I borrowed an image from Herbert's answer without his permission.
User defined data:
\def\M{3}% columns
\def\N{3}% rows
\def\scale{1}% scale
\def\filename{herbert}% filename
% Specify the cropping area.
\def\L{-2}
\def\B{-1.5}
\def\R{2}
\def\T{3}
Steps:
- Specify the number of columns and rows. The greater values, the more accurate coordinates. Avoid changing these values after completing the 3rd step, unless you are happy to redo the 3rd step.
- Specify the scaling factor. It does not depend on other steps.
- Specify the cropping area. You might need a trial and error approach to find it.
- Compile the following code with either
xelatex or latex-dvips-ps2pdf. See the result, if the cropping region does not suit your requirement, do the 3rd and 4th again.
Hopefully, the given comments in the code are self-explanatory.
\documentclass[pstricks,border=12pt]{standalone}
\def\M{3}% columns
\def\N{3}% rows
\def\scale{1}% scale
\def\filename{herbert}% filename
\usepackage{graphicx}
\newsavebox\IBox
\savebox\IBox{\includegraphics[scale=\scale]{\filename}}
\usepackage{pstricks}
\psset
{
xunit=0.5\dimexpr\wd\IBox/\M\relax,
yunit=0.5\dimexpr\ht\IBox/\N\relax,
}
\begin{document}
% The following figure shows an image with a grid enabled.
% Use the grid to find the cropping area.
\begin{pspicture}[showgrid=true](-\M,-\N)(\M,\N)
\rput(0,0){\usebox\IBox}
\end{pspicture}
% Specify the cropping area.
\def\L{-2}
\def\B{-1.5}
\def\R{2}
\def\T{3}
\begin{pspicture}[showgrid=false](\L,\B)(\R,\T)
\begin{psclip}{\psframe[linestyle=none,framearc=0.5,dimen=middle](\L,\B)(\R,\T)}
\rput(0,0){\usebox\IBox}
\end{psclip}
\end{pspicture}
\end{document}
Output:
Original image with a grid.

Cropped image.
