Knowing how much \resizebox scales

Question

Is it possible to know how much a \resizebox scales something for further use in a \scalebox?

To clarify, take this example:

\documentclass{article}
\usepackage[paperwidth=12cm]{geometry}
\usepackage{graphicx}
\begin{document}
\def\figurea{\includegraphics[width=5cm]{example-image-a}}
\def\figureb{\includegraphics[width=2.5cm]{example-image-b}}
This is \texttt{fig-a} with its natural size:

\figurea
\bigskip

This is \texttt{fig-b} with its natural size:

\figureb
\bigskip

This is \texttt{fig-a} scaled to fit the page width:

\resizebox{\textwidth}{!}{\figurea}
\bigskip

How do I rescale \texttt{fig-b} to keep its relative size compared to \texttt{fig-a} without knowing its actual size?
\bigskip

\texttt{Insert a nice piece of code here :)}

\end{document}

I want to have fig-b with the same relative size to fig-a without actually knowing the size of any of them.

Also, as in the example, there will be text in between the figures, so putting them in the same \resizebox is not an option.

David Carlisle · Accepted Answer · 2018-01-09T23:11:16.333

11

\resizebox is just \scalebox with a scale factor being the number that you ask for. So you can just persuade it to expose that number rather than just use it in a local group and discard it.

\documentclass{article}
\usepackage[paperwidth=12cm]{geometry}
\usepackage{graphicx}
\makeatletter
\let\zz\Gscale@box
\long\def\Gscale@box#1{%
\xdef\thelastscalefactor{#1}%
\zz{#1}}

\makeatother
\begin{document}
\def\figurea{\includegraphics[width=5cm]{example-image-a}}
\def\figureb{\includegraphics[width=2.5cm]{example-image-b}}
This is \texttt{fig-a} with its natural size:

\figurea
\bigskip

This is \texttt{fig-b} with its natural size:

\figureb
\bigskip

This is \texttt{fig-a} scaled to fit the page width:

\noindent%you need this:-)
\resizebox{\textwidth}{!}{\figurea}
\let\savethis\thelastscalefactor
\bigskip

How do I rescale \texttt{fig-b} to keep its relative size compared to \texttt{fig-a} without knowing its actual size?
\bigskip

\noindent
\scalebox{\savethis}{\figureb}

\end{document}

edited Jan 09 '18 at 23:11

answered Jan 09 '18 at 22:53

David Carlisle

757,742

Thanks for this! But now my curiosity lies on "@CarLaTeX's comment". Must be something deep to justify three post edits :) (four if we count that @egreg already changed it on the first time). – Phelype Oleinik Jan 10 '18 at 11:07
@Carlatex is a lady and Italian and google suggests that perhaps your macro name wasn't a good word to use in the presence of such a person:-) (egreg is Italian and probably didn't require a nudge from Carlatex:-) – David Carlisle Jan 10 '18 at 11:09
Ohhhhh... Didn't expect that... I'll be a little more careful with my abbreviations from now on :) – Phelype Oleinik Jan 10 '18 at 11:12

Werner · Answer 2 · 2018-01-09T23:05:31.300

You can use

\resizebox{\fpeval{(2.5cm) / (5cm)}\textwidth}{!}{\figureB}

where \fpeval is provided by xfp.

Essentially you're resizing the image to a scaled version of \textwidth based on the ratio of the two figure's widths. This is known in this case, so it seems superfluous to evaluate (2.5cm) / (5cm) rather than just using .5. But in general this might not be known.

The following example is slightly different, using 2.5pc for the smaller image:

\documentclass{article}

\usepackage[paperwidth=12cm]{geometry}
\usepackage{graphicx,xfp}

\setlength{\parindent}{0pt}% Just for this example

\begin{document}

\def\figureA{\includegraphics[width=5cm]{example-image-a}}
\def\figureB{\includegraphics[width=2.5pc]{example-image-b}}

This is \texttt{figureA} with its natural size:

\figureA
\bigskip

This is \texttt{figureB} with its natural size:

\figureB
\bigskip

This is \texttt{figureA} scaled to fit the page width:

\resizebox{\textwidth}{!}{\figureA}
\bigskip

How do I rescale \texttt{figureB} to keep its relative size compared to \texttt{figureA} without knowing its actual size?
\bigskip

\resizebox{\fpeval{(2.5pc) / (5cm)}\textwidth}{!}{\figureB}

\end{document}

You could also use

\resizebox{\fpeval{\textwidth * (2.5pc) / (5cm)}pt}{!}{\figureB}

since the result from \fpeval on dimensions is expressed in points.

If the figure dimensions are unknown, you can store the figures in boxes from which one can readily extract the width and/or height. Here is the above example written with that in mind:

\documentclass{article}

\usepackage[paperwidth=12cm]{geometry}
\usepackage{graphicx,xfp}

\setlength{\parindent}{0pt}% Just for this example

\begin{document}

\newsavebox{\figureAbox}% Store figure a in a box
\savebox{\figureAbox}{\includegraphics[width=5cm]{example-image-a}}
\newsavebox{\figureBbox}% Store figure b in a box
\savebox{\figureBbox}{\includegraphics[width=2.5pc]{example-image-b}}

This is \texttt{figureA} with its natural size:

\usebox\figureAbox% figure a
\bigskip

This is \texttt{figureB} with its natural size:

\usebox\figureBbox% figure b
\bigskip

This is \texttt{figureA} scaled to fit the page width:

\resizebox{\textwidth}{!}{\usebox\figureAbox}% Scaled figure a
\bigskip

How do I rescale \texttt{figureB} to keep its relative size compared to \texttt{figureA} without knowing its actual size?
\bigskip

\resizebox{\fpeval{\textwidth * (\wd\figureBbox) / (\wd\figureAbox)}pt}{!}{\usebox\figureBbox}% Scaled figure b

\end{document}

To use this I must know the actual size of the pictures T_T. Is it possible to somehow hack into \resizebox to get the scaling factor? Or maybe measure them before and after scaling... I ask this because in my case I don't know the size of the pictures prior to loading them. (I load them with a \forLoop, and they usually change in size between one compilation an another so... Yeah, I'm a boring person :)). But I didn't know about fpeval. It'll be very useful. Thanks! — Phelype Oleinik, Jan 09 '18 at 21:17
@PhelypeOleinik: You can store the pictures in a box and then retrieve the width/height as needed. I'll add some detail. — Werner, Jan 09 '18 at 21:49
@PhelypeOleinik the first thing \resizebox does is calculate the scale factor but normally it does not return that value it just uses it to call scalebox internally. — David Carlisle, Jan 09 '18 at 23:15

score 4 · Answer 3 · answered Jan 09 '18 at 21:35

Here I define \Resizebox, a variant of \resizebox that takes an optional argument; if absent it does the same as \resizebox, if present, it should be a (definable) control sequence where the scale factor is stored, for subsequent use.

\documentclass{article}
\usepackage[paperheight=40cm,paperwidth=21cm]{geometry}
\usepackage{graphicx}
\usepackage{xfp}

\newcommand\figureA{\includegraphics[width=5cm]{example-image-a}}
\newcommand\figureB{\includegraphics[width=2.5cm]{example-image-b}}

\makeatletter
\newcommand{\Resizebox}[4][]{%
  \if\relax\detokenize{#1}\relax
    \resizebox{#2}{#3}{#4}%
  \else
    \begingroup
    \sbox0{#4}%
    \sbox2{\resizebox{#2}{#3}{#4}}%
    \@ifdefinable{#1}{\xdef#1{\fpeval{\wd2/\wd0}}}%
    \usebox{2}%
    \endgroup
  \fi
}
\makeatother

\begin{document}
\raggedright
This is \texttt{figure-a} with its natural size:

\figureA

\bigskip

This is \texttt{figure-b} with its natural size:

\figureB

\bigskip

This is \texttt{figure-a} scaled to fit the page width:

\Resizebox[\scaleforfigureA]{\textwidth}{!}{\figureA}

\bigskip

How do I rescale \texttt{figure-b} to keep its relative 
size compared to \texttt{figure-a} without knowing its actual size?

\bigskip

\texttt{Insert a nice piece of code here :)}

\scalebox{\scaleforfigureA}{\figureB}

\end{document}

Knowing how much \resizebox scales

3 Answers3

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