22.2 Integration White-Black Point

In this guide, we will look into integrating an element with live-action footage. This is a simple matte painting element, but the process is a good starting point to familiarise yourself with the concept of white and black point, which can be applied to basic CG integration as well

On the right side, the distant buildings are positioned fine but the colors don’t match, we want a better integration

Analysing the Footage

In our aim for integrating the matte painting element with the background, we need to analyze and understand the colors of the background footage, and then adjust our element’s colors to match

The first thing to look into is the white and black point values

The white point is the brightest point in our image – the black point the darkest

We can’t judge these with our naked eye, we need assistant of the color picker and Nuke’s viewer exposure and gamma sliders

Analyzing with Color Picker

Hovering over an area, Nuke shows the color picker values under the viewer

To sample one point crtl-click, an area shift-crtl-drag, clear the selection ctrl-shift-click

White is 1, black 0 in Nuke’s linear color space

Exposure and Gamma Sliders

exposure on left, gamma on right

Viewer Gamma Down

Pushing Nuke’s viewer gamma down reveals a clearer look at the highlights

Although the brightest point looked full white, even burned-out with the naked eye, it is really only around 0.7 and it is warm

Viewer Exposure Up

Pushing Nuke’s viewer exposure up reveals a clearer look at the shadows

The darkest point is below 0.01, sounds very low but we are in linear color space

Blue is the highest of the three values

Saturation Up

Adding a saturation node and pushing the value up reveals that the shadows are bluish

With these simple steps, we’ve learned: How bright is the brightest point and how dark is the darkest point exactly. And which color tone do they have

We now know our footage’s white and black point

Adjusting White and Black Point

The first step of integrating the matte painting is to match the element’s white and black point to the background

We have plenty of color correction tools to adjust white and black point

Nuke’s Grade node offers seven sliders – six of them adjust the white or black point

whitepoint, gain, multiply do all the same thing – changing the white point

blackpoint and lift change the black point

offset changes both, white and black point simultaneously

exposure is another tool to change the white point

And of course the curves in the ColorLookup node

(More on the page: White and Black Point Controls)

Before Correction

This is the matte painting element before white and black point correction

Comparing White Points

Gamma down shows the matte painting’s whites are way too high and too yellow

Grade Node

Tick the 4 to unfold channels

I’m using multiply. Gain and whitepoint do the same thing

Adjusting White Point

Adjust the individual RGB multiply values to match your source footage

Toggle viewer’s gamma on and off with the Y left of slider

Comparing Black Points

Exposure up shows the matte painting’s blacks go as low as zero, the source’s are around 0.2

For the source footage, find a reference point at a similar distance to the camera

Grade Node Blackpoint

Tick the 4 to unfold channels

I’m using blackpoint. Lift would work, too

Adjusting Black Point

Adjust the individual RGB blackpoint values in small steps

I’m assuming the element is further away than my reference point, so I increased all 3 values above the source footage

Toggle viewer’s exposure on and off with the left of slider

Result of Correction

With only two adjustments, it’s a massive step forward

There’s always room for improvement, the red rooftops pop out too much and we could tweak the shadows to be a tat cooler

Shadows – Midtones – Highlights

The ColorCorrection node allows to adjust shadows, mid-tones or highlights individually

In this example, I want to adjust the roof and the shadows. Several ways to approach this, to simplify we will include the roof in the shadow correction by using the ColorCorrection node’s ranges

Adjusting any of the shadows-midtones-highlights without checking and setting the ranges is pretty useless

Comparing HSV Values

Saturation-up test on the right shows rooftops really pop

Saturation of source roof is ~0.5 and of element roof at ~0.8

gamma affects everything between black and white but has more effect on darker values, ideal to correct the shadows

Shadow Correction

Adding green and blue to remove the warm tone of the shadows

Gamma and saturation influence each other dramatically, doing both at the same time is tricky, better to do the saturation last

CC Ranges Default

Yellow line is the roof value, it’s not included in the shadow range, but only in the midtone range

Adjusting the shadow values would not affect the roof

CC Ranges Adjusted

Shadow ranges adjusted to include the roof value, at least partly

Adjusting the ranges to include the values intended to be corrected is crucial to make the correction useful

Result of Correction

Result of the shadow correction on the right side

The rooftops are better now

The bluish shadow is subtle, a bit more noticeable in the saturation-up test