Generic info on screening
Frequency Modulated (FM)
Whereas conventional screening methods place dots in a grid pattern to reproduce a continuous tone image with FM screening, tone densities are varied by placing different numbers of small dots within a given area rather than by changing the sizes of a fixed number of dots as in conventional AM screening.
Tonal characteristics are simulated by enlarging or reducing the dot size in a particular area of an image. With FM screening, the dots are dispersed in a less structured manner. Varying shades are created by the irregular frequency, or dispersal of the screening dots.
Dots seem to disappear, resulting in exceptional clarity and detail, especially effective in printing images of jewellery, fabrics, fine automobiles and skin tones. FM screening also eliminates moiré effects, color shifts and rosettes which can form in conventional halftone images.
Error Diffusion (ED)
It is sometimes the case that there are visible artefacts in the resulting image. To circumvent this problem, so-called error diffusion ED techniques can be used. As the name implies, the error (difference between the exact pixel value from the original image and the approximated value being displayed in the result) is distributed to the neighbouring pixels, thus introducing a kind of “smoothing” into the dithered image. There is a computational overhead to the calculation of this screening method.
Spatial Distributed (SD)
Spatial Distributed screening distributes the dots equally over the available area and respecting each others relative position. This avoid clustering of dots and thus gives a very smooth equally distributed output especially in the light tones. This screening can only be used on printing processes and printing heads that are very precise on the dot placement, else the spatial distribution effect will be anulled due to the unprecise positioned dots. In general this screening if very suitable for small object printing, which pairs high precision printing and small surfaces.
As the calculation respects all positions in all plates in generally slower than for example FM Screening and thus only suitable for smaller areas.
Static Ordered (SO)
Static Ordered screening intentially clusters dots to form smaller islang or worms to make sure the ink sticks to the media. This screening is ideal for materials where placing a single dot is not possible because of physical reasons. It combines will be high speed printing as due to the cell based properties the processing speed is high.
Dynamic Ordered (DO)
Dynamic Ordered screening is similar to SO, but dynamically calculates the clusters based on the image and print mode. Which makes the initial job start slower as the cell is calculated per job.