A Pseudo Continuous Tone Step Wedge for Digital Platemaking

The Agfa Digital Plate Control Wedge, or DPCW, provides a means of optimizing the exposure of direct digital platemakers by visual inspection. It does this by using a pseudo continuous tone step wedge consisting of an array of checkerboard patterns with varying screen rulings. The DPCW was tested on an Agfa Selectset Avantra 25 film/platesetter using polyester based Setprint media, and on another platesetter using aluminum based Lithostar Plus media. After the plates were made, the dot areas were measured with an image analysis system. These measurements show that there was zero platemaker dot gain, and that the halftone reproduction for the system was linearized, but that aluminum and polyester media may differ in their response to exposure. The DPCW's use precludes the need for making dot area measurements of printing plates with densitometers, which has been shown to be unreliable for such applications. Regardless of the platesetter or media being used, the pseudo continuous tone step wedge is the most sensitive way to monitor platemaking variables.