Look for identical resolution of horizontal and vertical lines. If these lines differ significantly from each other in resolution, there may be a mechanical problem either with drum rotation or with head transport.
There are inherent differences between lines written by the platesetter in the along-the-drum and the around-the-drum directions. Interpreting the appearance of the parallel lines depends on the design of individual platesetters.
The Parallel Lines section contains micro-lines that may reveal directional imaging artifacts caused by the plate setting system. This section allows quick assessment of writing and transport accuracy.
The image shows the areas in the Parallel Lines section. The upper left contains 1x1 pixel and 2x2 pixel horizontal lines; the lower left contains 1x1 pixel and 2x2 pixel vertical lines. The right side contains fine diagonal lines in each direction. In the middle, across the columns, is a 10x10 pixel checkerboard.
The “1 Pix” horizontal and vertical lines are made by imaging continuous pixels in a 1-pixel wide line, then skipping continuous pixels in a 1-pixel wide line. Similarly, “2 Pix” horizontal and vertical lines are 2 pixels wide, separated by 2-pixel spaces. The 10x10 pixel checkerboard area represents a 50% tint.
Printhead transport and drum rotation must be within tight tolerances for proper resolution and registration. The Parallel Lines section of the Plate Control Strip allows you to monitor changes in these mechanical tolerances.