AJP Figure Preparation
American Journal of Physics
Preparing Figures for Publication
The quality of the figures can make or break an AJP article. As you prepare an article for AJP, consider carefully how best to illustrate it with graphs, line drawings, and/or photos. Then, after you determine the content of each figure, you can begin working to prepare it for publication.
Preparing figures for publication demands higher quality and more attention to detail than, for instance, preparing them for a class handout, a slide show, or a Web page. To achieve the needed quality, authors must be somewhat familiar with the technicalities of computer graphics formats and file types.
Bitmap vs. Vector Graphics
Computers can store image data in two fundamentally different ways:
- A bitmap image, also called a raster image, is stored as a rectangular array of dots or pixels, each with a specific color (or gray level). It therefore has an inherent width and height, measured in pixels, and if you magnify it enough, you will see the individual pixels. Nearly all Web images are bitmaps, as are images made with scanners and digital cameras. For printed materials, however, it is best to use bitmap images only for photographs and screen captures. The most familiar file types for bitmap images are Graphics Interchange Format (.gif), Portable Network Graphics (.png), and Joint Photographic Experts Group (.jpeg or .jpg); all of these use compression to optimize storage space and data transmission speeds. For AJP, the preferred bitmap graphics format is Tagged Image File Format (.tiff or .tif).
- A vector graphic is stored as high-precision numbers and formulas, so the shapes can be reproduced at any size and resolution. A vector graphic has no inherent resolution (in dots per inch or dots per centimeter) and no inherent pixel dimensions. The resolution of the image you see is therefore limited only by that of the computer screen or printing press used for output. Vector graphic formats are best for graphs, line drawings, and text. For AJP the preferred vector graphic file format is Encapsulated PostScript (.eps), although Portable Document Format (.pdf) is also acceptable in most cases. Note, however, that both of these file types can also contain bitmap graphics, so the file type alone is not sufficient to ensure that a graphic is in vector format.
It's hard to show the difference between bitmap and vector graphics on a Web page, so please look at this pdf document to see the difference.
Graphs of formulas or data should ordinarily be plotted inside a frame, with tick marks around all sides and clear labels on both axes. Be sure to place labels where they don't cross over any of the plotted data. Also be careful that numerical axis labels use a consistent number of decimal places (for example, 0.5, 1.0, 1.5, 2.0; not 0.5, 1, 1.5, 2).
There are many software environments that can produce publication-quality graphs, including commercial packages such as Origin and Mathematica, as well as open-source software such as gnuplot and matplotlib. All of these can save graphs in AJP's preferred format, Encapsulated PostScript (.eps). The most ubiquitous plotting software, of course, is the spreadsheet program Excel. While it can sometimes work in a pinch, we do not recommend Excel because it is not designed for scientific plotting and it cannot save directly to .eps format.
Whatever software you use, your final graph should be a vector graphic, not a bitmap (see above). The preferred file type is .eps, although .pdf is usually an acceptable substitute. On rare occasions, a graph might be so complex that a vector format is impractical; you may then submit it as a bitmap .tiff image, but the resolution must be approximately 600 dots per inch at the final printed size (that is, about 2000 pixels across if it is to be printed one column wide).
Line drawings, like graphs, should be created as vector graphics, not bitmaps, and saved in .eps format if possible, or .pdf if necessary. The most commonly used software for line drawings in the publication industry is Adobe Illustrator. An open-source alternative is Inkscape. We do not recommend PowerPoint for creating publication-quality line drawings. (Again, on rare occasions when a vector format is impractical, a .tiff image is acceptable if its resolution is approximately 600 dots per inch.)
Be sure to compose and crop your photographs to make their essential features clear. Also be sure to make a test print on a black-and-white printer, at the final printed size, to check the brightness and contrast; this step is especially important for color photos.
Unlike graphs and line drawings, photographs are best submitted as bitmap images in .tiff format. The resolution should be approximately 300 dots per inch at its final printed size (that is, about 1000 pixels across if it is to be printed one column wide). Most image editing software can convert other bitmap formats to .tiff.
For your initial submission, it's usually best to create a lower-resolution .jpg version of your photo, with moderate compression. This will result in a much smaller file size when you incorporate the figure into your manuscript. Also, unfortunately, LaTeX cannot import .tiff images. Just be sure to save a high-resolution, uncompressed "master" version of your photo in .tiff format, and submit that for production when requested.
If you need to annotate a photo with text, it's best to import it into a graphics editing program like Adobe Illustrator and do the annotations there. Save the resulting image in .eps format. Then the photo will still be a bitmap, but the annotations will be resolution-independent vector graphic elements.
Whatever you do, don't open compressed .jpg images and edit them repeatedly. The .jpg format uses lossy compression, so each open/save sequence will reduce the quality. Again, it's best to save the original image as a .tiff.
In articles that are about computer systems, it's often helpful to include illustrations made from screen captures. These images are inherently bitmaps and usually have rather low resolution. Please leave the resolution unchanged (that is, don't resample the images), and convert them to .tiff format. For your initial submission, the best format is usually .png (incorporated into your .pdf manuscript as with any other figure). You should never convert a screen capture to .jpg format, due to the lossy compression.
Fonts and Text Labels
Fonts used to label figures must be easy to read, appropriately sized, and consistent. When saving a figure as a vector graphic, be sure to tell your software to embed the fonts in the file. Even then, try to avoid using nonstandard fonts. Sometimes it's best to convert the fonts into outlines, if your software offers this option.
Capitalize the first word of each text label, but for a multi-word label, capitalize only the first word and any proper nouns (as in an ordinary sentence).
Initial Submissions vs. Production Quality
When you initially submit your manuscript to AJP, it should be a single .pdf file incorporating all figures. Each figure should preferably appear near where it is first referenced—not at the end of the manuscript.
To facilitate the reviewing process, we prefer that your initial .pdf submission be no larger than 1 MB if at all possible. In order to limit the file size, you may need to use lower-quality versions of figures in your initial submission. This is fine so long as the content of the figures is still clear.
If and when your manuscript is conditionally accepted for publication, the editor will ask you to submit an editable manuscript (preferably LaTeX, but optionally MSWord), along with publication-quality figures that are each in a separate file. This is when you should submit your highest quality figures, using the formats recommended above. Name each figure file in the format "AuthorNameFig01.eps" or "AuthorNameFig02.tiff." Please package the manuscript and figure files into a single .zip archive for submission.
Most figures in AJP are printed at a width of one text column, about 3.4 inches (8.6 cm). When necessary, a wide figure can be printed across both columns. Try to design your figures with one or the other of these widths in mind, choosing the layout, font sizes, and line weights accordingly. Be sure to make a test print of each figure at its final size to check these details. Often a figure that looks great on a computer screen will have flaws that are obvious when it is printed.
A figure may be divided into parts, labeled (a), (b), and so on. Usually it is best to combine the multiple parts, including the labels, into a single figure file. Alternatively, you may (in your editable package for production) submit multiple figure parts as separate files, with names of the form AuthorNameFig01a.eps, AuthorNameFig01b.eps, etc. Always think carefully about how you would like the figure parts to be arranged on the page, and whether the combined figure is to be printed at a width of one column or two.
Color in Figures
AJP encourages the use of color to enhance the clarity and aesthetic appeal of figures. All figures submitted in color will appear in color in the online version of AJP.
However, the printed version of AJP ordinarily does not use color for figures, while some AJP readers will make personal copies of your article using a black-and-white copier or printer. AJP therefore discourages the use of color to convey essential information that would not be apparent in a black-and-white version of a figure. For example, in a graph showing multiple curves within the same frame, you should ordinarily distinguish the curves with different dashing patterns. Distinguishing them by color as well is then a nice touch, but not essential for the reader's understanding.
Similarly, the caption of a color figure, and any other text that refers to it, should not refer in any essential way to the colors used in the figure. So, for example, your caption should refer to different lines on a graph by their dashing patterns (or perhaps line weights or gray levels or locations), not by their colors. When appropriate, you may include a parenthetical "(color online)" in the figure caption, just to let readers know that the online version is prettier.
Be sure to make a test print of each figure on a black-and-white printer, to check that all the essential information is preserved.
If the use of color in a figure is essential to the content of an article, then authors may pay to have the figure printed in color. Color printing is expensive. The current rates are:
- $650 for the first figure;
- $325 for each additional figure.
In this case, it's fine—and probably necessary—to refer to the colors in the figure caption. Please let the editors know as early as possible if it is your intent to have a figure printed in color. Unless we hear otherwise, we will assume that all figures will be printed in black and white.