5.1 Introduction
Wayne Collins
Learning Objectives
- Explain why raster image processing requires so much data for print imaging
- Compare resolutions required for digital media and print media
- Compare and contrast the positive and negative attributes between using process and spot colours
- Discuss why Pantone colours are more accurate on a printed swatch than on screen.
- List a number of different industry standard spot colour systems
- Describe trapping issues that occur when adjacent colours are imaged independently
- Analyze different imaging technologies for trapping requirements
- Interpret how black ink is to be used in overprint and boost situations
- Define transparency within the context of prepress workflow management
- Differentiate between flattening transparency on the desktop, or at raster image processing
- Describe the most common press sheet imposition styles
- Analyze different binding styles to select the correct imposition required
- Identify opportunities for nesting multiple images to save materials
- Explain the importance of preflight within the context of pre-press workflow
North America’s fifth-largest manufacturing sector is graphic communications technologies. We can become aware of just how huge this industry is by listing all the manufactured images we see in our day. Your list might include the morning paper or magazine you read, the graphic on the side of the bus you ride to work, and the labels on the grocery shelf where you select your evening meal. Increasingly, more of the graphics that are driving that massive industry are produced with computer graphics software on personal computers. Most of the graphics software used to create the images for reproduction is designed to create images for electronic media — primarily the Internet. Computer graphics designers are not aware of, or concerned with, optimizing their designs for the manufacturing process they are driving. This problem is a root cause of less profitability in most sectors of the graphic communications industry. To tackle this problem, we must become aware of all that happens to a computer graphic from the time it leaves the picture created on the computer screen to the image on the label on the package on the grocery shelf, or the photograph on the side of a bus.
We must first distinguish between traditional pre-press technologies and the pre-imaging processes that are relevant in today’s graphic communications industry. Pre-press processes are different from the way we process images for electrophotographic imaging or imaging with an inkjet engine. We must also distinguish between preparing images for a lithographic press and a flexographic press. Electrophotography and inkjet are growing technologies used to produce customized — or individualized — communications materials. Lithography and flexography are used to manufacture mass-produced media products. These four imaging processes are the core imaging technologies that reproduce 90% of the images produced in the graphic communications industry.
Many graphic designers are not aware of what must happen to the computer graphics they produce in order to ready them for manufacturing reproduction. Their experience is limited to hitting ‘command P’ and their computer graphic magically transforming the illuminated masterpiece on their Apple Cinema Display, to the disappointing rendition that appears on the tray of their inkjet printer. Most of the pre-imaging processes are automated in software functions that are built into the print driver, so people are not aware of how a computer graphic must be prepared for an imaging device. Since more and more of the images produced through inkjet, electrophotography, lithography and flexography start their lives as computer graphics, it is important to understand these pre-imaging processes to properly design computer graphics for the manufacturing process.
This chapter will analyze six pre-imaging processes in detail, and describe how they are altered to prepare computer graphics differently for each of the four imaging technologies. We will refer back to the computer graphic design/creation process to outline how graphics could be altered so they can be more effectively reproduced with each imaging technology. This is the missing link in the graphic communications business in today’s marketplace. Designers create computer graphics in software that is increasingly designed for electronic image creation. They do not realize that the same graphic they created for a home page on the Internet should not be used for the cover of a book. They email the image to a lithographic print production facility and the pre-press department of that facility does hand springs trying to alter the image to work on their sheet-fed presses. This adds time and cost to the job that is usually buried. The designer never gets feedback on how the design could be altered to be more effective for lithographic production.
When pre-press was a computer-to-film process, there were two important factors that ensured designers got this critical feedback. The software for computer graphic production was specialized for print creation and content could be photographed or computer-generated and combined on film. Computer graphic designers knew their image was only going to be used for the cover of a book and created it appropriately. They also had to submit their computer graphic to a graphic communications production facility that was separate from the lithographic print facility. If there were extra costs incurred to prepare the computer graphic for a lithographic press, the designer was informed and invoiced for the extra work the image preparation entailed. So the designers were working with computer graphic software that would not let them create imagery that was not appropriate for print production, and if they did dream up an image that did not work well, they were immediately informed of the extra costs they were incurring.
In the 21st-century marketplace, all graphics that drive our four primary imaging technologies are created on the computer. Computer graphics software is designed to create effects for images that will stay in the electronic media: web, broadcast, digital film, and hand-held communication technologies. Pre-imaging processes are either automated or a part of the print manufacturing business and usually considered the painful part of feeding the print machinery that no one wants to talk about. So computer graphic designers drive software that lets them create outrageous images for imaging reproduction manufacture. They are less concerned about the ‘print’ part of a media campaign, and manufacturers are hesitant to inform them that their designs incurred extra costs to reproduce. We can contribute to a solution to this problem by analyzing all of the pre-imaging processes for each type of reproduction manufacture and link them back to the computer graphic design software.
We will examine six pre-imaging processes:
- Raster image processing (RIP) technologies that are common to all four manufacturing processes
- Colour management for repeatability, as a part of the RIP process
- Trapping to lithographic and flexographic specifications
- Transparency, which is a visual effect that has a great impact on imaging
- Imposition for pre-RIP and post-RIP for media utilization
- Preflight analysis and automation for computer file creation