Pages: 1 [2] 3   Go Down

Author Topic: Raw DR ratings based on one camera!  (Read 7136 times)

ErikKaffehr

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 10564
    • Echophoto
Re: Raw DR ratings based on one camera!
« Reply #20 on: May 20, 2016, 03:29:12 PM »

Hi,

It may be that DxO, Guillermo, Roger Clark, Bill Janes, Bart van der Wolf and myself know a couple of things about this…

If you have some point of view, please write down, explain and motivate…

Best regards
Erik

Hi, Guillermo,
The sentiments you expressed are exactly the reason that we were surprised to find variance in the extra raw-accessible dynamic range (ERADR) beyond the clipping point for the JPEG-adjusted histogram frame among camera's of the same model.
That repeated tests for ERADR at different ISOs on a variety of camera models have yielded consistent results (to 1/3 stop) has reinforced reliance in the test procedure. We are not, in the manner that we test, determining the actual DR of any tested camera, simply the "extra raw-accessible dynamic range" which is then added to the ETTR exposure in an effort to utilize the maximal available dynamic range of each of our cameras. The fact remains that different cameras of the same model have yielded different numbers of 1/3 stops of ERADR. On that basis has rested the recommendation that each camera be tested for its individual allotment of ERADR. Perhaps you can explain how  different amounts of determined ERADR among cameras of the same model might not, in fact, conflict with the concept of the accuracy of a single  total DR determination.  I've been in contact with DxO Mark but have not received helpful information in this regard nor been able to engage in any substantive discussion on the matter.

It would seem most informative if someone without a "dog in this fight" would undertake similar tests for ERADR  in several cameras of each of the same models and report those results.
I appreciate your interest and would appreciate any further thoughts you may have.

Best regards,
Dave

AlterEgo

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 1996
Re: Raw DR ratings based on one camera!
« Reply #21 on: May 20, 2016, 03:52:17 PM »

The fact remains that different cameras of the same model have yielded different numbers of 1/3 stops of ERADR.

you still did not show actual test procedure...  neither links from your prev. postings in this topic showed, for example, how did you exactly test (exact OOC JPG parameters) and what was the exact camera model in question... also may be you can stop using the wording "we" , it does not add any substance.
Logged

uuglypher

  • Newbie
  • *
  • Offline Offline
  • Posts: 17
Re: Raw DR ratings based on one camera!
« Reply #22 on: May 20, 2016, 06:19:16 PM »

you still did not show actual test procedure...  neither links from your prev. postings in this topic showed, for example, how did you exactly test (exact OOC JPG parameters) and what was the exact camera model in question... also may be you can stop using the wording "we" , it does not add any substance.

I've been using EBTR for over a decade and it has been an interesting trip. I've been most pleased with its results when used under appropriate conditions. I've no intent to proselytize, just to explain how those of us who use the technique use it. If I tell you more than this, I'd be telling you more than I know for sure, and I'd rather not do that , considering how much of that is already going around!
You'll like it or you won't. Good luck.
Here y'Go!

If you want to get started with Expose Beyond the Right and start taking advantage of all your camera’s available dynamic range, here’s how to start !:

Here's the easiest way to get a handle on how much extra raw-accessible dynamic range (ERADR) your particular camera has at base ISO.

On a somewhat overcast day (soft-edged shadows) find a scene with a dynamic range less than that of your sensor. In other words, a scene that produces a histogram that falls completely within your camera's histogram frame with no clipped shadows at the left (dark) end or clipped highlights at the right (bright) end..
Set the camera to its native ISO (usually ISO 100...or ISO 200 if you usually use that as the low end).
Set to a specific WB (doesn’t matter which one, just NOT AutoWB). 
Set “Creative” or “Personal Preference” Settings (brightness, contrast, Sharpness, and Saturation to “neutral”. 
Establish a metered exposure for the scene:
    Take a spot meter setting from a middle gray region of the scene using either a hand-held spot-reading meter or your camera’s spot meter function.
     Set to “ manual exposure”. 
     Set to “manual focus”
     Attach your camera to a sturdy tripod or other solid support.
    Start exposing with progressively larger apertures (smaller F-Numbers) until the extreme right end of the "light pile" just barely "kisses" the right side of the histogram frame without triggering the highlight clipping warning "blinkies" (the ETTR exposure)
     Now, start a series of exposures by increasing each subsequent exposure by 1/3 stop of shutter speed,
     Add four full stops of exposure (that's twelve exposures, each 1/3 stop longer in shutter duration than the previous one). Note that the previous recommendation was for three full stops, but recent reports of a camera with more than three full stops of ERADR have suggested we ought look beyond three stops! Who knows? Your camera may be a record setter!

     Download the image files into your raw converter. Open the exposures in sequence and tonally normalize it by left-sliding the "Exposure" slider. As each "washed out, too bright" image is tonally normalized, you'll see the histogram slide left and fully into the histogram frame. Do this in sequence until you find the histogram that contains a "spike" at the right end of the light pile that indicates blown highlight detail. Just a caution here... if the scene contained some specular highlights, then a very thin, one-pixel wide spike is permissible. If you see such a "specular highlight spike", go ahead and open the next frame, which should have a substantial spike of blown/clipped highlights at the right end of the light pile. 

The number of exposures between your brightest possible JPEG exposure (the ETTR exposure) and the first exposure with actual blown highlights( not just specular highlights) constitutes your camera's ERADR (Extra Raw-Accessible Dynamic Range).
1 exposure? 1/3 stop
2 exposures? 2/3 stop
3 exposures? one full stop.
4 exposures? one and 1/3 stops (as illustrated in the case discussed above)
5 exposures? one and 2/3 stops
6 exposures? two full stops
7 exposures? two and 1/3 stops
8 exposures? two and 2/3 stops
9 exposures? three full stops
10 exposures? three and 1/3 stops
11 exposures? three and 2/3 stops (not seen one of these yet...!!!!)
12 exposures? four full stops (not seen one of these yet ...!!!!!)


Caveat:
You should test your camera's ERADR at the ISOs you most commonly Use
As ISO increases, the camera's amount of ERADR gradually and irregularly decreases. As an example, I've a camera that, at ISO 100 has one and 1/3 Stops of ERADR. At ISO 400 it drops to one full stop, and at ISO 3200 the ERADR is 2/3 stop.




How to Use that Extra Dynamic Range:
So, how do you actually use that ERADR once determined? Set your exposure as for a JPEG file using either  your camera's meter, or a hand-held reflective, spot-reading, or incident light meter. Enter the exposure into your camera, and, adjust that exposure so that the right end of the "light pile" of the histogram moves right to barely kiss the right side of the histogram frame juuuuuust before clipping the highlights clipping warning/the "blinkies". It doesn't matter if the right end of the light pile is a sizeable "lump" or a just a slender white line extending along the frame's base. When it just barely touches the right side of the frame. THAT is the ETTR exposure -your starting point. THEN.... add your known stops of ERADR using either slower shutter speeds or larger apertures (or a combination) and make your exposure. Note: Most who regularly use EBTR normally use 1/3 stop less than their established ERADR ,just to " play it safe" as regards possibly clipping highlights. Why "play it safe"? Because in some cameras there is some inaccuracy in tripping the "blinkies".

REMEMBER:
When you start using that extra dynamic range, realize that your camera's LCD display of the viewed thumbnail will, with most scenes, likely appear "washed out" with "blown highlights" (because it "thinks" it is displaying an "overexposed" JPEG file instead of a correctly exposed raw image file. So... DO NOT INTERPRET SUCH WASHED-OUT IMAGES AS "OVEREXPOSED"!!! THEY ARE CORRECTLY EXPOSED RAW IMAGE DATA FILES !!!
Download the files into your computer's raw converter (Adobe Camera Raw is fine), move the "Exposure" slider to the left, and you'll see the image become tonally normalized with its full, expected tonal range and tonal spectrum! When you are new to EBTR, every time you tonally normalize a washed-out image, it's like a miracle to watch that tonally perfect image appear right before your eyes! It sort of reminds me of watching an image appear in a print in the developing tray under the dim safelight in my dad's darkroom in the 1940s.

"So what's the big deal about a measly Stop?

It is at about this point in a class or workshop that some back-row sitter pipes up with:
"C'mon, Dave, are you really telling me that just one measly stop is really worth all this trouble?"
So I ask him, "What's your best, fastest lens?

"Er...that'd be my Summilux-M 50mm f/1.4 ASPH.  , why?"
"
"we'll, would you mind if I took your lens and superglued it so it it couldn't open up beyond f/2 ?"

or....

"What if you couldn't, simply by increasing raw exposure by one stop, thereby reduce the amount of noise you might routinely capture?"

or

"Think of the times that limited illumination have made you wish for "just one more "measly" stop?"

or,

what about being able to cut your already fast shutter speed in half to permit hand-holding with a longer lens, or using a monopod instead of a tripod?

Yeah, I'd say there's considerable advantage to getting every bit of extra dynamic range as you can out of that sensor that amounted to 2/3 of the cost of that new snazzy-a-sed camera body you just bought!

Here we're talking about pulling out, at the very least, 2/3 stop of exposure up to two an ⅔ stops to possibly more than three stops of exposure beyond what your camera's lying JPEG-adjusted histogram suggests you can actually use!


'Tain't chicken feed, McGee!


"One measly stop of exposure? I wouldn't give that up, as we said back in the day, "...for love nor money"'



Why don't I just compile a list of camera brands and models and state the tested ERADR of each? Because three camera's of the same make and model can have three different amounts of ERADR at a given ISO! Also, I’ve received some unpleasant responses from camera owners who used the ERADR amount that I had found in their camera model  and they overexposed some important “irreplaceable” images. (they just hadn’t caught on that they had to test their own camera!) So, I'm sorry...but you just gotta test each individual camera!


As the spirit moves and time permits, I’m happy to help anyone test their own camera. or to examine their ERADR series of exposures. If appropriately prepared, I’ll report back the ERADR determined. Just contact me by personal message.

So far, I’ve encountered two camera models represented by more than one camera. Two cameras of one model and four of another...and so far no two cameras of the same model have had the same allotment of ERADR.  The two-camera pair were ⅔ stop apart, and the four camera quartet had a range difference of one and ⅔ stops.  Go test some cameras. Find out for yourself!  I’ll be glad to help evaluate your ERADR exposures as time permits. I’m glad to help anyone pursuing this interesting phenomenon (and to discover a way to assure that you are using your camera’s maximal available dynamic range).

Give it a go! Some wil try it, like it, and never look back! For others it’ll be too much trouble. I’ve been using EBTR for twelve years when conditions were appropriate. Give it a go! You’ll never know if you’ll like  it or not until you actually try it. But by this time I’ve realized that there will always be some sideline sitters who’ll carp about why it won’t work, yet never try it themselves.

 It has been ever thus!

Best regards, and let me know how you do.

Dave





Logged

Guillermo Luijk

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 1603
    • http://www.guillermoluijk.com
Re: Raw DR ratings based on one camera!
« Reply #23 on: May 20, 2016, 07:55:11 PM »

Hi Dave, some of us have already walked through the paths you are following time ago. What you call ERADR is not DR but highlight headroom between the camera JPEG and the RAW file, and will strongly depend on camera processing. This includes adjusted WB, output color profile, contrast/saturation settings,... Also the kind of light will have an influence becase the spectral components will impact in the RAW channel distribution itself.

More logical than measuring "JPEG vs RAW" headroom, is to measure the "Metering vs RAW" headroom, i.e. know how many stops you can add to the exposure meter 0.0 point before having actual RAW clipping. Still the scene lighting will have a strong impact here.

E.g. RAW file metered over a gray uniform surface under tungsten light and exposed accordingly:

RAW histograms:

Canon 350D:


Canon 5D:


Even with that reddish light the G channel captures photons the most, having around 3,5 stops of RAW headroom vs camera metering (apparently a bit more in the Canon 350D, but remember we are exposing in 1/3EV steps so there is room for a slight deviation).

Regards


« Last Edit: May 20, 2016, 08:02:16 PM by Guillermo Luijk »
Logged

AlterEgo

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 1996
Re: Raw DR ratings based on one camera!
« Reply #24 on: May 20, 2016, 09:12:54 PM »

I've been using EBTR for over a decade and it has been an interesting trip. I've been most pleased with its results when used under appropriate conditions. I've no intent to proselytize, just to explain how those of us who use the technique use it. If I tell you more than this, I'd be telling you more than I know for sure, and I'd rather not do that , considering how much of that is already going around!
You'll like it or you won't. Good luck.
Here y'Go!

If you want to get started with Expose Beyond the Right and start taking advantage of all your camera’s available dynamic range, here’s how to start !:

Here's the easiest way to get a handle on how much extra raw-accessible dynamic range (ERADR) your particular camera has at base ISO.

On a somewhat overcast day (soft-edged shadows) find a scene with a dynamic range less than that of your sensor. In other words, a scene that produces a histogram that falls completely within your camera's histogram frame with no clipped shadows at the left (dark) end or clipped highlights at the right (bright) end..
Set the camera to its native ISO (usually ISO 100...or ISO 200 if you usually use that as the low end).
Set to a specific WB (doesn’t matter which one, just NOT AutoWB). 
Set “Creative” or “Personal Preference” Settings (brightness, contrast, Sharpness, and Saturation to “neutral”. 
Establish a metered exposure for the scene:
    Take a spot meter setting from a middle gray region of the scene using either a hand-held spot-reading meter or your camera’s spot meter function.
     Set to “ manual exposure”. 
     Set to “manual focus”
     Attach your camera to a sturdy tripod or other solid support.
    Start exposing with progressively larger apertures (smaller F-Numbers) until the extreme right end of the "light pile" just barely "kisses" the right side of the histogram frame without triggering the highlight clipping warning "blinkies" (the ETTR exposure)
     Now, start a series of exposures by increasing each subsequent exposure by 1/3 stop of shutter speed,
     Add four full stops of exposure (that's twelve exposures, each 1/3 stop longer in shutter duration than the previous one). Note that the previous recommendation was for three full stops, but recent reports of a camera with more than three full stops of ERADR have suggested we ought look beyond three stops! Who knows? Your camera may be a record setter!

     Download the image files into your raw converter. Open the exposures in sequence and tonally normalize it by left-sliding the "Exposure" slider. As each "washed out, too bright" image is tonally normalized, you'll see the histogram slide left and fully into the histogram frame. Do this in sequence until you find the histogram that contains a "spike" at the right end of the light pile that indicates blown highlight detail. Just a caution here... if the scene contained some specular highlights, then a very thin, one-pixel wide spike is permissible. If you see such a "specular highlight spike", go ahead and open the next frame, which should have a substantial spike of blown/clipped highlights at the right end of the light pile. 

The number of exposures between your brightest possible JPEG exposure (the ETTR exposure) and the first exposure with actual blown highlights( not just specular highlights) constitutes your camera's ERADR (Extra Raw-Accessible Dynamic Range).
1 exposure? 1/3 stop
2 exposures? 2/3 stop
3 exposures? one full stop.
4 exposures? one and 1/3 stops (as illustrated in the case discussed above)
5 exposures? one and 2/3 stops
6 exposures? two full stops
7 exposures? two and 1/3 stops
8 exposures? two and 2/3 stops
9 exposures? three full stops
10 exposures? three and 1/3 stops
11 exposures? three and 2/3 stops (not seen one of these yet...!!!!)
12 exposures? four full stops (not seen one of these yet ...!!!!!)


Caveat:
You should test your camera's ERADR at the ISOs you most commonly Use
As ISO increases, the camera's amount of ERADR gradually and irregularly decreases. As an example, I've a camera that, at ISO 100 has one and 1/3 Stops of ERADR. At ISO 400 it drops to one full stop, and at ISO 3200 the ERADR is 2/3 stop.




How to Use that Extra Dynamic Range:
So, how do you actually use that ERADR once determined? Set your exposure as for a JPEG file using either  your camera's meter, or a hand-held reflective, spot-reading, or incident light meter. Enter the exposure into your camera, and, adjust that exposure so that the right end of the "light pile" of the histogram moves right to barely kiss the right side of the histogram frame juuuuuust before clipping the highlights clipping warning/the "blinkies". It doesn't matter if the right end of the light pile is a sizeable "lump" or a just a slender white line extending along the frame's base. When it just barely touches the right side of the frame. THAT is the ETTR exposure -your starting point. THEN.... add your known stops of ERADR using either slower shutter speeds or larger apertures (or a combination) and make your exposure. Note: Most who regularly use EBTR normally use 1/3 stop less than their established ERADR ,just to " play it safe" as regards possibly clipping highlights. Why "play it safe"? Because in some cameras there is some inaccuracy in tripping the "blinkies".

REMEMBER:
When you start using that extra dynamic range, realize that your camera's LCD display of the viewed thumbnail will, with most scenes, likely appear "washed out" with "blown highlights" (because it "thinks" it is displaying an "overexposed" JPEG file instead of a correctly exposed raw image file. So... DO NOT INTERPRET SUCH WASHED-OUT IMAGES AS "OVEREXPOSED"!!! THEY ARE CORRECTLY EXPOSED RAW IMAGE DATA FILES !!!
Download the files into your computer's raw converter (Adobe Camera Raw is fine), move the "Exposure" slider to the left, and you'll see the image become tonally normalized with its full, expected tonal range and tonal spectrum! When you are new to EBTR, every time you tonally normalize a washed-out image, it's like a miracle to watch that tonally perfect image appear right before your eyes! It sort of reminds me of watching an image appear in a print in the developing tray under the dim safelight in my dad's darkroom in the 1940s.

"So what's the big deal about a measly Stop?

It is at about this point in a class or workshop that some back-row sitter pipes up with:
"C'mon, Dave, are you really telling me that just one measly stop is really worth all this trouble?"
So I ask him, "What's your best, fastest lens?

"Er...that'd be my Summilux-M 50mm f/1.4 ASPH.  , why?"
"
"we'll, would you mind if I took your lens and superglued it so it it couldn't open up beyond f/2 ?"

or....

"What if you couldn't, simply by increasing raw exposure by one stop, thereby reduce the amount of noise you might routinely capture?"

or

"Think of the times that limited illumination have made you wish for "just one more "measly" stop?"

or,

what about being able to cut your already fast shutter speed in half to permit hand-holding with a longer lens, or using a monopod instead of a tripod?

Yeah, I'd say there's considerable advantage to getting every bit of extra dynamic range as you can out of that sensor that amounted to 2/3 of the cost of that new snazzy-a-sed camera body you just bought!

Here we're talking about pulling out, at the very least, 2/3 stop of exposure up to two an ⅔ stops to possibly more than three stops of exposure beyond what your camera's lying JPEG-adjusted histogram suggests you can actually use!


'Tain't chicken feed, McGee!


"One measly stop of exposure? I wouldn't give that up, as we said back in the day, "...for love nor money"'



Why don't I just compile a list of camera brands and models and state the tested ERADR of each? Because three camera's of the same make and model can have three different amounts of ERADR at a given ISO! Also, I’ve received some unpleasant responses from camera owners who used the ERADR amount that I had found in their camera model  and they overexposed some important “irreplaceable” images. (they just hadn’t caught on that they had to test their own camera!) So, I'm sorry...but you just gotta test each individual camera!


As the spirit moves and time permits, I’m happy to help anyone test their own camera. or to examine their ERADR series of exposures. If appropriately prepared, I’ll report back the ERADR determined. Just contact me by personal message.

So far, I’ve encountered two camera models represented by more than one camera. Two cameras of one model and four of another...and so far no two cameras of the same model have had the same allotment of ERADR.  The two-camera pair were ⅔ stop apart, and the four camera quartet had a range difference of one and ⅔ stops.  Go test some cameras. Find out for yourself!  I’ll be glad to help evaluate your ERADR exposures as time permits. I’m glad to help anyone pursuing this interesting phenomenon (and to discover a way to assure that you are using your camera’s maximal available dynamic range).

Give it a go! Some wil try it, like it, and never look back! For others it’ll be too much trouble. I’ve been using EBTR for twelve years when conditions were appropriate. Give it a go! You’ll never know if you’ll like  it or not until you actually try it. But by this time I’ve realized that there will always be some sideline sitters who’ll carp about why it won’t work, yet never try it themselves.

 It has been ever thus!

Best regards, and let me know how you do.

Dave

Dave, a lot of words - so what were the cameras and then you probably can show us couple of raw files as a proof  ;) so that we can see how everything was identical yet the 2 different cameras of the same model/make/etc did so differently in the identical conditions (identical scene & framing, light, OOC JPG parameters, camera settings, lens, firmware version, etc, etc - everything is the same) are producing identical JPGs (OOC JPG histogram-wise) yet with a lot (>> 1/3 EV) different saturation in raw channels ... that will be (the only) really interesting point in your posting, sorry... so far you did not produce any proof at all.

as for everything else, thank you, but I am using rawdigger ( www.rawdigger.com ) to find how my camera's spot metering is calibrated and settings I outlined above do serve me well (as verified by rawdigger again)... so do other people and Guillermo Luijk most probably likes to use his own tool (histogrammar)
Logged

BartvanderWolf

  • Sr. Member
  • ****
  • Online Online
  • Posts: 6702
Re: Raw DR ratings based on one camera!
« Reply #25 on: May 21, 2016, 06:27:36 AM »

Dave, a lot of words - so what were the cameras and then you probably can show us couple of raw files as a proof  ;) so that we can see how everything was identical yet the 2 different cameras of the same model/make/etc did so differently in the identical conditions (identical scene & framing, light, OOC JPG parameters, camera settings, lens, firmware version, etc, etc - everything is the same) are producing identical JPGs (OOC JPG histogram-wise) yet with a lot (>> 1/3 EV) different saturation in raw channels ... that will be (the only) really interesting point in your posting, sorry... so far you did not produce any proof at all.

as for everything else, thank you, but I am using rawdigger ( www.rawdigger.com ) to find how my camera's spot metering is calibrated and settings I outlined above do serve me well (as verified by rawdigger again)... so do other people and Guillermo Luijk most probably likes to use his own tool (histogrammar)

I agree. My experience with multiple camera bodies does not indicate large variations, on the contrary. It's more likely to cause variations by illumination or exposure metering not being constant.

As for determining the Raw headroom to achieve ETTR, a tool like Rawdigger, or even Fast Raw Viewer, is indispensable.

Rawdigger will let you see exactly what the maximum DN is per color plane, although some cameras digitally amplify (some) channels to facilitate lossy compression with minimal impact on image quality. Subsequent WhiteBalancing could affect the compromises one makes regarding acceptable clipping.

FRV will allow to determine an Auto Exposure correction based on the amount of clipping one can tolerate, if any (see attached settings). With an exposure bracketed series, only the 'under-exposed' images get a positive exposure correction, others stay at zero because some data is already clipped.

Even in the case of one or two channels being clipped in Raw, modern Rawconverters do a reasonable job of reconstruction the missing channel data whit their Highlight recovery algorithms.

There is also another potential issue with ETTR, and that has to do with some Rawconverters that introduce color twists when pulling the ETTR exposure of a low contrast scene to a more normal level during the conversion.

Cheers,
Bart
« Last Edit: May 21, 2016, 10:10:11 AM by BartvanderWolf »
Logged
== If you do what you did, you'll get what you got. ==

TonyW

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 361
Re: Raw DR ratings based on one camera!
« Reply #26 on: May 21, 2016, 12:12:10 PM »

Hi Dave
Interesting points but I guess that your audience may be novice users and the intent is to show that there is more headroom shooting raw than JPEG and proving the point that the camera LCD histogram display and the blinkies are based on and only reliable indicators for JPEG camera images?  Of course I may be misunderstanding.

In other words a 'correctly' exposed JPEG will be an underexposed raw, or perhaps more correctly an image with less than optimal exposure.

Exposure Beyond The Right (EBTR) is not a term that I care for as it implies that you can pass the far right 'wall' of any­ histogram which of course is/may be correct for most/all in camera histograms for raw but not necessarily the case for all raw editors due to the potential for behind the scenes activity to present an 'acceptable' on screen rendering

For instance Adobe are among those that apply a baseline correction for specific cameras and this coupled by other background changes with process versions and rendering can lead a user to believe that they may be overexposing when in fact the opposite is true - possibly up to 2 EV.

Others such as RawTherapee seem to show the image close to that captured by the sensor i.e. without much in the way of brightening the image

Most camera exposure meters (and separates) are likely to be calibrated to around 12-14% and I would expect that the you may have a maximum of around +3 stops before clipping with many cameras.  So once you find this point you can meter your important highlight areas and apply the correction without being concerned with the camera histogram display

I also agree with others that large variations with cameras is likely to be variations in illumination, metering or even (rare I think) shutter speed or aperture variations
« Last Edit: May 21, 2016, 12:16:30 PM by TonyW »
Logged

Tim Lookingbill

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2036
Re: Raw DR ratings based on one camera!
« Reply #27 on: May 21, 2016, 02:05:29 PM »

There are no identical conditions when shooting outdoors.

What NEVER gets proven or demonstrated in threads of this sort is how to measure and characterize the SPEED the camera's sensor nears full saturation according to varying DR changes that can't be readily seen by eye shooting outdoors.

The camera's sensor is far more "over-reactive" to slight changes to light intensities and so it may appear one camera is more sensitive than another when it isn't. But even in a controlled studio environment shooting a flat piece of white, hot press illustration board will show variation of intensities spread across the entire surface area no matter how evenly lit. This is especially evident shooting artwork where it doesn't matter if white looks slightly brighter in one area over another because it won't be seen in the low dynamic range of a print.

So how about somebody test, measure and characterize for sensor speed to full saturation tied to dynamic range variances?
Logged

Lundberg02

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 345
Re: Raw DR ratings based on one camera!
« Reply #28 on: May 21, 2016, 06:12:45 PM »

Semiconductor mfgs deal with process variability by assigning different model numbers to the units in different sigmas of the output lots.
Logged

uuglypher

  • Newbie
  • *
  • Offline Offline
  • Posts: 17
Re: Raw DR ratings based on one camera!
« Reply #29 on: May 23, 2016, 01:34:04 AM »

Hi Dave, some of us have already walked through the paths you are following time ago. What you call ERADR is not DR but highlight headroom between the camera JPEG and the RAW file, and will strongly depend on camera processing. This includes adjusted WB, output color profile, contrast/saturation settings,... Also the kind of light will have an influence becase the spectral components will impact in the RAW channel distribution itself.

More logical than measuring "JPEG vs RAW" headroom, is to measure the "Metering vs RAW" headroom, i.e. know how many stops you can add to the exposure meter 0.0 point before having actual RAW clipping. Still the scene lighting will have a strong impact here.

E.g. RAW file metered over a gray uniform surface under tungsten light and exposed accordingly:

RAW histograms:

Canon 350D:


Canon 5D:


Even with that reddish light the G channel captures photons the most, having around 3,5 stops of RAW headroom vs camera metering (apparently a bit more in the Canon 350D, but remember we are exposing in 1/3EV steps so there is room for a slight deviation).

Regards

Ye Gads...Take off for the weekend  and return to find everyone's been  busy refuting much of what I may have long held as carefully considered reliable opinion, if not actually irrefutable fact!

Guillermo states:
" ....some of us have already walked through the paths you are following time ago. What you call ERADR is not DR but highlight headroom between the camera JPEG and the RAW file, and will strongly depend on camera processing. This includes adjusted WB, output color profile, contrast/saturation settings,... Also the kind of light will have an influence because the spectral components will impact in the RAW channel distribution itself."

I do find it strange that, having trudged these same paths for so long, we have arrived at such differing conclusions.  Being firmly of the opinion that if something swims, flies, and quacks like a duck I am highly likely to conclude it to be not a zebra, but in fact , a duck.
 Hence, what some peremptorily proclaim to be merely highlight "headroom" tucked discretely just past the JPEG frame, I (and others of the EBTR persuasion) have concluded to be a fully
functional patch of extra raw-accessible dynamic range that does, in fact, characterize the complete raw dynamic range, the full employment of which is  the aim of those hoping to capture files of image data of the highest possible quality, without sacrificing either the tonal or chromatic spectra that are the legacy of their bit-depth.  Certainly, somewhere out near the ragged edge  there is a zone of functional "highlight overhead" incidental to one or two still striving and not-quite-blown color channels. But...out to that point, dynamic range seems still to be dynamic range. Easily performed exposure tests readily confirm its presence and amount.

 The actual amount of the unacknowledged and formally unexplained extra DR clearly varies from sensor to sensor. The most reasonable explanation, may likely be the pervasive phenomenon that besets the semiconductor production industry, "process variance". Of the twenty or twenty-one cameras I have helped test none have had less than 1/3 stop of ERADR, the great majority have at least one full stop of ERADR, and the greatest ERADR I've personally tested was two  and 2/3 stops! Rumors of a camera with three full stops of ERADR are bruited about.  Now, given that even 1/3 stop of ERADR can demonstrably reduce the amount of noise captured, it seems unconscionable that even greater amounts of dynamic range should be allowed to languish incognito... incommunicado...and worst,  un-used.

 We users of ERADR via EBTR have long seen the term "headroom"  being used as a means of subtly diminishing the significance of DR that exceeds that allotted to the JPEG format image data files, and making it easier to sweep that irregular excess" "under the carpet" so it need not be dealt with.


And so, in accordance with the advice of Michael Reichmann, Bruce Fraser and Jeff Schewe to recognize the exposure of raw data as a distinctly different, unique process from that used to expose film and the 8-bit depth JPEG image file.  Those required...and still demand  to expose a detail of a given value in order to specifically render its same value in the print. 

On the other hand, raw image data is a revolutionary, different imaging medium requiring exposing each value with the maximum number of photons proportionate to the brightness of each in their ultimate, brightest possible image, and  to the extent of coming as close as possible to blowing highlight detail...without actually doing so. And this is accomplished ONLY by utilizing the absolute maximum available dynamic range.  Leave out the brightest possible stop of exposure sacrificed 59% or more of the tonal spectra available to,the image! Leaving out the send-brightest stop of exposure sacrifices 25% more of the image’s tonal allotment.. So if your camera has two full stops of un-used ERADR, you have relegated your final image to a mere 25% of its brightness and color tones!
The brightest and darkest image values are exposed proportionately, regardless of whether exposed darkly (to the Left, wher the maximum amounts of noise are captures) or exposed brightly and as far to the right as possible.

The correctly exposed raw image capture, that can only be accomplished by full use of each sensor’s  individually determined ERADR, is an imaging resource that far exceeds the potential
of the oft’ mentioned photographic negative, or even of the unprocessed latent image. The creative, artistic potential of the properly exposed raw image file is most like an infinite collection of the greatest number of un-processed latent image imagineable! Now THAT’S one helluva creative resource. The phototographer’s previsualized image is, of course, guaranteed. As are an almost infinite variety of other creative imaginings!



And much of Guillermo's statement  has merit but for one exception:
It fails to mention that among the listed confounding factors should  also be included the significant effects of "process variance" that plagues  production of a wide variety of semiconductor devices.

It would seem that the observed ...and  productively utilized ...phenomenon of additional
stops of exposure "beyond the right" are supposed to be deemed imaginary (?) because some results from RawDigger/FastRawViewer imply that such additional stops  don't exist?  Indeed...problematic! ...particularly when RawDigger results are used  to reach the opposite conclusions by others.
http://diglloyd.com/blog/2012/20121213_1-D800E-ETTR.html


Guillermo has cogently suggested that:
"More logical than measuring "JPEG vs RAW" headroom, is to measure the "Metering vs RAW" headroom, i.e. know how many stops you can add to the exposure meter 0.0 point before having actual RAW clipping. Still the scene lighting will have a strong impact here."
Indeed, some adherents of EBTR do as Guillermo suggests, and are fully as successful as those of us who use the "ETTR" exposure as our touchstone for adding the ERADR stops at gaining full use of their camera's available extra raw DR...be it 2/3 stop or two and 2/3 stops (or more).
 
 Well, if, as I now hear, all that ERADER  that's been perceived to exist and been used  as DR for the past decade or more  is simply "headroom" of ragged ends of saturated color channels just playing their  hearts out in the role of extra dynamic range.    Well, if that's actually the case, all that ERADR  oughta get an Oscar...or a golden Globe at the very least.  Certainly, out at the tattered edge of its effort it becomes obvious  even to the untrained eye  by resultant muddied hues that it gets to the point  where merely two...or maybe one color channel is indulging in a masquerade, but, depending on the camera, there may be anywhere from 1/3 stop to two and 2/3 stops .(or more) available before that "tattered edge" is obviously reached.

The point that those of us long-time-users of EBTR ( Expose Beyond the Right) have relied upon is that from-camera-to-camera it is, on a practical basis, impossible to predict without individual testing how much of that seemingly perfectly valid dynamic range of exposure actually exists beyond and to the right of the clipping signal(s) at the right end of the manufacturer's selected JPEG histogram frame...that ostensibly represents the sensor's dynamic range.

Some of us who use EBTR got started on that course with the late Michael Reichmann's essay "Expose Right" here in LuLa in 2003 and were, in less than a year, strongly and pointedly encouraged by the late Bruce Fraser's  "Raw Capture, Linear Gamma, and Exposure" Adobe White Paper, in 2004
https://www.adobe.com/digitalimag/pdfs/linear_gamma.pdf

And, with time, additional fuel has been added to the supportive fires by a well-accomplished and most inquisitive photographer, one of my friends, Bob Malarz (who is included under the non-specific "we" when I refer, in a  non-specific manner, to those who practice EBTR) who posted an excellent example of inadvertent utilization of ERADR:
http://www.uglyhedgehog.com/t-133857-1.html

Another thoughtful and knowledgeable photographer of reasonable note, Jeff Schewe, has published another classic example of accidental, inadvertent EBTR in
 "Un-debunking ETTR"
http://schewephoto.com/ETTR/

In fact, Jeff's example of accidental EBTR  has undoubtedly sparked the interest of more than a few to pursue testing their own their own cameras for "whatever it is" beyond the right of the JPEG clipping spot that does a superlative job of standing in for extra raw-accessible dynamic range when, to our dismay, we hear that extra raw-accessible dynamic range being proclaimed not to exist.
And further, the extensive writings on ETTR ( actually EBTR) at

http://diglloyd.com/blog/2012/20121213_1-D800E-ETTR.html

are particularly illuminating, and seem to use results from RawDigger to strong supportive effect.


Indeed, the prophetic words of Winston Churchill come
to mind when we think of the number of times we have
stretched a bit the clipping hazards beyond the right of the JPEG histogram frame and discovered, to our immense relief, that supposedly "overexposed" and therefore "clipped" highlight details were recoverable with "overhead DR". "Wow! Dodged a bullet that time! Gotta be more careful....next time...."    (..right....?)

Churchill said:

"Man occasionally stumbles over the truth,
but usually manages to pick himself up,
 walk over or around it,
and carry on."

Further writings by Jeff Schewe in "the Digital Negative" and "The Digital Print" have simply reinforced the trend to at least investigate the implied promise of ( something incredibly similar to...) extra dynamic range beyond that available for the 8-bit, "pre-cooked" JPEG image file.

And it continues to impress some of us that  out to an impressive distance beyond the JPEG clipping point that so-called "headroom" does one helluva job making like good-ol'-fashioned dynamic range!

To the extent that it results in reduced capture of noise in the shadows, improves shadow detail definition, and even reduces noise in the face of ridiculously high ISOs,  whatever it actually is that we call ERADR succeeds, to an exceptional degree, in  providing the functional advantages that would seem, otherwise, to accrue only to maximal use of extra raw-accessible dynamic range.
"Curiouser and curiouser...."
"A rose by any other name...."  ??????

 A few examples below clearly illustrate why some of us have a hard time giving up use of the ERADR of each of our cameras simply because we are told it's not official dynamic range.  It would seem, we are told, that it can't do what we who have been  using the technique of EBTR  for ten to twelve years have concluded that it actually does do....doesn't it....?   ....or does it ?

IMAGES:

Again, I'm not proselytizing for EBTR, simply hoping to increase awareness of its functional and productive capabilities so that those who may be interested in accomplish the aim of maximizing photon capture to produce the brightest raw capture image possible without clipping highlights, but coming as close to that as possible, can actually succeed in that aim.

I should add that beyond the tests on my own cameras and those of a few local friends and evaluations of some ERADR exposure series received burned on DVDs from other photographers, the majority of the camera's I've helped test have been owned by photographers encountered where photographers gather: camera clubs, workshops, classes,and National Park overlooks and campgrounds. The camera owners have made the requisite ERADR exposure series at "native" ISO,  loaded the images into their laptops where we have then evaluated them. I've simply added the findings to a list in my wallet. That's how I encountered two camera models represented by more than a single camera. So no, I don't have image files to display and distribute to those insisting on them as a pre-requisite  assuring their continuing interest in the phenomenon of EBTR, but it should be no problem for anyone interested to do some testing themselves.  I suspect that most who have adopted the technique of EBTR have, as have I, ceased to maintain files proving its utility...we just use it reliably, like gravity, and... water's tendency to flow downhill...and the Sun rising in the East...and a plethora of other "theories" supported, sadly, only by inductive evidence....which reminds me....when did inductive reasoning start getting such a bad rap?

I make time,  and take time, time-and-time again to help those few who make personal contact and ask that I check their ERADR exposure series, but I'm not up to the increase in submissions that surely would result were I to publicize the two camera models that have demonstrated, among their representatives, variations in sensor function as regards their individual allotments of ERADR. Those cameras are in fact, the reason for the recommendation that every individual camera be tested.

Anyone interested in this interesting phenomenon - whether considered extra raw-accessible dynamic range or "pseudo-dynamic range beyond JPEG clipping"...or "Erzatz DR" or...whatever... - should simply start by testing their own camera's ERADR allotment.

Try it. You'll either be convinced of the utility of EBTR or you won't. Take it or leave it. Makes me no never-mind.  At the very worst you'll have wasted a bit of time and the cost of all those exposu....oh...wait....we're talkin' digital here....
Whatever you may call it, off to the right side- beyond the JPEG clipping warning - you will, if you actually look for it, find something that acts like more dynamic range accessible for raw capture. It may provide as little as 1/3 Stop (E.V.)., to as much as two and 2/3 stops (or more) of whatever you wish to call it..."ERADR"? "Pseudo stops"? "Headroom"? "Ersatz Dynamic Range"?  And be not of faint heart upon seeing those washed-out with blend highlight thumbnails you see on your camera’s display. The ARE NOT...I REPEAT NOT OVEREXPOSED. it’s just that your camera thinks it's a JPEG! Just you wait until you tonally normalize it in your raw converter ...that same sensation you felt years ago,watching an image develop in the tray under that weak safelight will come back with a frisson of recollection!

 And you can take heart in the observation that the majority of cameras tested by those of us using EBTR have been found to have at the very least one full stop of exposure "Beyond the Right".

In the spirit of full disclosure I must admit that, though I have recently acquired RawDigger and RapidRawViewer, I am still in the process of commencing to proceed beginning to prepare to climb that rather daunting learning curve, so any and all available examples of how their use incontrovertibly negates observations of the actual utility of EBTR would be humbly accepted and studied.  In the meantime, I, and I suspect most of the others in my EBTR cohort will continue on our present course of pursuing the benefits of this exposure system that, we’ve used for a decade, but now learn....can't really work.

It is perplexing to me that folks who have paid through the nose for a mega-maxi-pixelated full frame, snazzy-assed camera are satisfied to have it deliver image files with a DR truncated by several stops and thereby, depending on file bit-depth, sacrifice several thousands to tens-of-thousands of tonal levels as well as dulled colors from similar loss of chromatic levels.  It is all the more perplexing when the amount of un-used dynamic range can easily be determined and as easily used via EBTR...whether one believes that that stuff masquerading as DR (beyond the right of the JPEG histogram frame) is really DR or not...it sure as heck acts like it's DR, so why not use it as such?

And I guess I ought admit to another point of curiosity..
to wit:
who, among those who have corresponded here, have actually and seriously tested their own cameras in the manner described for the possible existence of extra raw-accessible dynamic range...or for something that seems to function as if we're ERADR?

Just curious.... just askin'....

Best regards,

Dave

Logged

bjanes

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 3234
Re: Raw DR ratings based on one camera!
« Reply #30 on: May 23, 2016, 07:26:57 AM »

Ye Gads...Take off for the weekend  and return to find everyone's been  busy refuting much of what I may have long held as carefully considered reliable opinion, if not actually irrefutable fact!

Guillermo states:
" ....some of us have already walked through the paths you are following time ago. What you call ERADR is not DR but highlight headroom between the camera JPEG and the RAW file, and will strongly depend on camera processing. This includes adjusted WB, output color profile, contrast/saturation settings,... Also the kind of light will have an influence because the spectral components will impact in the RAW channel distribution itself."

IMHO, Guillermo is exactly correct. Differences in highlight headroom between cameras of the same make and model derive not from variations in the sensor itself, but from variations in the in camera processing by the JPEG engine settings that Guillermo mentions and/or from differences in raw converters. For example ACR/LR have a BaselneExposure tag (see page 38 of the DNG specification 1.4.0.0) that adjusts the exposure setting of the converter and also a BaselineExposureOffset (page 71) that further adjusts exposure when a DNG profile is in use. ACR/LR also are image adaptive and apply automatic highlight recovery with PV2012. For these reasons, ACR/LR are not good tools to evaluate highlight headroom, and use of Rawdigger or a similar program is essential for this purpose.

Another thoughtful and knowledgeable photographer of reasonable note, Jeff Schewe, has published another classic example of accidental, inadvertent EBTR in
 "Un-debunking ETTR"
http://schewephoto.com/ETTR/

In fact, Jeff's example of accidental EBTR  has undoubtedly sparked the interest of more than a few to pursue testing their own their own cameras for "whatever it is" beyond the right of the JPEG clipping spot that does a superlative job of standing in for extra raw-accessible dynamic range when, to our dismay, we hear that extra raw-accessible dynamic range being proclaimed not to exist.

Jeff's points are well taken, but if you look at the raw file of Jeff's waterfall image with Rawdigger, you will see that the ACR histogram is misleading and that the image is not so severely overexposed as the ACR histogram would lead one to believe and "highlight recovery" is less impressive than the example would leave one to believe.

If highlight colors are clipped, there is really no way to recover them exactly and intelligent guesses are necessary. ACR/LR tend to render received highlights as neutral gray/white and this often works well, since many highlights are indeed neutral. However, in many cases the highlights may not be neutral. See Guillermo's DCRaw section on white balance and look at Figure 9. ACR recovers the blown skin highlights as neutral, but DCRaw offers an option to look at colors adjacent to the blown highlights, and deduce that the blown colors of the face are skin tones.

Since modern sensors such as found in the Nikon D810 and other recent cameras have such a high dynamic range, ETTR is less valuable than previously. With this camera, it is better to have slight under-exposure of the highlights than risk the data loss that blown highlights impose.

Regards,

Bill
« Last Edit: May 23, 2016, 07:31:44 AM by bjanes »
Logged

uuglypher

  • Newbie
  • *
  • Offline Offline
  • Posts: 17
Re: Raw DR ratings based on one camera!
« Reply #31 on: May 23, 2016, 08:55:44 AM »

IMHO, Guillermo is exactly correct. Differences in highlight headroom between cameras of the same make and model derive not from variations in the sensor itself, but from variations in the in camera processing by the JPEG engine settings that Guillermo mentions and/or from differences in raw converters. For example ACR/LR have a BaselneExposure tag (see page 38 of the DNG specification 1.4.0.0) that adjusts the exposure setting of the converter and also a BaselineExposureOffset (page 71) that further adjusts exposure when a DNG profile is in use. ACR/LR also are image adaptive and apply automatic highlight recovery with PV2012. For these reasons, ACR/LR are not good tools to evaluate highlight headroom, and use of Rawdigger or a similar program is essential for this purpose.

Jeff's points are well taken, but if you look at the raw file of Jeff's waterfall image with Rawdigger, you will see that the ACR histogram is misleading and that the image is not so severely overexposed as the ACR histogram would lead one to believe and "highlight recovery" is less impressive than the example would leave one to believe.

If highlight colors are clipped, there is really no way to recover them exactly and intelligent guesses are necessary. ACR/LR tend to render received highlights as neutral gray/white and this often works well, since many highlights are indeed neutral. However, in many cases the highlights may not be neutral. See Guillermo's DCRaw section on white balance and look at Figure 9. ACR recovers the blown skin highlights as neutral, but DCRaw offers an option to look at colors adjacent to the blown highlights, and deduce that the blown colors of the face are skin tones.

Since modern sensors such as found in the Nikon D810 and other recent cameras have such a high dynamic range, ETTR is less valuable than previously. With this camera, it is better to have slight under-exposure of the highlights than risk the data loss that blown highlights impose.

Regards,

Bill

Hi, Bill,
I appreciate your comments and and certainly am aware of the pervasive concern that perhaps sacrificing some DR may be preferred to loosing some detail to clipped highlights in the normalized EBTR exposure. The saving grace of EBTR is that the described method of determining the ERADR --the extra raw-accessible dynamic range - if practiced with reasonable care at the chosen ISO - is a guar-an-day-um-tee that highlights will not be blown. It is the common mantra that clearly identifies those who have not actually tried to determine ERADR and practice EBTR.
Here is another example of EBTR:
Logged

uuglypher

  • Newbie
  • *
  • Offline Offline
  • Posts: 17
Re: Raw DR ratings based on one camera!
« Reply #32 on: May 23, 2016, 09:01:15 AM »

I agree. My experience with multiple camera bodies does not indicate large variations, on the contrary. It's more likely to cause variations by illumination or exposure metering not being constant.

As for determining the Raw headroom to achieve ETTR, a tool like Rawdigger, or even Fast Raw Viewer, is indispensable.

Rawdigger will let you see exactly what the maximum DN is per color plane, although some cameras digitally amplify (some) channels to facilitate lossy compression with minimal impact on image quality. Subsequent WhiteBalancing could affect the compromises one makes regarding acceptable clipping.

FRV will allow to determine an Auto Exposure correction based on the amount of clipping one can tolerate, if any (see attached settings). With an exposure bracketed series, only the 'under-exposed' images get a positive exposure correction, others stay at zero because some data is already clipped.

Even in the case of one or two channels being clipped in Raw, modern Rawconverters do a reasonable job of reconstruction the missing channel data whit their Highlight recovery algorithms.

There is also another potential issue with ETTR, and that has to do with some Rawconverters that introduce color twists when pulling the ETTR exposure of a low contrast scene to a more normal level during the conversion.

Cheers,
Bart

Hi, Bart
"As for determining the Raw headroom to achieve ETTR, a tool like Rawdigger, or even Fast Raw Viewer, is indispensable. "
(Which surprises me, having used the process described for EBTR for a decade without recourse to RawDigger/FRV.  Of course, The technique I am using may not be disclosing "Raw headroom" ...but if not, what is that stuff acting as if it really were useful dynamic range?  That's a totally serious question, by the way...

Another example:

Best regards,
Dave
Logged

uuglypher

  • Newbie
  • *
  • Offline Offline
  • Posts: 17
Re: Raw DR ratings based on one camera!
« Reply #33 on: May 23, 2016, 09:12:21 AM »

Semiconductor mfgs deal with process variability by assigning different model numbers to the units in different sigmas of the output lots.

Hi, Lundberg02,
You state:
"Semiconductor mfgs deal with process variability by assigning different model numbers to the units in different sigmas of the output lots."

 I think I understand what that means, but
do not understand how it accounts for the demonstrable (but definitionally arguable?) breadth of dynamic range of whatever it is that is acting in the role of extra raw-accessible dynamic range off to "the right" of the JPEG-adjusted histogram frames in our different models of camera's.

best regards,
Dave
Logged

uuglypher

  • Newbie
  • *
  • Offline Offline
  • Posts: 17
Re: Raw DR ratings based on one camera!
« Reply #34 on: May 23, 2016, 09:26:02 AM »

Hi Dave
Interesting points but I guess that your audience may be novice users and the intent is to show that there is more headroom shooting raw than JPEG and proving the point that the camera LCD histogram display and the blinkies are based on and only reliable indicators for JPEG camera images?  Of course I may be misunderstanding.

In other words a 'correctly' exposed JPEG will be an underexposed raw, or perhaps more correctly an image with less than optimal exposure.

Exposure Beyond The Right (EBTR) is not a term that I care for as it implies that you can pass the far right 'wall' of any­ histogram which of course is/may be correct for most/all in camera histograms for raw but not necessarily the case for all raw editors due to the potential for behind the scenes activity to present an 'acceptable' on screen rendering

For instance Adobe are among those that apply a baseline correction for specific cameras and this coupled by other background changes with process versions and rendering can lead a user to believe that they may be overexposing when in fact the opposite is true - possibly up to 2 EV.

Others such as RawTherapee seem to show the image close to that captured by the sensor i.e. without much in the way of brightening the image

Most camera exposure meters (and separates) are likely to be calibrated to around 12-14% and I would expect that the you may have a maximum of around +3 stops before clipping with many cameras.  So once you find this point you can meter your important highlight areas and apply the correction without being concerned with the camera histogram display

I also agree with others that large variations with cameras is likely to be variations in illumination, metering or even (rare I think) shutter speed or aperture variations

hi,Tony,
Your first two paragraphs are spot-on! well and concisely expressed!

Your concern regarding the raw converter used may well have merit. My experience over the years has been limited to Adobe Camera Raw in its various iterations, except for having started with some plug-in raw converters prior to the advent of ACR. ACR was a breath of fresh air hat has continued to improve phenomenally as time has gone on.

Cheers,
Dave
Logged

BartvanderWolf

  • Sr. Member
  • ****
  • Online Online
  • Posts: 6702
Re: Raw DR ratings based on one camera!
« Reply #35 on: May 23, 2016, 11:20:26 AM »

Of course, The technique I am using may not be disclosing "Raw headroom" ...but if not, what is that stuff acting as if it really were useful dynamic range?  That's a totally serious question, by the way...

Since you seem to base the 'analysis' on the JPEG histogram, it could be many things, ranging from actual Raw headroom to recreated (=invented) highlight detail from clipped colorplanes. Since JPEG histograms include Whitebalancing, Contrast, Saturation, and Sharpening adjustments, there may be a significant disconnect with the underlying Raw histograms.

JPEGs are processed data, not Raw data. Many different JPEGs (with their different histograms) can be produced from Raw data.

That's why tools like RawDigger or Fast Raw Viewer will be a great help in telling what it is that you are actually looking at. If the Raw channels are underexposed, it is unused Raw headroom, if one or more channels are clipped, it is Highlight recovery/reconstruction.

I've attached 2 FRV screen print crops which show 2 cases of ETTR in Raw. The camera JPEGs showed blinking highlights, but I know from experience how much I can allow to them blink, or I'll bracket.

The first example has a huge Dynamic range (exceeding the Camera's capabilities, with clipping in both the shadows and highlights), although the lower part is going to be rendered almost black anyway, and the specular highlights are only in a few pixels fully clipped in three channels (clipping indicators shown) at the same time,  so no color accurate recovery is possible in those isolated pixels, nor is it needed.

The second example shows that the front lit scene dynamic range was less than the camera can handle, with only 5 green Bayer CFA channel pixels clipped in Raw, and none at the underexposure side, so full color accuracy was possible in the highlights because all Raw channels were present and exposed to the right (of the Raw histogram).

Very easy to pick the correct exposure from a bracketed series.

I've searched for an underexposed file, but I could not find that many I can show. But in case one does underexpose in Raw, then FRV can apply an Auto-expose correction if there is Raw headroom, and I've set the program's defaults to 1/6th of a stop accuracy. Then in a bracketed series one picks the most exposed file with the smallest Auto exposure boost before reaching significant clipping which would result in zero auto exposure correction. Easy as pie.

Cheers,
Bart
Logged
== If you do what you did, you'll get what you got. ==

BartvanderWolf

  • Sr. Member
  • ****
  • Online Online
  • Posts: 6702
Re: Raw DR ratings based on one camera!
« Reply #36 on: May 23, 2016, 11:50:00 AM »

Your concern regarding the raw converter used may well have merit. My experience over the years has been limited to Adobe Camera Raw in its various iterations, except for having started with some plug-in raw converters prior to the advent of ACR. ACR was a breath of fresh air hat has continued to improve phenomenally as time has gone on.

Hi Dave,

ACR (Process version 2012) applies massive tone curve corrections (even exposure boosts) to some Raw camera data. The resulting output (if not adjusted) is also significantly compressed in the highlights (rendering them lifeless, without any punch). So out of camera previews do not show a reliable headroom and histograms are not reliable, and what seems to be highlight recovery, may be something else (either not recovery but reduced prior HL compression or reduced Exposure boost, or an attempt to reconstruct highlights from clipped data).

In addition, ACR PV2012 offers a significant reconstruction of blown highlights, but they have not much basis in Raw captured data. You are leaning on ACRs capability to make a plausible highlight reconstruction, which is fine if it works, but has little to do with dynamic range. All you do is improve shadow detail, because you sacrifice highlight accuracy, which may or may not work. The highlight dynamics and actual colors are compromised in that case.

It's a trade-off, not dynamic range.

Cheers,
Bart
Logged
== If you do what you did, you'll get what you got. ==

Guillermo Luijk

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 1603
    • http://www.guillermoluijk.com
Re: Raw DR ratings based on one camera!
« Reply #37 on: May 23, 2016, 12:36:44 PM »

My experience over the years has been limited to Adobe Camera Raw in its various iterations, except for having started with some plug-in raw converters prior to the advent of ACR. ACR was a breath of fresh air hat has continued to improve phenomenally as time has gone on.

ACR is a RAW developer, and a good one. It's a more than inadequate analyse tool. Whatever you can find out with ACR, it is just a reflection of the reality. In other words: you are using ACR for something it was never designed. All your pictures just show that there is highlight headroom from camera JPEG (or from a basic RAW development, i.e. ACR set to 0.0 in exposure) to the RAW data, nothing new, and unnecesarily ellaborating all that EBTR theory. But you don't know exactly how much headroom actually exists for the many effects mentioned (WB, contrast, recovery,...).

This is the very first slide I used to display when I taught workshops on RAW:



Users trying to find out what's going on through camera JPEG, ACR or Photoshop are just looking at a mirrored RAW reality over the wall in Plato's cave. If you are a RAW shooter, and you really want to take RAW shooting to the more precise limits (something that with today's sensors is becoming unnecesary), you have to use RAW analysing tools instead of RAW displaying ones.

Regards
Logged

TonyW

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 361
Re: Raw DR ratings based on one camera!
« Reply #38 on: May 23, 2016, 02:08:44 PM »

You may come to realise, with the benefit of hindsight that the thread (at least after the first post) may have been better posted in the beginners section. 

As I am sure you may now realise there are some very experienced 'Photo Grannies' on this site (no offence intended guys  ;D) to whom your comments could be seen as trying to teach the sucking of eggs.  The comments offered by them are right on the ball.

Nobody is arguing the fact that we cannot rely on the camera LCD histogram to report anything but JPEG.  Further I suspect that all the respondents and many others here have undertaken practical testing to establish camera limits relating to clipping and are aware of how much headroom available over meter reading of important highlights

AFAIK the original and subsequent articles about ETR only addressed raw capture and there was no mention of this being particularly useful for JPEG capture? 

....Your concern regarding the raw converter used may well have merit. My experience over the years has been limited to Adobe Camera Raw in its various iterations, except for having started with some plug-in raw converters prior to the advent of ACR. ACR was a breath of fresh air hat has continued to improve phenomenally as time has gone on.

Cheers,
Dave
As already stated by Bart and Guillermo ACR is not a good tool for analysis. Some examples you may care to look at images SOOC.  Default settings ACR with Camera Neutral profile.  No auto highlight corrections with Raw Therapee:

Upper Left Raw Therapee, upper right ACR defaults.  Bottom left ACR at default, bottom right ACR adjusted to negate baseline corrections and brightening in Process 2012.  The RT and ACR adjusted images match closely those images in Raw Digger



This image illustrates FRV view of an underexposed image in raw and how JPEG brightens (still UE but obviously brighter than the raw).  I believe this to be close enough to -2 stops under and the correction shown in last frame.  You need to wait about 5 seconds between frames 1st FRV raw, 2nd FRV JPEG, 3rd +2 stops correction applied



Finally a first test using a Sekonic spot meter and associated software to calibrate the meter to match the camera sensor characteristics.  This involved a series of 5 exposures, Normal, -4, -8, +4, +8 of a Colour Checker Passport with the software producing the chart.  As you should see the DR is 12 EV from 0 - 255.  This agrees with Bill Claffs testing on a number of Pentax 645's.  Clipping points I really need to set after a little fine tuning as I believe that +3.5 EV is somewhat optimistic  ;).







Logged

bjanes

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 3234
Re: Raw DR ratings based on one camera!
« Reply #39 on: May 23, 2016, 02:12:47 PM »

Hi, Bill,
I appreciate your comments and and certainly am aware of the pervasive concern that perhaps sacrificing some DR may be preferred to loosing some detail to clipped highlights in the normalized EBTR exposure. The saving grace of EBTR is that the described method of determining the ERADR --the extra raw-accessible dynamic range - if practiced with reasonable care at the chosen ISO - is a guar-an-day-um-tee that highlights will not be blown. It is the common mantra that clearly identifies those who have not actually tried to determine ERADR and practice EBTR.
Here is another example of EBTR:

Camera makers provide "highlight headroom" to prevent clipped highlights. They could do this by adjusting the metering calibration, but this would complicate the use of hand held light meters, so they provide highlight headroom by adjusting the ISO rating of the sensor. The ISO 12232:1998 saturation standard is the easiest to understand, but is no longer used by most camera makers. However, DXOmark continues to use it for determining the ISO sensitivity when dealing with raw files; for details of the DXO method look here. The Wikipedia article filmspeed has a good section on the current standards and also covers the original 1998 standard.

The 1998 saturation standard specifies that when an 18% reflective target is exposed according to a standard light meter reading, the sensor will achieve 18%/sqrt(2) or 12.7% saturation, which allows 0.5 EV of headroom as compared to 18%. Note that 18% is 2.47 EV below 100%. According to this standard, if you expose an 18% gray card according to the light meter reading, the raw file should have 12.7% saturation, which is 119 in sRGB. One way of placing the highlights of the scene is to take a spot meter reading of the highlights and add about 2.5 EV to the indicated reading.

As an example, I photographed a gray card with my D800e using both JPEG and raw. I rendered the raw file with ACR 9.5.1 using the Adobe Standard profile and PV2012, both with the default exposure and negative exposure of -0.35 EV to account for the BaselineExposure correction that ACR uses for this camera. The results are shown in the table below. The camera JPEG rendered 18% gray at a sRGB value of 153, well above the nominal value of 119. The default ACR rendering was 157 and application of -0.35EV exposure in ACR gave a more reasonable value of . Rawdigger gave a 14 bit reading of 1970 in the green channels, which is 12.52% saturation. This is very close to the sSAT 12.7%. To complete the analysis, one could do an exposure series and note the correlation between the camera histogram and blinking highlights with clipping as shown by Rawdigger.

DXO lists the Manufacturer rated ISO vs Measured ISO of the cameras they test. Values for the Nikon D810 are 64 and 47 respectively and these values for the D800e are 100 and 73; the difference is 0.45 EV (log 100/73, base 2), which is consistent with my data. Values for the Canon 5Ds are 100 and 77 and those for the 1Dx are 100 and 80. Phase One rates the IQ180 at 100 whereas the measured is 29. These differences are to allow for highlight headroom, which seems excessive for the IQ180.

I invite you to do a similar analysis for your camera. Personally, I find the ERADR term confusing and unnecessary. Why not raw headroom?

Regards,
Bill
« Last Edit: May 23, 2016, 02:28:00 PM by bjanes »
Logged
Pages: 1 [2] 3   Go Up