Preparing Graphs for Journal or Web Publication
This document provides guidelines for how to prepare your graphs for submission to journals or other printed form. It is the document form of a future SigmaPlot feature, the Publication Assistant, which will guide you through this process. This early form simply provides the information you will require to properly create files for figure submission.
This process is not necessarily simple and requires some understanding of both the figure requirements of the publication, as well as graphic file formats and terminology.
Creating Files for Figure Submission
The ultimate destination for most SigmaPlot graphs is a publication, and most publishers are now equipped for digital pre-press. This requires graphic files with specific formats and properties. You must also keep in mind the requirements of the different journals and other publications. These tend to vary, but are generally available at the web site for the journal submission requirements.
Here are some URLs with requirements for some of the major publications:
The Proceedings of the National Academy of Sciences:
Journal of the American Chemical Society: http://pubs.acs.org/page/4authors/submission/index.html
Many journals also use the Cadmus Communications electronic prepress service. Their requirements can be found at: http://www.cadmus.com/preparing-digital-art-for-online-viewing-and-print-production.htm
What you need to know before creating a file
When preparing a figure for file export, you first need to determine/learn the following. This information has to come from the publisher (see above).
- The final size of the figure, including the size of text (usually inches or millimeters)
- The required line weights
- Acceptable typefaces (especially important for EPS – Encapsulated PostScript – files)
- The desired final dpi (the dots-per-inch resolution), if necessary
Step-by-step Figure Production
Here are the basic steps to producing a file for publication. These can vary somewhat from publisher to publisher.
- Determine the final size of the figure, and the heights of text and thicknesses of lines. Also, whether the figure will be color, grayscale, or black and white.
- Determine what file formats are acceptable, and choose the best one. SigmaPlot supports them all. Commonly accepted formats are:SigmaPlot, EPS, TIFF, JPEG and PDF. These are regardless of whether the graph is color or not.Some publishers will directly accept SigmaPlot files. Most others accept EPS, TIFF or both.
- Using the size of your current figure, determine how much the figure is going to be scaled. For example, if your graph is 5 inches wide, but the figures are printed at 3.25 inches wide, then your graph will be scaled by a factor of 3.25/5, or .65.
- Increase text labels and line widths accordingly on your SigmaPlot graph. For example, your graph is being reduced to .65 the original size, and text must be 10pt in height, you will need to increase your labels to at least 15.5pt (10 x 1/0.65). If line thicknesses must be If line thicknesses must kept to 1 pt, you will also need to increase those to 1.54 pt.Alternately, you can reduce the graph itself to the final publication size.See Tips on Resizing a SigmaPlot Graph.
- Make any other changes to your graph to meet the publisher’s requirements, such as typeface, labeling, etc.
- Once you have your graph formatted, produce the selected file. Make sure that you select the figure (click it) before choosing export-this will automatically crop your figure for you.
If you are producing an EPS file, you don’t need to pay attention to dpi at all. If you are interested in file formats and dpi, these are described in detail below.
If you must use TIFF format, make sure you use the CMYK-compressed TIFF format. Uncompressed TIFF files are too big to easily handle. Also, you will now have to do some dpi calculations.
For example, if you are producing a file that requires a final printed dpi of 600, and the graph is being reduced by a .65 ratio, do not set the file dpi to 600. Instead, use a dpi of 390 (600*.65). When this file is shrunk to the final printed size, the final dpi will be 600.
What most people don’t understand about dpi (dots per inch) is that “dpi” is a completely misleading term. dpi is a printer term. A better, more accurate term would be resolution. What dpi determines is how many pixels are used to create the figure. You can increase the final dpi of a raster figure simply by shrinking it-this creates more pixels within a smaller space, increasing the dpi.
Also, most printed figures do not require a dpi higher than 600 for grayscale figures, and 300 dpi for color figures. The 1200 dpi number you often see is for black and white figures only, that have no half toning. If you really have to produce a 1200 dpi figure, you will have to use Photoshop or some other similar program to compress it before your publisher will accept it. In general, this is a good idea if you have to use a TIFF file and have Photoshop (see below).
Post-Processing TIFF files
If you have access to Photoshop, you should always use it to optimize the file. SigmaPlot does not have access to the expensive, proprietary compression formats available in Photoshop. This means that SigmaPlot files will always be much larger than Photoshop files saved with the LZW compression algorithm. Also, SigmaPlot does not support Monochrome or Grayscale TIFF, which are also proprietary export formats.
Opening and resaving a SigmaPlot file using LZW compression and the correct color mode can create dramatic differences in file size. A 100-fold reduction in size is fairly typical.
- For color figures, leave the figure as a CMYK TIFF, but save it using LZW compression
- For grayscale figures, change the Image Mode to Grayscale
- For black and white figures, change the Image Mode to Duotone
Why use EPS?
Most publishers request either EPS or TIFF formats. If you have a choice, you should always choose EPS. Why? Because EPS is what’s known as a vector format. This means that the image is not made up of pixels, but instead graphic descriptions of lines, fills, text, etc. A vector format has no “size”-it is dimensionless.
This means you can shrink it as small as you want, or grow it as big as you want, with absolutely no change in resolution. dpi has no meaning for a vector file.
This format is ideal for a graph figure, since there is no degradation of the quality of the figure as it is rescaled. It is also means that when a vector format file is placed in a document, it often first appears at an arbitrary size, and must be scaled to the final desired size. This can often startle, annoy or confuse someone not familiar with the behavior of vector files.
The other vector format supported by SigmaPlot is the Windows Metafile format.
EPS and PostScript Fonts
Note that most publishers that accept EPS files will also require that you use one of the standard set of Adobe PostScript fonts in your figure. The required fonts are typically either Helvetica or Times, or Symbol for Greek fonts. SigmaPlot automatically detects printer fonts made available with your current printer driver, so make sure your current printer is set to a PostScript printer to insure these fonts are available.
Also, if you want to properly visualize the fonts on the page, you may need to install Adobe Type Manager.
Publishing on the Web
Along with your other files, we recommend that you use the SigmaPlot Save as Web Page command to create .htm, .jnb and .jpg files that your publisher can use in the online version of the publication.
Tips and Tricks
If you need to make changes to text and lines, you can make global changes by simply selecting the graph, or multiple items, then using the Graph Page ribbon commands to make these changes globally.
If you need to resize you graph for publication, you may be better off setting your fonts and line widths first, then turning the automatic rescaling of these objects off before resizing your graph. Choose the Main button and Options command, click the Page tab, and uncheck the Graph Objects Resize with Graph option. To rescale the graph precisely, right click the graph and use the Object Properties Size and Position command.
Select the Graph Before Exporting
Make sure you select the graph before you export; otherwise, you will export the entire page including unnecessary white space surrounding the graph.
Make Sure You Have Enough Disk Space and Memory Before Trying to Export a Big Graphic
For a large file, you’ll want at least 200 megabytes or more free on both your system drive (for swap and temp file space) as well as the same on your destination drive. You can also increase your Virtual Memory to a very large size, but this generally isn’t necessary if you have sufficient hard drive space available. Note that it can take awhile to generate these files, depending on your system’s speed and available RAM.