Ellerhold has licenced ScreenPro with PrintFlat from Global Graphics Software to overcome visible banding on output caused by variations between printheads. ScreenPro is a very fast and efficient multi-level screening engine that mitigates artifacts on printed output that occur from the inkjet printing process. PrintFlat corrects for density non uniformity, which results in banding commonly caused by variation within a printhead or between printheads.
Ellerhold manufactures and operates 6 double side 2.5 metre wide scanning head web systems for printing 200 x 252 dpi billboard displays. The company was experiencing quality issues on its large format posters, known in Germany as Mega-Lights. The printheads showed variation in printed density both between the heads and across each head, which produced clearly visible bands within some types of printed output.
Frank Ellerhold, founder of Ellerhold AG, commented: ‘Certain jobs were worse than others. We knew the problem lay in the fact that the printheads were not balanced. We had seen Global Graphics Software's Martin Bailey introduce ScreenPro at The Inkjet Conference in Düsseldorf and believed this new technology might be the answer to this problem.’
Global Graphics Software’s Technical Services team worked with Ellerhold to enhance the quality of the printed output using ScreenPro’s PrintFlat technology.
In ScreenPro every nozzle can be addressed separately on any head/electronics to achieve very fine granularity. PrintFlat adjusts the density within ScreenPro to produce uniform density across a print bar. The process can be automated for closed loop correction, and unlike correction by adjustment of voltages, there is no effect on jetting stability or head lifetime, nor ink pressure and timing/drop speed variation. The team also used a variant of Global Graphics Software’s Advanced Inkjet Screens (AIS), available with ScreenPro and with the Harlequin RIP which they adapted specially for scanning head systems and which proved very effective.
The Technical Services team carried out tests, analysed the scanned prints and created a PrintFlat calibration workflow designed to compensate for the non uniformity in output across the print bar.
Dr Danny Hall, developer of the Advanced Inkjet Screens and Global Graphics Software’s chief screening scientist, commented: ‘The project brought many unique challenges. As it was a multi-pass process we needed to efficiently capture repeating density variations across the entire print area in an unbiased way. The project confirms that PrintFlat is a significant enabling technology, allowing the uniformity typical of analogue printing to be achieved routinely on a wide range of digital presses.’
Now Ellerhold uses Global Graphics Software’s online inkjet press calibration service, printflat.com, to upload the scans and automatically receive the correct calibrations. The printflat.com service is available to registered users who upload their PrintFlatscans and receive the calibrations they need to run their inkjet press at optimum quality.