For the digital sign shop or any shop producing inkjet-printed, large-format graphics, software is like the military’s arsenal or the chef’s utensils or the doctor's medical bag — a set of tools to get the job done. To know what software you need to handle any job, it's helpful to know the purpose of different file formats and the software you need to work with them. In this article, we will examine various types of file formats, their uses and applications.

RASTER GRAPHICS
Raster, or bitmap images (see Figure 1), are pixel-based images that are depicted as a grid of microscopic picture elements known as pixels. The raster image can be photo-realistic and is most often used for digital photographs, including digital camera photos and scans. Raster images are resolution-dependant, so the size and quality of the raster image is directly linked to the number of pixels in the file. Thus, changing the size of the file affects its resolution. Resolution of raster images is generally depicted by the number of pixels per square inch (ppi) contained in the file. The proper resolution is dependent on the end-use of the image and the scale to be used.

Figure 1: Examples of a BMP graphics. The same image is shown at 300 ppi for normal printing and at too-low 25-ppi resolution, showing individual pixels. BMP images are photo-realistic but are use-specific and must be captured for the intended output size. (Photo courtesy of Printing Industries of America, www.gain.net.)

VECTOR GRAPHICS
Vector graphics (see Figure 2) are based on mathematical descriptions of points, lines, and curves, like a connect-the-dots puzzle. Vector images are resolution independent. They have no resolution until printed, and the final value depends on the output device used. Images can be scaled to any size without losing quality. The file sizes of vector graphics are usually much smaller than bitmapped images.

Figure 2: A circle is shown as a vector (left) and BMP (right) graphic with too-low resolution. Vector graphics are defined mathematically by points, lines and arcs. They are infinitely scalable and have small file size but are not photo-realistic.

Typically, page-layout programs combine vector-based text with raster-based graphics on any given page. Page-layout programs are useful for multi-page documents and may not be necessary for large-format digital sign work, but, increasingly, printed signage applications will also combine vector with raster files.

FONT FORMATS
Fonts generally are vector-based graphics (see Figure 3). Some fonts may be free while others must be purchased. There are various font formats. Adobe PostScript Type 1 fonts have long been considered the highest quality fonts for printed output. Type 1 fonts consist of two files: a screen font for image display, and a printer font for output to the printer. The screen font contains a rasterized version of the font that cannot be resized but looks smooth on screen. The printer font includes outlines of all the characters, which can be resized or scaled to various sizes without any loss of quality.

Figure 3: Icons for PostScript, TrueType and OpenType fonts.

TrueType fonts were developed in collaboration with Microsoft. TrueType fonts include the screen font and printer font in the same file and are scalable. OpenType is a font format developed by Adobe and can contain up to 65,000 characters. OpenType has facilitated the development of type for non-Roman languages, such as Japanese, Chinese and Korean. Also, this font format can contain extra foreign-language characters, glyphs, accents, symbols and other special characters.

Type 1 and the original TrueType fonts were single-byte fonts, which mean they used one byte (8 bits) to address characters. These fonts could have a maximum of 256 characters. TrueType and OpenType can migrate between Mac and Windows platforms. PostScript fonts are platform-specific and must be used with a font-conversion utility.

FILE FORMATS
Standard file formats for vector graphics include EPS (encapsulated PostScript) and PDF. Adobe Illustrator, Macromedia Freehand and their closest competitors can read and write both EPS- and PDF-formatted files. Page-layout programs, like InDesign, can also import both file types.

Standard file formats for bitmap/raster graphics include TIFF, EPS, PDF, JPEG, Camera Raw and numerous other formats for Web graphics, such as GIF and PNG. Adobe Photoshop and their competitors can read all of these formats, and page layout programs can place these formats (see chart for detailed file format information).

PORTABLE DOCUMENT FORMAT
The PDF was originally conceived and introduced by Adobe in 1991 and has been widely adopted by the graphic-arts industry. This file format permits users to freely exchange electronic documents. Documents can be independent of the creating application, computer platform, fonts and linked graphics. Acrobat is the Adobe application that creates and reads PDF files while PDF is the file format of Acrobat documents. Most current graphic applications can directly export documents as PDF, including Adobe’s Illustrator, InDesign and QuarkXPress. Popular software RIPs used in large-format, digital-printing applications also accept PDFs.

PDF format holds several distinct advantages for print production. It is platform-independent, application-independent, self-contained, compressed and viewable. This means that if a job was created on a PC, you can easily open it on a Macintosh and vice versa. If the customer created a job using QuarkXPress, you don’t need to have Quark to open, view and print the document. Further, as PDFs are self-contained, missing fonts and broken-linked graphics are not an issue. Since a PDF file is compressed, it is easier to transmit over the Internet than application files and their associated documents. And PDF documents can be viewed with Adobe’s free Acrobat Reader.

Chart taken from Digital Photography for Print by Adams, Gilewicz, Habekost, and Lisi, PIAPress, 2009, chapter 3, “File Formats and Applications”.

Click here to read Part 2 of this article series.