\begin{figure}[b]
	\centering
	\addtolength{\tabcolsep}{-4pt}
	\setlength{\resLen}{0.81in}
	\begin{tabular}{cccc}
		\begin{overpic}[width=\resLen]{results/grad_vis/orig_full.png}
			\put(2, 3){\small \color{white} $\Lv$}
		\end{overpic}
		&
		\begin{overpic}[width=\resLen]{results/grad_vis/orig_med.png}
			\put(2, 3){\small \color{white} $\kernelT\,\kernelC\,\Lv$}
		\end{overpic}
		&
		\begin{overpic}[width=\resLen]{results/grad_vis/orig_surface.png}
			\put(2, 3){\small \color{white} $\kernelS\,\Lv$}
		\end{overpic}
		&
		\begin{overpic}[width=\resLen]{results/grad_vis/orig_emitted.png}
			\put(2, 3){\small \color{white} $\Ldir$}
		\end{overpic}
		\\
		\begin{overpic}[width=\resLen]{results/grad_vis/grad_full.png}
			\put(2, 3){\small \color{white} $\dLv$}
		\end{overpic}
		&
		\begin{overpic}[width=\resLen]{results/grad_vis/grad_med.png}
			\put(2, 3){\small \color{white} $\sdev \kernelT\,\kernelC\,\Lv$}
		\end{overpic}
		&
		\begin{overpic}[width=\resLen]{results/grad_vis/grad_surf.png}
			\put(2, 3){\small \color{white} $\sdev \kernelS\,\Lv$}
		\end{overpic}
		&
		\multirow{2}{*}[2.3em]{%
			\begin{overpic}[width=\resLen]{results/grad_vis/grad_src.png}
				\put(2, 3){\small \color{white} $\dLdir$}
			\end{overpic}
		}
		\\
		\begin{overpic}[width=\resLen]{results/grad_vis/grad_full_noedge.png}
			\put(2, 3){\small \color{white} $\dLv$ (nb)}
		\end{overpic}
		&
		\begin{overpic}[width=\resLen]{results/grad_vis/grad_med_noedge.png}
			\put(2, 3){\small \color{white} $\sdev \kernelT\,\kernelC\,\Lv$ (nb)}
		\end{overpic}
		&
		\begin{overpic}[width=\resLen]{results/grad_vis/grad_surf_noedge.png}
			\put(2, 3){\small \color{white} $\sdev \kernelS\,\Lv$ (nb)}
		\end{overpic}
		&
	\end{tabular}
	\\[-3pt]
	\includegraphics[width=0.45\textwidth]{results/grad_vis/colorbar.pdf}
	\caption{\label{fig:per_component}
		\textbf{Component-wise visualizations} of interior radiance~$\Lv$ and its (partial) scene derivative~$\dLv$.
		In these images, each pixel stores a single radiance value corresponding to the ray going through the center of that pixel.
		(Top)~original radiance values; (middle)~radiance derivatives (of the red channel) with respect to the vertical displacement of the area light and the box encoded in false colors; (bottom)~same as the middle but with all the boundary integrals neglected (indicated as ``nb'').
	}
\end{figure}
