cropping some part of a png image with tikz

Question

A follow up to this answer:

I am clipping a png image to which I want to specify scaled coordinates for the crop command.

So that

\clip (0,0) rectangle + (1,1);

crops nothing, and

\clip (0,0) rectangle + (0.4,0.6);

crops 40% in the x direction and 60% in the y direction.

How can I do it?

MWE

\documentclass{article}
\usepackage{tikz}
\begin{document}
Lorem ipsum
\begin{tikzpicture}
\clip (0,0) rectangle + (1,1);
{\includegraphics[width=\textwidth]{image01.png}};
\end{tikzpicture}
\end{document}

where image01.png is here

Answer 1

First you need to measure the width and height of the image using a savebox (or at least the height if you specify with width).

The only way I know of to use \includegraphics (or \usebox) is inside a node.

\documentclass{article}
\usepackage{tikz}
\begin{document}
Lorem ipsum
\begin{tikzpicture}
\sbox0{\includegraphics{example-image}}% get width and height
\begin{scope}[xscale={\wd0/1cm}, yscale={\ht0/1cm}, local bounding box=A]
\clip (0,0) rectangle (1,1);
\node[above right, inner sep=0pt] at (0,0) {\usebox0};
\end{scope}
\begin{scope}[xscale={\wd0/1cm}, yscale={\ht0/1cm}, shift=(A.north west)]
\clip (0,0) rectangle (0.4,0.6);
\node[above right, inner sep=0pt] at (0,0) {\usebox0};
\end{scope}
\end{tikzpicture}
\end{document}