An Introduction to Figure Formats

Figure formatting can be a surprisingly challenging aspect of preparing a research article for publication. The preferred figure format varies by scientific field (and subfield!), and even journals within the same field will have different guidelines for figures. If you have ever wondered why your target journal specifies TIFFs over JPGs, or what “vector graphics” are, this explainer will help clarify some of the differences between the most common figure formats.

Below we introduce several figure formats that can be divided into two types, vector graphics and raster graphics, and discuss which ones to use depending on image type.

Vector graphics

In a vector file, an image is saved as points, lines, curves, and other shapes that are generated according to mathematical statements. Vector images are created in digital applications such as Adobe Illustrator or computer-assisted design software.

The advantage of the vector format is that because vector graphics are made up of generated geometric shapes, they do not have a “resolution”. Consequently, a vector graphic can be made as large or as small as needed, and it will always retain its sharpness. Familiar vector graphic formats include Adobe Illustrator (AI), Encapsulated PostScript (EPS), and Scalable Vector Graphics (SVG).

Often, scientific journals will prefer graphics to be saved in a vector format, especially in fields where the images (such as maps and circuit diagrams) require high precision. Vector formats are also an excellent choice for line art and flow charts.

Raster graphics

Generally, photographs and imaging outputs (such as MRIs and ultrasounds) use a grid of colored dots called pixels to create images and are, therefore, output as raster graphics. Unlike vector graphics, all raster files have a specific resolution based on their pixel count.

However, raster files are not all created alike; it is important to distinguish between “lossy” and “lossless” file formats. Common lossy and lossless formats include Joint Photographic Experts Group (JPG) and Tagged Image File Format (TIFF), respectively. With lossy formats, compression removes data from the image to reduce file size. However, this compression permanently reduces resolution and degrades the image quality. In contrast, with lossless raster graphics, no data is lost during compression. As a result, image quality and resolution are not degraded. However, file sizes are usually substantially larger than those of lossy formats.

JPG files are commonly used for online publications because the compression used does not degrade the image quality very much, while still reducing the file size. Journals will often accept JPGs for the initial submission of a manuscript, especially to compress very large files, such as radiographs. However, if a manuscript is accepted for publication, journals may require the authors to provide their figures in a lossless format. Hence, TIFF remains the gold standard.

Container formats

Notably, there are file formats, such as Portable Document Format (PDF), that can contain both raster and vector graphics. The drawback of PDF images is that they are more difficult to edit than some of the other file formats presented here. Nevertheless, PDFs are widely accepted, offer security, and can accommodate a wide array of images in one document. This makes them another outstanding option for figure submissions.

General advice

Because journals’ preferred file formats vary, it is essential to consult the target journal’s guidelines for authors prior to submission. It may also be helpful to hire professional graphic designers, such as LetPub’s figure formatting service, to help prepare figures, particularly for complex projects. Doing so can make the process simple and ensure your figures meet all of your formatting requirements. Importantly, you should always retain the original images output by a camera, image acquisition software, or digital application as a reference.