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Author Topic: Shooting to the right and raw conversion  (Read 33944 times)
mwookie
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« Reply #40 on: June 28, 2007, 12:45:06 AM »
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No comments on the analysis?

Bill
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Thanks for sharing this analysis. This whole discussion is helping me to see some of the things I am doing wrong. I think I resist going up to a higher ISO fearing noise, but I end up pushing it up on the computer and maybe coming up with even more noise (I use a 20D primarily)

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Ray
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« Reply #41 on: June 28, 2007, 02:16:53 AM »
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Modifying the contrast seems like a good idea.
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It is a good idea, but you have to experiemnt with whatever camera you are using. Try different settings of jpeg contrast and see how 'no clipping' or 'moderate clipping' on the camera's LCD screen (flashing red patches)translates to the degree of recoverable highlights in your RAW converter.

I've got my 5D set so that I know a small amount of red flashing in the brightest parts of the sky is recoverable in ACR, but not if a large area of the sky is flashing.

I think that setting is minimum contrast (it's a long time since I set it). At maximum contrast, I'd have a situation where the histogram and blown highlight warning would have the whole sky flashing, causing me to underexpose.
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Guillermo Luijk
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« Reply #42 on: June 28, 2007, 04:54:13 AM »
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Quote from: Ray,Jun 28 2007, 08:16 AM
recoverable highlights in your RAW converter.

"Highlight recovery" is a usual term when talking about RAW developing, but it's most of the times wrong. What you get in ACR pushing down the exposure slider is not any highlight recovering at all. If your previously blown highlights become not blown through underexposure tuning, is because they were actually never blown on the RAW file. It was YOU in the developing process, commonly with the white balance (which implies heavy channel scaling by factors usually greater than 2.0 in linear, i.e. +1EV correction, and easily beyond 2.5, nearly +1.5EV), who blowed those areas.

ACR does not apply any real recovery of highlights. DCRAW in its -H2 to -H9 modes does; DCRAW interpolates truly blown pixels to values close to those in the boundaries; it "invents" colours where they were previously blown.

I just wanted to point this as most people talk about hightlight recorvery when thery are just simply referrering to "no-blowing underexposure".

Here is a sample that demonstrates how white balance can blow image areas that were not in the original RAW file. This image was developed without applying any white balance (hence the greeny colour):




If you look into the window area and compare that result (ANTES) to the one obtained with an ACR type white balance applied (con balance de blancos) you can see how much information YOU are blowing just with your white balance:

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wmchauncey
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« Reply #43 on: June 28, 2007, 06:30:41 AM »
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I've read this topic over and over and only grasp about a quarter of what you folks are saying.  And I keep asking myself, so what!  Are you only discussing theory or is there some real world benefit to your debate.  

I ask simply because I'm so new to photography and because of my advancing years, don't have time to theorize.  If I'm unsure about exposure, I bracket.  If I still think that I still have not gotten the whole range, I bracket and merge to HDR.

Please don't think that I'm being disrespectfull, because that is not my intent.

To give you an idea where I'm coming from, my work is for personal enjoyment, don't sell or show.  But rest assured, I do have a very demanding audiance.

FWIW
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bjanes
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« Reply #44 on: June 28, 2007, 06:38:00 AM »
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I'm pretty certain I have addressed this before.  Regardless, the fact is that cameras are *NOT* counting electrons, even if that is what we'd really want them to do.  The discreet electrons come packaged in a bundle of analog noise caused by reading, amplifying, transporting, (possibly amplifying again,) and digitizing the electron charge.  This extra read noise is *NOT* in units of electrons; it is analog until digitization.

With customized circuitry, Canon has been able to get the level of read noises at the highest ISO down to the equivalent of a few electrons (not a few discreet electrons!).  They have been able to do this at the *highest* amplification used in the cameras.  Nothing that Roger writes on his website addresses what may or may not happen with more and better amplification; he simply jumps to the conclusion that nothing is gained, and uses the fact that his 1Dmk2 has the same total read noise in electrons at ISO 3200 as it does at ISO 1600.  That is not any real support for his conclusion, because ISO 3200 *IS* ISO 1600 on that camera.  Had he used a Minolta K7, which uses real amplification at ISO 3200, he would have measured slightly less noise at ISO 3200, and if he had actually looked at the shadows, there would be slightly less line noise at 3200, and less chromatic noise in a RAW at 3200 than 1600 pushed to 3200.  I'd offer the 1Dmk3's ISO 3200 as additional support for my claim, but the fact that it is 14 bit may make you feel that the goal post for unity gain has moved (despite the fact that mk3 ISO 3200 quantized to 8 bits is still far less noisy than the mk2's ISO 3200).

I'm sure I have shown you this chart before, in previous refutations of the "unity gain" limit:



That is the total read noise, and the isolated horizontal and vertical line noises.
The total read noise, the yellow line, is scaled to 10% to fit in with the others, and the vertical axis is the read noise normalized to ISO 100 for all other ISOs, as standard deviation in ADUs (which can be considered arbitrary units of electrons).  The noises clearly show no sign of flatlining completely by 3200, as far as the trends up to 1600 are concerned, especially the line noises, which are far more visible than their statistical strength suggests.  Horizontal line noise *is*, without a doubt, the most troublesome aspect of high-ISO shadow areas in Canon cameras.

Roger has nothing to really support his unity gain hypothesis; he is simply applying the concept of one equals one, but these ones are really apples and oranges; one is discreet integer values, and the other is discreet multiples of a single value, with variance at a finer degree.  The ADC in these cameras can *NOT* count electrons.  They can only get so close to counting them, and by all appearances, with Canon's technology, the more you amplify the signal, the more you can reduce the inaccuracy, which is why it is illogical to declare that something as arbitrary as the ADU unit is a meaningful limit to practical amplification.  And the ADU truly *is* arbitrary when it is fine enough not to cause posterization of RAW data.  Only when it is coarse enough to cause posterization does the actual absolute meaning of the ADU have any value (the ability to posterize).
[a href=\"index.php?act=findpost&pid=125309\"][{POST_SNAPBACK}][/a]

I provided a link of John's post to Roger Clark and invited him to respond, and he was kind enough to provide the following explanation.


Hi Bill,

You can post this response if you wish to the luminous-landscape forum
as I have not registered to post there.

John Sheehy posted a plot of noise versus ISO for a Canon 20D.
The way I read the plot is that the noise at ISO 1600 is the
same as ISO 3200 and the noise is greater at ISO 800.
This is the same as other people's measurements.

The Unity Gain ISO for the 20D is 1200, so one would expect
a slight improvement from ISO 800 to 1600 (ISOs in between
these factor of 2 values are reportedly scaled and not true gains).
Amateur astronomers are pushing these cameras to their limits
and everyone I know has concluded that there is no benefit in
going to ISO 3200 (query the literally thousands of people
on the digital_astro yahoo group).  Most are using ISO 1600
and some ISO 800.  So I don't see John's plot in conflict with
the Unity Gain implications.  I also have never seen a clear demonstration
that you could actually get more out of an image at ISO 3200
versus 1600 on the current suite of 12-bit/pixel cameras.
A number of amateur astronomers have tested this too and
come to this conclusion (that ISO 1600 "gets it all").
In fact you actually lose a stop of dynamic range in going from
ISO 1600 to 3200.

Regarding the 1D Mark III, part of the "read noise" is A/D converter
noise.  The use of a 14-bit A/D reduces that noise and Canon reportedly
has a half to one stop better noise floor performance.
More importantly, Canon has reportedly reduced the fixed-
pattern noise (e.g. line noise).  That improves the
perception of noise making the higher ISO images look
better.  Until these cameras get into the hands of people
who run rigorous tests we really won't know the
implications of ISO, 14-bits, and noise floors.

Roger


The implications for shooting in very dim light are that it does not really make much sense to exceed the unity gain under these conditions. You get no more information and lose one f/stop of dynamic range. The unity gain of the Nikon D200 is 800 according to Roger's tests. According to the unity gain theory, when shooting in dim light with this camera in raw mode, it would be best to set the camera to ISO 800 rather than 1600. If there is enough light to expose at ISO 800, you get better dynamic range and less noise. If "underexposure" occurs at ISO 800, you merely use the exposure control of ACR (or whatever raw converter you are using) to brighten the image.

Bill
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jani
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« Reply #45 on: June 28, 2007, 07:02:35 AM »
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I provided a link of John's post to Roger Clark and invited him to respond, and he was kind enough to provide the following explanation.

Amateur astronomers are pushing these cameras to their limits
and everyone I know has concluded that there is no benefit in
going to ISO 3200 (query the literally thousands of people
on the digital_astro yahoo group).  Most are using ISO 1600
and some ISO 800.  So I don't see John's plot in conflict with
the Unity Gain implications.  I also have never seen a clear demonstration
that you could actually get more out of an image at ISO 3200
versus 1600 on the current suite of 12-bit/pixel cameras.
A number of amateur astronomers have tested this too and
come to this conclusion (that ISO 1600 "gets it all").
In fact you actually lose a stop of dynamic range in going from
ISO 1600 to 3200.
He seems to have missed the point.

Perhaps you should ask him to re-read John's post, particularly the part about the ISO modes above 1600 on pre-1D MkIII Canon cameras.
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« Reply #46 on: June 28, 2007, 07:30:33 AM »
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I've read this topic over and over and only grasp about a quarter of what you folks are saying.  And I keep asking myself, so what!  Are you only discussing theory or is there some real world benefit to your debate. 
[a href=\"index.php?act=findpost&pid=125381\"][{POST_SNAPBACK}][/a]

wmchauncey -- Here's the real deal: Current megapixel digital sensors are like film with no shoulder at all.  When someone says "this looks digital" they really mean that the highlights are clipped hard.  No one exposes film to clip highlights hard; they haven't for decades.  I'm not sure why we're supposed to expose our digital sensors that way, even though they have the smoothest response right up near that wall of clipped highlights.  So what if they are?  Am I going to regret a minor amount of additional more noise by boosting my RAW file if doing so makes a scene look natural?  No.  I am not, my curators are not, and my customers are not.  They will look at my photos and say, "wow."

The dumb thing is that most digicams push the metering right up near that wall so that signal/noise ratios are as low as possible (probably for marketing's sake) -- at the cost of hard clipped highlights.  Well, I don't know about you, but I don't sell "signal/noise ratios".  I sell pictures.  And I've found that I can make the kind of pictures I want by shooting  "underexposed" according to the camera, then "push-processing" the resulting RAW file.  I get a little bit more noise, but a much more natural looking result.  



This is an extreme example.  Exposed -2EV, shadows recovered up to 4 stops.  Detail visible in the shadowed brush on the left and around the telegraph pole on the right.  And the highlights on the rails look natural, and the sky isn't blown out, and it feels just like it felt when I was there -- a bright, clear, early morning.

Remember that Canon has added a "highlight tone priority" mode to the 1DmkIII -- which does exactly what I describe above.  If you don't trust me, trust Canon.  The era of hard clipped digital highlights is finally coming to an end.  It's been a long time coming.  And if you don't have a 1DmkIII, you can still do this by "underexposing" in camera, and "push-processing" in RAW.


-s

[edit -- removed unnecessary editorializing  -s]
« Last Edit: June 28, 2007, 08:43:53 AM by SeanPuckett » Logged

John Sheehy
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« Reply #47 on: June 28, 2007, 08:05:05 AM »
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The implications for shooting in very dim light are that it does not really make much sense to exceed the unity gain under these conditions.

Really?  Where is the proof for that?

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You get no more information and lose one f/stop of dynamic range.

You get no more information BECAUSE THEY REALLY AREN'T TRUE AMPLIFIED 3200.  How many times do I have to repeat this extremely relevant fact?  Roger's conclusions, and those of the astronomers he's asked, are all based on ISO 3200s that are really ISO 1600s under-exposed, with the RAW values doubled and almost a stop of hightlights clipped away for no good reason.

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The unity gain of the Nikon D200 is 800 according to Roger's tests. According to the unity gain theory, when shooting in dim light with this camera in raw mode, it would be best to set the camera to ISO 800 rather than 1600. If there is enough light to expose at ISO 800, you get better dynamic range and less noise. If "underexposure" occurs at ISO 800, you merely use the exposure control of ACR (or whatever raw converter you are using) to brighten the image.[a href=\"index.php?act=findpost&pid=125384\"][{POST_SNAPBACK}][/a]

What does that have to do with unity gain?

It is true for most Nikon cameras more than a year or two old, because most of the read noise occurs at the initial read on the sensor, and only a clean, low-gain amplifier is used to feed the ADC.  Total read noise in electrons is very similar at all ISOs, and only varies because the absolute_signal-to-ADC_noise is different.

The same principle can apply between ISO 200 and 400, as well as 400 and 800 with cameras that do not have lower absolute (electron) noise at higher ISOs (like the Pentax K10D).  Nothing special happening at unity gain.  Even when the ADC noise makes a difference between ISOs, it makes the most difference between lower ISOs, explaining why there is less loss pushing 800 to 1600 than 200 to 400.  The higher the noise before the ADC, the less increase there is in total noise from the ADC, because of the non-linear way in which noise sums.

Only poor circumstantial evidence exists for the unity gain theory.  An ADU:electron ratio is only completely relevant if the total read noise is low enough so that no two quantities of electrons are digitized as one.  That actually requires far greater than 1:1 with even 0.1 adu of analog read noise, for total accuracy in counting.

As far as 14 bits are concerned, they do nothing for IQ at ISO3200 with the mk3.  Truncated to 8 bits, and then converted to RGB, the mk3 has less noise than the 1dmk2 with 12 bits.  Even 12 bits at high ISOs is overkill for 99.99% of uses.

Roger's idea of testing this type of thing is to take a linear conversion, and then quantizing it.  That is nothing at all like quantizing the RAW data, and then interpolating/demosaicing it and performing WB.
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bjanes
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« Reply #48 on: June 28, 2007, 08:51:19 AM »
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Modifying the contrast seems like a good idea. But in the final analysis, the camera manufacturers have let us down. There are not enough bins in the histogram and it comes from the jpeg, not the raw. Because there are so few bins in the histogram, its shape is poorly defined. This matters most in the highlights.  In some case parts of the histrgram can be distorted becasue the bin-width is too large.  One experiment for someone with ambition and too much time is to measure the in-camera histogram and compare its shape  to the one in photoshop. It would be good to do this experiment for several lighting conditions
[a href=\"index.php?act=findpost&pid=125328\"][{POST_SNAPBACK}][/a]

I don't have unlimited time on my hands, but have done part of the experiment that you suggest with a Nikon D200. Illumination was 5000K. I took shots of a Stouffer step wedge, increasing the exposure in 0.33 EV increments until I observed clipping on the camera histogram with contrast set to normal. I then examined the contents of the raw files (converted with DCRaw) and the preview in Adobe Camera Raw. The displayed results are for the last exposure without clipping.

Here is the camera histogram. Note that the head of the wedge (which includes step 1) is just short of clipping and is the large spike towards the right. The small spike to the extreme right is blown background without the base density of the wedge.

[attachment=2711:attachment]

Here are the pixel values in the raw file (in 8 bit notation). Note that step 2 (down 0.3 EV) is not blown in any channel, whereas the green is in step 1 is near maximum.

[attachment=2712:attachment]

And this is how ACR views the file:

[attachment=2713:attachment]

Since the highlights are 255, I used the exposure control to decrease exposure until the value fell below 255, which took place at -0.2:

[attachment=2714:attachment]

With my particular camera, the camera histogram from the JPEG preview gives an accurate indication of clipping. For most exposures, I like to have the exposure just short of clipping. If the highlights are not critical and I want better shadow detail, then  I may allow some highlight clipping and perform recovery in ACR.

Bill
« Last Edit: June 28, 2007, 08:57:06 AM by bjanes » Logged
bjanes
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« Reply #49 on: June 28, 2007, 09:18:52 AM »
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Roger's idea of testing this type of thing is to take a linear conversion, and then quantizing it.  That is nothing at all like quantizing the RAW data, and then interpolating/demosaicing it and performing WB.
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John,

I don't really feel qualified to comment on the fine points of the work that you and Roger have done. At this point, I would look at the qualifications and background of the authors. Roger has a PhD in astrophysics from MIT and is professionally involved in various imaging projects at NASA and has 179 peer reviewed scientific papers ([a href=\"http://www.clarkvision.com/rnc/index.html]Bio RN Clark[/url]). What are your qualifications?

Bill
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John Sheehy
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« Reply #50 on: June 28, 2007, 04:28:57 PM »
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I don't really feel qualified to comment on the fine points of the work that you and Roger have done.

I see.  Your role is to quote and link without any personal understanding.

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At this point, I would look at the qualifications and background of the authors.

Really?  A discerning reader would look at the logic and quality of the arguments, critically.  Test these things for yourself.  Why would you want to trust someone else for something you can test yourself?  

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Roger has a PhD in astrophysics from MIT and is professionally involved in various imaging projects at NASA and has 179 peer reviewed scientific papers (Bio RN Clark).

That doesn't impress me to the same level it apparently does you.  The world is full of people who fudge their way through their careers.  Statistically speaking, he is likely to know more than someone who has not taken such a career path, but it does not license him to guaranteed truth.

I am impressed by quality of argument, and depth of thought.  Do you think that there are no errors in 179 scientific papers?  Do you think that no one objected to any of his ideas?
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What are your qualifications?
[a href=\"index.php?act=findpost&pid=125415\"][{POST_SNAPBACK}][/a]

The quality of my arguments is my qualification.  There is nothing mysterious, either in what I say.  You can test most of it for yourself.

If you can't understand them, then go idolize an "expert" who jumps to conclusions.
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Guillermo Luijk
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« Reply #51 on: June 28, 2007, 04:48:35 PM »
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I may allow some highlight clipping and perform recovery in ACR.

ACR does not do any highlights recovery. Correcting the Exposition down and therefore apparently recovering blown areas is not recovery at all, is simply compensate the blowing effect of white balance scaling, with the scaling provided by Exposition compensation to the left.

Your camera's histogram is pesimistic, as it will show blown areas where in the RAW file they have not still begin to blow. Reason? it's an histogram calculated on a white balanced RAW file using greater than 1.0 multipliers.
I see you use DCRAW to develop, just do this experiment: take the first RAW file in your series that started to appear blown on some channel in your camera0's histogram. Now develop it with -H 1 or better -H 2 options in DCRAW that ensure through smaller than 1 multipliers not to blow anything that was not already blown in the RAW file. Surely there will be nothing blown.

So if your camera's histogram shows nothing blown, no channel is. If it does, you don't know what you will find in the RAW file until you develop it in your PC.
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« Reply #52 on: June 28, 2007, 04:54:04 PM »
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ACR does not do any highlights recovery.
[a href=\"index.php?act=findpost&pid=125479\"][{POST_SNAPBACK}][/a]

Maybe we have to define what highlight recovery means.

ACR can build data in highlights IF one of the three color channels has data. If all three are blown out, nada.
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« Reply #53 on: June 28, 2007, 05:19:47 PM »
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I see.  Your role is to quote and link without any personal understanding.
Really?  A discerning reader would look at the logic and quality of the arguments, critically.  Test these things for yourself.  Why would you want to trust someone else for something you can test yourself? 
That doesn't impress me to the same level it apparently does you.  The world is full of people who fudge their way through their careers.  Statistically speaking, he is likely to know more than someone who has not taken such a career path, but it does not license him to guaranteed truth.

I am impressed by quality of argument, and depth of thought.  Do you think that there are no errors in 179 scientific papers?  Do you think that no one objected to any of his ideas?
The quality of my arguments is my qualification.  There is nothing mysterious, either in what I say.  You can test most of it for yourself.

If you can't understand them, then go idolize an "expert" who jumps to conclusions.
[a href=\"index.php?act=findpost&pid=125476\"][{POST_SNAPBACK}][/a]

John,

Thus far all the data you have presented is one graph showing noise characteristics of a camera with results similar to those obtained by others. Then you draw conclusions that, in my view, are not supported by the graph. Any scientific paper has a materials and methods section where the experimental technique is described in sufficient detail to allow others to replicate the experiment and confirm the results. If you look at Roger's web site, he describes his methods in detail and gives references in the scientific literature to support his conclusions. Please direct us to an explanation of your work.

Science is not logic and the validity of a hypothesis can not necessarily be determined from the quality of the argument and the depth of thought. You need data and need to show how it was obtained.

I have worked through many of Roger's methods with my own camera. However, thus for you not described any methods that I can verify. Thus, while you seem to know quite a bit, you have less credibility with me than does Roger. Let other forum members draw their own conclusions. It they want to set their cameras to ISO 3200 and lose dynamic range.

Bill
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John Sheehy
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« Reply #54 on: June 28, 2007, 07:27:35 PM »
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So if your camera's histogram shows nothing blown, no channel is. If it does, you don't know what you will find in the RAW file until you develop it in your PC.
[a href=\"index.php?act=findpost&pid=125479\"][{POST_SNAPBACK}][/a]

If you have an RGB histogram, and nothing is blown in it, then probably nothing is blown in the RAW, but if the histogram is a luminance one, blown red and blue channels can easily be missed by the histogram, as they have weak luminance weighting.
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bjanes
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« Reply #55 on: June 28, 2007, 09:07:01 PM »
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ACR does not do any highlights recovery. Correcting the Exposition down and therefore apparently recovering blown areas is not recovery at all, is simply compensate the blowing effect of white balance scaling, with the scaling provided by Exposition compensation to the left.
[a href=\"index.php?act=findpost&pid=125479\"][{POST_SNAPBACK}][/a]

Whether what ACR does should be called recovery is a matter of semantics. With daylight white balance, the green channel can show severe clipping of the highlights when the blue and red channels are still intact. These tones in the green channel are lost and ACR does more than just scale back the green channel, but rather rebuilds it from intact data in the other channels using an algorithm to prevent color shifts as much as possible. This feat was demonstrated in the analysis I did on Digidog's overexposed file. Bruce Fraser and some other knowledgeable and articulate people have called this recovery. Your mileage may vary.

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Your camera's histogram is pesimistic, as it will show blown areas where in the RAW file they have not still begin to blow. Reason? it's an histogram calculated on a white balanced RAW file using greater than 1.0 multipliers.

So if your camera's histogram shows nothing blown, no channel is. If it does, you don't know what you will find in the RAW file until you develop it in your PC.
[a href=\"index.php?act=findpost&pid=125479\"][{POST_SNAPBACK}][/a]

With Nikon cameras it is a simple matter to upload a custom white balance to the camera with the red and blue multipliers set to 1.0. The resulting RGB camera histogram gives a good preview of what is in the raw file without resorting to one's computer. If the camera has several banks in which to store camera settings, one of these can be used for the UniWB (coined by Julia Borg, a Nikon guru). This UniWB does mess up Adobe Camera Raw; when it sees Red and Blue multipliers set to 1.0, it thinks it is dealing with a multiple exposure. This problem can be addressed by making the coefficients nearly 1.

Bill
« Last Edit: June 28, 2007, 09:09:37 PM by bjanes » Logged
Ray
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« Reply #56 on: June 28, 2007, 10:10:02 PM »
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"Highlight recovery" is a usual term when talking about RAW developing, but it's most of the times wrong. What you get in ACR pushing down the exposure slider is not any highlight recovering at all. If your previously blown highlights become not blown through underexposure tuning, is because they were actually never blown on the RAW file. It was YOU in the developing process, commonly with the white balance (which implies heavy channel scaling by factors usually greater than 2.0 in linear, i.e. +1EV correction, and easily beyond 2.5, nearly +1.5EV), who blowed those areas.

ACR does not apply any real recovery of highlights. DCRAW in its -H2 to -H9 modes does; DCRAW interpolates truly blown pixels to values close to those in the boundaries; it "invents" colours where they were previously blown.

I just wanted to point this as most people talk about hightlight recorvery when thery are just simply referrering to "no-blowing underexposure".

[a href=\"index.php?act=findpost&pid=125372\"][{POST_SNAPBACK}][/a]

Let's put it this way. Blown highlights was more of a problem for me before I started using ACR several years ago. Canon's ZoomBrowser and othe popular RAW converters like BreezeBrowser could not do nearly as good a job as ACR in 'so-called' highlight recovery.

I remember being amazed at how much more detail in a grey sky I could recover using ACR. BreezeBrowser at that time could not compete, in my view. I don't know what BreezeBrowser is like now. I'm sure it has improved.

One RAW converter I still use is Raw Shooter Premium. I like the ease with which I can get solid, vibrant colors with almost a painterly effect, yet still retaining full detail. However, when it comes to recovering detail or color in a blown sky, ACR is marginally better than RSP.

It might well be true that DCRAW is even better at reconstructing lost data. I'm led to believe it is, from comments from John Sheehy and others and yourself.

But it's not a programs that's easy to use, is it? I get the impression it's a program that appeals more to computer programmers.
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« Reply #57 on: June 29, 2007, 07:28:29 AM »
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Whether what ACR does should be called recovery is a matter of semantics. With daylight white balance, the green channel can show severe clipping of the highlights when the blue and red channels are still intact. These tones in the green channel are lost and ACR does more than just scale back the green channel, but rather rebuilds it from intact data in the other channels using an algorithm to prevent color shifts as much as possible. This feat was demonstrated in the analysis I did on Digidog's overexposed file. Bruce Fraser and some other knowledgeable and articulate people have called this recovery. Your mileage may vary.
With Nikon cameras it is a simple matter to upload a custom white balance to the camera with the red and blue multipliers set to 1.0. The resulting RGB camera histogram gives a good preview of what is in the raw file without resorting to one's computer. If the camera has several banks in which to store camera settings, one of these can be used for the UniWB (coined by Julia Borg, a Nikon guru). This UniWB does mess up Adobe Camera Raw; when it sees Red and Blue multipliers set to 1.0, it thinks it is dealing with a multiple exposure. This problem can be addressed by making the coefficients nearly 1.

Bill
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Yes, this is what you can read almost everywhere about ACR, but I never saw an example where it was clear that ACR recreated a blown channel (mean blown even in the RAW data) with the information of the other two. "This feat was demonstrated in the analysis I did on Digidog's overexposed file"-> where exactly can I find this analysis? I would be interested in looking at it.

What DCRAW calls recovery, despite the results can be better or worse, is real interpolation of values in a channel according to values in the same channel but in non-blown surrounding pixels.

Something (very argueable) that makes me think DCRAW does something more than ACR is that if you activate recovery on DCRAW you clearly see an increment in the processing time (in fact DCRAW tells you when the recovery stage begins), while ACR always seems to take the same time to develop a RAW, no matter how much highlights were blown or not.

This is a sample of an image with important enough real blown areas (in the RAW data) in the green and blue channels:

(developed with -H 1 in DCRAW to avoid WB clipping and be aware of real blown areas):
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ACR produces (look at the water fall and the shiny rock) disgusting final tones. Shouldn'd it recover the blown channels from the red one?
On the other hand -H option in DCRAW produces a pleasant highlight recovery specially in the water fall. In this case -H 9 was used; with -H 6 the tone on the rock becomes more pleasant (less red).

ACR with -3EV exposure correction to minimise highlight blowing:


Developed using DCRAW and -H 6 recovery option:




The 1.0 EB multipliers on the Nikon is a cool option. With no doubt I would make use of it.


Best.
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jani
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« Reply #58 on: June 29, 2007, 01:41:45 PM »
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One RAW converter I still use is Raw Shooter Premium. I like the ease with which I can get solid, vibrant colors with almost a painterly effect, yet still retaining full detail. However, when it comes to recovering detail or color in a blown sky, ACR is marginally better than RSP.
Have you tried ACR 4.1 with either Photoshop Elements (4.01/Mac or 5.0/Windows), Photoshop CS3 or Lightroom 1.1?

Already in Lightroom 1.0, the "vibrance" slider seems somewhat similar to a Raw Shooter feature with the same name. I can't say whether it works in exactly the same way, because I stopped using RSE shortly after starting to use it.

(I'm not saying that ACR 4.1 replicates what you like about RSP, but I'm wondering whether it does.)
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« Reply #59 on: June 29, 2007, 05:53:00 PM »
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Already in Lightroom 1.0, the "vibrance" slider seems somewhat similar to a Raw Shooter feature with the same name. I can't say whether it works in exactly the same way, because I stopped using RSE shortly after starting to use it.
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Jani,
I have Lightroom 1.0 but don't use it, and I tried the CS3 demo until it expired. I'll eventually upgrade to CS3. I found the vibrancy slider very tame in ACR in CS3, however.

There's something about that combination of 'hot pixel/pattern noise suppression', 'noise suppression', 'detail extraction' and 'vibrance' in RSP that's difficult to emulate in ACR. There's a quality there that seems just right for some images, but not all images.
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