# Is there a way to “colorize” a line drawing?

I have a few line drawings (see the attached example; pardon the hideous green), basically black & white with occasional shades of gray and a transparent background (in .png format). I know how to include these pictures in my documents.

Is there a way to “colorize” them, for want of a better word, so that the black lines will appear in a different color? I can, of course, do this in image editing software, but would like to be able to do this on the fly in LaTeX(any flavor).

Any pointers?

You can use the decodearray={rmin rmax gmin gmax bmin bmax} option to \includegraphics (the default colour coding is decodearray={0 1 0 1 0 1}).

\documentclass{article}
\usepackage{graphicx}
\begin{document}
\noindent
\includegraphics[decodearray={0 1 0 1 0 1},width=\textwidth]{ingmar.png}\\
\includegraphics[decodearray={1 1 0 1 0 1},width=\textwidth]{ingmar.png}\\
\includegraphics[decodearray={0 1 1 1 0 1},width=\textwidth]{ingmar.png}\\
\includegraphics[decodearray={0 1 0 1 1 1},width=\textwidth]{ingmar.png}
\end{document}


• This is exactly what I was looking for. Thanks! – Ingmar Feb 19 at 12:17
• Uhm, any idea why this doesn't work with example-image? – campa Feb 19 at 12:20
• @campa Try example-image.png instead of .pdf. The Decode array will be applied to a single object in the pdf, but an image from a pdf file contains more than a single object, so decodearray isn't used – Phelype Oleinik Feb 19 at 12:23
• @campa Also example-image.png seems to be monochrome (not only visually, but some property of the image) because only the first two channels of decodearray have any effect on it. The other ones are just ignored. For example, \includegraphics[decodearray={1 0}]{example-image.png} inverts the colour – Phelype Oleinik Feb 19 at 13:01
• @Ingmar Yes, decodearray will just act on each channel of the image, so if it has only one channel it won't "add" colour. It sort of "tunes" the existing channels. I'm was looking for an official reference on this, but couldn't find one that explains exactly how it works... – Phelype Oleinik Feb 19 at 17:05

TikZ offers lots of possibilities of "filters" (not what kids these days know as filters, please) to apply over an image by using PDF transparency layers. Section 23.3 (Blend Modes) of the TikZ manual explains this feature with the possible "blend modes": normal, multiply, screen, overlay, darken, lighten, color dodge, color burn, hard light, soft light, difference, exclusion, hue, saturation, color and luminosity. Taking the example from this post, you can mix different blend modes to get interesting effects:

\documentclass{article}
\usepackage{tikz}
\begin{document}

\includegraphics[width=10cm]{hBg1w.png}

\newcommand\colorize[2]{
\begin{tikzpicture}
\begin{scope}[blend group=#1]
\begin{scope}[blend group=#2]
\node[inner sep=0pt] (logo) {\includegraphics[width=10cm]{hBg1w}};
\fill[white] (logo.south west) rectangle (logo.north east);
\end{scope}
\fill[red] (logo.south west) rectangle (logo.north east);
\end{scope}
\node (logo.south) [below=.5cm,font=\Large] {#1/#2};
\end{tikzpicture}

}

\colorize{screen}{overlay}
\colorize{overlay}{saturation}

%\colorize{screen}{normal}
%\colorize{screen}{multiply}
%\colorize{screen}{screen}
%\colorize{screen}{overlay}
%\colorize{screen}{darken}
%\colorize{screen}{lighten}
%\colorize{screen}{color dodge}
%\colorize{screen}{color burn}
%\colorize{screen}{hard light}
%\colorize{screen}{soft light}
%\colorize{screen}{difference}
%\colorize{screen}{exclusion}
%\colorize{screen}{hue}
%\colorize{screen}{saturation}
%\colorize{screen}{color}
%\colorize{screen}{luminosity}
\end{document}