How to Follow a Journal's Artwork Guidelines

The time has finally come to submit that paper. You have done experiments, analyzed results in the context of previous work. You've written and re-written the text until you started having dreams about Microsoft Word. A final polishing step is to get your figures into shape. The Journal—which you hope will receive your work with great fanfare—will have specific artwork guidelines that must be followed before your masterpiece is acceptable for publication. In this post, we walk through the artwork guidelines from the Nature family of journals.

Different journals will have different specific guidelines, but the goal is generally the same: to ensure easy readability and visual appeal in the final, printed form. To achieve this, journals will seek to ensure high resolution, readable text, good contrast between colors, and appropriate figure sizes to fit the printed page.

Resolution

Resolution refers to the number of pixels used in the image. More pixels = finer details can be displayed = higher resolution. The rule of thumb is that higher resolution is better, but keep in mind that higher resolution also means larger files. If your figure meets the journal guidelines, that is sufficient; no need to overdo things.

The pixel density is only part of the story when an image is destined for a printed manuscript. In printed materials, the common measure of resolution is Dots Per Inch or DPI. This refers to the number of ink dots that can be fit within a one inch line. Digital images are made up of pixels, not ink dots, but even so, a digital image needs to be labeled with a target DPI, and adjusted to an appropriate pixel density, so that a printer knows what size and resolution to print.

That said, it's easy to increase the resolution of an image that you have drawn. In an illustration program such as Inkscape, the image is stored as a vector graphic (that is, as a set of shapes, not a set of pixels), which means that it can be converted to a pixel-based graphic format such as PNG, JPG, or TIFF, at any desired resolution. In Inkscape, for example, you simply choose the DPI you want as you're exporting the image. We have posted previously on a simple workflow for making publication-quality figures in Inkscape and GIMP.

As indicated in the Nature artwork guidelines, it is impossible to increase the resolution of a low resolution image. If you are using a photograph or pixel-based image from any camera or software program,  you need to ensure that the resolution is sufficiently high. This is true, even if you plan to embed the image into a larger figure. Most plotting software will have options for specifying the resolution of any saved images.

Size

Journals also have accompanying rules for text and line sizes that will be easily visible given the figure size and resolution guidelines. For example, Nature requires line weights between 0.25 pt and 1 pt in drawings. PNAS requires fonts to be between 6 and 12 pt. It's always easiest to start making your figures with these things in mind.

Colors

Color format refers to the way that colors are represented in a digital image. For example, RGB refers to the Red, Green, Blue color model, where the color of each pixel is represented as a mixture of red, green and blue (where the intensity of each is between 0 and 255). For example, the color white is (255,255,255). Pure blue would be (0,0,255). CMYK refers to the colors used in some printers: cyan, magenta, yellow, and key (black). A pixel's color in CMYK format will be represented by four numbers.

GIMP currently does not support CMYK-format images, although there is a plugin that might do the trick. Commercial software such as Adobe products can perform this conversion. There are online tools for this conversion, too. You may or may not have to convert something to CMYK, that's not the point here. The point is that a journal's artwork guidelines may ask for something specific for which you'll need to go find the right tool.

Format

This could probably go without saying, but there are many ways to represent digital images, and journals have their favorites. Make sure you choose an appropriate format. Most software packages will allow you to save your image in many different formats. GIMP is a useful tool for converting one format to another.

Overview

The key to simplifying the process of designing, polishing, and submitting your figures is to anticipate the journal guidelines. Once you know where you plan to submit your manuscript, look up their expectations for artwork. In general, the most important thing to anticipate early is the figure size (one column or two?). Font and line size are also good to keep in mind. Color and format can generally be left until the polishing stage.