LaTeX of the APCA-W3 Base Formula The following is a trial of GitHub's new LaTeX and MathJax support. As you can see there are some bugs at the moment (browser dependent??) and there are some missing features or commands.
$$\begin{align} \\\
\mathbf{APCA}\ \mathbf{\bullet \ W3}\ \ &\mathbf{\scriptstyle version\ { 0.1.9}\ { developed\ for\ WCAG\ 3\ contrast\ guidelines}} \\\
{\scriptstyle Using:}\ & \ \mathit{\scriptstyle APCA\ Contrast\ Prediction\ Equation\ \ 0.0.98G-4g-base-W3} \\\\[3ex]
Light&ness\ Contrast = L^c \\\\[2ex]
\textstyle Where:\quad \quad \ & \ \\\
\scriptstyle (reverse\ notation)\ \ & \\\\[1ex]
{\scriptstyle Clamp\ Minimu} & {\scriptstyle m\ Contrast\ to\ \mathit1\mathit0 \% \ then\ Offset\ \& \ Final\ Scale} \\\\[0.5ex]
L^c = & \begin{cases}
\ 0.0 \ \ \ & if\ \big\vert S_{apc} \big\vert < W_{clamp}\\\\[0.25ex]
\big(\ S_{apc} - W_{offset}\ \big) \times 100.0\ \ & if\ \ S_{apc}\ > 0 \\\\[0.5ex]
\big(\ S_{apc} + W_{offset}\ \big) \times 100.0\ \ & if\ \ S_{apc}\ < 0
\end{cases} \\\\[1.5ex]
{\scriptstyle Determine\ Polar} & {\scriptstyle ity,\ Find\ Lightness\ Difference,\ \& \ Scale} \\\\[0.25ex]
S_{apc} = & \begin{cases}
\big(\ Y_{bg}^{Nbg} - Y_{txt}^{Ntx}\ \big) \times W_{scale} \ \ & if\ \ Y_{bg} > Y_{txt}\ \Big(\ ^{\ \ Normal\ Polarity}_{(dark\ text/light\ bg)} \Big) \\\\[0.5ex]
\big(\ Y_{bg}^{Rbg} - Y_{txt}^{Rtx}\ \big) \times W_{scale} \ \ & if\ \ Y_{bg} < Y_{txt}\ \Big(\ ^{\ Reverse\ Polarity}_{(light\ text/dark\ bg)} \Big)
\end{cases} \\\\[2.25ex]
{\scriptstyle Soft\ Clip\ \& \ C} & {\scriptstyle lamp\ Black\ Levels} \\\\[0.25ex]
Y_{txt} & = \ f_{sc}(Ys) \quad_{of\ the\ text,\ symbol,\ or\ object.}^{Where\ Ys\ is\ derived\ from\ the\ color} \\\\[1ex]
Y_{bg} & = \ f_{sc}(Ys) \quad_{used\ for\ the\ adjacent\ background.}^{Where\ Ys\ is\ derived\ from\ the\ color} \\\\[1ex]
Y_{fld} & = \ \mathrm{\scriptstyle Unused\ in\ W3\ version} \\\\[1.5ex]
f_{sc} & (Y_c) = \begin{cases}
0.0 \ \quad \ & if\ \ Y_c < 0.0 \\\\[0.5ex]
Y_c + \big( B_{thrsh} - Y_c \big)^{B_{clip}} \ & if\ \ Y_c < B_{thrsh} \\\\[0.5ex]
Y_c \ \quad \ & Otherwise
\end{cases} \\\\[1.5ex]
{\scriptstyle Estimate\ Scr} & {\scriptstyle een\ Luminance\ Using\ sRGB\ Coefficients} \\\\[0.25ex]
Ys & = \displaystyle\sum \begin{cases}
{\color{#f8a}\ (\mathbf R^\prime \div 255.0)^{S_{trc}} \times 0.2126729} \\\
{\color{#6f6} (\mathbf G^\prime \div 255.0)^{S_{trc}} \times 0.7151522} \\\
{\color{#8bf} (\mathbf B^\prime \div 255.0)^{S_{trc}} \times 0.0721750} \\
\end{cases} \\\\[1ex]
\hline
Constant&s\ for\ \mathit0\mathit.\mathit0\mathit.\mathit9\mathit8G-\mathit4g-sRGB: \\\
&\begin{alignedat}{3}
{\scriptstyle Powercur} & {\scriptstyle ve\ Exponents} \quad \quad & \quad {\scriptstyle Clamp} & {\scriptstyle s\ \& \ Scalers} \\\
S_{trc} & = 2.4 \quad & \quad B_{clip} & = \ 1.414 \\\
Ntx & = 0.57 \quad & \quad B_{thrsh} & = \ 0.022 \\\
Nbg & = 0.56 \quad & \quad W_{scale} & = \ 1.14 \\\
Rtx & = 0.62 \quad & \quad W_{offset} & = \ 0.027 \\\
Rbg & = 0.65 \quad & \quad W_{clamp} & = \ 0.1 \\\
\end{alignedat} \\\\[0.5ex]
\hline
INPU&T:\ \ {\color{#f8a}R^\prime}, {G^\prime}, {\color{#8bf}B^\prime}\ \mathbf{\in\ sRGB} \ \ (Range: 0.0-255.0) \\\\[0.5ex]
\hline
\mathit{\scriptscriptstyle Copyright\ ©\ 2019-2022\ by\ Andrew\ Somers.\ All\ Rights\ Reserved.} \\\
\\\
\end{align}$$
For more on APCA, please see: git.myndex.com for more.
Copyright © 2019-2022 by Andrew Somers. All Rights Reserved.
NOTICE: "APCA is a method for predicting text contrast on self-illuminated displays for web-based content. Some use-cases are prohibited by license, including the following: use in medical, clinical evaluation, human safety related, aerospace, transportation, military applications, are strictly prohibited without a specific license in writing granting such use."