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Author Topic: Can you expose too far to the right even if not clipping?  (Read 16727 times)
hjulenissen
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« Reply #60 on: December 17, 2010, 05:16:42 AM »
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I see.

So camera non-linearity (besides channel clipping) should be minor, and raw-processor non-linearity to correct it should only make things more linear. Channel clipping can be partially hidden by highlight recovery, but that is not something that should be happening with "ETTR".

Since commercial raw converters may not use XYZ or any other known intermediate representation (that we can access) we can only observe the input and the end-result. Someone did and concluded that it was non-linear/signal-dependent.

A hue-twist that is a smooth function of input level may be "large" and "visible", but I believe it to be still correctable (using a potentially large amount of effort). Clipping is not generally corectable. Did someone try to compare the color differences using ETTR and using a more conservative exposure? Even if Lightroom & friends really is color non-linear, that does not mean that a moderate difference in exposure will look 1)significantly different or 2)worse color-wise.
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dmerger
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« Reply #61 on: December 17, 2010, 09:47:23 AM »
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I hope it’s not inappropriate to ask this question in this thread, but there is a lot of knowledge here about linear.

Since my Minolta 5400 scanner outputs 16 bit linear tiff files, I've done so for positive film scans, then assigned the Minolta linear profile (which applies gamma encoding to produce a normal looking image), converted to my working color space (now ProPhoto) and then edited my photos in PS/ACR. 

I’ve wondered, would there be any benefit if I could make my edits in ACR in linear mode?  I’ve assumed that this is merely an academic question since ACR doesn’t support a “RAW” mode for my scanner and when ACR sees an untagged tiff file it assumes it is gamma encoded sRGB.  However, if the answer to my first question is yes, then is there a way to process my linear files in ACR?
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Dean Erger
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« Reply #62 on: December 17, 2010, 10:39:45 AM »
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I hope it’s not inappropriate to ask this question in this thread, but there is a lot of knowledge here about linear.

Since my Minolta 5400 scanner outputs 16 bit linear tiff files, I've done so for positive film scans, then assigned the Minolta linear profile (which applies gamma encoding to produce a normal looking image), converted to my working color space (now ProPhoto) and then edited my photos in PS/ACR. 

I’ve wondered, would there be any benefit if I could make my edits in ACR in linear mode?  I’ve assumed that this is merely an academic question since ACR doesn’t support a “RAW” mode for my scanner and when ACR sees an untagged tiff file it assumes it is gamma encoded sRGB.  However, if the answer to my first question is yes, then is there a way to process my linear files in ACR?


ACR internally operates in linear mode anyway, so no, there would be no benefit, even it were possible.

But more broadly, the various ACR controls operate on the assumption that the profile attached to a file correctly represents the data (linear data = linear profile); to try to, for example, use a different profile to what the data actually is will just result in very odd control behavior.

Sandy
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Guillermo Luijk
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« Reply #63 on: December 17, 2010, 01:34:12 PM »
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Gamma is not only used for still images. If you read Poyntons books, I think that you will find that he supports my claim that Gamma exists for primarily two reasons:
  • The first reason is to compensate for CRT native behaviour (and it was cheaper to do this once in the camera instead of in every customers tv set back in the days of analog signal processing).
  • The second reason is to make it easier for lossy compression or any other dsp thath wants to work on "perceptually linear" data. I think that in dsp terms, this could be called a homomorphic transform.

The first reason is irrelevant today, since it can be corrected in the output device without any need to affect the image editing values.
For the second reason, is again irrelevant in the context we are interested here: digital photography edition. So following joofa's comment I will restrict my claim: "Gamma, in digital photography edition, is per se unnecessary. A floating point linear editor is totally possible, and gamma would play no role in it".

Regards
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hjulenissen
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« Reply #64 on: December 17, 2010, 02:01:26 PM »
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The first reason is irrelevant today, since it can be corrected in the output device without any need to affect the image editing values.
You would still need gamma to be able to traverse DVI connections limited to 8 bits of precision without banding. Doing Gamma "right" is quite difficult, and current LCD displays use all kinds of dirty tricks to pretend that they have a gamma-like response.
Quote
For the second reason, is again irrelevant in the context we are interested here: digital photography edition. So following joofa's comment I will restrict my claim: "Gamma, in digital photography edition, is per se unnecessary. A floating point linear editor is totally possible, and gamma would play no role in it".
Sure. But what editors are using floating point today? I have read that Adobe tried using linear light values in Photoshop, but there were so many customers complaining after being brought up on gamma-space values that they brought it back in?

-h
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Guillermo Luijk
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« Reply #65 on: December 17, 2010, 02:07:03 PM »
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You would still need gamma to be able to traverse DVI connections limited to 8 bits of precision without banding. Doing Gamma "right" is quite difficult, and current LCD displays use all kinds of dirty tricks to pretend that they have a gamma-like response.
Sure, but irrelevant from the point of view of image edition. I am talking all time about the need vs no need of gamma in the image RGB values, which is the field in which the photographer edits his image.

Sure. But what editors are using floating point today?
No idea, but again this is irrelevant. I am talking about the need vs no need of gamma in the image RGB values, not about any particular (sub-optimal) implementation. In fact in my previous example of the dogs, the linear 1.0 gamma image is wrongly displayed (banding appears, although the image is not posterized in its RGB numbers) when not zoomed at 100%. Photoshop is not well suited to deal with linear images, even if it allows you to use linear colour profiles.

Regards
« Last Edit: December 17, 2010, 02:09:21 PM by Guillermo Luijk » Logged

Ray
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« Reply #66 on: December 20, 2010, 08:48:11 PM »
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I've read this thread from beginning to end and I'm amazed that those who claim there might be a problem with ETTR exposures due to a non-linearity of sensor output as exposure approaches full-well capacity, and/or a problem with the capacity of RAW converters to handle this non-linearity, have not provided any 'real-world', photographic images demonstrating the problem.

Gullermo is the only one to provide images which demonstrate that there really is no problem here.

I frequently auto-bracket 3 exposures in situations where I don't have the time to use procedures to get a precise exposure, either because I'm trying to capture the moment which might pass quickly, or because I'm in transit, as on a guided tour, and have little time in general to get my shots.

I therefore have lots of examples of identical scenes that differ in exposure by two stops (I usually auto-bracket  +/-  one stop).

I can honestly claim that I have never experienced a problem with hue and color shifts as a result of choosing the ETTR exposure out of the 3 instead of one that has either 1 or 2 stops less exposure.

What I do find is that sometimes the longest exposure of the 3 might be very marginally overexposed in the sense that one channel is clipped, and as a consequence I might prefer to use one of the underexposed shots. I might decide to use the shot that is underexposed by 2/3rds of an EV in preference to the one that is overexposed by 1/3rd of a stop.

Even if it's too difficult to merge the 3 shots to HDR because of movement in the scene or movement of the hand-held camera, having 3 different exposures increases one's options in processing. For example, sometimes it might be easy to use the sky in the least exposure and the foreground in the greatest exposure, if the horizon is not to complicated.

DXOMark in one of their 'insights' articles have very clearly explained the relationship between noise and exposure. For example, underexposing a shot by 1 EV has a greater effect on the shadows than it does on the midtones.

As a consequence of a 1 stop underexposure, the midtones and upper midtones will have approximately a 3dB lower SNR. However, the shadows will have a 6dB lower SNR.

Of course, this is an oversimplification. In practice there's no such clear-cut delineation. There will be a sliding scale. The upper midtones will lose about 2dB of SNR, the midtones about 3dB, the lower midtones about 4dB, the moderate shadows about 5dB and the deep shadows about 6dB. The very deep shadows will lose even more than 6dB of SNR.

How significant is a 3dB loss in SNR? Well, that depends upon print or monitor enlargement. At 100% on the monitor, a 3DB difference in SNR is clearly noticeable, and a 6dB difference smacks you in the face. But on a postcard size print it wouldn't.

Generally, the ETTR principle is only of benefit to those who wish to maximise the potential image quality of their camera, either by printing large now, or at some time in the future.

The practical photographer, as opposed to the armchair theoretician, needs to see the practical relevance and significance of these subtle issues which are discussed in this thread.

There are certain individuals on this forum, whom I shall not name because my intention is not to embarrass, who seem very technically competent and who appear to have a deep understanding of the digital technology of cameras, but who never post any real-world images to demonstrate what they are talking about.

I often wonder why. Is it because such individuals are very, very shy, or is it because (more likely) that many people on such forums as this appear to judge the worth of an argument or technical point on the artistic merits of the photos that demonstrate the point.

Some of you may have noticed that not all of the photos that I use to demonstrate a technical point are photographic masterpieces. The reason is, when I search for a photo to demonstrate a technical point, I'm not searching for a photo that I'm particularly proud of, which I think is great, that I think has signifiant artistic merit, that I want to 'show off' as a fine example of the best in my portfolio.
I search for an image which best demonstrates the point I'm making. If it also happens to be an interesting or 'artistic' image in its own right regardless of any technical issues, then that's also fine, but that's not the priority.

Okay! Now I've got that off my chest, I'm going to present a couple of images that differ in exposure by 2 stops. They've been chosen because the back-lighting situation has created some deep shadows, and because the auto-bracketed exposures were taken at ISO 800 (perhaps needlessly) because I didn't have time to change it. However, a couple of seconds later the birds changed their posture. I also like this particular shot. I like the silhouette effect. It's a keeper, and I won't be raising the shadows.

The fact that these shots were at ISO 800 demonstrates the greater need for an ETTR exposure at high ISO. Dynamic range at ISO 800 is always reduced considerably (compared with base ISO), whatever the camera. Therefore a 6dB reduction of SNR in the shadows is of major concern at ISO 800.

These shots have had zero sharpening and no processing, apart from the lightening of the shadows to demonstrate differences in shadow noise. I simply hit the 'auto' button in ACR, then converted. The auto button in ACR gave the longest exposure a -0.2 EV adjustment plus a bit of highlight recovery, and the shortest exposure received a +1.5 EV adjustment plus a bit of additional brightness and contrast. One could argue that the longest exposure is not quite a full ETTR. It could perhaps have received an addition 1/3rd of a stop exposure. But let's not quibble.

No sharpening or noise reduction has been applied to either image.

The first image is of the full scene comparing exposures differing by 2 stops. Which is which?

The second is a 200% crop showing the increased noise in the sky, in the underexposed shot.

The third is a 67% crop showing the dramatically increased shadow noise in the 2 stop's underexposed image.

What more is there to say on the subject?
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pegelli
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« Reply #67 on: December 21, 2010, 06:26:09 AM »
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I've read this thread from beginning to end and I'm amazed that those who claim there might be a problem with ETTR exposures due to a non-linearity of sensor output as exposure approaches full-well capacity, and/or a problem with the capacity of RAW converters to handle this non-linearity, have not provided any 'real-world', photographic images demonstrating the problem.

.....

What more is there to say on the subject?

To answer your question let me try to provide a real world example taken with my Sony A850 and a Minolta 50/1.7 lens in the recently renovated Antwerp Central Station.
Auto exposure bracket + 2EV, 0 and -2 EV, all within 1 second. Lightroom 3.3 and Auto adjustment, with afterwards a slight play with exposure and brightness to get the overall tone somewhat more similar (all the other setting were the same and all 3 shots were AWB and came back identical 5000/10 "as shot")

-2EV:

  0EV:

+2EV:

My conclusion is there is a slight hue shift between all three pictures, especially apparent if you look at the background old stone building. A shorter exposure warms up the grey stone consistently in this bracketed series.

Don't know which one is "better" but the hue shift can be easily seen in this case.

I do support Ray's conclusion (can provide crops if needed) that the noise in the - 2EV picture boosted with + EV in Lightroom is significantly more than the "measured" exposure @ 0EV and the +2EV example.

Btw, I never HDR'd this picture, too much movement in the people om the escalator  Embarrassed
« Last Edit: December 21, 2010, 06:27:53 AM by pegelli » Logged

pieter, aka pegelli
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« Reply #68 on: December 21, 2010, 08:27:31 AM »
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Quote
My conclusion is there is a slight hue shift between all three pictures, especially apparent if you look at the background old stone building.

It would be useful if the term hue shift were better defined. Some hue’s in color space shift while others do not? Everything is shifting slightly? Is this the effect of ETTR or due to slight differences in rendering needed to bring the ETTR and “normal” exposure to match tone? All raw converters?

In the last example below, the +2EV and the others show differences in color (the orange and green “flags” on the left wall) but they also show exposure/tone differences as illustrated in the sky peaking through the glass in the upper right area of the image. There’s more here than a difference in “hue” to my eye.
« Last Edit: December 21, 2010, 08:29:39 AM by digitaldog » Logged

Andrew Rodney
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« Reply #69 on: December 21, 2010, 08:35:23 AM »
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Is the +2EV raw file available for inspection?  It is quite possible that the places identified as having a "hue shift" are simply instances where one or more channels is blown (either in the raw, or due to white balance amplification) and the raw converter can't recover accurate color information.
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emil
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« Reply #70 on: December 21, 2010, 08:53:00 AM »
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I've read this thread from beginning to end and I'm amazed that those who claim there might be a problem with ETTR exposures due to a non-linearity of sensor output as exposure approaches full-well capacity, and/or a problem with the capacity of RAW converters to handle this non-linearity, have not provided any 'real-world', photographic images demonstrating the problem.

<Bunch of text cut>

The first image is of the full scene comparing exposures differing by 2 stops. Which is which?

The second is a 200% crop showing the increased noise in the sky, in the underexposed shot.

The third is a 67% crop showing the dramatically increased shadow noise in the 2 stop's underexposed image.

What more is there to say on the subject?

Oh dear. Now the real photographers have arrived, all us mere "armchair theoreticians" should bow out  Grin Grin Grin Grin

Before I bow out, just so we're all on the same page, I think that everybody on all sides of the ETTR debate would agree with almost all of what you said. Specifically:
  • Yes, absolutely, if you underexpose you will get more noise
  • Yes, if you are for some reason limited in ISO selection, ETTR is a good idea - if you read the blog post I referenced right at the beginning of this, you'll see that I specifically identify already being at base ISO as the one situation where ETTR makes sense.

But the question is not, to use your ISO 800 example, whether if you take two exposures both at ISO800 one with 2 stops overexposure, one with normal exposure, that you will get lower noise in the overexposed version. Everybody on this thread (so far as I know anyway) agrees that at a single ISO, ETTR makes sense.

The question that's actually being addressed, and I'm afraid your example isn't relevant to, is what if you just changed the ISO setting to 200? Those of us on the "ETTR is over hyped" side of the fence will say that you get the same noise levels, with none of the problems as you would with the "ISO800 plus 2 stops of ETTR".

<Sandy politely bows out of conversation>

Sandy

Post script to Andrew: If you haven't seen them, I did some articles on hue shifts here: http://chromasoft.blogspot.com/2009/02/adobe-hue-twist.html

The term "hue twist" is actually Eric Chan's. Although I think he now regrets coining the term(!) As regards what raw converter, etc. Certainly most "new generation" Adobe profiles, but not all. Capture One also seen to use hue twists, judging by some of the hue variations I've seen, although not as much as Adobe.
« Last Edit: December 21, 2010, 08:55:20 AM by sandymc » Logged
NikoJorj
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« Reply #71 on: December 21, 2010, 09:38:01 AM »
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Lightroom 3.3 and Auto adjustment, with afterwards a slight play with exposure and brightness to get the overall tone somewhat more similar
Thanks for having let the metadata in the file ; one can see the changes are caused by vastly different LR settings (there are some local editing with both brush and gradient in the 0EV shot only, some recovery for the +2EV and 0EV shots causing probably much of the hue shift, the exposure setting are not matched and the brightness/blacks/contrast tweaked...). That still leads to a valid conclusion : the application of some LR settings may adjust the hue and tone of your images. Wink

However, it might be more interesting (once you've verified nothing is blown in the +2 shot, as said Emil) to get the 3 shots reset at default and then only "match total exposures" between them?
« Last Edit: December 21, 2010, 09:40:56 AM by NikoJorj » Logged

Nicolas from Grenoble
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« Reply #72 on: December 21, 2010, 03:26:22 PM »
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@ digitaldog, sorry can't define it better. I was looking for colour/hue shifts in the midtones where there seems to be no clipping. don't know if it's universal and based on the comments from NikoJorj I tinkered too much with the files to be representative anyway. There are unrecoverable blown highlights in the dome, but I was keeping those out of my comparison.

@ ejmartin, no problem. I'll try to put them in a dropbox site or something. Need to sort it out to see how to do that but when I've done that I'll post the links here. Might well be you're right, I have no knowledge nor software to test it so any help you can give is more than welcome.

@ NikoJorj, thanks, and I think you're right (or almost, because all three files have similar (not the same) local adjustments and gradients), but you're absolutely right I tinkered too much with the files in an inconsistent manner to draw any conclusions.

I've found 3 more files (from my A700) so here's 6 center crops (A700: 1370x914, then reduced to 800 for web posting||A850: 2834x1884, reduced to 800 for web posting) where the only differences are the EV slider to make them look roughly the same (so +2EV from default for the -2EV shot, default for the 0EV shot and -2EV for the +2EV shot). Colour shifts are much less now, and those still present are probably due to unrecoverable blown channels. Exif should again be fully included in the file for you to take a look at.

A700 series:







A850 series (the same frames as posted before, only now a center crop)






Advice and comments more than welcome, I need to learn a lot in this field so thanks for all your reactions so far.

« Last Edit: December 21, 2010, 03:28:13 PM by pegelli » Logged

pieter, aka pegelli
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« Reply #73 on: December 21, 2010, 03:46:45 PM »
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Post script to Andrew: If you haven't seen them, I did some articles on hue shifts here: http://chromasoft.blogspot.com/2009/02/adobe-hue-twist.html
The term "hue twist" is actually Eric Chan's. Although I think he now regrets coining the term(!) As regards what raw converter, etc. Certainly most "new generation" Adobe profiles, but not all. Capture One also seen to use hue twists, judging by some of the hue variations I've seen, although not as much as Adobe.

But in the above context, this isn’t necessarily an ETTR related issue?
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Andrew Rodney
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Ray
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« Reply #74 on: December 21, 2010, 06:54:01 PM »
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Oh dear. Now the real photographers have arrived, all us mere "armchair theoreticians" should bow out  Grin Grin Grin Grin

Before I bow out, just so we're all on the same page, I think that everybody on all sides of the ETTR debate would agree with almost all of what you said. Specifically:
  • Yes, absolutely, if you underexpose you will get more noise
  • Yes, if you are for some reason limited in ISO selection, ETTR is a good idea - if you read the blog post I referenced right at the beginning of this, you'll see that I specifically identify already being at base ISO as the one situation where ETTR makes sense.

But the question is not, to use your ISO 800 example, whether if you take two exposures both at ISO800 one with 2 stops overexposure, one with normal exposure, that you will get lower noise in the overexposed version. Everybody on this thread (so far as I know anyway) agrees that at a single ISO, ETTR makes sense.

The question that's actually being addressed, and I'm afraid your example isn't relevant to, is what if you just changed the ISO setting to 200? Those of us on the "ETTR is over hyped" side of the fence will say that you get the same noise levels, with none of the problems as you would with the "ISO800 plus 2 stops of ETTR".

<Sandy politely bows out of conversation>

Sandy

Post script to Andrew: If you haven't seen them, I did some articles on hue shifts here: http://chromasoft.blogspot.com/2009/02/adobe-hue-twist.html

The term "hue twist" is actually Eric Chan's. Although I think he now regrets coining the term(!) As regards what raw converter, etc. Certainly most "new generation" Adobe profiles, but not all. Capture One also seen to use hue twists, judging by some of the hue variations I've seen, although not as much as Adobe.


Since you intend to 'bow out', perhaps there's no point in responding. However, for the benefit of others, I shall.

My first reaction to your post was one of confusion. Then I looked at your blog in an earlier post and all is clear. You have failed to distinguish between the two basic methods that cameras of different types handle ISO increases. One type, usually CCD such as many P&S cameras and most MFDBs, are essentially 'one-ISO' cameras.
With such cameras no image quality benefit is derived by using a correct ETTR at a higher ISO than base. One might as well underexpose at base ISO and get the increased assurance that one will at least not overexpose, even though the LCD review might appear unhelpfully dark.

The other type of camera, usually most DSLRs, and particularly Canon DSLRs with which I have the most experience, provides a distinct IQ advantage when raising the ISO to create an ETTR exposure at the increased ISO setting, as opposed to underexposing at base ISO.

There's no doubt about this. I've tested it, although it has to be said the most dramatic improvement will be observed when the ISO increase is great. For example, an ETTR at ISO 1600 exhibits very significantly less noise, from shadows to upper midtones, than the same exposure at base ISO, which would of course be 4 stops underexposed.

As far as I understand, the reason for this improved IQ when using the same exposure at higher ISOs, is due to a boosting or amplification of the analog signal prior to A/D conversion and of course prior to all other signal processing further up the chain before the data is eventually written to the memory card.

Such amplification in itself cannot reduce noise. In fact, whatever noise is present in the sensor at the precise time of amplification will also be amplified. The reduced SNR in the final output is not due to a reduction in absolute noise but a reduction in relative noise, that is, the noise introduced after amplification is smaller as a proportion of the larger signal.

In other words, with DSLRs the higher ISO setting is merely an instruction to the camera to amplify the analog signal by a specific amount, at the earliest possible stage, even before A/D conversion. Whereas, with the other type of sensor, mostly CCDs I believe (and that would include the Canon G10 you used), the ISO setting would appear to be an instruction to the camera's processor to boost the signal at the end of the processing chain. There's a big difference.

However, with the introduction of Sony's latest sensor used in the Pentax K5 and Nikon D7000, we have a new development whereby it seems that only one analog boost takes place, and that's at base ISO. This provides no additional advantage at very high ISO, but does result in lower noise at base ISO and lower noise even up to ISO 400 where, remarkably, DR in this cropped format is even higher than that of the 5DMk2 at ISO 400, whether at pixel level or at normalised print sizes.

In summary, unless one is using one of the 'effectively' one-ISO cameras, such as the CCD type, and now the D7000 and Pentax K5, it's always advisable to raise ISO till one gets an ETTR exposure, rather than underexpose at base ISO.

And of course, for maximum image quality across the entire tonal range from deep shadows to highlights, an ETTR at base ISO provides the best image quality the camera can deliver, assuming shutter speed and f/stop are appropriate for the conditions and the composition.

Hue shifts or twists are not a problem for me. If I were to see any, I'd fix them. Most of my images are given individual treatment in Photoshop. I'm changing hues, color saturation, shadows, midtones etc all the time. Let's not create imaginary problems.  Grin
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Ray
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« Reply #75 on: December 21, 2010, 07:44:05 PM »
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To answer your question let me try to provide a real world example taken with my Sony A850 and a Minolta 50/1.7 lens in the recently renovated Antwerp Central Station.
Auto exposure bracket + 2EV, 0 and -2 EV, all within 1 second. Lightroom 3.3 and Auto adjustment, with afterwards a slight play with exposure and brightness to get the overall tone somewhat more similar (all the other setting were the same and all 3 shots were AWB and came back identical 5000/10 "as shot")

My conclusion is there is a slight hue shift between all three pictures, especially apparent if you look at the background old stone building. A shorter exposure warms up the grey stone consistently in this bracketed series.

Don't know which one is "better" but the hue shift can be easily seen in this case.

I do support Ray's conclusion (can provide crops if needed) that the noise in the - 2EV picture boosted with + EV in Lightroom is significantly more than the "measured" exposure @ 0EV and the +2EV example.

Btw, I never HDR'd this picture, too much movement in the people om the escalator  Embarrassed

Pegelli,
Thanks for taking the trouble to at least try to demonstrate the problem.

My impression is that all these images are overexposed. Not even the shortest exposure at 1/1600th is an ETTR, judging by the histogram.

'Expose to the right' does not mean that the histogram is pushed against the right side like a cliff face, although taken literally the expression could mean that.

What I consider to be an ETTR is a histogram that barely touches the right vertically and has no obvious spikes in the vicinity of that right vertical after a reasonable, negative EC adjustment in ACR, such as -0.67 EV.

It's possible to get a histogram of a significantly overexposed shot looking as though it's representative of an ETTR, by throwing everything at it, in ACR. For example, by applying a -2 EV adjustment (or greater), moving the 'recovery' slider to its maximum of 100, shifting the 'brightness' slider to zero or less, and moving the highlight slider of the 'Tone Curve' to its minimum of -100.

It's very easy to inadvertently blow out one of the channels without it appearing obvious, as a result of Adobe's clever reconstruction of blown highlights.

If one is comparing different exposures which are all overexposed to varying degrees, then it's quite possible there will be hue shifts in the upper midtones.

This is how the histogram of your shortest exposure appears in PS.



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pegelli
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« Reply #76 on: December 22, 2010, 04:02:01 AM »
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@ digitaldog, I think what sandymc is saying is that you get colour shifts when for instance you compare a 0 EV shot with another one that got +1 EV in the camera followed by -1 EV in the raw converter. That's the "root problem" she is describing. Since this is what you do with ETTR it's only sideways an ETTR problem.

@ Ray, sorry for posting such a confusing example. I know there are blown regions in the frame. However I was more looking to colour changes in the "mid tones" (the red beam left in the frame and the facade in the background. Since I was reading the problem more as described to digitaldog above, and am not looking at colour shifts in blown regions it still demonstrated the effect in these mid tone regions (I thought). However NikoJorj poited out I had "trown" too many other different setting at the picture (causing the shifts), hence posting my second series where the only difference is the EV slider in my raw converter and voila, the colour changes are virtually gone which supports the position you're taking in this discussion.  
One thing though, the white spike you demonstrate in the histogram is there, but since I used white lettering to mark the shots it's bigger than of the picture without the lettering. Also this picture got quite a bit of +EV in the converter, at the default import settings the histogram of the shortest exposure is just touching the right side, and I get only something like 10 pixels highlight warning when pressing "alt" + recovery slider.

Btw, here's another experiment I did.
Used the EV slider to "normalise"everything to the -2EV shot in camera.
Also put the black slider at 0 for all 3, rest at default settings







Conclusion: plenty of blown channels in the + 2EV shot to cause all kind of weird shifts  Cool

Btw, changed the colour of the lettering typed in, so they don't show up as inadvertent "blown highlights"

« Last Edit: December 22, 2010, 04:44:35 AM by pegelli » Logged

pieter, aka pegelli
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« Reply #77 on: December 22, 2010, 05:47:27 AM »
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Conclusion: plenty of blown channels in the + 2EV shot to cause all kind of weird shifts  Cool
Ditto ; this one is definitely not exposed to the right.
It's really a matter of "it's fun to play with matches but it hurts to burn your fingers".

For the 2 other ones, I don't see any hue change but do see a minor exposure change (inaccurate shutter, which is quite probable for speeds way beyond X-sync, or maybe slightly stuck aperture?).
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Nicolas from Grenoble
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« Reply #78 on: December 22, 2010, 09:30:44 AM »
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Conclusion: plenty of blown channels in the + 2EV shot to cause all kind of weird shifts

Btw, changed the colour of the lettering typed in, so they don't show up as inadvertent "blown highlights"

Here are my own tests using the Nikon D3, a Colorchecker, and Imatest for an ETTR expsoure with no blown channels and a Minus 1.4 EV exposure with exposure correction in ACR. I used ACR 6.3 with the AdobeStandard profile and linear settings in ACR (sliders on main tab all set to zero). The images appear somewhat flat, since a linear tone curve was employed. The color shifts are minimal. The Colorchecker images used for analysis were in 16 bit ProPhotoRGB, but are converted to 8 bit JPEG for web display. Manual white balance in ACR on the second brightest neutral square was employed. The raw files were analyzed with Rawnalize.

Rawnalize view of ETTR exposure:


Rawnalize view of Underexposure:


JPEG for ETTR exposure:


JPEG for corrected underexposure:


Imatest analysis of ETTR exposure:


Imatest analysis of the corrected underexposure:
« Last Edit: December 22, 2010, 11:27:51 AM by bjanes » Logged
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« Reply #79 on: December 22, 2010, 09:48:41 AM »
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@ digitaldog, I think what sandymc is saying is that you get colour shifts when for instance you compare a 0 EV shot with another one that got +1 EV in the camera followed by -1 EV in the raw converter. That's the "root problem" she is describing. Since this is what you do with ETTR it's only sideways an ETTR problem.

But that doesn’t put the blame if that’s the correct term, solely on the use of ETTR as I read this. How do we know that when using correct ETTR techniques, we don’t have to apply differing rendering settings in one or all raw converters to produce a result that has no such “hue shifts”? Just normalizing the exposure slider (A Michael term but one that makes sense) is all that is necessary? For all raw converters?

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Andrew Rodney
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