Print the "scale factor" on each figure as a watermark

Question

From a previous question (\includegraphics: get the "scale" value of a figure whose size is expressed by "width") I learned how to get the scale factor of a figure inserted by the \includegraphics command.

Now I'd like to print, as a watermark, the scaling value on each figure in my document. I started from this:

\documentclass{article}
\pdfoutput=1
\usepackage{graphicx}
\usepackage{color}

\makeatletter
\let\ORG@Gscale@box\Gscale@box
\long\def\Gscale@box#1{%
  \xdef\thelastscalefactor{#1}%
  \ORG@Gscale@box{#1}}
\makeatother

\begin{document}

\includegraphics[width=0.4\textwidth]{example-image}
\colorbox{red}{\the\thelastscalefactor}

\end{document}

The best solution would be to redefine the \includegraphics command to do this but it would be ok also to define a \myincludegraphics command like in another issue of mine https://tex.stackexchange.com/a/455293/33634.

Finally I also have an issue with the string \the\thelastscalefactor:

! You can't use `the character 0' after \the.
\thelastscalefactor ->0
                       .3437

score 3 · Answer 1 · answered May 23 '19 at 21:17

TikZ might be a bit overkill, but at least I know how to do it ...

\documentclass{article}
\pdfoutput=1
\usepackage{tikz} % loads graphicx and xcolor

\makeatletter
\let\ORG@Gscale@box\Gscale@box
\long\def\Gscale@box#1{%
  \xdef\thelastscalefactor{#1}%
  \ORG@Gscale@box{#1}}
\makeatother

\newcommand\myincludegraphics[2][]{%
\begin{tikzpicture}
\node [inner sep=0] (img) {\includegraphics[#1]{#2}};
\node [below right,fill=red,draw=black] at (img.north west) {\thelastscalefactor}; % no \the needed
\end{tikzpicture}%
}

\begin{document}

\myincludegraphics[scale=1]{example-image}

\myincludegraphics[width=0.6\textwidth]{example-image}

\myincludegraphics[scale=0.5]{example-image}

\end{document}

Ok. I would modify your code adding \let\oldincludegraphics\includegraphics and using \renewcommand\includegraphics[2][]{... instead so you can keep the \includegraphics commands in the rest of the file. — Gabriele, May 23 '19 at 21:37

frougon · Accepted Answer · 2019-05-23T23:05:01.237

Here is one solution:

\documentclass{article}
\usepackage{graphicx}
\usepackage{xcolor}

\makeatletter
\let\ORG@Gscale@box\Gscale@box
\long\def\Gscale@box#1{%
  \xdef\thelastscalefactor{#1}%
  \ORG@Gscale@box{#1}}
\makeatother

\newsavebox{\mybox}

% Make the top left corner of the annotation box start at 10% (1-0.9)
% from the left edge of the image and at 10% (0.1) from the top edge (this
% is why it lies exactly on the diagonal in the screenshot).
\newcommand*{\putimagescale}[1]{%
  \sbox{\mybox}{#1}%
  \usebox{\mybox}%
  \hbox to 0pt{\kern-0.9\wd\mybox
               \vbox to \ht\mybox{%
                 \kern0.1\ht\mybox
                 \hbox{\colorbox{red}{\thelastscalefactor}}%
                 \vss
               }%
               \hss
  }}

% Alternative method: the placement is done differently. In particular, the
% vertical offset is counted from the baseline of the image to the baseline of
% the annotation box.
% \newcommand*{\putimagescale}[1]{%
%   \sbox{\mybox}{#1}%
%   \usebox{\mybox}%
%   \makebox[0pt][r]{%
%     \raisebox{0.8\ht\mybox}[0pt][0pt]{%
%       \rlap{\colorbox{red}{\thelastscalefactor}}%
%     }%
%     \hspace*{0.9\wd\mybox}%
%   }%
% }

% You can uncomment the following if you want \includegraphics to be redefined
% so as to always print the image scale (obviating the need to manually call
% \putimagescale).
%
% \let\includegraphicsORI\includegraphics
% \renewcommand*{\includegraphics}[2][]{%
%   \putimagescale{\includegraphicsORI[#1]{#2}}}

\begin{document}

\putimagescale{%
  \includegraphics[width=0.4\textwidth]{example-image}}

\end{document}

The alternative method gives (the vertical placement is not the same):

Nice. I suggest this editing: \let\oldincludegraphics\includegraphics and \renewcommand\includegraphics[2][]{\putimagescale{\oldincludegraphics[#1]{#2}}}. Thank you. — Gabriele, May 23 '19 at 21:47
Feel free to do it in your document, but I find it maybe a bit excessive for general use, as it will then apply to all \includegraphics commands. Well, I can put it in the form of a comment. — frougon, May 23 '19 at 21:51
I've put your suggestion in the form of a comment, ready to be used, and added a different implementation for \putimagescale (most notably, vertical placement of the annotation is different). Look at the comments for details. — frougon, May 23 '19 at 23:08

Print the "scale factor" on each figure as a watermark

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