant surprises.
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I agree it is sometimes to set ACR to linear by setting contrast, brightness, and black to zero and using a linear tone curve. However, in this instance, it does not make that much difference in the rendering of the highlights as shown here:
(http://bjanes.smugmug.com/photos/306874178_tRoDh-O.png)
In my own tests, I too have found that the camera histogram reflects the status of the raw histogram to within 0.3 EV, so your ETTR via the camera histogram is likely pretty close. Here is the camera histogram for the previously shown raw histogram. It shows slight clipping, which disappears with an exposure reduction of 0.3 EV.
(http://bjanes.smugmug.com/photos/306891717_qSYt3-O.png)
(http://bjanes.smugmug.com/photos/306877692_ewjsc-M-0.png)
I don't know how what Rawanalyze would show with the Canon, but it would be interesting to find out. Why don't you download it and see for yourself and report back to us.
[a href=\"http://www.cryptobola.com/PhotoBola/Rawnalyze.htm]Rawanalyze[/url]
Anyway, thanks for your excellent work. It will take some time to digest all the material.
Bill
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ACR does the same thing for my D300 files. I could not for the life of me figure out why my D300 NEF's look overexposed when I got them back to the computer even though the histogram looked like exactly what I wanted in-camera (I often use UniWB and linear tone curve in-camera). I've since set my ACR defaults for the D300 to use -.5EV exposure adjustment and the images look as I expect. I know some have tried to explain in other threads why ACR's approach to 'normalizing' things makes sense, but in the case of the D3/D300 somebody screwed up.
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I don't know how what Rawanalyze would show with the Canon, but it would be interesting to find out. Why don't you download it and see for yourself and report back to us.
Anyway, thanks for your excellent work. It will take some time to digest all the material.
Bill
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Bill, thanks, appreciated.
Actually I do have Rawanalyze - but I haven't played with it yet. Your suggestion is a very good one, which I shall do; but it will have to wait a few days as I have a tight deadline on a piece of work related to the other part of my life. I'll report back here once I've had a chance to do it.
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ACR does the same thing for my D300 files. I could not for the life of me figure out why my D300 NEF's look overexposed when I got them back to the computer even though the histogram looked like exactly what I wanted in-camera (I often use UniWB and linear tone curve in-camera). I've since set my ACR defaults for the D300 to use -.5EV exposure adjustment and the images look as I expect. I know some have tried to explain in other threads why ACR's approach to 'normalizing' things makes sense, but in the case of the D3/D300 somebody screwed up.
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Jeff, I'm not sure I would try to explain this in terms of somebody "screwing-up". We're talking about two indicators of exposure (and Bill refers to a 3rd, which makes a lot of sense). Each of those indicators is driven by all the assumptions that go into how they behave. So which do you want to use as the benchmark - the camera's histogram or the ACR histogram, and with what combination of default settings to render these histograms? The raw data of course is the raw data regardless of the in-camera JPEG settings which influence the camera's histogram, and ACR has suggested defaults (which we can change). The essential challenge here is to try to make them as coherent as possible in order to minimize unpleasant surprises. How one meters the scenes and what the camera does with that information should also influence these outcomes. I think this is less a matter of anyone screwing-up and more a question of alligning the variables to get results that are as close to coherent as possible and useful.
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Jeff, I'm not sure I would try to explain this in terms of somebody "screwing-up". We're talking about two indicators of exposure (and Bill refers to a 3rd, which makes a lot of sense). Each of those indicators is driven by all the assumptions that go into how they behave. So which do you want to use as the benchmark - the camera's histogram or the ACR histogram, and with what combination of default settings to render these histograms? The raw data of course is the raw data regardless of the in-camera JPEG settings which influence the camera's histogram, and ACR has suggested defaults (which we can change). The essential challenge here is to try to make them as coherent as possible in order to minimize unpleasant surprises. How one meters the scenes and what the camera does with that information should also influence these outcomes. I think this is less a matter of anyone screwing-up and more a question of alligning the variables to get results that are as close to coherent as possible and useful.
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Mark,
My understanding of the ACR [a href=\"http://www.adobe.com/products/dng/pdfs/dng_spec.pdf]BaselineExposure [/url] compensation is to ensure that for a given exposure (say 1/60 s, f/8, ISO 1600), the resulting rendered images taken with various cameras will have the same appearance. Is this what you found in your testing with the Canon and Nikon cameras?
The issue revolves around how much headroom one should leave for specular highlights. The official ISO Specification (http://en.wikipedia.org/wiki/Film_speed) for digital camera ISO speed ratings leaves 0.5 EV headroom for specular highlights and my own testing shows that the Nikon metering conforms to ISO standards.
However, for practical ETTR exposure it is often best to place non-specular highlights just short of clipping and let the specular highlights blow out. One can use negative exposure compensation in the raw converter to recover the specular highlights if desired. I understand that this is your approach and I agree that it is the best approach in most instances.
If my assumptions are correct, Canon does not leave this headroom for specular highlights.
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Mark,
My understanding of the ACR BaselineExposure (http://www.adobe.com/products/dng/pdfs/dng_spec.pdf) compensation is to ensure that for a given exposure (say 1/60 s, f/8, ISO 1600), the resulting rendered images taken with various cameras will have the same appearance. Is this what you found in your testing with the Canon and Nikon cameras?
The issue revolves around how much headroom one should leave for specular highlights. The official ISO Specification (http://en.wikipedia.org/wiki/Film_speed) for digital camera ISO speed ratings leaves 0.5 EV headroom for specular highlights and my own testing shows that the Nikon metering conforms to ISO standards.
However, for practical ETTR exposure it is often best to place non-specular highlights just short of clipping and let the specular highlights blow out. One can use negative exposure compensation in the raw converter to recover the specular highlights if desired. I understand that this is your approach and I agree that it is the best approach in most instances.
If my assumptions are correct, Canon does not leave this headroom for specular highlights.
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Bill,
Regarding the exposures, the first idea was to focus on the shape and position of the in-camera histogram (whether the aim was an ETTL or an ETTR) and get that looking approximately the same between the three cameras for each ISO, whether or not it resulted in the same aperture and shutter speeds between them. So for ETTL the idea was to expose to just before the point of clipping blacks, and for ETTR, as you mention, the idea was to tolerate some specular highlight clipping. [But it turned out that a slightly more aggressive approach to ETTR ("ETFR" for the Canons) worked out better, after a bit of Recovery in ACR.]
It happened that the exposure compensation settings were quite different between the Canons and the Nkon to achieve this. Which takes us to the question of headroom. It looked very much to us that both Canons allowed more headroom for specular highlights in the sense that they average down the exposure in order to avoid clipping specular highlights - hence the midtones end-up further to the left than where ideally one would want them, whereas the Nikon produced a more central positioning of the midtones at the expense of some highlight clipping. These findings emerge from examining the histograms in ACR at the footnote 6 settings for that scene.
I think it would be good to revisit these histogram comparisons using Rawanalyze and see whether it confirms the initial observations. I intend to do that as soon as time permits. Meanwhile, your impression of my preferred exposure strategy is correct, except that once in ACR, whether to deal with clipping via implementing some Recovery or reducing the Exposure depends on the image: if the mid-tones look over-exposed at the same time the highlights are clipped, then of course it makes sense to reduce Exposure, but if the mid-tones look OK and there are clipped highlights one wishes to recover, then Recovery would be the tool of choice.
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Just a question--it's probably answered in the article, but I didn't see it. In Figure 4, the article shows a comparison of tight crops from the 1Ds and 1Ds3, taken at 45mm and f/6.3 and f/7.1. Now, those cameras have the same sensor size, and those images are taken at the same focal length, so my initial assumption as to what I was looking at in that picture must have been wrong--that is, I had assumed that the two pictures were quote-one-hundred-percent-pixel-crops-unquote. Had that been true, the 1Ds3 image would have been larger in screen dimensions to show the same area of the scene.
So, there are at least four possible explanations I've come up with so far, but to entirely make sense of the resolution results it's important to know which is the case.
First, it's possible that that the 1Ds image is "100% pixels" and the other is downsampled.
Second, it's possible that the 1Ds3 image is "100% pixels" and the 1Ds is upsampled.
Third, it's possible that both images are resampled.
Fourth, it's possible that those images are both photographs of the print.
In any of these cases, I'd be curious what Figure 4 actually represents, and, by extension, what's happening in any of the other figures (it appears that a comparison of Figure 2 with Figure 3 leads to the same questions, as an example.)
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I think it would be good to revisit these histogram comparisons using Rawanalyze and see whether it confirms the initial observations. I intend to do that as soon as time permits. Meanwhile, your impression of my preferred exposure strategy is correct, except that once in ACR, whether to deal with clipping via implementing some Recovery or reducing the Exposure depends on the image: if the mid-tones look over-exposed at the same time the highlights are clipped, then of course it makes sense to reduce Exposure, but if the mid-tones look OK and there are clipped highlights one wishes to recover, then Recovery would be the tool of choice.
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Mark,
We have discussed the use of the recovery and exposure sliders before and our approaches are different but not incompatible. In CR_09 of the ACR tutorial by Michael and Jeff Schewe, Thomas Knoll discusses the use of these tools. His preferred approach is to use the exposure slider to set the highlights short of clipping and then to use the brightness slider to set the mid tones. An alternate method, introduced in Lightroom, is to use the recovery slider to set the highlights and the exposure slider to set the mid tones. He states that the two methods are equally valid. Personally, I prefer the first method and you appear to prefer the second method.
To correct the BaselineExposure offset used by ACR with the D3, I think the proper tool is the exposure slider. The +0.5 EV offset used by ACR for the D3 moves the entire tonal scale (shadows, mid tones and highlights) 0.5 EV to the right and an exposure setting of -0.5 EV in ACR undoes this adjustment. Use of the recovery slider would move the highlights to the left, but the mid tones and shadows would still be too bright.
The situation in which I have found the Recovery slider to be most useful is with backlit and sidelit shots where the overall exposure is correct but the highlights are burnt out.
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Just a question--it's probably answered in the article, but I didn't see it. In Figure 4, the article shows a comparison of tight crops from the 1Ds and 1Ds3, taken at 45mm and f/6.3 and f/7.1. Now, those cameras have the same sensor size, and those images are taken at the same focal length, so my initial assumption as to what I was looking at in that picture must have been wrong--that is, I had assumed that the two pictures were quote-one-hundred-percent-pixel-crops-unquote. Had that been true, the 1Ds3 image would have been larger in screen dimensions to show the same area of the scene.
So, there are at least four possible explanations I've come up with so far, but to entirely make sense of the resolution results it's important to know which is the case.
First, it's possible that that the 1Ds image is "100% pixels" and the other is downsampled.
Second, it's possible that the 1Ds3 image is "100% pixels" and the 1Ds is upsampled.
Third, it's possible that both images are resampled.
Fourth, it's possible that those images are both photographs of the print.
In any of these cases, I'd be curious what Figure 4 actually represents, and, by extension, what's happening in any of the other figures (it appears that a comparison of Figure 2 with Figure 3 leads to the same questions, as an example.)
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None of the above .
The dimensions (width and height) of a photograph can be altered by entering the Image Size dialog, unchecking the resample "Resample" box, and entering the W and H one wants. The PPI will vary inversely with the change in dimensions but there will no resampling. As long as PPI is 180 or above it suffices for the purposes of this article.
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Mark,
He states that the two methods are equally valid. Personally, I prefer the first method and you appear to prefer the second method.
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Bill, no problem with what you're syaing, but the approach I prefer depends entirely on what I think the image needs. So, over-exposed highlights, decent mid-tones and shadows: I use Recovery. Over-exposed everything: I reduce Exposure; Under-exposed shadows, over-exposed highlights but decent mid-tones: I leave Exposure alone and use Fill+Blacks and Recovery. I.O.W. "it all depends" - basic principle - target the adjustment to where the problem is. That's what makes the latest incarnations of ACR such valuable image editing tools - I'm sure you would agree; lots of flexibility to do many things in a more targeted way than how it was in 3.7 and earlier.
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In my own tests, I too have found that the camera histogram reflects the status of the raw histogram to within 0.3 EV, so your ETTR via the camera histogram is likely pretty close. Here is the camera histogram for the previously shown raw histogram. It shows slight clipping, which disappears with an exposure reduction of 0.3 EV.
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Are the camera histograms based on the RAW file or the camera's jpeg preview?
Since the image displayed on the camera screen is a jpeg preview not a RAW image am I correct in assuming that the histogram is derived from that data, not the actual RAW data.
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Are the camera histograms based on the RAW file or the camera's jpeg preview?
Since the image displayed on the camera screen is a jpeg preview not a RAW image am I correct in assuming that the histogram is derived from that data, not the actual RAW data.
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Nick, this is exactly the issue - the histograms on the camera screen are generated from the JPEG settings.
Mark
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Nick, this is exactly the issue - the histograms on the camera screen are generated from the JPEG settings.
Mark
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The other issue is that the in-camera histogram (at least for the non pro cameras, don't know about the 1 series) is some undefined (as far as i know) averaging of the three channels. Probably mostly influenced by the green channel. So you can get clipping in one or two channels, which will show as clipping in your raw converter, but as long as the 'averaged' value is not clipping, the in-camera histogram will not show clipping. It would be good to be able to configure through firmware how the in-camera histogram actually performs.
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My 5D Picture Style jpeg (and therefore histogram) is set to minimum contrast, minimum sharpening and minimum saturation. The image review on the camera's LCD panel doesn't look too impressive when I sometimes decide to show someone the shot I've just taken.
On one occasion, a young fella after seeing a few reviews of some recent shots on my 5D's LCD, pulled out his iPhone with built-in 3mp camera and 3" screen and proceeded to display a number of sparkling and colorful shots which he reckoned were much better .
I understand that ACR will try to reconstruct a blown channel from information contained in the other two channels. I don't know how this is possible or to what extent it can be done. However, if a processed image with approprite -EC adjustment does not appear to have any clipped channels, then for most practical purposes it doesn't have any clipped channels. The fact that a program like Rawanalyze can demonstrate that a particular channel is actually clipped is only of academic interest.
When attempting to maximise the camera's S/N by pushing exposure to its maximum, just short of clipping, one inevitably gets a few shots that are truely and irredeemably clipped, due to miscalculation. Common examples of obvious clipping in my own situation are blue skies with a distinct shift towards cyan and reddish skin tones that turn grey.
I recall some years ago seeing an elaborate technique on LL describing a method of reconstructing such blown channels. I decided it was much easier to be more careful at the shooting stage and bracket exposure when in doubt .
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It would be good to be able to configure through firmware how the in-camera histogram actually performs.
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To some extent you can with whatever JPEG settings the camera firmware provides. Ray's post gets into that.
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I understand that ACR will try to reconstruct a blown channel from information contained in the other two channels. I don't know how this is possible or to what extent it can be done.
When attempting to maximise the camera's S/N by pushing exposure to its maximum, just short of clipping, one inevitably gets a few shots that are truely and irredeemably clipped, due to miscalculation.
I decided it was much easier to be more careful at the shooting stage and bracket exposure when in doubt .
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Ray,
ACR has a great Recovery function. Needless to say I don't know the math - I suppose it would haveto be some form of borrowing from unclipped data. What I do know, however, is that very often it is really, really effective. It does liberate the photographer from being overly-concerned about minor amounts of clipping. I agree with you that in attempting to maximise an ETTR one can miscalculate and over-do it, but depending on how one has the in-camera JPEG configured, at least with the Canons I've been using one is usually warned (after the fact) and can then adjust and retake - as long as it's not one of those "fleeting moment" images. When in doubt of course bracketing is good practice, but with a !ds3 and its 25~30 MB raw files it fills cards QUICKLY!
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The other issue is that the in-camera histogram (at least for the non pro cameras, don't know about the 1 series) is some undefined (as far as i know) averaging of the three channels. Probably mostly influenced by the green channel. So you can get clipping in one or two channels, which will show as clipping in your raw converter, but as long as the 'averaged' value is not clipping, the in-camera histogram will not show clipping. It would be good to be able to configure through firmware how the in-camera histogram actually performs.
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Bernie raises a good point about in camera histograms. They are said without much proof to represent luminance histograms where the RGB channels are weighted. [a href=\"http://www.cambridgeincolour.com/tutorials/histograms2.htm]Sean McHugh[/url] has a good tutorial in his Cambridge in Color site, where he discusses luminance and RGB histograms. The RGB weighting factors he gives are 59%, 30%, 11% for GRB respectively. Since the factor for blue is only 11%, luminance histograms are not sensitive for detecting clipped blues.
Most higher end cameras have an option to display separate histograms for the RGB channels. These are similar to the histogram one sees in ACR and by default in Photoshop (PS has an option to display luminance histograms). These RGB camera histograms are white balanced and do not show the true status of the RGB channels. To achieve white balance the red and blue channel values are multiplied by a coefficient greater than unity and the green channel is left alone.
Julia Borg (http://www.pochtar.com/NikonWhiteBalanceCoeffs.htm) has published these coefficients for some Nikon cameras according to the color temperature of the illuminant. For daylight, the red channel is most underexposed and needs the largest multiplier, while the blue is most underexposed with tungsten illumination. For the Nikon D3 with daylight, the RGB multipliers are about 2.2, 1.0 and 1.19. Shown below is a typical raw histogram for the D3 with daylight WB:
(http://bjanes.smugmug.com/photos/307719863_6diXG-O.png)
As is evident from the histogram, the red channel has the greatest headroom, followed by the blue channel. The bold tic marks are full f/stops and the other marks indicate thirds of a stop. In this case, proper ETTR was not achieved since the green channel is considerably below clipping, about 2/3 of an f/stop. With increased exposure, the green channel would start to clip, but the other channels would still be intact and highlight recovery in ACR would be possible. With still more increased exposure, the blue channel would start to clip, followed by the red channel. When all channels are clipped, highlight recovery in ACR is not possible. The red histogram is about 1 f/stop below the green, which indicates that a maximum of about 1 stop of highlight recovery is possible with this camera and daylight illumination.
With ACR at default settings, the above image appeared slightly overexposed according to the ACR histogram, due in large part to the +0.5 EV baseline exposure compensation that ACR uses for the D3. This demonstrates the importance of checking the raw histogram, which is easily done with Rawanalyze. If one wants the camera RGB histogram to give a better picture of the status of the RGB channels, one can upload to the camera a white balance where the WB multipliers are all unity (1.0). Search UniWB for details.
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With ACR at default settings, the above image appeared slightly overexposed according to the ACR histogram, due in large part to the +0.5 EV baseline exposure compensation that ACR uses for the D3. This demonstrates the importance of checking the raw histogram, which is easily done with Rawanalyze. If one wants the camera RGB histogram to give a better picture of the status of the RGB channels, one can upload to the camera a white balance where the WB multipliers are all unity (1.0). Search UniWB for details.
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Bill, as usual an informative post - but I have a question re the para I retained above: When you say there is a +0.5 exposure compensation which ACR uses for the D3, is that "under the hood" or is it a function of the slider and tone curve settings which come packaged as "ACR defaults" for that camera?
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Bill, as usual an informative post - but I have a question re the para I retained above: When you say there is a +0.5 exposure compensation which ACR uses for the D3, is that "under the hood" or is it a function of the slider and tone curve settings which come packaged as "ACR defaults" for that camera?
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Mark,
The ExposureOffset is not well documented, but I understand that it is packaged under the "ACR defaults" for that camera, and ACR applies +0.5 EV of compensation to all D3 NEFs. If you convert the NEF to DNG, you can use an EXIF reader and read the ExposureOffset that the DNG converter writes to the ExposureOffset tag of the metadata. I have not figured out how to do that with my available software, but perhaps someone can tell us how it is done. You could then find out the offset for your 1DsMIII. From what you have reported, I suspect that it is closer to zero than +0.5.
Bill
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Yup, for the Canons that would be my suspicion too. Still, as you say, it would be interesting to get some hard info on how it's done. From what you are saying, it seems this is done "under the hood" - not by slider defaults. Even if so, and if one finds this for some reason (say related to personal preferences or imaging environment) systematically bothersome, one can always set a counteracting Exposure reduction as a personal ACR preset for the camera. But before going there, undoubtedly a lot of research went into those ACR defaults for each supported camera, so what's more interesting is to know how/why the ACR team would have arrived at the judgment to set the exposure default the way they may have done for the D3.
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Some notes to issues touched above.
1. Careful with interpreting the in-camera histogram. As long as it is not purely raw-based, the histogram even with neutralised WB and other settings will not even resemble the raw histogram for following reasons:
a. de-mosaicing
b. color space conversion from camera to sRGB or whatever
These steps mix the raw channels into the RGB channels.
c. non-linear encoding ("gamma"). This step causes the distribution to be "compressed".
The effects of a. and b. are not very bad, except for very special illumination.
The effect of c. is very large; see the different histograms below from three images with different exposures: one is the raw, then the linear luminance displayed by Canon's DPP, and the RGB, again by DPP.
Consequently, the amount of clipping or close to clipping can not be judged from the in-camera histogram, but the indication, that probably clipping occured is reliable - and that's the point. If the camera displays clipping on the LCD (I guess this is the norm these days), that is more reliable.
I have been using the neutral setting for months, and I am absolutely satisfied; the clipping indication (blinking on the LCD) matches exactly with that based on the raw analysis (as far as it is discernable on the LCD). However, apparent "underexposure" (from the perfect ETTR) is much more, than the histogram indicates.
2. The automatic exposure adjustment is recorded in the tag BaselineExposure. It can be seen only in DNG format. The adjustment is not visible on the slider.
3. Images from the Canon 1DsMkIII will be automatic adjusted by +0.35 EV.
Note, that not only the exposure, but noise reduction and sharpening too are recorded in DNG format (BaselineNoise and BaselineSharpness). I really do not know, how far these affect the ACR processing, but I guess they do. In other words, the noise reduction is unavoidable. Furthermore, I don't know, if this noise reduction and the one specified are additive. Plus, this specification does not distinguish between luminance and chrominance NR.
4. The "recovery" slider appears to have nothing to do with true recovery of clipping; that is apparently automatic. It works well on uniform or quasy-uniform areas, for example on skies, but not on very fine details - this is understandable.
5. *All* TIFF tags can be extracted by http://www.cryptobola.com/PhotoBola/free/RawnalyzeTL.exe (http://www.cryptobola.com/PhotoBola/free/RawnalyzeTL.exe)
This program creates a text file named "original file name.taglist.txt" in the same folder as the input was. It can be used on any TIFF. When started in Windows, it will stop running after having created the text file. It can be started from command line as well (one can specify a function for example "Taglist" in Windows Explorer, and create the tag list by right-clicking on the file name). If someone wants to do that, I post the details.
[attachment=6917:attachment][attachment=6918:attachment][attachment=6919:attachm
ent][attachment=6920:attachment][attachment=6921:attachment][attachment=6922:atta
chment][attachment=6923:attachment][attachment=6924:attachment][attachment=6928:a
ttachment]
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Bernie raises a good point about in camera histograms. They are said without much proof to represent luminance histograms where the RGB channels are weighted. Sean McHugh (http://www.cambridgeincolour.com/tutorials/histograms2.htm) has a good tutorial in his Cambridge in Color site, where he discusses luminance and RGB histograms. The RGB weighting factors he gives are 59%, 30%, 11% for GRB respectively. Since the factor for blue is only 11%, luminance histograms are not sensitive for detecting clipped blues.
[a href=\"index.php?act=findpost&pid=199887\"][{POST_SNAPBACK}][/a]
This is what I have found with skies in particular. No clipping on the camera histogram, but when analysing the raw data, blue has clipped.
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This is what I have found with skies in particular. No clipping on the camera histogram, but when analysing the raw data, blue has clipped.
[a href=\"index.php?act=findpost&pid=199956\"][{POST_SNAPBACK}][/a]
Yes. and this is precisely what happened with our Nikon D3 ETTR exposures; it happened to the Canon 1Ds3 exposures only when I implemented "ETFR" (Expose to the Further Right) - which was a bit more EC. as explained in the article But in this case, the sky clipping did show on my Canon LCD as well as in Camera Raw.
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Some notes to issues touched above.
I have been using the neutral setting for months, and I am absolutely satisfied; the clipping indication (blinking on the LCD) matches exactly with that based on the raw analysis (as far as it is discernable on the LCD). However, apparent "underexposure" (from the perfect ETTR) is much more, than the histogram indicates.
[a href=\"index.php?act=findpost&pid=199946\"][{POST_SNAPBACK}][/a]
Hi Pano - very interesting post and thanks for contributing. I'm particularly interested in your comment that I retained above. When you speak of "neutral settings" could you please clarify where and what these are? Are you talking about the JPEG settings for the in-camera histogram, or something for Camera Raw, (or both) and for whichever, what specifically are you using that you would define as "neutral"?
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Weighting of the RGB channels is part of the JPEG encoding. Most JPEG images are JFIF compliant; that means among others, that the data is stored in YCbCr format, not in RGB. The calculation of Y depends on the applied standard; according to CCIR 601,
Y = 0.299R + 0.587G + 0.114B
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Looking at your images in the above post, am I correct to assume that by "neutral" you mean the illustrated "neutral" settings in Rawanalyze?
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When you speak of "neutral settings" could you please clarify where and what these are? Are you talking about the JPEG settings for the in-camera histogram
I meant only the sharpness, contrast, saturation, tone, and, of course the white balance.
this is precisely what happened with our Nikon D3 ETTR exposures
I don't understand this. The problem Bernie mentioned is characteristic to luminance histograms, but the D3 has color histogram, and that should not be much different from the raw histograms with a neutral setting.
Do you mind posting such a raw file?
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Consequently, the amount of clipping or close to clipping can not be judged from the in-camera histogram, but the indication, that probably clipping occured is reliable - and that's the point. If the camera displays clipping on the LCD (I guess this is the norm these days), that is more reliable.
I have been using the neutral setting for months, and I am absolutely satisfied; the clipping indication (blinking on the LCD) matches exactly with that based on the raw analysis (as far as it is discernable on the LCD). However, apparent "underexposure" (from the perfect ETTR) is much more, than the histogram indicates.
[{POST_SNAPBACK}][/a] (http://index.php?act=findpost&pid=199946\")
With my Nikon D3 with neutral settings, I have been quite satisfied with the histogram to indicate ETTR. The accuracy of the camera histogram for ETTR reportedly varies among cameras. The blinking highlights also work well on my D3.
2. The automatic exposure adjustment is recorded in the tag BaselineExposure. It can be seen only in DNG format. The adjustment is not visible on the slider.
3. Images from the Canon 1DsMkIII will be automatic adjusted by +0.35 EV.
[a href=\"index.php?act=findpost&pid=199946\"][{POST_SNAPBACK}][/a]
From the above, I infer that the BaselineExposure for the 1DsMkIII is +0.35 EV as compared to +0.5 for the D3.
5. *All* TIFF tags can be extracted by [a href=\"http://www.cryptobola.com/PhotoBola/free/RawnalyzeTL.exe]http://www.cryptobola.com/PhotoBola/free/RawnalyzeTL.exe[/url]
This program creates a text file named "original file name.taglist.txt" in the same folder as the input was. It can be used on any TIFF. When started in Windows, it will stop running after having created the text file. It can be started from command line as well (one can specify a function for example "Taglist" in Windows Explorer, and create the tag list by right-clicking on the file name). If someone wants to do that, I post the details.
[a href=\"index.php?act=findpost&pid=199946\"][{POST_SNAPBACK}][/a]
I downloaded and used the Rawnalyze program and obtained the following data from the DNG. The BaselineExposure is shown as negative, whereas I expected it to be positive. Thanks very much for the information and program!
1000000/1000000 651399/1000000
50730 BaselineExposure SRATIONAL -50/100
50731 BaselineNoise RATIONAL 60/100
50732 BaselineSharpness RATIONAL 100/100
50734 LinearResponseLimit RATIONAL 100/100
50736 LensInfo RATIONAL 1050/10
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Hold on Bill, something is fishy!
I verified in a dozen D3 images with different ISOs, and the BaselineExposure is everywhere PLUS 0.5.
You must have applied some in-camera setting, which caused the DNG converter to act differently. It is important to figure out, what that was.
First I thought of Active Daylight; however, I have a D300 image with ADL High (allegedly), and there the exposure adjustment is not different from Off.
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I meant only the sharpness, contrast, saturation, tone, and, of course the white balance.
I don't understand this. The problem Bernie mentioned is characteristic to luminance histograms, but the D3 has color histogram, and that should not be much different from the raw histograms with a neutral setting.
Do you mind posting such a raw file?
[a href=\"index.php?act=findpost&pid=199973\"][{POST_SNAPBACK}][/a]
Pano - I don't mind, but I'll have to get back to you on that.
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Hold on Bill, something is fishy!
I verified in a dozen D3 images with different ISOs, and the BaselineExposure is everywhere PLUS 0.5.
You must have applied some in-camera setting, which caused the DNG converter to act differently. It is important to figure out, what that was.
First I thought of Active Daylight; however, I have a D300 image with ADL High (allegedly), and there the exposure adjustment is not different from Off.
[{POST_SNAPBACK}][/a] (http://index.php?act=findpost&pid=200014\")
Gabor,
I have 20 NEFs from the D3 taken as part of an Experiment with a Stouffer wedge with manual exposure and the same camera settings. Some have a baseline exposure tag as shown by your program of +0.5 EV as expected, but a large number towards the end of the shoot have a baseline exposure of -0.5 EV. The camera settings were not changed except for shutter speed. The preview in ACR does not show an unexpected darkening.
I deleted the original DNGs and reconverted the NEFs to DNG with the same results. Here is a link to one NEF that gives the wrong baselineExposure.
[a href=\"https://download.yousendit.com/50DB929F6D40432A]Link[/url]
Bill
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Bill, please post one from the very same serie, which gets +0.5 EV.
Thanks
Gabor
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Bill, please post one from the very same serie, which gets +0.5 EV.
Thanks
Gabor
[{POST_SNAPBACK}][/a] (http://index.php?act=findpost&pid=200121\")
Gabor,
This file has +0.5 EV baselineExposure
[a href=\"https://download.yousendit.com/CA67B86200F440CB]Positive[/url]
And the very next in the series has a negative value:
Negative (https://download.yousendit.com/23F6FF26609B4D4E)
Bill
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Bill,
ISO 100 is the key. I do not have any other ISO 100 shot. I verified shots wityh perhaps all other ISOs, and all get +0.5.
I suggest you to make two shots of the same scenery (perhaps the Stouffer), with the same exposure, but one with ISO 100, the other with ISO 200, and compare their histograms. There should be some clipping as well.
Gabor
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I meant only the sharpness, contrast, saturation, tone, and, of course the white balance.
I don't understand this. The problem Bernie mentioned is characteristic to luminance histograms, but the D3 has color histogram, and that should not be much different from the raw histograms with a neutral setting.
Do you mind posting such a raw file?
[a href=\"index.php?act=findpost&pid=199973\"][{POST_SNAPBACK}][/a]
Gabor,
OK, I have permission to share a Nikon D3 file. You can let me know which you want. These files are about 12MB each. I would have to up-load it to a private website address from which you could download it. If you send me a private email we'll set this up offf-line, then you can analyse and bring the discussion back on-line.
Mark
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You can let me know which you want. These files are about 12MB each. I would have to up-load it to a private website address from which you could download it. If you send me a private email we'll set this up offf-line, then you can analyse and bring the discussion back on-line.
Mark,
the simplest way is to upload it/them to yousendit.com. You don't need to register, you don't even need to use your email address, nor mine, it can be a fictional one (though you can use my email address from the profile if you want to). In response you receive a URL for the uploading. You can post that, or if you don't want to "publish" them, then pls email me. You can use the forum's messaging, or my email address; look at my profile.
Regarding which one(s): you mentioned, that a blue cipping has not been indicated with the neutral profile. That one, which you deem the strongest case, i.e. you think the clipping was stong, but you don't see any clipping indication on the in-camera histogram.
I do not have Nikon Capture, so I don't see the original histogram, although if I extract the JPEG, then ACR should display the same one.
Thanks
Gabor
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Mark,
the simplest way is to upload it/them to yousendit.com. You don't need to register, you don't even need to use your email address, nor mine, it can be a fictional one (though you can use my email address from the profile if you want to). In response you receive a URL for the uploading. You can post that, or if you don't want to "publish" them, then pls email me. You can use the forum's messaging, or my email address; look at my profile.
Regarding which one(s): you mentioned, that a blue cipping has not been indicated with the neutral profile. That one, which you deem the strongest case, i.e. you think the clipping was stong, but you don't see any clipping indication on the in-camera histogram.
I do not have Nikon Capture, so I don't see the original histogram, although if I extract the JPEG, then ACR should display the same one.
Thanks
Gabor
[a href=\"index.php?act=findpost&pid=200155\"][{POST_SNAPBACK}][/a]
Gabor,
I didn't use Nikon Capture either - only ACR.
On the issue of the blue clipping and the histogram - indeed we were looking at the Luminance histogram on the D3. The D3 does have the capability to show either the aggregate or the individual R,G,B tonal distributions.
Re your email address - if your ISP allows you to receive 12 MB attachments we're in business and that's by far the easiest thing to do, except your email address is not in your L-L profile. Please send me a P-M with your email address and I'll ship you the file.
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Mark,
I sent you a direct email through the forum's system.
Gabor
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Bill,
ISO 100 is the key. I do not have any other ISO 100 shot. I verified shots wityh perhaps all other ISOs, and all get +0.5.
I suggest you to make two shots of the same scenery (perhaps the Stouffer), with the same exposure, but one with ISO 100, the other with ISO 200, and compare their histograms. There should be some clipping as well.
Gabor
[a href=\"index.php?act=findpost&pid=200150\"][{POST_SNAPBACK}][/a]
Gabor,
I went through my test shots and found what you want. The exposure is the same for both shots, 1/15 s, f/8. As the histograms show, the same values are written to the raw file for both exposures, but they are processed differently by ACR according to the BaselineExposure value, which is -0.5 for the ISO 100 and +0.5 for the ISO 200. If I cancel out these values by adding +0.5 EV in ACR for the ISO 100 and -0.5 EV for the ISO 200, the results are more or less the same.
BTW, Rawanalyze reports ISO 200 for the ISO 100 exposure.
Bill
Histograms, 100 left, 200 right:
[attachment=6958:attachment][attachment=6959:attachment]
ACR defaults, 100 left, 200 right:
[attachment=6954:attachment][attachment=6955:attachment]
ACR Plus 0.5 EV left, Minus 0.5 EV right:
[attachment=6956:attachment][attachment=6957:attachment]
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Bill,
this is now clear; the D3 does not have any ISO 100 gain. I find it incredible, that this will not be documented; if you don't know this and meter for ISO 100, you get everything burned out. Don't you think you should post it on DPReview?
Re the ISO display by Rawnalyze: Nikon plays a dirty game. In this case there is no ISO spec in the Exif section. There is a proprietory tag in MakerNote for ISO, that is invalid *in this case*. Then there is another proprietory tag, which specifies ISO 200 in this case, but there is something else in that tag, which I have not interpreted yet. Anyway, I will include this if not otherwise then hard wired. The way this appears with Canons (the Highlight Tone Priority changes the ISO internally): ISO 100/200, indicating the nominal and factual ISO.
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So is this a site about photography or camera equipment engineering? Or boys who think they are the latter?
Regards, Art.
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So is this a site about photography or camera equipment engineering? Or boys who think they are the latter?
Regards, Art.
[a href=\"index.php?act=findpost&pid=200294\"][{POST_SNAPBACK}][/a]
The site is largely un-moderated, so it's about whatever people post about.
I like that.
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So is this a site about photography or camera equipment engineering? Or boys who think they are the latter?
Regards, Art.
[a href=\"index.php?act=findpost&pid=200294\"][{POST_SNAPBACK}][/a]
This thread results from an article I contributed about noise and resolution, which are important aspects of image quality. The people contributing to this discussion are approaching it from the perspective of the underlying fundamentals. If that's of no interest to you, fine, but it's not a reason to dump on those for whom it is.
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I just love, when people - usually anaphabetes of the digital aspects of photography - are complaining about openly discussing subjects they don't understand.
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Bill,
I found the "fine print" to the "Lo" ISO setting, it is specified as Lo 0.3, Lo 0.5, Lo 0.7 and Lo 1.0. I have to translate these in ISO numbers.
I guess, the third stops are 125 and 160 on Nikon too. But how does the half-stop ISO between 100 and 200 appear? 140? I'm pretty sure it is not 141.
Do you mind checking these out? Then I can display the ISO properly, like 125/200 or 100/200.
Thanks
Gabor
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Mark,
the shot I received has not been created by a neutral WB (UniWB); this is apparent by looking at it in ACR: it appears in the right colors. With a neutral WB it would appear rather greenish. Thus it is not surprizing, that the in-camera histogram does not reflect the raw data.
However, I don't understand, why the clipping is not indicated on the in-camera display. I extracted the preview JPEG, and it is properly white balanced, and it is clearly blown. For example the top right window: there is some sheet (I think originally bluish) hanging on the glass pane inside; the green is blown overall and the blue on most of it. This sheet appears in the preview with RGB=(255,255,255).
If you have access to the camera again, you should put back this image on a card and check it out again.
Gabor
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I just love, when people - usually anaphabetes of the digital aspects of photography - are complaining about openly discussing subjects they don't understand.
[{POST_SNAPBACK}][/a] (http://index.php?act=findpost&pid=200313\")
Gabor,
The word is "analphabet" : [a href=\"http://www.smba.nl/en/newsletters/n-84-analphabet/]http://www.smba.nl/en/newsletters/n-84-analphabet/[/url]
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Mark,
the shot I received has not been created by a neutral WB (UniWB); this is apparent by looking at it in ACR: it appears in the right colors. With a neutral WB it would appear rather greenish. Thus it is not surprizing, that the in-camera histogram does not reflect the raw data.
However, I don't understand, why the clipping is not indicated on the in-camera display. I extracted the preview JPEG, and it is properly white balanced, and it is clearly blown. For example the top right window: there is some sheet (I think originally bluish) hanging on the glass pane inside; the green is blown overall and the blue on most of it. This sheet appears in the preview with RGB=(255,255,255).
If you have access to the camera again, you should put back this image on a card and check it out again.
Gabor
[a href=\"index.php?act=findpost&pid=200317\"][{POST_SNAPBACK}][/a]
I believe the D3 shots were made using the camera's Auto WB. Looking at the file in Rawnalyze, I see that there is moderate red and blue channel clipping. This is what did not show on the camera's aggregate histogram. The stuff blown in the window should be considered specular highlights - white paper against glass with direct sunlight bouncing off of it. I doubt the card still contains those images. They'd have to be reloaded onto a card and reviewed in the camera. I'm not sure I'll be able to get that done, but if I can I'll report back. At this stage, let me just say that two of us obsrved the same phenominon.
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The word is "analphabet"
Thanks; actually, I happen to know that. However, my typing is getting worse with my new keyboard (formerly I have used the same IBM keyboard 14 years long), and these minisculous fonts on the forum don't help my aging eyes.
two of us obsrved the same phenominon
Right, but my issue was and is, why the camera did not indicate the clipping (that was my understanding).
Btw, the word is "observed", the other one is "phenomenon" (but I don't intend to get into a spelling war anyway; English is my third language).
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Thanks; actually, I happen to know that. However, my typing is getting worse with my new keyboard (formerly I have used the same IBM keyboard 14 years long), and these minisculous fonts on the forum don't help my aging eyes.
Right, but my issue was and is, why the camera did not indicate the clipping (that was my understanding).
Btw, the word is "observed", the other one is "phenomenon" (but I don't intend to get into a spelling war anyway; English is my third language).
[a href=\"index.php?act=findpost&pid=200324\"][{POST_SNAPBACK}][/a]
Touché - but didn't you like the content of the address I provided?
I had no doubt you knew the word, but I couldn't resist. And yes I need to use the spell check - going too fast for my own good.
Your understanding is correct - the camera did not indicate the clipping. It surprised us to see it as well when we opened the files in ACR. I can only think it is something to do with the JPEG settings.
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Bill,
I found the "fine print" to the "Lo" ISO setting, it is specified as Lo 0.3, Lo 0.5, Lo 0.7 and Lo 1.0. I have to translate these in ISO numbers.
I guess, the third stops are 125 and 160 on Nikon too. But how does the half-stop ISO between 100 and 200 appear? 140? I'm pretty sure it is not 141.
Do you mind checking these out? Then I can display the ISO properly, like 125/200 or 100/200.
Thanks
Gabor
[a href=\"index.php?act=findpost&pid=200314\"][{POST_SNAPBACK}][/a]
Gabor,
Using half stop increments, I was unable to determine the ISO for Lo 0.5. ViewNX reports the ISO as "0.5 EV under 200". ACR and Bridge leave the ISO blank and the BaselineExposure in the DNG is 50/100.
For third stop increments, ACR reports the ISOs as 125 and 160. The DNG BaselineExposure values are -17/100 and 17/100 respectively.
Bill