“Expose to the Right” & relation to ISO Invariance

[Ray]

 
Most papers are doing great when they show 7 stops of DR so you've got some latitude to play with in PP.  Heck most cameras from just a few years ago were lucky to capture 9 stops of DR...

Jack

Jack,
I hope you are not implying that there is no need for more than 7 stops of DR in the original image if one intends to print.

Fortuitously, that DR limitation of the print seems to match pretty closely the 'static' DR limitation of the human eye.
The following explanation is from Wikipedia.

"The retina has a static contrast ratio of around 100:1 (about 6.5 f-stops). As soon as the eye moves (saccades) it re-adjusts its exposure both chemically and geometrically by adjusting the iris which regulates the size of the pupil."

When we process an image of a contrasty scene for monitor display or for printing, we compress the DR rather than reduce it. In other words, we raise the shadows in post processing in order to mimic the effect of the dilating pupil of the eye that occurred when we viewed the real scene before we photographed it. This is why I consider the DR capabilities of a camera very important.

[bernie west]

I didn't see any raws posted.......

He posted a screen shot of his development settings in Lightrooom.

[bjanes]

5 stops! I don't think my Canon would come close to that, in fact I know it can't. LR can recover, rebuild, whatever you want to call it, 5 stops (darn, 1 stop) from true raw clipping?
I'd have guessed, in my case, nor more than 1/2 stop. Perhaps less.

I think you and Bart are looking at different scenarios. If I expose a Stouffer wedge so that step 1 (0.05 OD) is at clipping and then increase exposure further I can recover perhaps 1 stop. However, if I block off the brightest 15 steps (5 stops), I can expose so that step 15 is just short of clipping and then normalize the image with the raw converter to reproduce the appearance of those steps.

Bill

[Jack Hogan]

If a sensor has a 14 stop acceptable SNR (the engineering definition) then by recovering 5 stops you've essentially got 9 (14-5) to display.  Most papers are doing great when they show 7 stops of DR so you've got some latitude to play with in PP.  Heck most cameras from just a few years ago were lucky to capture 9 stops of DR...

Jack,
I hope you are not implying that there is no need for more than 7 stops of DR in the original image if one intends to print.

Your prayers have been answered Ray, I was not implying that  Merely pointing out that a 5 stop push at base ISO, resulting in about a 9 stop engineering DR with current Exmor cameras, may still provide quite a usable image, depending on uses.  Here for instance is a controlled 5 stop push on a D810 by Jim Kasson.

Note however that these captures are meant to show relative ISOlessness and they are not necessarily exposed to the right per this thread's context, potentially making the base ISO image 5 stops 'underexposed'.  In order to properly ETTR this (near) ISOless camera in static tripod conditions one would want to bump exposure up 5 stops, producing the best IQ possible at ISO 64 (and presumably blowing all higher ISO captures).

Jack

[Guillermo Luijk]

Sensors are pretty well linear devices, so you can go as low as you can stand in terms of SNR if your converter is well behaved without penalty (it turns out that LR is not but others are).  If a sensor has a 14 stop acceptable SNR (the engineering definition) then by recovering 5 stops you've essentially got 9 (14-5) to display.  Most papers are doing great when they show 7 stops of DR so you've got some latitude to play with in PP.  Heck most cameras from just a few years ago were lucky to capture 9 stops of DR...

Jack

Some time ago I measured the DR of my monitor and printing paper (just a regular cheap one with a cheap Epson printer), under regular indoor lighting conditions. I would have liked to measure a projector as well but I have none.

The resulting orders of magnitude were:

Monitor: 6,7 stops





Paper: 4,3 stops





Ambient light has a great influence in received DR. Specially a monitor will benefit from a big improvement when all the lights are turned off (deep blacks).

Regards

[Bart_van_der_Wolf]

Some time ago I measured the DR of my monitor and printing paper (just a regular cheap one with a cheap Epson printer), under regular indoor lighting conditions.

Hi Guillermo,

I think you were measuring how the camera translates subject contrast to ADUs (Analog Digital Units, or DNs  )

There is a difference between:
1. Subject contrast (as measured e.g. with an Exposure meter, Densitometer, or Spectrometer),
2. Camera system contrast (includes/combines optical transmission characteristics, and sensor characteristics) into an MTF response, and
3. Sensor characteristics (relatively easy to isolate by studying the Raw data).

Raw conversion effects are then a whole other can of additional worms.

The ETTR benefits/issues/opportunities are with 3. sensor characteristics. Combining 1 and 2 may make it difficult to see which element is responsible for what exactly. That's why focusing on 3. may help to see the effect on 2.  better.

Cheers,
Bart

[Guillermo Luijk]

In fact I used the camera sensor as a high precision tri-band exposure meter. White balancing the RAW data over the white patch helped to find out that the blacks on my (non-calibrated) monitor were a bit more bluish than its whites. The opposite happened in the print test, the ink was a bit more reddish than the blank paper.

This is something an exposure meter can't provide. The RGB sensor's CFA permitted to get one step closer to a genuine spectral analysis.

Regards

[Bart_van_der_Wolf]

In fact I used the camera sensor as a high precision tri-band exposure meter.

But what factor did the lens (and mirrorbox + filterstack with IR and OLPF filters) and interaction with the area sampling photosites of the sensor play? By adding a lens into the MTF equation, the whole system response changes the isolated sensor response. Imaging a white and a black patch in the same image will cause veiling glare in the lens, which differs between lenses, so one would need to calibrate that influence out.

I'm not saying it is not useful, it is useful in the end, but it clouds a clear view on the ETTR effects which are purely sensor and supporting electronic circuits related. It's a bit similar to the covering up of clipping or other tonecurve adjustments that Raw processors may introduce. It's better to cut them out of the equation if one wants to understand the sensor's role in isolation, and just study the Raw data (before demosaicing).

Cheers,
Bart

[Guillermo Luijk]

The influence of the lens system in the relative photon count, i.e. in the measured dynamic range between both patches (the brightest and darkest colour the devices under test can produce), is null since both patches are measured in a single capture and linearly processed. Those RAW histograms (just white balanced) are proportional to the number of photons impacting the observer's eyes.

Regards

[sandymc]

He posted a screen shot of his development settings in Lightrooom.

Lightroom does a whole host of processing behind the scenes to try to make images look better - "content aware processing", etc. If the raws could be posted, it might be possible to do more than speculate. BTW, the screenshot appears to show the file as DNG, so apparently not the original raws anyway. Unless Canon have suddenly found religion on the subject of DNG 

[digitaldog]

Lightroom does a whole host of processing behind the scenes to try to make images look better - "content aware processing", etc. If the raws could be posted, it might be possible to do more than speculate. BTW, the screenshot appears to show the file as DNG, so apparently not the original raws anyway. Unless Canon have suddenly found religion on the subject of DNG  

I found the so called 'religion' of DNG, so what? The data is as raw as the original, it makes zero difference in the results obtained in my tests. What would be gained by having those DNG's? The results of the ISO 800 speak for themselves and as to why, it's been explained. That LR does processing behind the scenes is also IMHO not pertinent unless the development of raws isn't a fact in all this, I believe it is. The facts about actual raw clipping values obtained from RawDigger was also provided.  And as Bernie pointed out, the development settings you missed were provided. So I'm at a loss as to what else is necessary for you to continue this discussion about ETTR and ETTR+D.

[sandymc]

I found the so called 'religion' of DNG, so what? The data is as raw as the original, it makes zero difference in the results obtained in my tests. What would be gained by having those DNG's? The results of the ISO 800 speak for themselves and as to why, it's been explained. That LR does processing behind the scenes is also IMHO not pertinent unless the development of raws isn't a fact in all this, I believe it is. The facts about actual raw clipping values obtained from RawDigger was also provided.  And as Bernie pointed out, the development settings you missed were provided. So I'm at a loss as to what else is necessary for you to continue this discussion about ETTR and ETTR+D.

The difference are most probably post processing, either in-camera or in a raw processor; I was curious to either confirm or deny that hypothesis. That's only possible with the original files. To me, it would seem better to take a look at the actual files rather than speculate for 8 pages. But that's me.  I'm weird that way - I like hard data. Mea culpa.

[Jack Hogan]

Some time ago I measured the DR of my monitor and printing paper (just a regular cheap one with a cheap Epson printer), under regular indoor lighting conditions.

Cool.

[Bart_van_der_Wolf]

The difference are most probably post processing, either in-camera or in a raw processor; I was curious to either confirm or deny that hypothesis. That's only possible with the original files. To me, it would seem better to take a look at the actual files rather than speculate for 8 pages.

I agree, it's the absence of concrete data that needlessly/purposely drags the 'discussion' on to no resolve, with only some hints at files being (not) clipped, or exposed to the right (but cropped so they cannot be verified visually) or not (anybody's guess) without measurement data.

I'll see f I can find the time to fill in that gap, and produce some examples, although I can only produce Canon files (ISO variant and thus not really on topic). So maybe I'll just simulate the data (and take the critique that it's not based on a known Raw format for granted).

Cheers,
Bart

[Bart_van_der_Wolf]

The influence of the lens system in the relative photon count, i.e. in the measured dynamic range between both patches (the brightest and darkest colour the devices under test can produce), is null since both patches are measured in a single capture and linearly processed.

Hi Guillermo,

When both white and black patches are measured/photographed together, then veiling glare (with a variable amount depending on the lens coatings and barrel design) will reduce contrast. Potentially, although you seem to have tried to avoid it, additional surface reflections of the patches will also reduce the contrast.

It's better to fill the frame with a single uniform brightness, and record (with a calibrated Photon Transfer Curve) the number of Photons (or if the same gain is used then the ADU's will suffice) that were actually recorded (can be derived from the standard deviation and the ADC gain). Then change the exposure time and measure the same.

Care must be taken to exclude Vignetting and uneven illumination from skewing the Raw counts of the same photosite positions, because they increase the apparent noise level. It's even more accurate if two identical frames are used per measurement, which allows to subtract them in quadrature to eliminate non-random noise, which leaves only photon shot noise.

Cheers,
Bart

[bernie west]

Lightroom does a whole host of processing behind the scenes to try to make images look better - "content aware processing", etc. If the raws could be posted, it might be possible to do more than speculate. BTW, the screenshot appears to show the file as DNG, so apparently not the original raws anyway. Unless Canon have suddenly found religion on the subject of DNG 

This has nothing to do with me pointing out your "jpg" answer was not applicable.  Your "jpg" answer is still not applicable.

[sandymc]

This has nothing to do with me pointing out your "jpg" answer was not applicable.  Your "jpg" answer is still not applicable.

Yes, the absence of posted raws or any screenshots that showed CR2s fooled me. My bad. But post processing is post processing. Whether its in-camera or in a raw processor on a PC doesn't make much difference. Other than if we had the raws it might be possible to work out what's happening whereas with in-camera processing we couldn't.

[Guillermo Luijk]

Hi Guillermo,

When both white and black patches are measured/photographed together, then veiling glare (with a variable amount depending on the lens coatings and barrel design) will reduce contrast. Potentially, although you seem to have tried to avoid it, additional surface reflections of the patches will also reduce the contrast.

It's better to fill the frame with a single uniform brightness, and record (with a calibrated Photon Transfer Curve) the number of Photons (or if the same gain is used then the ADU's will suffice) that were actually recorded (can be derived from the standard deviation and the ADC gain). Then change the exposure time and measure the same.

Care must be taken to exclude Vignetting and uneven illumination from skewing the Raw counts of the same photosite positions, because they increase the apparent noise level. It's even more accurate if two identical frames are used per measurement, which allows to subtract them in quadrature to eliminate non-random noise, which leaves only photon shot noise.

Ok I see now what you meant. Veiling glare was very far from being a problem here. With indoor indirect lighting nothing to worry.

Regarding the noise/vignetting issue, the analysis was done over a centred crop with a quite tele lens to avoid any vignetting. And to minimise the influence of noise I did a HDR composite 3 or 4 stops apart. The ultra-narrow RAW histograms are a proof of this.

Regards

[Bart_van_der_Wolf]

Ok I see now what you meant. Veiling glare was very far from being a problem here. With indoor indirect lighting nothing to worry.

Regarding the noise/vignetting issue, the analysis was done over a centred crop with a quite tele lens to avoid any vignetting. And to minimise the influence of noise I did a HDR composite 3 or 4 stops apart. The ultra-narrow RAW histograms are a proof of this.

Thanks for the additional information.

Cheers,
Bart

[digitaldog]

But post processing is post processing. Whether its in-camera or in a raw processor on a PC doesn't make much difference.

Is having to normalize the ETTR capture in a raw converter post processing and some new revelation to you? Is that what you mean by post processing? As Bernie stated, not that it's necessary if you follow the examples and text provided, this has nothing to do with JPEGs or post processing unless you feel that ETTR captures should have zero processing parameters applied to them in the raw processor. That would seem a rather silly approach.