What is a Waveform Monitor and How to read a Waveform Monitor (Part Two)

In Part One we learnt about white, black and middle grey levels, and understood the basics of how Luma is represented on a waveform. In this part we’ll apply our knowledge to learn how to expose any camera with a waveform monitor, and then how to use the same to also grade your footage in post production.

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The standards of Rec. 709

We saw in Part One that Rec. 709 calls on white, black and 18% grey to be at the following values:

  • Black – 0 IRE
  • 18% or Middle Grey – 45 IRE
  • White – 90 IRE (broadcast), 100 IRE for everyone else

This is a standard, sort of a waypoint. Every other log curve or gamma variant (known in cameras as custom profiles, picture profiles, cine profiles, presets, gammas, etc.) must define its Luma values based on this waypoint.

How do you expose and grade using a waveform monitor?

Here’s the second part of this series, enjoy:

Now that you have watched it, quickly go over the following notes for a refresher:

Tools you need to expose correctly

You don’t need a lot of tools in your arsenal. To learn how to expose any camera, all you need are the following:

  • A day of your time
  • A color chart like the DSC Labs OneShot or other, as explained in Part One
  • A production monitor with a waveform scope and other scopes
  • An NLE or grading application with a waveform scope and other scopes

These tools are your bread and butter, and will come in handy on a daily basis, and will stay with you even when you change cameras. It’s wise to invest in good tools.

Steps to expose and grade any format correctly

Here it comes:

Exposure is the art of fitting the scene to the display.

Now the concept of “fitting” will make more sense. When you are faced with log curves, you are in fact fitting it to your vision of the final image. How you do it is the ‘exposure’ part.

First, shoot for Rec. 709. All cameras have a Rec. 709 setting. If there’s no setting, it’s probably Rec. 709!

  • Shoot a chart under constant lighting conditions. For Rec. 709, the black, white and middle grey points will lie as shown above. Change the aperture, shutter or ISO till you get that result.
  • Watch the waveform while you shoot, take a picture for your records
  • Overexpose and underexpose and repeat
  • Bring the shot footage (don’t shoot stills!) into your grading or editing application and study the waveform scopes
  • Do the scopes match?

Next, shoot for log curves or RAW or any other preset that’s not Rec. 709.

Not all cameras have this feature.

  • Shoot a chart under constant lighting conditions. Study the manufacturers’ documents on where black, white and middle grey should lie and make sure they do.
  • Watch the waveform while you shoot, take a picture for your records
  • Overexpose and underexpose and repeat
  • Bring the shot footage (don’t shoot stills!) into your grading or editing application and study the waveform scopes
  • Do the scopes match?

Thirdly, compare Rec. 709 and the other:

  • Where do the black, middle grey and white points lie for both? If you have done the first two steps right, they’ll lie where they are supposed to lie.
  • Now use a grading tool or plugin (a simple one like Levels is all you need) to make them match. You’re matching everything to Rec. 709, because that’s what displays expect.
  • You can work in greyscale mode if you like. The colors will not match, and that is not what we’re trying to accomplish here. We are only concerned with the Luma levels.
  • Without much effort, you should be able to match them very close.

Fourthly, shoot for ISO groups:

  • Shoot both Rec. 709 and every profile at different ISOs.
  • Repeat with an overexposure and underexposure of 3 stops.
  • Study the results on a large monitor and try to group noise according to how I’ve shown in the video.
  • You will find groups of ISOs where the noise levels match somewhat. When you’re shooting a scene, you’ll have to shoot all shots within the same ISO group to save post-headaches later. Even if the scene doesn’t allow you to do that, you at least know what you’re in for, and can take measures.

Finally, shoot real-world scenes typical of your normal work:

  • You are aware how much work it takes to get your images to match Rec. 709.
  • While matching real-world scenes, you’ll notice something you didn’t see with test charts: How much shadow or highlight detail is preserved. That’s the extended dynamic range advantage of a log curve or flat preset.
  • You’ll know when to overexpose your camera and when to underexpose it, and by how much.
  • You’ll also see how ISO groups work for skin tones in the real world.

Does all this sound like a lot of work? Yes, but why are you surprised? This is what a cinematographer does day in and day out. You signed up for this!

What does it feel like to use a waveform monitor correctly?

It’s like seeing the Matrix:

  • You can easily check for contrast ratio or even lighting in a scene, as explained in the video. All it takes is a glance.
  • You can calmly walk into a set with any camera and know where your exposure limits lie. All it took you was one day of testing. Sometimes, when you rent a camera, that’s all the time you get.
  • You will be in a better position to choose the right camera for the job, rather than make the camera you’re more comfortable with work (which is like using the wrong screwdriver).
  • You’re using a production monitor anyway so it won’t take up any extra space or weight in your kit!
  • Even when Rec. 2020 comes, the waveform monitor will still work like it does today. You’re set!
  • It also works for RAW footage, if you’re using LUTs.
  • You won’t be surprised in post production!

I hope this long and detailed tutorial has been beneficial to you, and I hope you are confident enough to start using a waveform monitor right away. If you have been following along with a monitor as I had suggested, then you should be all set by now.

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9 replies on “What is a Waveform Monitor and How to read a Waveform Monitor (Part Two)”

  1. JonathonSendall I don’t know if it’s 16-bit, who knows? :) 

    For cinema it’s P3, yes. I don’t know much about P3, but if I remember the white point is precisely defined as 14 fL or 48 nits, and middle grey is still 18% (0.18, ACES).

  2. Sareesh Sudhakaran Also for cinema I would not normalize for Rec.709 but for P3?

  3. rsellars I don’t think we understand ETTR differently! What you explain is exactly what I’ve used in my S-Log2 exposure guide video – finding a balance between ETTR and matching exposure.

    Many photographers who start shooting video don’t understand that ETTR is an impractical strategy if you want to match shots. On the other hand, the Internet has also lowered the bar on what is acceptable quality – most people will never watch videos on anything better than an iMac.

    Thank you for sharing my content! Appreciate it.

  4. Sareesh, first of all I really appreciate your blog posts and your video tutorials.  You do a great job of explaining complex principals by using good analogies and visual aids.  I’ve passed on your tutorials to many of my students.  I believe that we are in basic agreement as far as exposure principles are concerned.  However, I believe that we have a different understanding of what ETTR (expose to the right) philosophy means.  When digital photography and cinematography first started getting popular, the prevailing advice recommended exposing for highlights at all costs. Of course, as you pointed out this can often lead to extreme underexposure for shadows and even mid tones.  ETTR as I understood it it from those promoting it, suggested getting more exposure in the shadows (possibly overexposing) as long as critical or desirable highlights are preserved (not clipped).  The key here is determining what highlights need to be preserved and what can be clipped – and that is of course an artistic judgement call.  I think that we agree that one needs to use a waveform to evaluate the shadows, mid tones, and highlights to make the best exposure decision.  Other tools like false color or zebras can help a cinematographer visualize how much of the image frame is going to clip or get crushed and where in the frame those elements are.  I also think that many young cinematographers rely too heavily on their camera to do all the heavy lifting in terms of contrast control. Sufficiently lifting shadows and mid tones with artificial lighting – or lowering window highlights with ND gel or scrims (when possible) is usually the best way to help get a good exposure.

  5. JonathonSendall RAW is linear, I was talking about 16-bit. As for the rest, yes, you need to normalize to Rec. 709 to know where the Luma levels lie. Camera sensors and image processing algorithms are engineered to make such a normalization easy – no special knowledge is expected of the operator.

  6. Sareesh Sudhakaran JonathonSendall So the white paper states that shooting with the RAW back means we are in 16bit linear space. Are you saying it isn’t? Not sure I quite understand that. The other thing is I can of course let in more or less light to that linear space and that does indeed affect my exposure in terms of what the camera reads as data. Still means I need to put values at levels that make sense, especially if I’m trying to attempt a certain split say between key, fill etc? So therefore I still need to know where in the image (according to amount of light, not colour space) where noise will kick in more strongly and so on?

  7. JonathonSendall There’s nothing you need to do (or can do) for linear post as far as exposure is concerned. The linearization in software has no interaction with how the camera records data. I guess shooting uncompressed RAW is as close as you can come!

    And just because it says 16-bit RAW doesn’t really mean it is. Just like you can change 8-bit to 16-bit in post, a camera manufacturer can do that too, you know.

  8. Thanks Sareesh. I read many arguments on ETTR, especially on the Sony forum (I shoot with an F5). Quite a few experienced people suggest it. Personally I’m not decided but I have a long RAW shoot coming up for cinema distribution. As I’m NOT a post guy how does 16bit linear fit into your view of things exposure wise? I’m guessing its simpler in terms of exposure.

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