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Author Topic: “Expose to the right” vs “JPEG Histogram to the right”  (Read 11335 times)

BJL

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There has been much discussion at this site of the idea of “Expose To The Right” [ETTR], but unfortunately it is stated in terms of the “photosite histogram”, with the right end corresponding to photosites at their full well capacity, but that is not directly available. Instead, there are histograms for standard JPEG output at the selected EI, and that is always further to the right, more so as the EI setting is increased above the sensor’s saturation based speed as measured by the ISO definition of SSat (often called “base ISO speed”). It gets worse when people think that pushing that JPEG histogram to the right at elevated EI settings has the same virtues as ETTR.

I am working on a good strategy, based on what the camera’s JPEG histogram or highlight overexposure blinkies tell me. One key is that the difference between the right-hand end of the JPEG histogram and the actual “photosite histogram”, in stops, is the gap between the Exposure Index setting (“ISO setting”) on the camera and the true SSat (base ISO speed) — plus a half stop. Also, we can get that true SSat from DXOL it is what DXO wrongly calls the “true ISO” in the case where the camera is at its lowest normal EI setting.

In this post, just comments on when true ETTR is usually done: with the camera at its minimum normal EI setting. Then as a guideline, one can get the JPEg histogram at the right edge, then increase the exposure by
    “EI - SSat + 1/2”.
For example, if the minimum EI setting is 100 but the SSat measure there  is 70 (1/2 stop less), the JPEG histogram is one stop to the right of the photosite histogram, and so you could increase exposure one stop beyond the “JPEG Histogram To The Right” level.

Also, you can probably use the highlight blinkies to find that “Histogram To The Right” level: reduce exposure till the blinkies disappear (except maybe in specular highlights that you do not mind being blown out) than add one stop of exposure (probably meaning doubling the exposure duration).

I use the blinkies method cautiously, only adding half a stop.


Details later (at least if there is any interest) like where that half stop adjustment comes from.
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digitaldog

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #1 on: March 13, 2018, 09:14:47 PM »

Use the right tool for the right job:
https://www.rawdigger.com
With respect and some love to Michael who coined the term ETTR, it's got to go away. It is optimal exposure for raw data (OEFR?). ;)
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Andrew Rodney
Author “Color Management for Photographers"

Chris Kern

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #2 on: March 13, 2018, 09:38:05 PM »

Use the right tool for the right job:
https://www.rawdigger.com

Or FastRawViewer.  But while working in-camera, is there really any alternative better than an educated guess?

digitaldog

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #3 on: March 13, 2018, 09:47:11 PM »

But while working in-camera, is there really any alternative better than an educated guess?
Decades before cameras had Histograms and some of us shot film, no educated guessing needed for transparency film (which requires optimal exposure).
Once you understand how your sensor behaves, with the aid of RawDigger or FastRaw Viewer, you work along the same lines.
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Andrew Rodney
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jrsforums

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #4 on: March 13, 2018, 09:50:57 PM »

Use the right tool for the right job:
https://www.rawdigger.com
With respect and some love to Michael who coined the term ETTR, it's got to go away. It is optimal exposure for raw data (OEFR?). ;)

Agree with RawDigger or the FRV variant.  Also, optimal exposure works. Years ago, Emil Martinec posted where he equated ETTR with Maximizing Exposure. Either worked.

When I was on cannot I would use camera (5D3) spot meter to measure significant highlight.  Now on GH5\G9, I use zebras.  Prior testing with RD allowed me to then know how many stops I could punch the exposure to optimize/maximize the RAW exposure
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John

Two23

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #5 on: March 13, 2018, 09:58:43 PM »

Or FastRawViewer.  But while working in-camera, is there really any alternative better than an educated guess?


Use an incident light meter?


Kent in SD
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jrsforums

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #6 on: March 13, 2018, 10:18:30 PM »


Use an incident light meter?


Kent in SD

Still have to “calibrate” to resultant RAW exposure
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John

digitaldog

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #7 on: March 13, 2018, 10:21:47 PM »

Still have to “calibrate” to resultant RAW exposure
Exactly! But yeah, an incident meter can come in handy considering how 'dumb' reflective meters can be in some cases (white dog on snow, black cat on coal).
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Andrew Rodney
Author “Color Management for Photographers"

jrsforums

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #8 on: March 13, 2018, 10:36:21 PM »

Exactly! But yeah, an incident meter can come in handy considering how 'dumb' reflective meters can be in some cases (white dog on snow, black cat on coal).

Reflective meters are dumb, but not in this case.  By metering the significant highlight and adjusting exposure up based on prior tests (so you know how you camera RAW limits are) you have an optimized exposure which you can now push around to optimize resultant image.

Incident meters were invaluable when using “dumb” film cameras....and still useful if you want to “get it right in camera”with jpegs.  They do not compare with properly using today’s digital cameras.
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John

digitaldog

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #9 on: March 13, 2018, 10:39:47 PM »

Reflective spot meters are not dumb when the photographer knows how to use them. Same with incident meters! Film or digital.
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Andrew Rodney
Author “Color Management for Photographers"

BJL

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #10 on: March 13, 2018, 10:40:14 PM »

Use the right tool for the right job:
https://www.rawdigger.com
Yes, I am sure that a more precise calibration could be made by comparing some JPEG histograms to raw histograms at the camera's minimum E setting — which is where having highlights go beyond maximum raw level is what one needs to avoid. (But only at the lowest EI setting level, and maybe at one or two higher EI setting values in cases where the lowest EI settings are special "low" ones.)

However, I think a far simpler calibration is possible; something like:
- Test with a uniformly bright main subject, to get a histogram with a spike at the right.
- Find the exposure level that puts the camera's histogram at the right — or in the blinkie method, the highest exposure before you get massive blinkies.
- Take a series of images starting at that exposure level and moving up though the next several levels (say 1/3 stop increments in shutter speed)
- Check how much higher the exposure can go before the raw histogram goes over the top: the difference is the " allowable JPEG overexposure".
- Maybe repeat with some different sort of scenes, to see if that measure of "allowable JPEG overexposure" is consistent — if not, I would play it safe and use the lowest result.

With respect and some love to Michael who coined the term ETTR, it's got to go away. It is optimal exposure for raw data (OEFR?). ;)
I agree that "ETTR" is no longer an ideal name. I would like a name which emphasizes that this idea of optimal exposure is not relevant in "limited light" situations where the maximum allowable exposure level leaves the photosite histogram well to the left (no photosite close to FWC), and the question is then how much analog gain to apply—that is, how high it is worth pushing the EI setting.
« Last Edit: March 13, 2018, 10:55:12 PM by BJL »
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digitaldog

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Andrew Rodney
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jrsforums

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John

BJL

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #13 on: March 13, 2018, 11:06:28 PM »

From
https://www.fastrawviewer.com/blog/in-camera-histogram-doesn%27t-represent-exposure
I am reassured by this observation:
Quote
while the in-camera histogram for #2640 is dangerously close to the right wall, indicating essentially no headroom (not to mention that the whole frame is one solid "flashing area", indicating overexposure), the RAW has a headroom of slightly more than 1/2 of a stop before highlight clipping;
That sounds exactly like the half stop adjustment that I mentioned in my OP, and it is no mystery once you compare the ISO 12232 specifications for (a) standard JPEG output placement, and (b) SSat. The later is explicitly described as allowing half a stop more headroom that standard JPEG output.
In brief:
- Exposing according to reflected light metering will place the metered subject brightness in standard JPEG output at level 112, just under 18% of maximum, about 2.5 stops below maximum level.
- SSat is the Exposure Index that will place that same meter subject brightness half a step lower, so about 3 stops below maximum level; about 12.5%.

P. S. There is an extra adjustment: as with every DSLR AFAIK, the minimum normal EI setting of the Nikon DF used in that test (100) is a bit higher than the SSat (75, according to DXO). That is an extra 1/3 stop, so raw placement will be 1/2 + 1/3 = 5/6 stop lower than JPEG placement.
« Last Edit: March 14, 2018, 11:42:02 PM by BJL »
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Jeremy Roussak

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #14 on: March 14, 2018, 03:22:18 PM »

Reflective spot meters are not dumb when the photographer knows how to use them. Same with incident meters! Film or digital.

As usual, you do not read...or maybe listen....or maybe understand what others are saying.

That is insulting and inappropriate. If you wish to argue, do so coherently and politely.

Jeremy
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Rob C

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #15 on: March 14, 2018, 03:54:02 PM »



That is insulting and inappropriate. If you wish to argue, do so coherently and politely.

Jeremy


What? Nobody screamed yet for this section to be closed down too?

:-)

David S

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #16 on: March 14, 2018, 04:18:44 PM »


What? Nobody screamed yet for this section to be closed down too?

:-)

Polite is all that is required. Rude isn't.

Dave S
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kirkt

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #17 on: March 16, 2018, 11:49:00 AM »

If you use a Canon camera supported by Magic Lantern firmware, then you can view a Live raw histogram on the display; the firmware also has a utility for automatically exposing to the right, or optimizing the raw exposure.  It is called Auto ETTR in ML.

https://www.magiclantern.fm

Auto ETTR is a "module" that the user needs to enable within the Magic Lantern interface.

There is really no guesswork once you use a meter (your in-camera meter or handheld) and examine the raw data - spot meter highlights that you want to contain detail, shoot an exposure sequence and examine the raw files in Raw Digger to see where sensor saturation occurs.  You may be able to eek out slightly more exposure if you use a raw converter that can reconstruct highlights effectively, especially if they are close to neutral.

On my Canon 5DIV, I use a handheld spot meter, meter the brightest highlights where I want to preserve detail and expose three stops higher and it is "spot" on (ha!).  I use a Sekonic 758-D that permits me to set up the second ISO button with a "filter factor" - I set it to read +3 stops and I get my exposure reading for the shot (for typical daylight lighting conditions).

With the 5DIV, in dual pixel mode, you can grab one more stop of highlights if you split the dual pixel raw into the two raw exposures, using the DPRSplit utility, and merge the two resulting DNGs into a single pseudo-HDR file.

https://www.fastrawviewer.com/DPRSplit

You can merge them into a single DNG using ACR/Lightroom or Anders Torger's LumaRiverHDR, if DNG is a better format than EXR, etc.

kirk

« Last Edit: March 16, 2018, 02:53:37 PM by kirkt »
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BJL

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #18 on: March 16, 2018, 09:49:33 PM »

On my Canon 5DIV, I use a handheld spot meter, meter the brightest highlights where I want to preserve detail and expose three stops higher and it is "spot" on (ha!).
That is a useful real-world observation. What ISO speed setting are you using on the camera, and on the light meter? Because three stops is very close to the expected gap between spot metered highlights and raw placement at base ISO speed.
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jrsforums

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Re: “Expose to the right” vs “JPEG Histogram to the right”
« Reply #19 on: March 16, 2018, 10:03:52 PM »

That is a useful real-world observation. What ISO speed setting are you using on the camera, and on the light meter? Because three stops is very close to the expected gap between spot metered highlights and raw placement at base ISO speed.

It has been a few years since I left Canon for m43, but, as I remember, the fine single point on the 5D3 was ~1.5°, which work great for spot metering...and 3 stops was the gap...2.5 if you want to be safe.

I would always advise for the user to check their camera and metering with a RAW histogram such as RawDigger.  Particularly if using an external light meter, which may not be calibrated to the camera light meter.

Edit:  actually, Canon states the spot meter is ~1.5% of viewfinder. I found this sufficient for my purposes.  The area of the meter is not the circle, but as shown below.
« Last Edit: March 16, 2018, 10:37:10 PM by jrsforums »
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John
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