The Optimum Digital Expsoure
-
-
New Article Announcements & Discussionson: November 18, 2020 at 7:17 pm
Bob DiNatale has shared with us today an extensive article on Optimum Digital Exposure. Many of us know this as ETTR, but Bob takes it further. Check it out HERE
Kevin Raber
Owner and Publisher of photoPXLRe: The Optimum Digital ExpsoureReply #4 on: November 19, 2020 at 9:51 pmAlways good to keep thinking about optimum exposure. I remember reading an earlier version of this article on the Luminous Landscape in 2014, and there was a discussion pointing out that “the top 3% contains 50% of your captured data!” was a myth. This idea is still doing the rounds. A search has brought up this: https://photomorrobay.wordpress.com/ but there are a lot of other references around if you look. David
Re: The Optimum Digital ExpsoureReply #5 on: November 19, 2020 at 11:34 pmDavid,
Thanks for the link. I found it interesting… but, I never said nothing about histograms or zones.
I’m an empirical kind of guy. We all can keep reading, or, we can do our own testing, or, we can stop the chase and watch this video by George Jardine “A Few Thoughts On Exposure & Tone Mapping“. In my mind, his video is the definitive work and best explanation I’ve seen on this subject.
You mentioned, “This idea is still doing the rounds” … maybe after watching George’s video, the idea should stop going round and we should get on with our photography!
Fun sharing thoughts,
Thank Again, BobRe: The Optimum Digital ExpsoureReply #6 on: November 20, 2020 at 4:57 amI watched George’s video and as usual, he does a fine job of explaining things simply, but…
Since ACR/Lr added Process Version 2012, it’s actually a lot more complicated largely because of Local Laplacian Filters…wait, WHAT?
What PV 2012 introduced is image sensitive range adjustments. Originally developed fo dealing with HDR images, the engineering elves at Adobe tweaked some of the algorithms to work on standard range digital captures. This Lightroom Journal blog post from Tom Hogarty explains is a bit: Magic or Local Laplacian Filters?
The work done by Adobe engineers and fellows from MIT & University College in London wrote a paper called Local Laplacian Filters: Edge-aware Image Processing with a Laplacian Pyramid. If you are a glutton for techie ness, you can read the paper HERE.
In a nut shell, what PV 2012 did was to modify the tone mapping of raw images and alter the nature of the way Highlights and Shadows worked to bing out what otherwise might be difficult image data. Highlights is a modern form of high light recovery that compresses image data but allows you to tease the data apart. Shadows is an updated algorithm that replaced Fill Light and helps boost shadow detail.
The net result is that tone mapping is a bit more complicated post PV 2012 because the actual “numbers” may mean different things to different images. That’s the image sensitive adaptive nature of PV 2012.
And PV 2012 actually made ETTR even easier to employ because PV 2012 can preserve a huge amount of highlight data without clipping. Clearly, complete saturation of a photo site will result in clipping, but what may at first appear as clipping is actually what I call “clumping”, meaning a whole lot of image data clumped at near clipping without actual clipping.
At that point you simply need to use the Highlights slider (either globally or locally) in combination with Exposure and Whites to tease the highlight detail out.
Similar images adjustments using the Shadows control in conjunction with the Blacks slider allows for seat separation in the shadow regions–which can often be amplified by adding Clarity (ideally locally as apposed to globally).
Of course, ETTR presupposes that the scene you are shooting has luminance values that fall within the dynamic range of your sensor–and don’t forget, you lose a stop of dynamic range for every stop you push ISO over the native optimal ISO of your sensor.
After Micheal wrote that original article–which was what Micheal learned from Thomas Knoll after taking a trip shooting together–he got a lot of grief largely because he made the mistake of mixing his metaphors when talking about bit depth and signal to noise ratios. A lot of people misunderstood what Michel (paraphrasing Thomas) was trying to get across–don’t shoot digital like you used to shoot chrome film, under expose to keep from blowing out the highlights. I wrote up a web page talking about the ETTR myth: Un-debunking ETTR
I took a quick look at Bob’s article, but I need to read it during the light of day (not late at nite).
Re: The Optimum Digital ExpsoureReply #9 on: November 21, 2020 at 12:17 pm… After adjusting the maximum acceptable exposure with aperture and shutter speed, and ETTR cannot be reached with native ISO, it is safer (risk of highlight clipping) to stay at metered ISO than increasing ISO to move the histogram to the right.
Short answer – yes, you are by-in-large correct.
First, thank you for mentioning the gorilla in the room – “without clipping the relevant highlights.” IMHO, the danger of trying to nail the perfect ETTR exposure, whatever method you use, is the accidental clipping of highlights. A little underexposure can easily be corrected in post-processing.
Details
I direct you to my article Noise, ISO and Dynamic Range Explained, in particular, Figure 4 which I’ve attached here. The camera has two dynamic ranges – the sensor DR and the ADC (= Analog-to-Digital Converter, which is the quantizer) DR. ISO sets the mapping of the sensor’s DR to the ADC DR, as illustrated in Figure 4.
Base ISO is the ISO value where the full sensor DR is contained within the ADC DR. (The definition of “base ISO” is the ISO value that maximizes overall DR.) Increasing ISO pushes the top end of the sensor’s DR off the top of the ADC DR, resulting in a 1 stop loss of overall DR for every doubling of ISO (which you will see in DPReview and DxOMark DR test data). ADC degradations are perceptible only at the bottom end of the ADC’s DR, which isn’t being used at ISOs above base ISO. So you are correct in the sense that above the base ISO ADC quantization distortions are just not in play.
However, photon and sensor noise SNR is determined by exposure (shutter speed and aperture). Forget about ISO and quantization levels for a moment. For a given shooting condition, to maximize SNR (reduce relative image noise) we want to increase exposure as much as possible without clipping at the sensor. There are two cases:
1) Sensor-limited (base ISO): In a bright environment, we can increase exposure so the image is at the top of the sensor’s DR, and then we need to use base ISO to map the full image range into the ADC ADC. When shooting at base ISO the ADC quantization distortion can be perceptible at the very bottom (like 10 stops below full scale). Nonetheless, ETTR is just the technique we use to maximize exposure with the primary effect of reducing photon and sensor noise, not quantization distortion. The cost of underexposing is a loss of overall DR. However, the overall DR at base ISO (= the sensor’s DR) for modern cameras is ~13 stops and the vast majority of images don’t use that full DR. A little underexposure won’t kill your image, but clipping can!
2) Exposure-limited (higher ISO): In darker environments, exposure is limited by aperture and/or shutter speed, not the sensor. In these cases, we can’t use the full sensor DR, but we still want to collect as many photons as possible. The usable part of the sensor DR (now limited by exposure) is well within the ADC DR. So, we have latitude in the setting of ISO. As long as you don’t set ISO too high so as to clip the image at the ADC, or too low so as to push the image down to the bottom of the ADC DR, images shot at the same exposure but different ISOs are identical after post-processing correction. In that sense you are correct!
The bottom line is that we always want to shoot at the largest exposure possible to maximize photon count. ETTR is just a technique to achieve that goal. It is 100% aligned with that goal in the sensor limited case, but there is latitude under exposure-limited conditions. The proposal, however, that in exposure-limited conditions you also need to fine-tune ISO to push the histogram all the way to the right, is not justified by image quality concerns, and introduces the possibility of ADC clipping. IMHO, that’s just not good advice. It is precisely in the exposure-limited case we have a surplus ADC dynamic range so there is no need to chance ADC clipping.
JSS
Re: The Optimum Digital ExpsoureReply #10 on: November 21, 2020 at 4:24 pmI watched George’s video and as usual, he does a fine job of explaining things simply, but…
Since ACR/Lr added Process Version 2012, it’s actually a lot more complicated largely because of Local Laplacian Filters…wait, WHAT?
What PV 2012 introduced is image sensitive range adjustments. Originally developed fo dealing with HDR images, the engineering elves at Adobe tweaked some of the algorithms to work on standard range digital captures. This Lightroom Journal blog post from Tom Hogarty explains is a bit: Magic or Local Laplacian Filters?
The work done by Adobe engineers and fellows from MIT & University College in London wrote a paper called Local Laplacian Filters: Edge-aware Image Processing with a Laplacian Pyramid. If you are a glutton for techie ness, you can read the paper HERE.
In a nut shell, what PV 2012 did was to modify the tone mapping of raw images and alter the nature of the way Highlights and Shadows worked to bing out what otherwise might be difficult image data. Highlights is a modern form of high light recovery that compresses image data but allows you to tease the data apart. Shadows is an updated algorithm that replaced Fill Light and helps boost shadow detail.
The net result is that tone mapping is a bit more complicated post PV 2012 because the actual “numbers” may mean different things to different images. That’s the image sensitive adaptive nature of PV 2012.
And PV 2012 actually made ETTR even easier to employ because PV 2012 can preserve a huge amount of highlight data without clipping. Clearly, complete saturation of a photo site will result in clipping, but what may at first appear as clipping is actually what I call “clumping”, meaning a whole lot of image data clumped at near clipping without actual clipping.
At that point you simply need to use the Highlights slider (either globally or locally) in combination with Exposure and Whites to tease the highlight detail out.
Similar images adjustments using the Shadows control in conjunction with the Blacks slider allows for seat separation in the shadow regions–which can often be amplified by adding Clarity (ideally locally as apposed to globally).
Of course, ETTR presupposes that the scene you are shooting has luminance values that fall within the dynamic range of your sensor–and don’t forget, you lose a stop of dynamic range for every stop you push ISO over the native optimal ISO of your sensor.
After Micheal wrote that original article–which was what Micheal learned from Thomas Knoll after taking a trip shooting together–he got a lot of grief largely because he made the mistake of mixing his metaphors when talking about bit depth and signal to noise ratios. A lot of people misunderstood what Michel (paraphrasing Thomas) was trying to get across–don’t shoot digital like you used to shoot chrome film, under expose to keep from blowing out the highlights. I wrote up a web page talking about the ETTR myth: Un-debunking ETTR
I took a quick look at Bob’s article, but I need to read it during the light of day (not late at nite).
Jeff,
First, thank you for your time and thoughts. We have met before and discussed some of these concepts. You may remember me, I’m the short fellow with the wavey hair.I understand PV 2012 is all about process benefits and was a big change (…but I must admit I didn’t know it was the “Local Laplacian Filters”). However, this processing all comes after capturing an optimum exposure which would benefit greatly from the advancement in PV 2012.I reference a discussion with Eric (Madman) Chan in an Adobe forum in 2012:BobDiN Community Beginner , Mar 13, 2012I have been using “Auto” as the 1st step then continue adjustments by image as needed– Do you agree with this approach?– Does “Auto-tone” loose PV2012’s powerful adaptive “Highlights” and “Shadows” capabilities?I guess the simple question is “Does “Auto-tone” take advantage of the adaptive “Highlights” of PV2012 while still finding a White & Black point?”MadManChan2000 Adobe Employee , Mar 19, 2012Yes, Auto Tone essentially works top-down.No, Auto Tone does not lose PV 2012’s adaptive highlights & shadows capabilities. Instead, it leverages them.Yes, it takes advantage of the adaptive highlights/shadows of PV2012 while still finding a white & black point.As for your post, I don’t know how to answer all your thought paragraphically so I will try to express my thing by segment. Any of your subsequent thoughts will be appreciated“I watched George’s video as usually, he does a fine job of explaining things simply, but…”I understand there has been a lot of advancements in processing software algorithms but the all happens after digital capture.“In a nut shell, what PV 2012 did was to modify the tone mapping of raw images and alter the nature of the way Highlights and Shadows worked to bring out what otherwise might be difficult image data. Highlights is a modern form of high light recovery that compresses image data but allows you to tease the data apart. Shadows is an updated algorithm that replaced Fill Light and helps boost shadow detail.”The updated “Fill Light” algorithm seems it would be especially beneficial with ETTR’s placement of shadow data above noise.“The net result is that tone mapping is a bit more complicated post PV 2012 because the actual “numbers” may mean different things to different images. That’s the image sensitive adaptive nature of PV 2012.”As I understand it, PV2012 create data from data which makes processing of each digital capture image-dependent! Which is why my first ACR step is to “AutoTone”… to set out Adobe’s it’s Laplacian/Lilliputians fairies to tie down the Gulliver-ian data from an optimum exposure and optimally process the data of that given capture.“Of course, ETTR presupposes that the scene you are shooting has luminance values that fall within the dynamic range of your sensor–and don’t forget, you lose a stop of dynamic range for every stop you push ISO over the native optimal ISO of your sensor.”Hmm, I respect your knowledge but empirically in all my optimum-exposure shooting over the last 7 years, I have not noticed this in my photographic results. Maybe I’ve benefited from the Lilliputians in PV2012 😊.I need to run my “Empirical Proof” test from my book at 2 extreme ISOs to validate.“After Michael wrote that original article–which was what Michael learned from Thomas Knoll after taking a trip shooting together–he got a lot of grief largely because he made the mistake of mixing his metaphors when talking about bit depth and signal to noise ratios. A lot of people misunderstood what Michel (paraphrasing Thomas) was trying to get across–don’t shoot digital like you used to shoot chrome film, under expose to keep from blowing out the highlights.“I agree with the misunderstanding of the chrome-film analogy… I’ve run into Zone System people who shoot their digital captures by shooting for minimum exposure for maximum black!Jeff, Your Thoughts on ThisWhen the shadows in a scene are captured at EV+2 (thus placing the shadow at Luminance of 40+), would you still call luminance at that value as being “shadows”?Thanks again for your time and thoughtsBobRe: The Optimum Digital ExpsoureReply #11 on: November 21, 2020 at 6:03 pmJeff,
First, thank you for your time and thoughts. We have met before and discussed some of these concepts. You may remember me, I’m the short fellow with the wavey hair.
I understand PV 2012 is all about process benefits and was a big change (…but I must admit I didn’t know it was “Local Laplacian Filters”). However, this processing all comes after capturing an optimum exposure which would benefit greatly from the advancement in PV 2012.
I reference a discussion with Eric (Madman) Chan in an Adobe forum in 2012:
BobDiN Community Beginner , Mar 13, 2012
> I have been using “Auto” as the 1st step then continue adjustments by image as needed
– Do you agree with this approach?
– Does “Auto-tone” loose PV2012’s powerful adaptive “Highlights” and “Shadows” capabilities?
> I guess the simple question is “Does “Auto-tone” take advantage of the adaptive “Highlights” of PV2012 while still finding a White & Black point?”MadManChan2000 Adobe Employee , Mar 19, 2012
> Yes, Auto Tone essentially works top-down.
> No, Auto Tone does not lose PV 2012’s adaptive highlights & shadows capabilities. Instead, it leverages them.
> Yes, it takes advantage of the adaptive highlights/shadows of PV2012 while still finding a white & black point.= = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
As for your post, I don’t know how to answer this paragraphically so I will try to express my thing by segment.
1. “I watched George’s video as usually, he does a fine job of explaining things simply, but…”
…I understand there has been a lot of advancements in processing software algorithms but the all happens after digital capture.2. “In a nut shell, what PV 2012 did was to modify the tone mapping of raw images and alter the nature of the way Highlights and Shadows worked to bring out what otherwise might be difficult image data. Highlights is a modern form of high light recovery that compresses image data but allows you to tease the data apart. Shadows is an updated algorithm that replaced Fill Light and helps boost shadow detail.”
The updated “Fill Light” algorithm seems it would be especially beneficial with ETTR’s placement of shadow data above noise.3. “The net result is that tone mapping is a bit more complicated post PV 2012 because the actual “numbers” may mean different things to different images. That’s the image sensitive adaptive nature of PV 2012.”
As I understand it, PV2012 create data from data which makes processing of each digital capture image-dependent! Which is why my first ACR step is to “AutoTone”… to set out Adobe’s it’s Laplacian/Lilliputians fairies to tie down the Gulliver-ian data from an optimum exposure and optimally process the data of that given capture.4. “Of course, ETTR presupposes that the scene you are shooting has luminance values that fall within the dynamic range of your sensor–and don’t forget, you lose a stop of dynamic range for every stop you push ISO over the native optimal ISO of your sensor.”
Hmm, I respect your knowledge but empirically in all my optimum-exposure shooting over the last 7 years, I have not noticed this in my photographic results. Maybe I’ve benefited from the Lilliputians in PV2012 😊.
I need to run my “Empirical Proof” test from my book at 2 extreme ISOs to validate.5. “After Michael wrote that original article–which was what Michael learned from Thomas Knoll after taking a trip shooting together–he got a lot of grief largely because he made the mistake of mixing his metaphors when talking about bit depth and signal to noise ratios. A lot of people misunderstood what Michel (paraphrasing Thomas) was trying to get across–don’t shoot digital like you used to shoot chrome film, under expose to keep from blowing out the highlights.”
I agree with the misunderstanding of the chrome-film analogy… I’ve run into Zone System people who exposure their digital captures by shooting minimum exposure for maximum black!= = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Jeff, Your Thoughts on This Question
When the shadows in a scene are captured at EV2 (thus placing the shadow at Luminance 40+), would you still call luminance at that value as being “shadows”?Thanks again for your time and thoughts
Bob
- You must be logged in to reply to this topic.