In just the past 24 hours, there have been something like 175 visits to an old article we posted announcing our intention to return to ETTR with the RED Komodo, so we’re guessing it’s a somewhat controversial topic! To the best of our knowledge, few DPs on big productions ETTR but there do exist some DPs, like Erik Messerschmidt, who vary their technique depending on the situation. So, is it really advisable to ETTR with RED cameras?
In ‘Cinematography: Theory & Practice’ Blain Brown writes,
“This method [ETTR] is not without its critics, however; most of them assert that it is no longer necessary as the noise level of cameras steadily improves. “Exposing to the right results in inconsistent noise from shot to shot, which can be jarring, and also tends to result in less consistency of exposure such that every shot needs its own grade,” says [Art] Adams. He adds, “Exposing to the right or to the left is great for one shot that stands alone… which almost never happens. When your images sit adjacent to others why would you base their exposures on the things that change the most between them?” Geoff Boyle comments, “I understand the expose to the right camp and I have done this at times in the past but not anymore.” He adds, “ETTR is not a practical method of working for us, every shot having to be graded individually and huge measures taken to match. Equally, whilst you can pull and push film you can’t do it on a shot by shot basis.” In practice, cinematographers rarely use ETTR on feature films or other long-form projects. As an exposure method, it might still be useful for isolated shots, such as landscapes or product shots, and on commercials which might consist of only a few shots in the day.”
RED.com’s own article on exposure strategy gives the following advice:
“Optimal exposure starts with a deceivingly simple strategy: record as much light as necessary, but not so much that important highlights lose all texture.”
Fair to say that they’re not huge fans of ETTR, either, though if you’re losing important highlight texture, you’re no longer exposing to the right – you’re overexposing. Furthermore, changing the ISO to redistribute the number of stops that fall above and below middle gray, such as increasing ISO to 1600 to capture more highlight information at the expense of shadow detail, can introduce jarring changes in texture – though we often lower ISO to 400 for indoor shots to reduce noise. Because so much of HDR’s dynamic range is located in the shadows where noise tends to be most prevalent, and as noise is far more distracting in HDR than in SDR, our own suggestion is to cut the manufacturer’s overly optimistic base ISO rating in half, then go ahead and bump the ISO to 800 or higher for bright scenes with lots of important highlight detail.
Lastly, a few days ago, we shared a screenshot of the curve we use for ETTR footage, where we grab the curve below middle gray and gradually pull it down, but highlights may still be overpowering and the image might be too flat, so we’re attaching a revised curve.
There is a large cadre of folks who isist on ETTR, and who interpret this old article as saying one can redistribute pixel data by changing the ISO in camera. RED , themselves, present a murky tech paper suggesting that the pixel data can be redistrubuted along the gamma curve, simply bt changing ISO. In fact, since RED applies ISO in post, not encoding in the raw data, changing ISO affects only the camera monitor, NOT the raw recorded data. If there’s any effect whatsoever, it’s because the change in camera monitor causes the op to change the aperture or change external lighting.
Yet, this cadre of beleivers persist, in quite an astonishing number of online articles, in telling people thet varying the ISO in-camera has a magical effect on the pixel distribution. Yes, I know the thrust of the discussion is about ETTR, but it goes hand in hand with this delusion about simply changing ISO.
“There is a large cadre of folks who insist on ETTR…”
1) On the contrary, no one to my knowledge is insisting that anyone expose to the right. In fact, my own most recent posts present strong arguments against doing so.
“RED , themselves, present a murky tech paper suggesting that the pixel data can be redistributed along the gamma curve…”
(2) Far from being murky, RED’s documentation clearly illustrates how ISO, or more accurately EI, works. Selecting a higher ISO allocates more stops above middle gray, while selecting a lower ISO shifts more stops toward the shadows, just as ARRI and other digital cinema cameras do. This is indispensible information for those accustomed to increasing ISO in low light and decreasing ISO in bright light. RED also makes it crystal clear that adjusting ISO does not change the raw image data, it only changes how the image is displayed.
“Yet, this cadre of beleivers persist, in quite an astonishing number of online articles, in telling people thet varying the ISO in-camera has a magical effect on the pixel distribution.”
(3) Is that so?
“Yes, I know the thrust of the discussion is about ETTR, but it goes hand in hand with this delusion about simply changing ISO.”
(4) Only it’s not a delusion. One need only seek out Art Adams’ excellent articles on ARRI cameras and ISO to realize that this is no gimmick or illusion. Understanding how ISO works is fundamental to the craft of filmmaking. Just as knowing that dynamic range falls off a cliff when recording at the second base ISO is absolutely essential information for BMPCC 6K owners.
“Selecting a higher ISO allocates more stops above middle gray, while selecting a lower ISO shifts more stops toward the shadows, just as ARRI and other digital cinema cameras do. This is indispensible information for those accustomed to increasing ISO in low light and decreasing ISO in bright light. RED also makes it crystal clear that adjusting ISO does not change the raw image data, it only changes how the image is displayed.”
Exactly right, I violently agree. Changing ISO DOES NOT change the RAW image data. If one was recording on ProRes, it would, but, not in RAW. So, given this fact, I don’t understand how changing the ISO in-camera, will affect exposure. It affects only the display, not the raw data.
Wouldn’t it be exactly equivalent to doubling the ISO, if one were to close the aperture down one stop and leave the ISO unchanged?
If you double the ISO, you’re making the image appear brighter, while closing the aperture one stop makes the image darker.
EI in a nutshell: As with ARRI and other cinema cameras, within certain limits, total dynamic range remains unchanged, you’re just balancing noise/overexposure latitude when choosing different ISO settings.
“If you double the ISO, you’re making the image appear brighter, while closing the aperture one stop makes the image darker.”
Yes, right. So this is my point: rather than, for example in a bright scene, doubling the ISO to retain hilites, one would simply leave the ISO unchanged but close the aperture one stop from the “normal” exposure. Conversely, in a scene where shadows dominate, leave the ISO unchanged, but, open the aperture one stop from the normal exposure. And, BTW, all this presupposes the traffic lights do not light up.
Do you understand what I’m saying? rather than fiddle with ISO, intentionally underexpose or overexpose your image from a normal exposure, depending on whether you’re protecting hilites or shadows.
EI in a nutshell: As with ARRI and other digital cinema cameras, within certain limits, total dynamic range remains unchanged, you’re just balancing noise/overexposure latitude when choosing different ISO settings. ISO 400 will have cleaner shadows and less highlight protection, whereas ISO 800 will have more latitude in highlights and noisier shadows.
Thanx for your time…
I can understand what you’re saying, and with Art Adams, when shooting a non-raw capture. (BTW, he tested LogC, not RAW). I understand how this applies to a camera like a BMPCC where the ISO is baked into the data. My misunderstanding happens when shooting REDRAW. I’m gonna go run some tests. It appears what you’re saying, is that ISO DOES affect exposure, stops above and below middle grey) even when shooting RedRAW
I performed 3 exposures of a static hi contrast scene….
1-ISO 400 aperture set to ETTR(using goalpost to barely extinguish)
2-ISO 6400 aperture set the same as no. 1(goal posts indicating a safe exposure)
3-ISO 6400 aperture reset to (using goalpost to barely extinguish)
Now, in Resolve, I set all clips to the same ISO 800 and examined shadow and hilite detail, as well as noise. Then examined the images at 600%.
I observe absolutely no difference between clips 1 and 2, implying the ISO change had zero effect when ISO is changed in post.
As I expected, I see, of course, a significant change between clips 1 and 3, which included an aperture change. My conclusion: changing ISO, alone, has no effect whatsoever when the clips are normalized in post. Changing aperture(while staying within the bounds of the goalposts) had a significant effect on noise and hilite detail.
So, back to my initial thought that there’s doesn’t appear to be any effect when ISO, alone, is changed. It’s entirely due to changing the exposure, either by aperture, available light, or shutter speed.
As you’ve ‘discovered’, you’ve got to change physical parameters, such as ND, IRIS or lighting, to impact exposure. For a good explanation of how RED ISO works, there are worse places to begin than with this video, reviewed by Graeme Nattress. https://youtu.be/x1uAMYq7yQk
Graeme Natress, on facebook, writes this in response to my comments:
“Yes, ISO gain is a “development” parameter, but in that respect it does alter the distribution of how raw code values get mapped to image code values. No, it doesn’t alter the raw data – *you* do that yourself by altering aperture/ND/shutter/scene lighting in response to the developed image.
It is the feedback loop that includes the operator that is important to remember…
ETTR is indeed a stills strategy. It’s not good for moving scenes as the lighting can and will change over the time, and you can easily go from “not clipping” to “clipping” during a scene. ETTR is not a strategy for movies specifically because in a movie, the exposure parameters aperture/ND/shutter are aesthetic decisions as well as exposure parameters, and continuity of aesthetic intent is an important consideration. That is why generally ETTR is not used for cinematography.”
Everyone is free to do as they like. In 2020, shortly after Mank began streaming on Netflix, Filmmaker Magazine interviewed one of the most gifted young cinematographers of our time, Erik Messerschmidt.
Filmmaker: With the early Red cameras—back in the Epic days—I remember people talking about how you needed to expose to the right on the histogram because if you underexposed you were in trouble. As Reds have evolved, do you not have to worry as much about the low end of the curve anymore?
Messerschmidt: No, I just protect the highlights. I feel like the camera has detail for days in the shadows. I do subscribe generally to the “expose to the right” approach, though. I didn’t use to, but I’ve turned around on that just because I feel like the color fidelity is superior if you put a little bit more light onto the sensor. I have that same opinion for every digital camera, not just Red.