clip a image with relative coordinate

Question

I want to clip a image with relative coordinate.

see below example:

\documentclass{standalone}
\usepackage{tikz}
\tikzset{mynode/.style={draw,solid,circle,inner sep=1pt}}

\usepackage{etoolbox}
\newbool{DEBUG}
\booltrue{DEBUG}
%\boolfalse{DEBUG}

\begin{document}
\def\infilename{tiger.pdf}
\begin{tikzpicture}[>=latex]
    \node[anchor=south west,inner sep=0] (image) at (0,0,0) {\includegraphics[width=5cm]{\infilename}};
    \begin{scope}[x={(image.south east)},y={(image.north west)}]
        \clip (0.4,0.6) rectangle (0.5,0.7);
        \ifbool{DEBUG}{\small
            \draw[help lines,xstep=.1,ystep=.1] (0,0) grid (1.001,1.001);
            \foreach \x in {1,...,9} { \node [anchor=north] at (\x/10,0) {\x};}
            \foreach \y in {1,...,9} { \node [anchor=east] at (0,\y/10) {\y};}
        };
    \end{scope}
\end{tikzpicture}

\end{document}

But it seems only clip the help lines but not on origin picture. I like relative coordinate because it's more easy to locate the exact position which I want.

Is it possible to fix it? In this example, I only want to extract the rectangle area (0.4,0.6) to (0.5,0.7). say full image is (0,0) to (1,1).

Answer 1

The problem is that you need to need to know how large the image is before you can apply a relative clip. The usual ways to do that are to use a savebox or use \phantom.

Using savebox:

\tikzset{mynode/.style={draw,solid,circle,inner sep=1pt}}
\usetikzlibrary{calc}

\usepackage{etoolbox}
\newbool{DEBUG}
\booltrue{DEBUG}
%\boolfalse{DEBUG}

\newsavebox{\tempbox}

\usepackage{mwe}% for example images

\begin{document}
\def\infilename{example-image}%
\savebox{\tempbox}{\includegraphics[width=5cm]{\infilename}}%
\fbox{
\begin{tikzpicture}[>=latex]
  \path (0,0) (\wd\tempbox,\ht\tempbox);% set bounding box
    \begin{scope}[x={\wd\tempbox},y={\ht\tempbox}]
        \clip (0.4,0.6) rectangle (0.5,0.7);
        \node[anchor=south west,inner sep=0] {\usebox\tempbox};
        \ifbool{DEBUG}{\small
            \draw[help lines,xstep=.1,ystep=.1] (0,0) grid (1.001,1.001);
            \foreach \x in {1,...,9} { \node [anchor=north] at (\x/10,0) {\x};}
            \foreach \y in {1,...,9} { \node [anchor=east] at (0,\y/10) {\y};}
        };
    \end{scope}
\end{tikzpicture}}

\end{document}

Using \phantom:

\documentclass{standalone}
\usepackage{tikz}
\tikzset{mynode/.style={draw,solid,circle,inner sep=1pt}}
\usetikzlibrary{calc}

\usepackage{etoolbox}
\newbool{DEBUG}
\booltrue{DEBUG}
%\boolfalse{DEBUG}

\usepackage{mwe}% for example images

\begin{document}
\def\infilename{example-image}
\fbox{
\begin{tikzpicture}[>=latex]
    \node[anchor=south west,inner sep=0] (image) {\phantom{\includegraphics[width=5cm]{\infilename}}};
    \begin{scope}[x={(image.south east)},y={(image.north west)}]
        \clip (0.4,0.6) rectangle (0.5,0.7);
        \node[anchor=south west,inner sep=0] {\includegraphics[width=5cm]{\infilename}};
        \ifbool{DEBUG}{\small
            \draw[help lines,xstep=.1,ystep=.1] (0,0) grid (1.001,1.001);
            \foreach \x in {1,...,9} { \node [anchor=north] at (\x/10,0) {\x};}
            \foreach \y in {1,...,9} { \node [anchor=east] at (0,\y/10) {\y};}
        };
    \end{scope}
\end{tikzpicture}}

\end{document}

Answer 2

I think it's better to combine savebox and phantom.

See result below:

\documentclass{standalone}
\usepackage{tikz}
\usepackage{etoolbox}

\tikzset{mynode/.style={draw,solid,circle,inner sep=1pt}}

\usepackage{etoolbox}
\newbool{DEBUG}
\booltrue{DEBUG}
%\boolfalse{DEBUG}

\begin{document}
\def\infilename{tiger.pdf}
\newsavebox{\graphbox}
\savebox{\graphbox}{\includegraphics[width=5cm]{\infilename}}
\begin{tikzpicture}[>=latex]
    \node[anchor=south west,inner sep=0] (image) at (0,0,0) {\phantom{\usebox\graphbox}};
    \begin{scope}[x={(image.south east)},y={(image.north west)}]
        \ifbool{DEBUG}{\small
            \draw[help lines,xstep=.1,ystep=.1] (0,0) grid (1.001,1.001);
            \foreach \x in {1,...,9} { \node [anchor=north] at (\x/10,0) {\x};}
            \foreach \y in {1,...,9} { \node [anchor=east] at (0,\y/10) {\y};}
        };
        \clip (0.4,0.6) rectangle (0.5,0.7);
        \node[anchor=south west,inner sep=0] {\usebox\graphbox};
    \end{scope}
\end{tikzpicture}

\end{document}

result picture (with helplines on):

Answer 3

Without tikz:

\documentclass{article}
\usepackage{graphicx,calc}
\def\mygraphic{\includegraphics{tiger}}
\newlength\gh \setlength\gh{\heightof{\mygraphic}}
\newlength\gw \setlength\gw{\widthof{\mygraphic}}
\begin{document}
\includegraphics[scale=0.5,trim= {.4\gw} {.6\gh} {.5\gw} {.3\gh}, clip]{tiger}%
\end{document}

Answer 4

Read all answers and got below result:

1. If open the debug option, it will print the help lines.
2. If comment out the debug option, it will only output the clip area.

code as below:

\documentclass{standalone}
\usepackage{tikz}
\usepackage{graphicx}
\usepackage{calc}

\usepackage{etoolbox}
\newbool{DEBUG}
\booltrue{DEBUG}
%\boolfalse{DEBUG}

\begin{document}
\def\infilename{tiger.pdf}

\newsavebox{\graph}\savebox{\graph}{\includegraphics[]{\infilename}}
\newlength\gh\setlength\gh{\heightof{\usebox\graph}}
\newlength\gw\setlength\gw{\widthof{\usebox\graph}}

\begin{tikzpicture}[>=latex,
  image/.style={anchor=south west,inner sep=0}]
    \ifbool{DEBUG}{
        \node[image] (NI) at (0,0){\phantom{\usebox\graph}};
        \begin{scope}[x={(NI.south east)},y={(NI.north west)}]
            \draw[help lines,xstep=.1,ystep=.1] (0,0) grid (1.001,1.001);
            \foreach \x in {1,...,9} { \node [anchor=north] at (\x/10,0) {\x};}
            \foreach \y in {1,...,9} { \node [anchor=east] at (0,\y/10) {\y};}
        \end{scope}
    };
    \clip (0.4\gw,0.6\gh) rectangle (0.5\gw,0.7\gh);
    \node[image] {\usebox\graph};
    %\draw[|<->|,very thick,red!60] 
    %    (0.5\gw,0.5\gh) -- node[pos=0.5, auto] {$600$} ++(0.2\gw,0\gh);
\end{tikzpicture}

\end{document}

Output when debug option on:

Output when debug option off: