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<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta property="og:image" content="http://connorgr.github.io/d3-cam02/static/mediathumb.png" />
<meta property="og:description" content="d3-cam02: a D3.js library to support CIECAM02 and CIECAM02-UCS color appearence models." />
<meta property="og:url"content="http://connorgr.github.io/d3-cam02" />
<meta property="og:title" content="d3-cam02" />
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<h1>
CIECAM02 Color
</h1>
<a href="http://gramaz.io">Connor Gramazio</a>
</section>
<div class="container">
<section>
<p><strong>d3-cam02</strong> is a beta-release
<a href="http://d3js.org">D3</a> extension
that supports CIECAM02-UCS Jab and CIECAM02 JCh color specifications.</p>
<p>d3-cam02 is open sourced
<a href="https://github.com/connorgr/d3-cam02">here</a>. If you want to take
a look at the extension in full, check it out on
<a href="https://unpkg.com/d3-cam02">unpkg</a>.</p>
<strong>Known Issues</strong>
<ul>
<li>There is undefined behavior when converting colors that substantially
fall outside of the sRGB gamut from CIECAM02 or CIECAM02-UCS to sRGB
(e.g., <code>d3.jch(12,90,90).rgb()</code>).
This behavior is, strangely, consistent with other CIECAM02 to XYZ to
RGB conversion implementations.
If you know why this happens, I'd love to know!
</li>
</ul>
<strong>Table of contents</strong>
<ol>
<li>
<a href="#installation">Installation</a>
</li>
<li>
<a href="#ciecam02">What is CIECAM02?</a>
<ol>
<li><a href="#perceptualUniformity">Perceptual Uniformity</a></li>
<li><a href="#cam02vsucs">CIECAM02 vs. CIECAM02-UCS</a></li>
<li><a href="#cam02vsLab">CIECAM02-UCS vs. CIELAB</a></li>
</ol>
</li>
<li><a href="#examples">Examples</a></li>
<li><a href="#furtherReading">Further reading</a></li>
</ol>
</section>
<h2>Installation <a name="installation" href="#installation">📎</a></h2>
<section>
<p>To access the latest version of d3-cam02, grab it on
<a href="https://unpkg.com/d3-cam02">unpkg</a>. Be sure to load d3-cam02
after d3-color is loaded (be it through d3.v4.js, d3-color.js, or
otherwise).</p>
<p>If installing and building from scratch, download the repo either through
<a href="https://github.com/connorgr/d3-cam02">GitHub</a> or through
<a href="https://npmjs.com/d3-cam02">npm</a>.
Once you've downloaded it, just run <code>npm install</code>, which will
install the required dependencies.
Note that building requires
<a href="https://nodejs.org/en/">node.js</a> and
<a href="https://www.npmjs.com/">npm</a>.</p>
<p>D3 module dependencies:
<a href="https://github.com/d3/d3-color">d3-color</a>.</p>
</section>
<h2>What is CIECAM02? <a name="ciecam02" href="#ciecam02">📎</a></h2>
<section>
<p>CIECAM02 is a color appearence model designed by the International
Commision on Illumination to accurately model human
color perception [<a href="#cam02wiki">1</a>]. d3-cam02
exposes two color specifications. One is CIECAM02 JCh, which defines color
in terms of lightness,
<a href="https://en.wikipedia.org/wiki/Chroma#Color">chroma</a>, and hue.
The second is CIECAM02-UCS Jab, which defines color in terms of human
opponent color processing: lightness (J), redness-to-greenness (a), and
blueness-to-yellowness (b).
The lightness of JCh and Jab are not equivalent given that Jab is put
through a lightness transform when defined by JCh color.
</p>
<div class="aside">
<strong>Aside for color scientists</strong>
<p>Given the variance in display output we assume average viewing
conditions when calculating CIECAM02, but include dim and dark transforms
in the source code.</p>
<p>While there are always precision concerns when defining color for online
audiences, Maureen Stone <em>et al</em> found that display color variance
was still small enough to preserve the utility of using CIELAB color
online [<a href="#stoneCIELAB">2</a>].
We make the assumption that this also holds true of CIECAM02 and
CIECAM02-UCS color.
</p>
</div>
<h3>Perceptual uniformity
<a name="perceptualUniformity" href="#perceptualUniformity">📎</a>
</h3>
<p><em>Perceptual uniformity</em> is the idea that Euclidean distance
between colors in color space should match human color perception distance
judgements. For example, a blue and red that are distance <em>d</em> apart
should look as discriminable as a green and purple that are distance
<em>d</em> apart.</p>
<p>Perceptual uniformity is important for visualization because color
distance often encodes meaning, and a visualization's effectiveness is
largely derived from its ability to accurately convey underlying data.</p>
<p>Digital color spaces like RGB and CYM <em>are not</em> perceptually
uniform, and should therefore not be used when creating visualization
color scales or palettes. Instead, designers should utilize spaces that
are modeled after human color perception such as CIELAB or CIECAM02-UCS
(see <a href="#cielabVsCam02ucs">below</a> for a comparison).</p>
<h3>CIECAM02 vs. CIECAM02-UCS
<a name="cam02vsucs" href="#cam02vsucs">📎</a>
</h3>
<p>CIECAM02 is a color appearence model that was designed to better simulate
typical human color vision. The goal of such models is to define color space
such that linearly changing color specifications like chroma or hue also
produces linear changes in human perception of chroma or hue. To achieve
this, CIECAM02 defines color by simulating responses of human long, medium,
and short cone cells with CIECAT02 [<a href="#lmsColorSpace">3</a>] and
translates those responses into familiar color terms (e.g., hue).</p>
<p>CIECAM02-UCS is a manipulation of CIECAM02 that makes the original space
perceptually uniform [<a href="#cam02ucsPaper">4</a>].
To calculate perceptual/color distance, you can use
<em>color</em>.de(<em>color</em>), which calculates an adjusted
Euclidean distance between the two colors. This distance is commonly
referred to as ∆E or DE [<a href="#deWiki">5</a>].</p>
<p>Because CIECAM02-UCS is a transform of CIECAM02, lightness (J) is not
equivalent between the two spaces.</p>
<h3 id="#cielabVsCam02ucs">
CIECAM02-UCS vs. CIELAB
<a name="cam02vsLab" href="#cam02vsLab">📎</a>
</h3>
<p>Perhaps the most common perceptually uniform color space that is currently
used by designers is CIELAB color space characterized with CIE Standard
Illuminant D65. If you've ever used d3.lab, you've used this color space.
So how does CIECAM02-UCS differ from CIELAB? Maybe the best way is to see
color interpolation differences:</p>
<div id="interpolationContainer"></div>
<p>As evident, even though CAM02-UCS and CIELAB are both perceptually
uniform approximations, they define color in different ways.
Also note how each compares to RGB, which is not perceptually grounded.
You can see the assymetry between CIELAB and CIECAM02-UCS in Li, Cuo, and
Luo's plot comparing uniformity results using colors from the Optical
Society of America, where more grid-like meshes reflect greater perceptual
uniformity:</p>
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<text transform="matrix(1 0 0 1 13.1667 225.5001)" class="st2 st3">x: a*</text>
<text transform="matrix(1 0 0 1 13.1667 247.1001)" class="st2 st3">y: b*</text>
<text transform="matrix(1 0 0 1 13.1667 268.7001)" class="st2 st3">tick: 10 units</text>
<text transform="matrix(1 0 0 1 100.9446 14)" class="st4 st3">CIELAB</text>
<text transform="matrix(1 0 0 1 344.9331 14)" class="st4 st3">CIECAM02-UCS</text>
</svg>
<p class="caption">CIELAB and CIECAM02-UCS comparison reconstructed from Li, Cui, and Luo
2006 [<a href="#uniformColorPaper">6</a>]. Non-skewed grids reflect
perceptual uniformity. Data based on fitting perceptually uniform colors
as determined by the Optical Society of America.</p>
<p>So, is it worth using CIECAM02-UCS instead of CIELAB? As with most design
decisions, there isn't a definite answer. Although CIECAM02 gives a more
uniform approximation, it is unclear what the actual magnitude of difference
would be on average for online audiences given the diaspora of displays that
an audience could use. But, greater precision never hurts either.
Ultimately, by even considering perceptual uniform spaces to begin with you
are taking a step in the right direction, regardless of which you
select.</p>
</section>
<h2>Examples <a name="examples" href="#examples">📎</a></h2>
<section>
<p><a href="http://bl.ocks.org/connorgr/0a299fe77d5c7feccd22e02f2ac5d69b">Interactive CIECAM02 and CIECAM02-UCS color picker</a></p>
</section>
<h2>Further reading <a name="furtherReading" href="#furtherReading">📎</a></h2>
<section>
<h3>Citations</h3>
<ol>
<li><a href="https://en.wikipedia.org/wiki/CIECAM02" id="cam02wiki">Wikipedia entry on CIECAM02 color</a></li>
<li><a href="https://research.tableau.com/paper/engineering-model-color-difference-function-size" id="stoneCIELAB">Stone, Szafir, Setlur. "An Engineering Model for Color Difference as a Function of Size," <em>22nd IS&T Color and Imaging Conference</em>. 2014.</a></li>
<li><a href="https://en.wikipedia.org/wiki/LMS_color_space" id="lmsColorSpace">Wikipedia entry on LMS color space</a></li>
<li><a href="https://scholar.google.com/scholar?q=CIECAM02+and+Its+Recent+Developments+luo" id="cam02ucsPaper">Luo and Li. "CIECAM02 and its recent developments," <em>Advanced Color Image Processing and Analysis</em>. 2013.</a></li>
<li><a href="https://en.wikipedia.org/wiki/Color_difference" id="deWiki">Wikipedia entry on color difference (∆E or DE)</a></li>
<li><a href="http://dx.doi.org/10.1002/col.20227" id="uniformColorPaper">Luo, Cui, and Li. "Uniform Colour Spaces Based on CIECAM02 Colour Appearance Model," <em>Color Research & Application</em>. 2006.</a></li>
</ol>
<h3>Other useful links</h3>
</section>
</div>
<p style="width: 100%; text-align: center; margin-top: 100px;color: #aaa;">Provided free-to-use and open-sourced. See Github for specific licensing information.</p>
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