An alternative approach to RED ISO

[Alberto Guglielmi]

I used RED since the time of the RED One, but it is only over a year since I decided to own one and use it as my main camera, for motion, and as much as possible for stills. I come from a photo background, and the hardest thing to wrap my head around was the concept on how RED was handling ISO as a metadata. Apparently it is a question that is still open for many people, as it was again discussed at Ketch Rossi workshop this past weekend (Thanks Ketch!)

This is my alternative mental approach that I am developing.

- Film Camera. You have 3 variables for your exposure: Aperture, Shutter speed, film speed (Iso). When you pick a roll of film, it is a set ISO for a set number of exposure. e.g. Kodak Tri-x 400. You shoot at 400 the whole film, or waste frames to switch film. You pick the film that matches your light needs and your artistic idea. You can also push or pull film according to certain rolls. For people not accustomed to it, it is the process of exposing at a different ISO from the film one, and then adjusting the development of the film accordingly. e.g. You would expose a 3200 Iso film at 1600 and have it develop at 1600 or 3200.

- Digital Camera. You have 3 variables for your exposure: Aperture, Shutter speed, ISO. When you shoot with a digital camera for photos, you pick a ISO first. The difference is that you can change ISO at each frame. Like changing roll of film at every shot. The ISO is "baked" in the photo, though. So you pick the ISO you want to use, knowing that you will have a certain amount of grain and highlight/shadow retention. The concept of pushing and pulling has been lost, in favor of changing ISO first, and eventually exposing to the right or left.

- RED. With the RED you pick a ISO, but it is just a metadata value, for exposure reference. You can change it afterwards. The struggle starts here, and I read every possible explanation, including the most common "it is for your monitor reference".

My alternative thinking now is considering that RED has a set ISO (film). Basically you have only 2 variables for your exposure: Aperture, Shutter speed (or angle). ISO is set at 800 for Dragon and it looks like it is the same for Helium. That ISO DOES NOT really change. You simply push or pull the ISO. If you go back to rolls of film, changing ISO while shooting with a RED is equivalent of displaying the results of pushing or pulling the film to one side or the other. You do not change film like a film camera, nor bake the ISO in the frame like a digital camera. You simply see what happens if you overexpose or underexpose the film at a given aperture/frame rate.
As an example if you set your ISO at 400, you see what the images look like shooting at 800 and overexposing 1 stop, by pulling to 400. If you shoot at 2000 is the equivalent of pushing 1+ stops and you see the result of the underexposed film. In post you can decide to move the "development" by pushing or pulling as you did while shooting, or change it.

A few more thoughts:
- Changing film for the RED can be partially achieved by changing the OLPF. You can use that as a different starting point for ISO.
- As for another thread, adjusting ISO in post with Redline-X as the advantage of being considerate of highlight clipping, compared to adjusting exposure. But you are still simply pushing or pulling filming development.
-Dragon and Helium react differently to pushing and pulling. Seems like Helium is more sensitive to light, therefore is less prone to noise when underexposed, but more sensitive to light when overexposed. It also seems that the added dynamic range of the sensor allows for a bit more room for pushing it to the limits, but that those limits are less "forgiving".

I would like to hear what you guys think and if it make sense for more than just me...

 

[Adrian Jebef]

This is a great, practical, and simple explanation. My additional 2 cents: a digital still camera acts very much like a RED in that you can adjust ISO or exposure comp later via photoshop etc. I think the biggest difference you're noticing is that with a digital still camera you get instant, consistent exposure results in the field when you shoot and adjust ISO on the fly. Unfortunately with a RED you can often times get quite unpredictable results when changing ISO during shooting as the camera's HD-SDI video out doesn't always align with what you might see later in Redcine or Resolve etc. I've always had better results with Reds by keeping their ISOs locked to a decided exposure value.

 

[Michael Tiemann]

Based on my experience with DRAGON (first DSMC and now DSMC2), I would agree that RED's variable ISO is very much like pushing/pulling film. And because I got my start with film (not because I interned with Quentin Tarantino, but because I'm over 50 and when I started film was all there was), I know that pushing/pulling film can create looks as different as different stocks. (Indeed, it usually creates a more different look because one of the goals of differently rated stocks was to make all the different speed stocks look as much like one another as possible using every chemistry trick in the book. Push-processing was a one-dimensional trick that tended to show itself pretty quickly.) The digital noise that comes from pushing ISO on RED is not exactly the same as having larger halide crystals on film, but it does get more grainy in its own digital/organic way.

I would also agree that RED's interchangeable OLPFs are very much like different film stocks. The sensitivity range of those stocks is fairly narrow (LLO to STH is at most +/- 1 stop of sensitivity difference vs. STD), but the range of push/pull is +/- 2 stops with good results and can be +/- 4 stops for specific/creative results. (I should also add that REDCODE and resolution size also behave somewhat like film formats--from 8mm to 35mm, affecting both detail and clarity of the digital negative as well as depth of field vs. field-of-view.)

For me, STH is ISO 400, STD is ISO 800, and LLO is ISO 1280, but I often find myself pushing these by a stop and not really suffering too much.

I think that far too many REDUSERs make the mistake of going wild with all the variables at once, rather than really developing a baseline understanding of the fundamental behavior of the camera and its imaging system. Once one knows RED as well as one had to learn a single film stock and format, then stock choices (OLPF), push/pull processing (ISO), compression (REDCODE), format (2K-6K or even 8K), etc., can be brought to bear, with great effect.

 

[Mark Phelan]

I have always thought of ISO on any digital camera this way. It has a set preference, 320, 800, whatever and any variance is simply pushing/pulling. The difference is the latittude available. Just like different film stocks, each camera has an acceptable width of latittude, some wider, some narrower.

 

[Daniel Stilling]

I have to disagree with this assessment.
I see all the exposure variables as tools that work together, but separate have the power to change the feel of the shot. It's all about knowing what each individual tool does for your image and ISO is one of those tools.
If you change the shutter speed, you are changing how much light reaches the sensor. But if your only reason to change your shutter speed was exposure, then you will have major consequences in how your shot will feel: having it all choppy or video-y depending what direction you went.
If you change the aperture, same thing: You change your depth of focus.
If you change the ISO, you are basically changing where middle gray is. Considering the large latitude of the Dragon and Helium, and if you have not turned on any of the stop lights to the right, there's little consequence to the picture.
Now, that's all disregarding what you can do in front of the lens with ND's and other light blocking filters, and I'm being overall very generic here. But my point is that ISO is as much of a tool for you to use as all the others the camera offers. You need to know what the strength, weaknesses and the consequences are and which of these tools should be used in a given situation.

 

[Alberto Guglielmi]

I agree that are all tools we use when needed, knowing what they do helps.

Personally, I believe that the ISO does have strong consequences on the quality of the picture, in the term of noise and grain. As you said, it depends on the actual dynamic range of the scene and your choices of lens, lighting and so on. But in the very generic, changing ISO changes the noise and quality.
With RED you do not actually change the ISO, you simply see what the exposure is at a different level of it. You are not changing the middle grey, you are changing where you see the middle grey. So for me it is easier to think in term of a fixed ISO that I see how much I am pulling/pushing, rather than thinking that I am actually changing it.

 

[Daniel Stilling]

Let me put it in a scenario base:
Night shoot, by a hotel pool deck, you have your key from a bounced HMI and you have a lot of practicals in the shot.
Camera is set at ISO 800, T1.4 180deg shutter. Exposed slightly to the right and no stop lights. Director loves the general feel, romantic.... but he says: It's a bit too bright overall. The balance between the practicals and key light is perfect and so is your ratio. What would you do?

 

[Patrick Tresch]

If you have Rokinons close your lens to T2 ;-)

 

[Björn Benckert]

Stop thinking of iso as film iso. Its a dynamic digital gain nothing else.

 

[Frank Glencairn]

Björn is right, there is no ISO on video cameras - it should be referred as db

 

[Antony Newman]

I'm a beginner on aesthetics - but for photographs, my first thought is visual complexity, and therefore the proportion of how much is in focus - fixing the Aperture. Sense of motion would then fix the time the shutter can remain open, and lastly digital gain - hoping the camera does not clip, and there is sufficient light for the sensor.

For motion - I think there is some forgiveness in human visual when it comes to the sense of motion when presenting a series of static images, but this art of compromise is one that I have yet to learn. But the Aperture would (I guess) still be the first step in limiting visual complexity and 'focus.

AJ

 

[Satsuki Murashige]

Stop thinking of iso as film iso. Its a dynamic digital gain nothing else.

That's not what Alberto and Michael are saying. They are saying that the sensor + OLPF (not ISO) in the Red ecosystem is equivalent to film EI/ISO/ASA (or digital gain, if you prefer), i.e. a fixed sensitivity value that results in repeatable image characteristics. This is a more accurate comparison than Red ISO and film ISO, so I think it is a useful tool for those who still think of photography and exposure in film terms.

From this viewpoint, Red ISO is actually more like film workprint printer lights, a preview of how bright the final image will look after exposure and processing.

 

[Satsuki Murashige]

Let me put it in a scenario base:
Night shoot, by a hotel pool deck, you have your key from a bounced HMI and you have a lot of practicals in the shot.
Camera is set at ISO 800, T1.4 180deg shutter. Exposed slightly to the right and no stop lights. Director loves the general feel, romantic.... but he says: It's a bit too bright overall. The balance between the practicals and key light is perfect and so is your ratio. What would you do?

Lower your ISO to 500, or in film terms 'print down' by 2/3 stop. Exposure on 'the negative' stays the same.

 

[Daniel Stilling]

Lower your ISO to 500

Exactly. Lower the ISO. Don't starve your sensor from light. After all, there's only 3 things you can do to physically change the amount of light being seen by the sensor:
- Filters and such. Anything you put in front of the lens that takes away light
- Iris. Close down the aperture and less light will hit the sensor
- Shutter speed. Increase or decrease exposure time of each pixel in the sensor.

As you can see, ISO does not physically alter the amount of light that hits the sensor.
Look, exposing a RED is one of the most discussed and polarizing themes you can discuss around here. There are many ways to skin this cat. Not to say that any of them is wrong or right.(although, in the example I gave before, starving the sensor from light is not the right way to go) Find "your" right way, test it and test it and come to your own conclusions.

 

[Satsuki Murashige]

I think the 'film' method is useful, simply because it allows you once again to use a light meter and get at least ballpark results when pre-lighting, or when checking photometric tables to order lights and lenses. Assigning a reliable EI/ISO/ASA/footcandle value to your camera system (based on personal preference of imaging characteristics) means you're speaking the same language with your lighting and camera technicians as well. I think it's not good when you pull out your meter on a 'digital' set and everyone immediately wants to know the stop without asking what ISO we should be working at first, as if all digital camera ISOs match up perfectly. Changing this kind of thinking should help to reverse this trend.

 

[Patrick Tresch]

Stop thinking of iso as film iso. Its a dynamic digital gain nothing else.

We had this discussion some years ago on this forum. But I'm quite convinced ISO is the best way when speaking digital RAW imagery as this takes into account the whole imagery system and not a specific physical part of it.

From Wikipedia :

The standard specifies the measurement of light sensitivity of the entire digital camera system and not of individual components such as digital sensors, ...

The choices are based solely on the manufacturer’s opinion of what EI values produce well-exposed sRGB images at the various sensor sensitivity settings. This is the only technique available under the (ISO) standard for output formats that are not in the sRGB color space.

 

[Phil Holland]

Here is my aggressively simplified answer.

Treat your ISO rating as a film stock.

By that I mean if you rate your sensor technology and OLPF combination at a particular ISO values expose for it accordingly. Capture and delivery resolution plays a role here as well to a subtle degree as it has a visible effect on the final image (and even workflow for some applications).

The Base ISO from manufacturers is typically the zone where you have equal stops above and below 18% Middle Gray. In the world of RED at the extreme ends this value has slight differences depending on what OLPF you have chosen to shoot with. The key thing here is there is nothing forcing you to shoot at the Base ISO if you prefer the look and texture from a lower or higher ISO rating.

It is important to know where and when your sensor and OLPF clips and crushes. In many ways working with this whole method is similar to working with film stocks.

Now the other stuff.

Yep. You can great it like film in terms of pushing and pulling a stop via ISO or FLUT adjustment, but the real secret here comes to how you expose.

If you are looking to creating rather cinematic and thick images do your best not to crush into the noise floor or clip into the blistering white abyss upon exposing and lighting. That's said you can clip and crush if you know that aren't trying to reaching into the empty buckets of darkness or brightness that simply have no information in them.

Side note and real world Hollywood experience talk. As if late I'm finding more and more DPs who are actually choosing higher ISO ratings because of the added texture and energy it generates. And I'm talking Dragon even. You have to make your images your own at some point and decide what's best for whatever project and rating your ISO accordingly is part of the whole picture as is exposing to the best of your abilities.

Other than that sound advice from others on a few other topics. RED cameras do indeed capture the maximum amount of Dynamic Range at all times. Changing your ISO doesn't effect the amount of light hitting your sensor. Your iris, filtration, and shutter speed does. Lighting I guess should be wrangled in there if course. ISO is primarily all about where values are placed using digital gain.

 

[Owen Rennie]

ISO has always confused the hell out of me. This thread helps a bit. I always just set to 320 on dragon skin tone and make sure it's exposed well. That way I seem I can't go wrong. I had way to many underexposed shots back in the day shooting at ISO 800

 

[Sabovic Adis]

Let me put it in a scenario base:
Night shoot, by a hotel pool deck, you have your key from a bounced HMI and you have a lot of practicals in the shot.
Camera is set at ISO 800, T1.4 180deg shutter. Exposed slightly to the right and no stop lights. Director loves the general feel, romantic.... but he says: It's a bit too bright overall. The balance between the practicals and key light is perfect and so is your ratio. What would you do?

"STFU, I didn't ask!", that's what I would do.

 

[Alberto Guglielmi]

Here is my aggressively simplified answer.

Treat your ISO rating as a film stock.

By that I mean if you rate your sensor technology and OLPF combination at a particular ISO values expose for it accordingly. .....

Pretty much the way I am thinking now.
Thanks for validating the approach, and more interesting insights, master Phil.

Let me put it in a scenario base:
Night shoot, by a hotel pool deck, you have your key from a bounced HMI and you have a lot of practicals in the shot.
Camera is set at ISO 800, T1.4 180deg shutter. Exposed slightly to the right and no stop lights. Director loves the general feel, romantic.... but he says: It's a bit too bright overall. The balance between the practicals and key light is perfect and so is your ratio. What would you do?

That's an easy answer. If you lower the ISO, you know that you are not changing the amount of light that hits the sensor, and you are not changing the quality of the image, as it is exposed properly already. You already know there is no degradation in quality by moving a stop down from 800. You are just showing the director how it will look once "pulled", or printed down, or however you want to call it.

Let's make it more interesting. Same scenario of above, but now the directors tells you that the image is too dark overall. What do you do?