To work with digital plate setters, better known as computer to plate devices, in a controlled manner, demands for appropriate control tools as all complex systems do to supervise the daily production process and as such allowing a safe production. The complexity of computer to plate systems emerges from the multitude of components, which are involved, like digital data from different applications with different data formats, variable RIP and output parameters, divers printing plate types and treatment parameters and requirements for the tone reproduction of the output device. This Situation demands high skills of the operators in order to rule the process.
Through a lot of analysis and practical tests a new control method for computer to plate devices was found. It is a further development of the well-known Ugra/Fogra Postscript Wedge, which was acquainted as the standard tool to control Postscript output devices by the industry. Later one doesn’t loose anything of its value for the control of film setters and the digital workflow.
The Ugra/Fogra Digital Plate Control Wedge contains
six functional groups or control fields, which are:
*Information fieldsix functional groups or control fields, which are:
*Resolution patches
*Line patches
*Checkerboard patches
*Visual reference steps (VRS)
*Halftone wedge
The novelty is the part with the eleven visual reference steps (VRS). Each VRS consists of two checkerboard fields, which are surrounded by a reference halftone field. There are eleven VRS, which are stepped in 5% increments from 35% to 85% dot areas. Under theoretical ideal conditions and a linear tone reproduction the two fields in VRS 50%should show the same tone value, that means there is visually and in measure no difference. Depending of the plate type, the plate setter calibration, the plate treatment and the tone reproduction this goal is not reachable.The same tone value of the checkerboard and the halftone field will be in a lower or higher VRS. Important for the daily production is that always the VRS is found right, which manufacturing conditions lead to the optimal printing result.
Further patches contain resolution sensible information and a halftone wedge, with which the tone reproduction characteristic can be tested. To eliminate productionrelated unevenness in the block, a full-tone patch was placed adjacent to the checkerboard patches. With the unset block outside the plate wedge, the positions for the densitometric measurement of zero (uncoated substrate), rendering and full tone are immediately adjacent to each other. Nevertheless Ugra promotes to use planimetric measurement methods on printing plates. The resolution patches consists of two star targets, the one generated with negative lines the other with positive lines. The line whit corresponds with the resolution setting of the plate setter. The line and checkerboard patches change their line or dot size with the resolution settings of the plate setter.
