Graphics and LATEX

Troy Henderson

Abstract

This exposition is a HOWTO for including graphics in LATEX. Many techniques and tools discussed here have alternatives that may be preferred by other TEXperts; however, this document outlines my preferences which arise from years of experience trying many tools and techniques. Feel free to email me if you would like to offer any suggestions. I will be glad to (at least) listen to your suggestions, but I make no promises that you will change my mind without sufficient evidence.

1 Personal Preference

Even though LATEX supports several graphic formats, I prefer ONLY two of these formats, namely

Since LATEX cannot compute the CropBox of a PDF graphic in order to allocate space in the document, EPS is my preferred format when using LATEX. Similarly, since PDFLATEX can do (virtually) no PostScript processing, PDF graphics are my preferred format when using PDFLATEX. I often have both formats of the same graphic available to my document so that the same source code can be built using both LATEX and PDFLATEX.

2 Inclusion

Inclusion of EPS/PDF graphics in LATEX/PDFLATEX is trivial using the graphicx package. If foo.eps and foo.pdf are the filenames of the EPS and PDF versions, respectively, then the graphic can be included in the LATEX document by using the following minimal template:

\documentclass{minimal} 
   
\usepackage{graphicx} 
   
\begin{document} 
   
\includegraphics{foo} 
   
\end{document}

Notice that the file extension is not specified in the filename argument of the \includegraphics command. The purpose of this omission is that .eps will be assumed when the document is built with LATEX and .pdf when it is built with PDFLATEX.

3 Raster Graphics

Raster graphics are graphics that are described by painting each individual element of a grid a particular color. A finer grid will constitute a “better” looking image because the colors will appear to be more continuous. Human eyes naturally see objects in this way except that the grid is radial and extremely dense. Computer screens rasterize all graphics since the screen is composed of pixels that are each painted a particular color. Higher resolution screens equate to a finer grid and thus display “better” looking images. Also, digital cameras capture natural images and rasterize these images for storage onto the camera’s memory card.

One disadvantage of raster graphics is its lack of scalability. Raster graphics cannot be scaled to higher resolutions since such scaling essentially increases the size of each grid element. This scaling produces a larger image, but the image looks no better than the original.

Another disadvantage of raster graphics is its large file sizes. Since each element of the grid must be painted its own color and since each color is typically described with 24 bits (or 3 bytes) of storage, a 1 megapixel image would require 3 megabytes or storage in its uncompressed form. Although lossy techniques may be used to compress the data, they often degrade the quality of the image.

Common raster formats include BMP, GIF, JPG, PNG, et. al.

4 Vector Graphics

Vector graphics are graphics that are described using pre-defined objects, transformations, colors, strings, and other mathematical and programmatic primitives. Unlike raster graphics, grid elements are not painted, and therefore vector graphics require a less na´ve method for constructing them. Virtually all mathematical drawings and graphs are (naturally) in vector format. However, as discussed above, many applications (such as digital cameras, computer screens, printers, etc.) in their final output rasterize all graphics.

The primary advantage of vector graphics is its scalability. An example of this would be in order to scale a circle centered at the origin to 200% of its original size, it is enough to simply multiply the radius of the circle by 2 and the new description is complete. Therefore, there is no loss in quality in performing such scalings.

Another advantage of vector graphics is its small filesize. Again, since the graphics are described by mathematical primitives, the storage required to denote this description is minimal.

Common vector formats include EPS, PDF, PS, SVG, et. al.

5 Vectorizing Raster Graphics

As mentioned above, EPS and PDF are the ONLY formats that I prefer to use with LATEX and PDFLATEX. Furthermore, EPS and PDF are both vector graphic formats. Therefore, in order to include raster graphics in my LATEX documents, I always do one of two things:

The former of these is performed when the raster image originates from line art graphics for which its original vector format is not available. There are several tools that can automatically trace these type of graphics including AutoTrace, Potrace, and VectorMagic; however, their results may be less than desirable.

The most common method of vectorizing a raster image is performed when the raster image comes from a photograph or a screenshot. In this case, a vector “wrapper” is placed around the raster graphic to transform the raster into a vector format. Consequently, the resulting vector graphic will maintain the same scalability and filesize limitations of the original raster version, but the work of transforming the graphic into EPS or PDF will already have been done. This new graphic is not a true vector graphic, but it will possess a convenient vector wrapper. Because it produces little overhead in filesize and maintains the image’s original quality, sam2p is my preferred application for this scenerio, and my web interface is useful when converting only a few graphics.

6 Generating Vector Graphics

Applications such as Adobe Photoshop, Corel Paint Shop Pro, Gimp, etc. are raster graphic editors. They generally can import vector graphics, but these graphics are rasterized the moment they are imported. There are a plethora of graphics programs designed to generate vector graphics. Among these include Microsoft Visio, CorelDraw, Inkscape, Dia, MetaPost, et. al. Furthermore, most mathematics software including Matlab, Octave, Maple, Mathematica, Maxima, et. al., can export graphics in at least an EPS vector format.

Most modern TEX distributions should contain epstopdf which is used to convert EPS graphics into PDF so that the BoundingBox of the EPS is preserved as the CropBox of the resulting PDF. For users that have command-line phobia, GSview is a nice tool for, among other things, converting EPS into PDF. GSview relies on Ghostscript to perform much of its backend processing.

A common problem that Microsoft Windows users often encounter is the inability of their applications to export EPS or PDF graphics. If these graphics are not raster in nature, then a simple solution to this problem is to install a generic PostScript printer driver and print to this printer. Any PostScript printer driver, e.g., the Apple Color LaserWriter 12/600, may be used, but the driver should be instructed to print to FILE instead of a physical printer port. Once this is configured, printing to this “printer” will prompt for a filename to save the resulting PostScript document. This PostScript document will generally not be an EPS since it will lack a BoundingBox. This problem can be solved using GSview by selecting “PS to EPS”. The user will then have the option of having GSview automatically compute the BoundingBox or manually specifying it.

7 MetaPost

MetaPost is a powerful graphics language based on Knuth’s METAFONT, but with PostScript output and facilities for including typeset text. There are many MetaPost resources available, but this section will highlight the fundamentals of including MetaPost graphics in a LaTeX document. I use the following minimal MetaPost template when labels exist and LATEX is used to process these labels.

prologues:=3; 
filenametemplate "%j_%c.mps"; 
verbatimtex 
%&latex 
\documentclass{minimal} 
\begin{document} 
etex 
beginfig(0); 
   
endfig; 
end

As of version 0.970 of MetaPost, the prologues:=3 feature provides embedding of used fonts into the MetaPost output. I generally set this variable when desigining my graphics, but when I include them into my LATEX document, I remove this line since LATEX will include the fonts itself anyway. Also, as of version 0.920 of MetaPost, the filenametemplate allows the user to set the naming scheme of MetaPost graphics. The graphicx package identifies a graphic with a .mps file extension as originating from MetaPost. If the example code above was saved as foo.mp, then the output would be foo_0.mps and the command

\includegraphics{foo_0.mps}

can be processed by both LATEX and PDFLATEX (thanks to Hans Hagan’s mptopdf). Both of the aforementioned new features of MetaPost are available in TEXLive 2007 as well as MiKTEX 2.6.

8 Conclusion

Vector graphics should always be used whenever the graphic is not raster in nature. The vector formats that I prefer are EPS and PDF depending on whether LATEX or PDFLATEX is used to typeset the document. If the graphic is characteristically raster, then the optimal method for vectorizing it usually involves placing a EPS or PDF wrapper around it using sam2p. Taking these steps to place graphics in a LATEX document requires a slightly more than na´ve solution, but the results should be of higher quality.