Hybrid Screening is a combination of AM and FM screening. Hybrid screening is designed to improve print quality by increasing the output LPI for any given resolution.

The areas that suffer most when trying to increase the LPI for a given printing condition (typically the substrate) are the loss of dots in the highlights and of dots in the shadow, resulting in loss of detail. Using current computer-to-plate imaging systems at 2400 DPI, it has been shown that a 0.5% dot can be produced on some plating material.

Unfortunately, only a very controlled printing system on the finest sheet fed presses with premium gloss paper stock can this 0.5% dot actually print over the course of a reasonable press run. This is where HXM comes in. HXM recognizes the issue and is designed to carefully control the dot size and placement in the 0-8% and 92-100% range within the tonal scale.

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Traditional AM dot shape is used for the 9–91% tonal region and a Frequency Modulated or FM dot for the two end regions. Two distinct features make this type of screen a true Hybrid. First is the use of two screening types to form a combined screen, and second the fact that the dot size is fixed at a known printable size, which ensures print quality at the extreme ends of the tonal scale. The number and placement of the dots in the FM regions use a randomization generator but are aligned with the traditional screens to ensure a smooth transition from the FM to AM or vice-versa.

The range of screens offered within the HXM screen set can handle both matte and gloss stock. Its use of hybrid screening allows the enlargement or reduction of images without affecting quality or detail.

This is achieved by controlling the dot size in the highlight and shadow, ensuring it is does not disappear in the light areas or merge in the dark areas.

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Why use Hybrid Screening?

Traditional AM Screening.A common artifact of conventional fixed screening (AM) is moiré. This can be reduced by careful manipulation of screen angles, adjusting the input resolution and increasing the output lines per inch (LPI). The challenge with conventional AM screening is to be able to print the smallest dots possible to enhance the detail, maintain highlight detail and to provide smooth gradients where present. Hybrid screens have been designed to solve the printing challenges that come from printing at higher screen rulings.

Traditional FM Screening. FM screening places dots of varying size in a pseudo-random way to produce the required tints. Advantages of this include increased apparent sharpness and the removal of cross screen and object moiré. This is achieved because the dots are dispersed instead of clustered as they are in a traditional periodic screen. Because of the variable dots, FM screening does have some limitations. These include printing blanket hardness, TVI, ink tack needed adjustment, not being printable for long runs and substrate quality which can cause piling. However, FM does make ink saving a possibility, and if process control is tightly maintained, has been shown to print purer colours.

HXM screening is a combination of AM and FM screening which allows higher screen rulings than is provided by AM screens alone. Available from Global Graphics as a plugin upgrade to the Harlequin RIP, HXM is a solution that addresses the issue of printing on lower quality papers while at the same time meeting higher customer expectations. HXM screening is a solution that addresses both these challenges.

**http://www.harlequinrip.com/store/hqnstore.nsf/products/hxm.html**
http://www.ripdownloads.com/HybridScreening.html