How to put 6 images in 3 columns-2 rows?
One more suggestion:
- make figure content centered with use of
\centering
- between sub figures insert
\hfil
- purpose of
\quad
is not clear, let remove it - centering of
subfigure
content is surplus. Rather make sub figure width smaller and adopt figure width to width of subfigure
Complete code:
\documentclass{article}
\usepackage{graphicx}
\usepackage{caption,subcaption}
\usepackage[showframe]{geometry}
\begin{document}
\begin{figure}[htb]
\centering % <-- added
\begin{subfigure}{0.25\textwidth}
\includegraphics[width=\linewidth]{example-image-a}
\caption{image1}
\label{fig:1}
\end{subfigure}\hfil % <-- added
\begin{subfigure}{0.25\textwidth}
\includegraphics[width=\linewidth]{example-image-b}
\caption{image2}
\label{fig:2}
\end{subfigure}\hfil % <-- added
\begin{subfigure}{0.25\textwidth}
\includegraphics[width=\linewidth]{example-image-c}
\caption{image3}
\label{fig:3}
\end{subfigure}
\medskip
\begin{subfigure}{0.25\textwidth}
\includegraphics[width=\linewidth]{example-image-a}
\caption{image4}
\label{fig:4}
\end{subfigure}\hfil % <-- added
\begin{subfigure}{0.25\textwidth}
\includegraphics[width=\linewidth]{example-image-b}
\caption{image5}
\label{fig:5}
\end{subfigure}\hfil % <-- added
\begin{subfigure}{0.25\textwidth}
\includegraphics[width=\linewidth]{example-image-c}
\caption{image6}
\label{fig:6}
\end{subfigure}
\caption{Fasi del processo di impregnazione}
\label{fig:images}
\end{figure}
\end{document}
The result is:
I don't think you need those \quads. Add a blank line between the rows.
\documentclass{article}
\usepackage[demo]{graphicx}
\usepackage{caption, subcaption}
\usepackage[showframe]{geometry}
\begin{document}
\begin{figure}[H]
\begin{subfigure}{0.3\textwidth}
\centering
\includegraphics[width=.8\linewidth]{imp₁.png}
\caption{image1}
\label{fig:1}
\end{subfigure}%
\begin{subfigure}{0.3\textwidth}
\centering
\includegraphics[width=.8\linewidth]{imp₂.png}
\caption{image2}
\label{fig:2}
\end{subfigure}
\begin{subfigure}{0.3\textwidth}\quad
\centering
\includegraphics[width=.8\linewidth]{imp₃.png}
\caption{image3}
\label{fig:3}
\end{subfigure}
\medskip
\begin{subfigure}{0.3\textwidth}
\centering
\includegraphics[width=.8\linewidth]{imp₄.png}
\caption{image4}
\label{fig:4}
\end{subfigure}
\begin{subfigure}{0.3\textwidth}
\centering
\includegraphics[width=.8\linewidth]{imp₅.png}
\caption{image5}
\label{fig:5}
\end{subfigure}
\begin{subfigure}{0.3\textwidth}
\centering
\includegraphics[width=.8\linewidth]{imp₆.png}
\caption{image6}
\label{fig:6}
\end{subfigure}
\caption{Fasi del processo di impregnazione}
\label{fig:images}
\end{figure}
\end{document}
You did \quad before the the third \includegraphics moving it behind it like in the other cases should fix it.
\begin{figure}[H]
\begin{subfigure}{0.3\textwidth}
\centering
\includegraphics[width=.8\linewidth]{imp_1.png}\quad
\caption{image1}
\label{fig:1}
\end{subfigure}%
\begin{subfigure}{0.3\textwidth}
\centering
\includegraphics[width=.8\linewidth]{imp_2.png}\quad
\caption{image2}
\label{fig:2}
\end{subfigure}
\begin{subfigure}{0.3\textwidth}%"\quad" not here since this will insert a spacing before the image.
\centering
\includegraphics[width=.8\linewidth]{imp_3.png}\quad %but here
\caption{image3}
\label{fig:3}
\end{subfigure}
\medskip
\begin{subfigure}{0.3\textwidth}
\centering
\includegraphics[width=.8\linewidth]{imp_4.png}\quad
\caption{image4}
\label{fig:4}
\end{subfigure}
\begin{subfigure}{0.3\textwidth}
\centering
\includegraphics[width=.8\linewidth]{imp_5.png}\quad
\caption{image5}
\label{fig:5}
\end{subfigure}
\begin{subfigure}{0.3\textwidth}
\centering
\includegraphics[width=.8\linewidth]{imp_6.png}
\caption{image6}
\label{fig:6}
\end{subfigure}
\caption{Fasi del processo di impregnazione}
\label{fig:images}
\end{figure}