Portal de Periódicos da CAPES

Maintaining Journal Figure Quality

2010; Wiley; Volume: 57; Issue: 3 Linguagem: Inglês

10.1111/j.1550-7408.2010.00478.x

1550-7408

Sonia L. Wilson, Alastair G. B. Simpson, Denis H. Lynn,

Research Data Management Practices

FOR many years, members of the International Society of Protistologists, formerly the Society of Protozoologists, have taken pride in the outstanding quality of illustrations and figures published in The Journal of Eukaryotic Microbiology. For many of us “older folks,” our assessment of figure quality was honed in the darkroom, laboring over dodging and burning and achieving through trial and error the ideal level of contrast. Or, we pulled out the tube-point drawing pens and worked diligently to create that perfect graph or line drawing of our new taxon. Today's technology has liberated us from the darkroom and has made the creation of graphical results a simple task, but we are still needed to create those complex synthetic schematics. While these technologies have been liberating, they have been accompanied by their own set of problems. Foremost among them has been the absence of standards, although this is changing. Wiley-Blackwell has provided a good set of guidelines on submitting high-quality artwork to The Journal. These guidelines can be found at their Web site at http://authorservices.wiley.com/bauthor/illustration.asp. However, despite these guidelines, the Editorial Office is experiencing continuing problems with the formatting and quality of images submitted for review and publication in The Journal. In the interest of increasing the quality of images, we thought it useful to highlight some of the important and significant factors in creating the highest quality electronic images. Kinds of graphics files. Image files are either one of two general types—raster files or vector files. Raster files convert an image to pixels. The more pixels there are in a defined area—usually measured in dots per inch (dpi) or per cm—the higher resolution the image. Vector files encode an image as a set of functions that contain the instructions on how to create an image. Since these instructions are inherent to the file, vector images can be scaled up or down without loss of quality. Images in raster files cannot be scaled up without loss of quality but, if done properly, can be scaled down and still maintain figure quality. The Journal accepts raster files in the Tagged Image File Format (TIFF), a format that is appropriate for electron micrographs, photomicrographs, photographs, and detailed schematic drawings. Vector files should be submitted in either the Encapsulated PostScript (EPS) format or the Portal Document Format (PDF). Both formats are appropriate primarily for line artwork, graphs, and charts. Creating the electronic source images. Images can be captured directly by digital cameras mounted on or in most microscopes today. These images should be captured at the highest resolution practical, as it is always possible to cast away resolution, but one cannot normally increase the original effective resolution of a digital image. If your device has the RAW file format option, so named because it is a minimally processed image file, choose this option for the “master” file as it retains the most information about the image. Always make a duplicate or backup of this file before image manipulation. The duplicate RAW file can then be imported into an image management program, such as Adobe Photoshop, manipulated, and then saved as a TIFF or a PDF file. Schematic drawings, line artwork, graphs, and charts might be created either by free-hand drawing or by other software. It is recommended that you use actual artwork and image manipulation programs to create your artwork. Spreadsheet software, such as Microsoft Excel, can be used to create graphs and charts, but we do not accept these images or those saved as Microsoft PowerPoint files. Should you have Microsoft Office–created artwork, you may convert them to the appropriate file formats by copying from the Microsoft document and pasting into an actual artwork and image manipulation program and then saving the file as EPS. Alternately, you can use Adobe Distiller or other PDF-creation software to create a PDF; Microsoft Word 2007, for example, has a “Save as PDF” option. As another alternative, you may print to file using a PostScript printer driver. For more details on converting Microsoft Office documents, consult page 3 of the Wiley-Blackwell Electronic Artwork Guidelines at http://authorservices.wiley.com/electronicartworkguidelines.pdf. Modifying the electronic source images. It is crucial to remember that your figures will ultimately be printed as hard copy in The Journal. Therefore, your first decision should be the dimensions of the illustrations: a one-column figure should be 3.5″ or 8.8 cm wide; and a two-column figure should be 6.75″ or 18 cm wide. The maximum length should be no more than 9.25″ or 23.0 cm. This will then determine whether the figures can be submitted at their original size or whether they must be reduced. Of course, you must ensure that any text will be readable at the final printed size: The Journal Instructions to Authors specify that text should be at least 2 mm at the final printed size. Remember that vector files (e.g. EPS or PDF) are not made up of pixels or dots, but rather contain instructions on how to create the image. Since the instructions are inherent to the file, vector images can be scaled up or down without loss of quality, in contrast to raster images made up of pixels. One of the most important features of vector files is that it is possible to embed fonts within the file. It is important that if submitting vector files in the PDF file format you ensure that the fonts are embedded. Raster (e.g. TIFF) files can be reduced in size while maintaining or increasing resolution, but they cannot be enlarged from original size without lowering the effective resolution. If the original resolution is too low, resampling (or up-sampling) will add pixels to the file, but this will not increase the resolution and will not result in a higher-quality image. Rather, the image can appear pixelated with a grainy quality, or blurry quality (See Fig. 1–2). Raster (TIFF) files should be saved at a minimum 300-dpi effective resolution at the size that the image will appear in the final printed plate (see above for sizing), or 600 dpi if a combination of halftones and line art (see below). Two manipulations of the same transmission electron micrograph. 1. The original image manipulated at 300 dpi. 2. The same image, exported at 72 dpi, then resaved at 300 dpi. Although the two images have the same nominal resolution now, the effective resolution of Fig. 2 is much lower. Figure 2 would clearly be unsuitable for publication in a research article. Original image courtesy of Dr. Jong Soo Park, Dalhousie University, Canada. Here are some important things to attend to: Ensure that the original captured image has sufficient resolution in the first place (see above). Ensure that resolution is not lost when you handle an image in software packages. Take particular care when saving/exporting images. Some programs will default to exporting TIFF images at quite a low resolution (e.g. 72 dpi), and this is an easy way to drastically degrade image quality (see Fig. 2). It is essential to check and, if necessary, change the appropriate settings. Pay attention to image size as well as image resolution. A 300-dpi image that is only 5 cm in width cannot be turned into a 2-column-width figure (18 cm wide) that still has 300-dpi effective resolution. Combination figures, meaning images that combine photographic art and line art, such as in the labels, symbol keys, and drawings, are acceptable for submission. However, if you do submit a combination image, it must be supplied at a higher resolution than a standard halftone to prevent loss of quality in the line art. Combination figures must be saved at a minimum 600 dpi at final size (see above for sizing). Assembling the electronic source images. Once you have determined the dimensions of each figure element of a composite plate, these images can then be imported into a software package, such as Adobe Photoshop or Adobe Illustrator, and assembled. Powerpoint is not recommended for halftones—there is typically a loss of image quality that results from manipulation of images in Powerpoint, even if resolution is maintained. Ensure at this point that ALL figure elements are of the same or minimum resolution at final printed size (i.e. 300 dpi for TIFF and PDF; 600 dpi for combination figures) and that the contrast and brightness of ALL figure elements is comparable. Be especially careful with compatible contrast levels when a plate includes micrographs derived from very different kinds of microscopy. White lines should be added to separate the photographic images on a composite plate. Finally, line art, symbols, and labels should be added and the composite figure saved at the minimum required resolution. File sizes can get extremely large when preserving resolution. Thus, The Journal recommends saving files with an image compression option. It is essential that you employ “lossless” compression, which means that when saving there is no quality loss due to compression. LZW compression is one recommended type of lossless compression available; JPEG compression is not lossless—it results in a loss of information from the image—and should not be used. Again, be wary of any default settings in the programs you use. The Tagged Image File Format (TIFF) is appropriate for electron micrographs, photomicrographs, photographs, and detailed schematic drawings. The Encapsulated PostScript (EPS) format or Portable Document Format (PDF) are appropriate primarily for line artwork, graphs, and charts. TIFF and PDF image files must be a minimum of 300 dpi, and images with combined photographs and line art must be a minimum resolution of 600 dpi at the final printed size. Digital images cannot be increased in size and maintained at the original resolution. Therefore, it is critical that images be created initially at the highest practical resolution, and that useful resolution is not lost during image processing or export. Default settings of equipment/programs should be checked before any work is undertaken. Harmonize brightness and contrast among the images on a composite plate. Line art, symbols, and labels should be added as a final step and at the minimum resolution required for the chosen file format: If the figure is a combination of line art and halftones, it must be saved at 600 dpi. Use only lossless file compression options (e.g. LZW), not “lossy” methods such as JPEG compression.