This method places dots at even intervals and varies the size of the dots. The larger the dot, the more ink is placed, and the darker the image gets at that point. This is the method used by conventional screen printers. However, digital printing devices print fixed-size dots. These devices can simulate AM screening by grouping dots together to form clusters at fixed intervals. However, the detail level of the image is limited by the number of clusters (lines or frequency) used to halftone the image. When color images are produced using AM screening, the screens are usually rotated so that the dots are not printed on top of each other. (For example: printing 50% black on top of 10% yellow without rotation results in 50% black - the yellow disappears). This rotation results in the familiar rosette pattern.

 

Both the Dither and Screen dot patterns use AM screening.

This method places fixed-size dots at varying intervals depending upon how much coverage is desired. There are many ways to vary the interval between the dots, ranging from completely random, through stochastic (based upon the laws of probability), to a regimented order such as Dither. How dots are placed affects smoothness, color, and detail. FM screening is generally preferred over AM screening because it results in greater detail on digital devices and provides better detail and smoothness in tone reproduction.

 

The following patterns use FM screening: FDRP Diffusion, FDRP Line, and Stochastic.

ONYX Graphics, Inc. VirtualPixel technology allows the creation of dots of different sizes. This reduces processing times while retaining color fidelity. The VirtualPixel dot patterns are displayed as the process resolution, followed by the @ character, followed by the print resolution. An example of a VirtualPixel resolution is 360@720. In this case RIP-Queue processes 360 dpi, but prints 720. Using VirtualPixel resolutions will greatly decrease processing time, however "pixelation" may occur when using images that contain a large amount of detail.

Dot placement in RIP-Queue is based on one of two methods: desired color combined with area analysis, or desired color only. AM screening uses only desired color, but FM screening can be based upon either method. Dot patterns based on area analysis are usually slower to generate because more computation is required. Dot patterns based on desired color only may lose detail because surrounding detail is not considered when placing dots.