Useful Information

CMYK

Stands for the colors Cyan-Magenta-Yellow-Black. In print design, colors are defined as a percentage of each of these 4 colors. For example, the CMYK abbreviation for the color black would be 0-0-0-100. In contrast, display devices (i.e. computer monitors) typically define colors using RGB.

DPI

Stands for dots per inch. DPI specifies the resolution of an output device, such as a printer or printing press machine. Print resolution usually runs from 300-1200 dots per inch on a Laser Printer and 125-225 dots per inch for photographic images on a print brochure. (For information on input device measurements see ppi.)

FTP

Stands for File Transfer Protocol. FTP allows you to copy or send files (HTML-documents, graphic images, spreadsheets) from one computer to another via the Internet.

GIF

Stands for Graphics Interchange Format. GIF images are the most widely used graphic format on the web. GIF images display up to 256 colors.

HTML

Abbreviation for Hypertext Markup Language; a cross-platform text-formatting system for creating web pages, including copy, images, sounds, frames, animation and more.

PDF

Stands for Portable Document Format. Created by Adobe Systems in its software program Adobe Acrobat as a universal browser. Files can be downloaded via the web and viewed page by page, provided the user is computer has installed the necessary plug-in which can be downloaded from Adobe’s own web site.

PPI

Stands for pixels per inch. PPI specifies the resolution of an input device, such as a scanner, digital camera, or monitor. Web page resolution ranges from 72-96 pixels per inch. (For information on output device measurements see dpi.)

RGB

Stands for the colors Red-Green-Blue. In web design and design for computer monitors, colors are defined in terms of a combination of these three colors. For example, the RGB abbreviation for the color blue shown below is 0-0-255. In contrast, print designers typically define colors using CMYK.

File Formats Glossary

The BMP file format

BMP is a standard file format for computers running the Windows operating system. The format was developed by Microsoft for storing bitmap files in a device-independent bitmap (DIB) format that will allow Windows to display the bitmap on any type of display device. The term “device independent” means that the bitmap specifies pixel color in a form independent of the method used by a display to represent color. The default filename extension of a Windows DIB file is .BMP.

Use in a prepress environment

Everything that can be done with BMP, can also be done with TIFF files (or EPS). Because TIFF is an established and more versatile file format for prepress applications, it is better to avoid BMP-files for prepress production. BMP is also limited to RGB-images only while CMYK data are prefered in prepress. You could say that the only sensible use of .BMP files on a prepress system is for putting a nice background picture on the monitor.

The EPS file format

Encapsulated PostScript (EPS) is a standard file format for importing and exporting PostScript files. It is usually a single page PostScript program that describes an illustration or entire page. The purpose of an EPS file is to be included in other pages. Sometimes EPS files are called EPSF files. EPSF simply stands for Encapsulated PostScript Format. An EPS file can contain any combination of text, graphics and images. Since it is actually a PostScript file, it is the most versatile file format that is available. To avoid the need for a PostScript interpreter, EPS-files usually contain a small preview image that is used to visualize its content.

EPS files can be generated by all drawing applications as well as most layout applications. Image manipulation programs like Adobe PhotoShop can also save bitmap images as EPS-files. Some printer drivers are also capable of generating EPS-files as well as PostScript files.

Remarks

Although an EPS file contains PostScript data, you cannot always sent it straight to a printer to have it printed. Some interpreters cannot handle the preview data that may be included in the EPS file. Others don’t output the file because the ‘showpage” operator is missing. It can also happen that the printer does process the job but outputs a blank page because the content of the EPS-file was located outside the printable area.

Specsheet

This table gives a quick overview of the possibilities of the EPS file format:

• Name -EPS
  
• Developer -Adobe
  
• Release date -mid 80’s
  
• Type of data -vector, bitmap & fonts
  
• Number of colours -unlimited
  
• Ideal use -information exchange between prepress applications
  
• Extension on PC-platform -.EPS
  
• Macintosh file type -EPSF (sometimes TEXT)

JPEG File Format

JPEG stands for Joint Photographic Experts Group, which is a standardization committee. It also stands for the compression algorithm that was invented by this committee. To complicate things a bit more, JPEG compressed images are often stored in a file format called JFIF (JPEG File Interchange Format), which a lot of people also refer to as JPEG!

What many people call the JPEG file format, is actually called JFIF or the JPEG File Interchange Format. It is a minimal file format which enables JPEG bitstreams to be exchanged between a wide variety of platforms and applications. JFIF conforms to the JPEG Draft International Standard (ISO DIS 10918-1).
Specsheet

This table gives a quick overview of the possibilities of the JFIF file format:

• Name -JFIF (JPEG file)
  
• Developer -JPEG committee
  
• Release date -late 80's, early 90's
  
• Type of data -bitmap
  
• Number of colours -256, 16777216 or 4294967296
  
• Colour spaces -grayscale, RGB, YCbCr, CMYK
  
• Compression algorithms
  
• internet publishing
  
• Extension on PC-platform -.JPG

GIF File Format

GIF is a file format that should not really be used for prepress, it is far more suited for web design or to exchange images through e-mail or newsgroups. Unfortunately, GIF images keep popping up in pages made by amateurs (not to mention books about the internet ;-) ) so it is worthwhile to know a bit about the format. You can also use this description to explain to people why GIF is not suited for prepress use.

General information

GIF is the abbreviation of Graphics Interchange Format. It was originally developed by CompuServe (an on-line service that was pretty successful in the early nineties). The format includes some key features which makes it a unique and valuable format for the internet. These features include file compression, transparency, interlacing and storage of multiple images within a single file which allows for a primitive form of animation.

This is an overview of the different features of the GIF file format, from the perspective of a prepress operator.

Limited colour palette

A GIF image can contain 2, 4, 8, 16, 32, 64, 128 or 256 colours which are stored in a colour palette or colour table within the image file. Each colour in the GIF colour table is described in RGB values, with each value having a range of 0 to 255. CMYK colours are not possible in GIF.

Although the GIF format has access to over 16.8 million colours, only a maximum of 256 colours can be referenced within a single GIF image. While this limited palette keeps down file size and is perfectly acceptable for on-screen viewing, it leads to posterized images when they are printed. Most preflighting tools like PitStop can generate a warning when they encounter images with a fixed colour palette.

Resolution

Although GIF does not require a specific resolution, most GIF images have a resolution between 72 and 90 dpi, ideal for on-screen viewing but insufficient for prepress use.

Specsheet

This table gives a quick overview of the possibilities of the GIF file format:

• Name -GIF
  
• Developer -CompuServe
  
• Release date -1987
  
• Type of data -bitmap
  
• Number of colours -2, 4, 8, 16, 32, 64, 128 or 256
  
• Colour spaces -RGB
  
• Compression algorithms
  
• LZW
  
• Ideal use -internet publishing
  
• Extension on PC-platform -.gif
  
• Special features -transparancy, interlacing, animation