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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta name="viewport"
content="width=device-width, initial-scale=1, shrink-to-fit=no">
<meta name="author" content="Colour Developers">
<meta name="description"
content="John Hunter - Excellence in Plotting - 2020 - colour-science">
<meta name="keywords"
content="color, color-science, color-space, color-spaces, colorspace, colorspaces, colour, colour-science, colour-space, colour-spaces, colourspace, colourspaces, data, dataset, datasets, display-referred, gamut-mapping, output-referred, scene-referred">
<title>John Hunter - Excellence in Plotting - 2020 - colour-science</title>
<link href="./resources/css/bootstrap.min.css" rel="stylesheet">
<style>
body {
background-color: rgb(18, 18, 18);
color: rgb(208, 208, 208);
font-size: 1.15rem;
}
a,
a:hover {
color: #3498DB;
}
.navbar {
background-color: #242424 !important;
}
.navbar-brand {
color: #3498DB !important;
}
.hand-pointer-on-hover {
cursor: pointer;
}
#content {
margin-top: 5rem;
}
</style>
</head>
<body data-gr-c-s-loaded="true">
<nav class="navbar navbar-expand-md navbar-dark bg-dark fixed-top"
style="z-index: 1024">
<a class="navbar-brand"
href="https://acescentral.com/c/aces-development-acesnext/vwg-aces-gamut-mapping-working-group/80">Academy
ACES -
VWG</a>
<button class="navbar-toggler" type="button" data-toggle="collapse"
data-target="#navbarDefault" aria-controls="navbarDefault"
aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="navbarDefault">
<ul class="navbar-nav mr-auto">
<li>
<a class="nav-link" href="https://jhepc.github.io/">John Hunter -
Excellence in Plotting - 2020</a>
</li>
</ul>
<ul class="nav navbar-nav navbar-right">
<li><a class="nav-link"
href="https://colour-science.org">colour-science.org</a></li>
</ul>
</div>
</nav>
<main role="main" class="container">
<div id="content" class="container-fluid">
<div class="row">
<div class="col">
<figure class="figure">
<img src="./resources/images/Gamut_Medicina_01.png"
alt="Mansencal and Scharfenberg (2020) - HSV Control Based Study Model"
class="figure-img img-fluid hand-pointer-on-hover gamut-medicina-1">
<figcaption class="figure-caption">
<p>
<span class="font-weight-bold">Colour Developers Scientific
Plot Entry</span> for <a href="https://jhepc.github.io/">
<span class="font-weight-bold">John Hunter - Excellence in
Plotting - 2020</span></a>: An interactive <a
href="https://ipywidgets.readthedocs.io/en/latest/">Jupyter
Widget</a> driving <em>Mansencal and Scharfenberg (2020) HSV
Control Based Study Model</em>, and performing gamut mapping
on scene-referred synthetic imagery.
</p>
<p>The <a
href="https://github.com/colour-science/colour-mitsuba">Cornell
Box</a> is spectrally rendered with <a
href="https://github.com/mitsuba-renderer/mitsuba2">Mitsuba
2: A Retargetable Forward and Inverse (Open Source)
Renderer</a>.
</p>
<div class="alert alert-dark" role="alert">
<b>Note:</b> Click on the image to show the effect of the
gamut mapping study model.
</div>
</figcaption>
</figure>
<h2 id="Abstract">Gamut Mapping of Scene-Referred Light Values<a
class="anchor-link" href="#Abstract"></a>
</h2>
<p>
The <a
href="https://www.oscars.org/science-technology/sci-tech-projects/aces">Academy
Color Encoding System
(ACES)</a> is a free, open, device-independent color management
and image interchange system used in the production of movies,
series and games. ACES adoption has increased during the last
decade and the system is becoming a successful standard in the
Media and Entertainment Industry. However, amid of the growing
success, ACES users are frequently reporting defects occurring on
their imagery while using the system.
</p>
<div class="alert alert-dark" role="alert">
<b>Note:</b> It is assumed that the reader has basic knowledge
about image processing and colour management in the Media and
Entertainment Industry. An introductory publication on these topics
is <a href="https://cinematiccolor.org/">Cinematic Color: From Your
Monitor to the Big Screen</a> by Selan (2012).
</div>
<p>The artefacts are often generated by digital still or
motion-picture cameras: their spectral sensitivities do not satisfy
the <a
href="https://en.wikipedia.org/wiki/Tristimulus_colorimeter">Maxwell-Ives
criterion (Luther condition)</a>. Put another way, they are not
colorimetric and capture the world differently than the <a
href="https://www.hunterlab.se/wp-content/uploads/2012/11/CIE-Standard-Observers.pdf">Standard
Observer</a>, i.e. a standardised average human viewer.
Ultimately, they produce non-physically realisable values outside
the <a href="https://en.wikipedia.org/wiki/Spectral_color">Spectral
Locus</a>, i.e. the volume bounding the extent of the
<em>Standard Observer</em> sensitivity to the electro-magnetic
spectrum. Colour grading tools used to infuse the creative vision
into the imagery are also source of defect generation.
</p>
<figure class="figure">
<img
src="./resources/images/5DMarkII_Spac-o-ween_001_GamutMedicinaHSVControlWidget.png"
alt="Show Out-of-Gamut Colours"
class="figure-img img-fluid hand-pointer-on-hover out-of-gamut-1">
<figcaption class="figure-caption">
<p>
The <a href="https://en.wikipedia.org/wiki/Chromaticity">1976
UCS Chromaticity Diagram</a> on the left highlights
particularly well the non-colorimetric behaviour of the Canon
EOS 5D Mark II. The <em>Spectral Locus</em> is represented by
the largest colour-varying and rounded triangle.
The red triangle defines the primaries of the standard ACES
RGB working colourspace, i.e. ACES AP1, and the gray triangle
that of the display colourspace, i.e. sRGB.
</p>
<p>
Note how the astronaut suits, and the luminous tiles on the
floor, whose colours are outside of the
<em>Spectral Locus</em>, are looking posterised.
</p>
<div class="alert alert-dark" role="alert">
<b>Note:</b> Click on the image to show the ACES AP1
out-of-gamut colours.
</div>
</figcaption>
</figure>
<p>
In the context of this document, and the portion of interest of the
ACES pipeline, the imagery is said to be in a
<em>scene-referred</em> state. A scene-referred image encodes light
values as they were captured at the camera focal plane in a given
scene. The encoded values are intrinsically linear, and
proportional, relatively, to the incident light from the scene to
the camera.</p>
<p>
The <a href="https://www.oscars.org/">A.M.P.A.S</a> formed a new
<a
href="https://community.acescentral.com/t/new-aces-working-group-gamut-mapping">Virtual
Working Group</a> with the objective of finding strategies to
manage and correct the artefacts. The Working Group is researching
a source-agnostic model that performs the mapping of scene-referred
light values from any source, i.e. any light capturing device,
irrespective of its sensitivities, to a target RGB colourspace
primaries, e.g. ACES AP1.
</p>
<p>As a contribution to the initiative, the <a
href="https://colour-science.org/">Colour Developers</a> have
designed and built an <a
href="https://github.com/colour-science/gamut-mapping-ramblings/blob/master/notebooks/gamut_mapping_medicina_01.ipynb">interactive
Jupyter Widget</a>
to explore the problem space. The widget leverages <a
href="https://github.com/colour-science/colour">Colour</a>, an
open-source Python package providing a comprehensive number of
algorithms and datasets for colour science, and <a
href="https://matplotlib.org/">Matplotlib</a>.</p>
<p>
As of this writing, the widget implements two gamut mapping study
models via sub-classes:
<ul>
<li><em>Mansencal and Scharfenberg (2020) HSV Control Based Study
Model</em> built on top of the <a
href="https://en.wikipedia.org/wiki/HSL_and_HSV">HSV
colourspace</a></li>
<li><em>Smith (2020) - RGB Saturation Study Model</em> built on
top of the <a
href="https://en.wikipedia.org/wiki/Color_spaces_with_RGB_primaries">RGB
colourspace</a></li>
</ul>
<figure class="figure">
<img src="./resources/images/Gamut_Medicina_03.png"
alt="Mansencal and Scharfenberg (2020) - HSV Control Based & Smith (2020) RGB Saturation Study Models"
class="figure-img img-fluid hand-pointer-on-hover gamut-medicina-3">
<figcaption class="figure-caption">
<p>
<em>Mansencal and Scharfenberg (2020) HSV Control Based Study
Model</em> compared with <em>Smith (2020) RGB Saturation
Study Model</em>. Out of the box, Smith (2020) model
produces less hue clumping and more pleasing output. It is
also simpler, faster and more elegant but lacks hue twists
controls.
</p>
<div class="alert alert-dark" role="alert">
<b>Note:</b> Click on the image to compare the effect of
both gamut mapping study models.
</div>
</figcaption>
</figure>
Various gamut mapping controls are offered such as changing the
compression function and its effect, or, hue twist controls for the
<em>HSV Control Based Study Model</em>. The widget also implement
various viewing controls such as showing the out-of-gamut colours
or image exposure adjustments.
</p>
<figure class="figure">
<img src="./resources/images/Gamut_Medicina_02.png"
alt="Mansencal and Scharfenberg (2020) - HSV Control Based Study Model"
class="figure-img img-fluid hand-pointer-on-hover gamut-medicina-2">
<figcaption class="figure-caption">
<p>
<em>Mansencal and Scharfenberg (2020) HSV Control Based Study
Model</em> applied onto a photograph.
</p>
<div class="alert alert-dark" role="alert">
<b>Note:</b> Click on the image to show the effect of the
gamut mapping study model.
</div>
</figcaption>
</figure>
<p>
While being order of magnitude slower than commercial applications
such as <a
href="https://www.blackmagicdesign.com/products/davinciresolve">Davinci
Resolve</a> or <a
href="https://www.foundry.com/products/nuke">The Foundry
Nuke</a>, the interactive widget is extremely useful as it allows
to tap directly into the entire Python scientific ecosystem while
promoting <em>Open Source Software</em> and reproducible research.
</p>
<p>
More information is available on the <a
href="https://github.com/colour-science/gamut-mapping-ramblings">colour-science's
Gamut Mapping Ramblings repository</a> and <a
href="https://community.acescentral.com/c/aces-development-acesnext/vwg-aces-gamut-mapping-working-group/80">ACESCentral</a>.
</p>
<p class="text-center font-weight-bolder">
Copyright © 2020 – Colour Developers – <a
href="mailto:[email protected]">[email protected]</a>
</p>
</div>
</div>
</div>
</main>
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