EPS graphics with Akustyk and Praat
What is EPS?
(EPS) An extension of the PostScript graphics file format developed by Adobe Systems. EPS is used for PostScript graphics files that are to be incorporated into other documents. An EPS file includes pragmas (special PostScript comments) giving information such as the bounding box, page number and fonts used. PostScript is an unusually powerful printer language because it is a full programming language, rather than a series of low-level escape sequences. For years PostScript has been the industry standard for graphical output. One of the main advantages of EPS files is that they are relatively small in size, as they contain instructions sent to the printer, rather than pixel information. Images that contain pixel information are called bitmaps. EPS graphics are resolution-independent, which makes them ideal for high quality output for graphs, charts, and plots.
Note that most of these remarks are specific to the Microsoft Windows environment. I have tested all the steps I describe below on Windows 7, Adobe Illustrator CS5, Ghostscript 9.0, IrfanView 4.28, and Microsoft Word 2010.
Praat picture file
Praat can store any graphical object created by the Praat picture module. It is a good idea to save all of your images as Praat picture files. You will always be able to open them in Praat and modify, if necessary. Note that it is rather difficult to delete or edit existing elements, but you will be able to add new pieces, such as titles, arrows, bounding boxes, etc. Also, these files are usable by Praat only. To save a Praat picture file:
- Create a graphic object
- Select it by clicking and dragging (the pink border in MS Windows)
- Choose File, Write to praat picture file...
- Save the file as "filename.prapic"
Screen resolution
You might be tempted to simply take a screen shot of the image. However, this technique will only let you rasterize such images at the typical screen resolution of 72 dpi. While such images look fine on a computer screen, their resolution is not high enough to use them in print. You should try to always work with the EPS format, which, being a vector format, is resolution independent, i.e., it can be rasterized (converted to a computer-readable bitmap image) at any resolution, with appropriate software.
The images below show a fragment of a Praat-generated image at the 400x magnification. The bitmap image (left) shows significant degradation, while the EPS image (right) offers unchanged resolution throughout.
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Save as EPS file...
The Praat picture format can only be opened with Praat. EPS is certainly the best distribution format for your graphics. To create an EPS image:
- create a graphic object
- select it by clicking and dragging (the pink border on MS Windows)
- choose File, Write to EPS file...
- save the file as "filename.eps"
As you look through the File menu you will notice that there are two other commands that write EPS files: "Write to fontless EPS file (XIPA)..." and "Write to fontless EPS file (SILIPA)..." Both these formats write EPS files that do not include embedded fonts, but only reference to the appropriate font and character. This is useful only if the software you are going to open these files with (e.g., a typesetting program) has the fonts installed on its system. There's a file size advantage, of course, though the EPS files produced by Praat are small, even with embedded fonts, so perhaps this is not too much of a concern. Either way, I recommend using the "Write to EPS file..." command.
Using EPS graphics in Microsoft Word or OpenOffice Writer
If you have a PostScript compatible printer
Since Postscript is a technology designed for print, EPS graphics created by Akustyk and Praat are ready for print. There is no need to rasterize them (convert them to a bitmap format). However, you need to print those images on a PostScript compatible printer. Fortunately, most laser printers these days support PostScript. Chances are that the networked printers at your school or office will be PostScript compatible. Also, Microsoft Word (2007 and 2010), which is the most popular word processing software, comes equipped with a PostScript import filter. You can simply insert your EPS images into MS Word. The same is true of OpenOffice Writer. Follow these steps:
- open MS Word
- place the cursor where you want to insert your image
- go Insert, Picture, From file
- locate your image on your hard drive
- you're done
The image will appear jagged and many of the phonetic symbols will not look correct. However, this is no reason to worry. In fact, your image will appear razor-sharp once you print it on a PostScript compatible printer. Note that you can also resize the image in MS Word by double-clicking on the inserted EPS graphic and clicking on the "Resize" tab. It is best to check "Lock aspect ratio" before resizing.
If you don't have a PostScript compatible printer.
Convert to PDF in MS Windows
If you do not have a PostScript compatible printer, you may still insert EPS images into MS Word, but you will have to convert your MS Word document before printing. Adobe Distiller, which is part of the Adobe Acrobat package, installs in MS Windows as a printer. All you need to do is choose Adobe Distiller as your printer, launch the print command from MS Word, and your entire MS Word document will be converted to PDF. Since Adobe Distiller emulates a PostScript printer, your EPS graphics will be rendered beautifully.
Save as Windows metafile...
The Windows version of Praat gives you an additional option to save images as Windows metafile (the EMF format). The obvious advantage of this format is that it will work perfectly in the Windows environment and in Microsoft Office applications. It is a vector file format that is native to Windows and compatible with many graphics applications. However, it is not nearly as commonly used as EPS in the publishing industry so it may not be your best choice for sending images to your publisher. You should check with your publisher as the EMF files can be easily converted to EPS (with Adobe Illustrator, for example), so perhaps they will accept EMF files after all. You can also edit EMF files created by Praat just as easily as EPS images with Adobe Illustrator CS5 (and possibly earlier versions), provided you have the phonetic fonts used by Praat installed on your system (check the Praat website for a list of these fonts). You can very easily insert an EMF into your MS Word document and simply send it to your printer.
Copy to clipboard
Finally, you can simply copy your Praat picture into your Windows clipboard by using the "Copy to clipboard" command from within the Praat Picture window. You can then paste the image into your MS Word document and it will print nicely on your standard desktop printer. The disadvantage is that you cannot easily send such a file to your publisher. You can save it out of Word, but you will only be able to save it as a bitmap image (e.g., a TIFF or PNG), so it's not ideal. My advice is to use this method only as a quick-and-dirty technique.
Rasterize EPS
Often, you will need to rasterize your EPS images in order to insert them into a PowerPoint presentation or publish on the Web. My advice is to use the PNG file format for all types of images produced by Praat. In order to rasterize EPS images, you will have to have an EPS interpreter installed on your Windows computer. Ghostscript is the most common, free choice. Other options include Adobe Acrobat or Adobe Illustrator. I personally prefer Ghostscript. I have found it to interpret Praat-generated EPS images perfectly well. However, Ghostscript itself will not be able to rasterize EPS images. You will have to have another program to do that. There are several choices out there, but my personal favorites are IrfanView with the Postscript plug-in (both free) and ReaConverter (not free but very versatile). Both programs use Ghostscript, so you will have download and to install it first. Then, download and install IrfanView and the plug-in pack. Finally, you can associate the .eps extension with IrfanView so that the EPS files open automatically in IrfanView when double-cliked. The last thing you need to do is tell IrfanView what at what resolution to rasterize EPS images (see the image below). The rule of thumb is that 72 dpi is for screen, while 600 dpi is good for print. Once an EPS image is open in IrfanView, you can simply save it as PNG or any other bitmap format you might need.
