Technologies to Simulate Output on Offset Printing Press
Recent years have seen a rapid diversification of the printing workflow involving digital color printing presses as well as offset printing presses. As full digital now dominates the print process, color proofing methods have also changed from flatbedNote1 to digital. In addition, the use of a hybrid workflow of both offset and digital printing presses, enabling high value-added printing, is starting to spread. To respond to these changes and the demand for high value-added printing, Fuji Xerox aims to faithfully reproduce the final color output on offset printing presses, to increase the compatibility of its products with other systems used in the printing workflow, and to contribute to higher workflow efficiency.
Data transferred between companies as well as different stages in the workflow must meet certain specifications (such as total ink coverageNote2 and overprintNote3 settings). It is also important to confirm that data conforms to specifications in the prepress process in order to obtain the desired final output on press and prevent unexpected results or unnecessary rework. This is often accomplished by using tools such as preflightNote4 software at certain points in the workflow. However, the results shown in text-based log files are difficult to understand intuitively. Furthermore, one must be trained and experienced to some extent in order to be able to check these log files. If problems are not discovered until the final output is produced on press, the materials printed before the discovery of the problem are rendered useless, resulting in a great deal of waste. Therefore, proofing before going to press is extremely important.
To assist the proofing process, Fuji Xerox has developed "warning functions" that let the user intuitively know which objects may cause problems on press (Fig. 1). When proofs are printed on Fuji Xerox printers, the areas that may cause problems on press can be printed in designated ways, so that the user can immediately identify these potential problems and accurately diagnose the cause in advance. If no problem is found, our printers will print no warnings so that these proofs can be used just like other color comps. In developing these functions, we maintained the compatibility of our printers with other systems in the workflow and added our own features.
Fig. 1 shows the five types of warning that can be printed on our printers.
Fig. 2 describes the two steps for delivering these warnings. In Step 1, any objects with spot color, overprint, or hairline issues are first detected and processed (e.g., extracted, deleted) by using our unique technologies. The processed data is then rendered by Adobe® PostScript® Interpreter. In Step 2, RBG/CIE images and areas with total ink coverage equal to or greater than a set value are first detected by color space analysis using Adobe® PostScript® Interpreter and a CMS module. Our image processing technologies are then employed to change the color of any area having such issues to the specified color (e.g., cyan, magenta). The total ink coverage is calculated for each pixel, and any pixel with total ink coverage equal to or greater than the set value is printed in the specified color. By designing these warning functions to be compatible with Adobe® PostScript® Interpreter, we have successfully provided a highly reliable proofing environment.
- Note1 Once the most commonly used method of color proofing, this method prints a proof on a flatbed proofing press using the actual paper and inks to be used on press.
- Note2 The total percentage of all inks (CMYK) in each pixel (usually between 300% and 360%).
- Note3 Refers to printing a color on top of another. While overprinting black on a color can often prevent gaps from appearing between black and colored areas, overprinting colors other than black can result in an unintended color.
- Note4 The process of confirming the validity of all digital files required for the printing process.
- Note5 Special ink used to reproduce a color that cannot be reproduced accurately by standard CMYK.
- Note6 Very thin lines that are visible on monitor screens, but may not be printed on press.
- Note7 Configurable PostScript® Interpreter.