Control Your Mastering White Point, Control Your Highlights

June 12, 2024

Learn how to use white points in color management and how to choose them creatively, in this interview with FilmLight's Daniele Siragusano.


Series

Part 1: FilmLight’s Daniele Siragusano discusses the colour grading impact of custom white points

I had the unique opportunity and pleasure of talking with (interrogating?) FilmLight Image Engineer Daniele Siragusano. He agreed to delve deep into the foundational ‘white points’ topic in different colour spaces. It’s a rather confusing topic – with lots of cryptic terms and overlapping acronyms – and I hoped he could unwind these concepts for me.

Join me as I sit with FilmLight engineer Daniele Siragusano to discuss white points, the neutral axis, and its application to colourists and finishers.

Daniele is an enthusiastic presenter who passionately dove into this technical concept and clearly explained what workflows utilize differing white points. I think I found the right person to deconstruct this for us.

Understanding the neutral axis and using White Points effectively and aesthetically

The White point (or neutral axis) is a technical concept that can be difficult to understand. Working as a Baselight assistant early in my career, this colour management principle went over my head. This Insight aims to relieve any post-production professional who has not grasped why custom White points would be used in a workflow.

“When we expose the image upwards… You can see in the chromaticity diagram that we are always moving toward the white point. I cannot escape that compression towards the white point, right? Especially for bright highlights and things like clouds. To make warm highlights, you cannot just go into the highlights and make them warm because, at some point, the DRT will desaturate to D65.”

Daniele Siragusano, Image Engineer, FilmLight
Daniele Siragusano is an Image Engineer at FilmLight and an explainer of techy things to semi-techy people.

The White Point Journey

There are various “white points” at different stages in a color-managed pipeline.

  • Scene White Point
  • Mastering White Point
  • Display White Point

Scene White Point

The white point journey starts on-set with the “scene white point.” Lights are rigged and pointed towards the subject, which illuminates the scene. Various objects within that scene interact with the visible light spectrum differently, and the colour temperature of the available light will create colour casts.

For example, a candle-lit scene will push the neutral elements in the scene toward warmth, whereas cool sunlight will render the opposite effect.

At this stage, the on-set white point is corrected using a neutral reference patch or “grey card” to eliminate or reduce colour casts. The neutral reference patch has a flat spectral reflectance curve, ensuring that red = green = blue. This white-balancing process establishes the scene white point.

Display White Point

Skipping briefly over the middle part of the journey–the white point journey ends with your display. A “display white point” is measured as one of the four primaries of an RGB display: red, green, blue, and white (where all three colour channels are fully powered). The display white point is derived from the RGB primaries that your display standard can reproduce. Combining equal amounts of red, green, and blue renders white (or a neutral tone) in an additive colour model.

Image3

The four colour primaries are plotted on a graph

Different displays have different display standards and colour primaries, so naturally, there are different white points (with different visual characteristics). Different RGB coordinates such as special red [r1,g0,b0], special green[r0,g1,b0] and special blue [r0,g0,b1] can be added together to render special white [r1,g1,b1]–or the white point–in a few different variations.

Image1

Multiple colour primaries plotted on a graph, showing the impact on the white point

Mastering White Point

This Insight would be very dull if the middle part of the white point journey, the “mastering white point,” didn’t exist, but luckily, it does. If the mastering white point didn’t exist, the neutral tones in our videos would reflect the white point of the output display. For example, if a colourist were grading a show for television, the white point standard of D65 would be the only option that they would have. D65’s interpretation of neutral tones, as determined by the display technology, would provide no room for flexibility. Luckily for us, the mastering colour space does exist, and it can be used to change the neutral tones or the “neutral axis” of our image to emulate other white points and output this look to different displays.

White Point vs Neutral Axis

Let’s clarify an important term: Although “white point” is referred to throughout this Insight, it can be interchanged with the term “neutral axis.” The neutral axis is probably more accurate.

Image4

A graph showing the full luminance range for each display primary, including the middle ‘neutral axis’ [Source – https://vimeo.com/310759883]

The four display primaries shouldn’t be considered singular points but rather a colour chromaticity axis containing varied luminance values. When discussing the white point, the axis we’re referring to is called “the neutral axis” and contains all of the coordinates between peak luminance (white) and minimum luminance (black) where red = green = blue at all points along that axis.

Creatively controlling your white point

Let’s discuss the middle section of this white point sandwich: the “mastering white point,” which can be manipulated in a colour-managed environment to emulate a different white point instead of the “display white point”. There are a few well-known names in the white point line-up:

  • D60 is a common white point in the world of cinema
  • D65 is a common white point in the world of television
  • DCI-White is a legacy white point used to verify a correctly calibrated DCI projector
  • CIE-E is a technical encoding white point for digital cinema packages (DCPs).
Image5

Different white points are plotted, with visual patches emulating different white points. These patches have been designed to be viewed on an sRGB display with a D65 neutral axis [Source – https://vimeo.com/310759883]

For example, when grading in a broadcast television workflow in Baselight, choosing a warmer “mastering white point” such as D60 will render warmer neutral tones. This will shift the RGB values in the scopes so that r=g=b will start pushing to a warmer neutral tone as a natural consequence of your grading manipulations.

“Black and white images are a great tool to analyze the white point, as the color volume is reduced fully to the neutral axis. I would encourage Baselight users to fully desaturate an image and play with different mastering white point settings.”

Daniele Siragusano, Image Engineer, FilmLight

As discussed in the video portion of this Insight, it can be tricky to tint the neutral tones in the image effectively if you don’t change the “mastering white point”, especially specular highlights. These bright highlights will desaturate as they reach peak white and pull towards the project’s white point. To achieve warmer specular highlights (and all neutral tones across the image), changing the ‘mastering white point’ to D60 or D55 is an effective choice.  

White points–or the neutral axis–are one of those rabbit holes that you can tumble down endlessly. All interesting colour science topics tend in that direction… but I hope this blog post has primed you for Part 2 of my interview with Daniele and provided some good food for thought on your colour grading journey!

Key takeaways from this Insight

By the end of this Insight you should understand:

  • The concept of a white point (the neutral axis)
  • The three stages of the white point journey
  • Common industry white point standards
  • How to choose a creative mastering white point
  • Filmlight Tutorials: Managing White Points – “We take a closer look at the neutral axis, or white points, and their handling with the Truelight Colour Spaces framework. The video explains how to manage creative white points for different viewing conditions, and how to correctly import display-referred material into a grading scene, for example, to verify a render.”

Questions or Comments? Leave a comment!

I’m curious about the Mixing Light community’s current interactions with white points in their workflows. Have you never heard of the term before? Is it an essential part of your workflow that you consider or change for each project? Do DOPs ever walk into your suite with a strong white point preference? Do you have any tips for achieving these results in DaVinci Resolve? Let me know in the comments below!

– Luke

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