Subfloat inside multicols environment

Question

I would like to place 4 images next to each other, with a single caption underneath. Normally, I would use the following for this:

\begin{figure}[htb]
\centering
\subfloat{\includegraphics[width=0.25\linewidth]{fig1.pdf}}\hfill
\subfloat{\includegraphics[width=0.25\linewidth]{fig2.pdf}}\hfill
\subfloat{\includegraphics[width=0.25\linewidth]{fig3.pdf}}\hfill
\subfloat{\includegraphics[width=0.25\linewidth]{fig4.pdf}}\hfill
\caption{Single caption underneath all 4 images!}
\label{fig:four-figs}
\end{figure}

However, since I am in a multicols environment, I get the following error:

Package multicol Warning: Floats and marginpars not allowed inside `multicols' environment!.

How can I achieve the same effect of the subfloat, but within the multicols environment?

Here is my MWE:

\documentclass[a0,portrait]{a0poster}

\usepackage{multicol} 
\columnsep=100pt 
\columnseprule=3pt
\usepackage[svgnames]{xcolor}
\usepackage{palatino} 
\usepackage{graphicx}
\usepackage[font=small,labelfont=bf]{caption} 
\usepackage{amsfonts, amsmath, amsthm, amssymb}
\usepackage{wrapfig}
\usepackage[caption=false]{subfig}
\captionsetup[figure]{labelfont={color=NavyBlue}}

\begin{document}

\begin{multicols}{2} 

\begin{figure}[htb]
\centering
\subfloat{\includegraphics[width=0.25\linewidth]{fig1.pdf}}\hfill
\subfloat{\includegraphics[width=0.25\linewidth]{fig2.pdf}}\hfill
\subfloat{\includegraphics[width=0.25\linewidth]{fig3.pdf}}\hfill
\subfloat{\includegraphics[width=0.25\linewidth]{fig4.pdf}}\hfill
\caption{Single caption underneath all 4 images!}
\label{fig:four-figs}
\end{figure}

\end{multicols}
\end{document}

Answer 1

the same result you obtain without use of minipage:

\documentclass[a0,portrait]{a0poster}

\usepackage{multicol} 
\columnsep=100pt 
\columnseprule=3pt
\usepackage[svgnames]{xcolor}
\usepackage{palatino} 
\usepackage{graphicx}
\usepackage[font=small,labelfont=bf]{caption} 
\usepackage{amsfonts, amsmath, amsthm, amssymb}
\usepackage{wrapfig}
\captionsetup[figure]{labelfont={color=NavyBlue}}

\usepackage{lipsum}

\begin{document}
\begin{multicols}{2} 
\lipsum[1]
\begin{center}
    \includegraphics[width=0.25\linewidth]{fig1.pdf}%
    \includegraphics[width=0.25\linewidth]{fig2.pdf}%
    \includegraphics[width=0.25\linewidth]{fig3.pdf}%
    \includegraphics[width=0.25\linewidth]{fig4.pdf}
\captionof{figure}{Single caption}
\end{center}
\lipsum[2]

\end{multicols}
\end{document}

if you like to have space between images, than you need to reduce image width and inserts \hfill between them:

\begin{center}
    \includegraphics[width=0.22\linewidth]{fig1.pdf}\hfill
    \includegraphics[width=0.22\linewidth]{fig2.pdf}\hfill
    \includegraphics[width=0.22\linewidth]{fig3.pdf}\hfill
    \includegraphics[width=0.22\linewidth]{fig4.pdf}
\captionof{figure}{Single caption}
\end{center}

Answer 2

I found a solution using minipage and the captionof command of the caption package. Here it is:

\documentclass[a0,portrait]{a0poster}

\usepackage{multicol} 
\columnsep=100pt 
\columnseprule=3pt
\usepackage[svgnames]{xcolor}
\usepackage{palatino} 
\usepackage{graphicx}
\usepackage[font=small,labelfont=bf]{caption} 
\usepackage{amsfonts, amsmath, amsthm, amssymb}
\usepackage{wrapfig}
\captionsetup[figure]{labelfont={color=NavyBlue}}

\begin{document}

\begin{multicols}{2} 

\begin{minipage}{0.25\linewidth}
    \centering
    \includegraphics[width=\linewidth]{fig1.pdf}
\end{minipage}%
\begin{minipage}{0.25\linewidth}
    \centering
    \includegraphics[width=\linewidth]{fig2.pdf}
\end{minipage}%
\begin{minipage}{0.25\linewidth}
    \centering
    \includegraphics[width=\linewidth]{fig3.pdf}
\end{minipage}%
\begin{minipage}{0.25\linewidth}
    \centering
    \includegraphics[width=\linewidth]{fig4.pdf}
\end{minipage}
\captionof{figure}{Single caption}

\end{multicols}
\end{document}