Controlling the Platemaking Process

Understanding how to correctly expose and process plates, as well as film, is a critical part of process control in the prepress department. With the advent of CTP systems and digital printing, these imaging controls have moved to the forefront of the pursuit of quality print.

A few questions that a prepress operator might want to ask: How color-critical is the customer? Does the image subject matter have a lot of flesh-tones or neutral grays? What about fine detail in highlight and shadow areas? is there any fine-line work or very small text that will need to be addressed? Does the artwork file resolution correspond with the output device resolution? Is there any feedback that can or should be monitored from plate to plate or day to day?

Controlling the variables within a CTP workflow takes a knowledgeable prepress operator. Considerations such as managing different files from multiple applications and deciding which workflow will achieve the best results for the pressrun becomes second nature. The prepress operators have to deal with multiple RIPs, each with their own unique characteristics. Prepress is also responsible for maintaining the imaging units’ calibrations and curve balancing and the processors’ cleanliness.

In many instances it is helpful to have feedback from the imaging device and the RIP within the workflow. Plate Control Targets help the prepress operator know when a plate has been correctly imaged or exposed. Many plate control targets query the adjoining RIP for information regarding the output device’s name, dot size, linescreen, PostScript version (if applicable), etc. This is helpful if comparing results from different output devices, especially if they vary in output resolution.

Many plate control targets can detect both resolution (dot size) and addressability (dot placement) that the output device can handle. Patches such as positive and negative microlines show the resolution in both the horizontal and vertical directions, and checkerboard patterns show the smallest dot that is addressable by the platesetter. Star targets are also helpful for looking at output resolution and directional effects. Because highlight and shadow areas can be particularly problematic during imaging, a useful plate control target will employ tone patches that range from 0% dots to up to 5% dots, and conversely 95% dots to 100% dots. If the dots disappear in the highlight, or plug in the shadow, the plate exposure needs to be adjusted. For proper imaging, a tone scale with patches ranging from 10% to 90% is one of the most helpful areas of a plate control target. Usually, the dot percentages have the greatest variation close to the 50% dot patch. The tone scale allows the user to read density differences of how the dot is being imaged at different intervals. Using this information from a plate reader, the prepress operator can linearize the output device, develop curves, and check for miscalibration.

Printing Industries of America Plate Control Products
The Printing Industries of America Digital Plate Control Target is an easy-to-use tool designed to monitor electronic imaging devices, particularly platesetters and imagesetters. It confirms that an imaging device recognizes input and that the output is at a consistent level of quality. The digital file, which is written in PostScript language, displays data obtained directly from the raster image processor (RIP) and diagnoses whether the device is capable of performing as requested It provides a consistent means of monitoring exposure level, checking imaging resolution, diagnosing directional effects or image inconsistencies, and confirming platesetter/imagesetter linearization. The Printing Industries Digital Plate Control Target is small enough to fit in the margin or platebend of most production plates.

Ugra Plate Control Targets
The Ugra products have been specifically designed so the prepress operator has a clear understanding of the status of their imaging unit(s). These tools are perfect for maintaining CTP or film imaging units’ calibration. If monitored daily, the visual feedback that these targets provide can diagnose which device is out of calibration or there is another problem with the output device. They focus on digital imaging areas of concern such as resolution, addressability, type rendition, highlight dot reproduction, tone scale reproduction, RIP-specific settings, curve characteristics. These products can also be helpful comparing one RIP to another or device to device. Ugra also offers similar targets that are specifically designed for the special requirements of digital printing. Because of their small size, both the Ugra/Fogra targets can fit in the margins of most any layout or plate bend area.

For those still using a film-based workflow, the challenges of maintaining quality during the film/platemaking process are just as daunting, if not more so. In addition to file problems and mechanical issues, an analog process adds the inefficiencies of human interaction to the exposure and developing process. Not only does the prepress operator have to monitor the chemicals for processing, but also the illumination of the exposure unit and light integrator, the operation of the vacuum frame, and the precision in which the films are stripped together.

The Ugra/Fogra Digital Plate Control Wedge is specifically designed for CTP systems. It includes visual reference steps (VRS) that allow the user to determine the optimal settings for exposure through visual analysis.

The Ugra Film Plate Control Wedge, also known as the Ugra Offset Control Wedge, has a world-renowned reputation in the offset-print industry for controlling exposure of film or plates in an analog workflow. This product is available as a film negative. The prepress operator cannot forget about variables such as balancing multiple vendors’ materials. These vendors offer a wide array of plate brands in both positive and negative-processing plates for chemistry and water-based processors, not to mention varieties of thickness gauges for changeable run lengths. Each type of plate has its own strengths and weaknesses in certain situations. If processing with a chemistry-based processor, the operator needs to be aware of how old the chemistry is and its temperature; both will affect the amount of emulsion that rinses off of the plate. When checking plates for accuracy, the prepress operator needs to be aware that every plate reader’s sensitivity is not the same. Even the angle of the plate reader (plainometer) to the patch can give differing results.

The products listed above are both Macintosh and PC compatible. For more information on these or any other quality/process control products, email qcproducts@printing.org or call 412-259-1786.

Published on Friday, October 10, 2008 (updated 05/28/2014)

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