Advantages of Stochastic Screening

Reduced ink volume consumed

Fine type that is screened has smoother edges.

Moiré due to screening are eliminated.

Visual results are more consistent when there are slight ink density variations

Smoother process screen tint builds

Improved detail, especially in the highlight areas of image

Improved color fidelity

Simulates the appearance of a continuous tone image

Conventional vs. Stochastic Screening comparision

Conventional lithographic printing reproduces photographic images with a grid like screen. This grid is defined as lines per inch. On a grid line that is one inch long, if there are 100 dots it is called a 100 line screen, if there is 200 dots on that one inch line then it is a 200 line screen. The screen ruling that is used is dependent on print quality of the offset press, types of plate, and the surface of the paper.

Shades of color are achieved by varying the size of the dots. A single dot is a square of space. A solid square would be a 100% dot. A smaller dot allows for white paper to show through the square area. When the printed dot is half of the square area allowing for the paper to show through on the other half of the square area this is a 50% dot.

Four-color process printing cyan, magenta, yellow and black (CMYK) uses a combination of different size dots printing in a overlapping arrangement called a rosette. The combination of CMYK dots creates subtractive color. To eliminate a Moiré pattern each row is angled off 30 degrees from each other with the yellow being angled 15 degrees off of the magenta or cyan angles.

Stochastic screening varies the pattern of dots rather than placing the dots in a straight row. Additionally each dot is the same size instead of changing the size of dot, i.e. 50% or 100%.

The stochastic dots create shades of color by increasing or decreasing the number of dots. Highlights will have fewer dots than the midtone or shadow areas. An advantage of this system is that images have a smoother or continuous tone appearance.

Printing Ink Consumption is Reduced

The consistent dot size and random distribution pattern of stochastic screening create optical and mechanical effects impacting the printing process. Using stochastic screens yield cleaner (higher chroma) color. The many, many small dots create much more "edge" interface where the edge of the dot and paper each contribute to the visual effect. Each dot has a fixed area of "optical dot gain" due to the refraction of light through the ink film. The distance from the true edge of the dot and the "apparent" edge of the dot remains the same regardless of dot size. Where there are many small dots instead of a few large dots, the area of "optical dot gain" is much larger, thus reducing the direct reflection of paper. This produces higher apparent chroma (cleanliness) and more color overall with a reduction in amount of ink consumed.

Fine type that is screened has smoother edges

Because of the random pattern and the consistent size of the stochastic dot there is no potential for a saw tooth effect on the vertical or horizontal edges of type. When printing conventionally the saw tooth effect occurs when the edge of the type cuts through a row of dots just missing the printed dot and showing only the white paper. Another example is printing black and white photos as a single color halftone. If any other angle other than 45 degrees a saw tooth edge appears on the edges of the printed photo.

Moiré due to screening are eliminated

A printed Moiré is created when screened conventionally and the image has a continuous line that is straight such as a piece of cloth. The reason for this is the intersecting lines are at angles that are in conflict with required 30 degree angle for the row of dots.

Stochastic screening uses random patterns of dots rather than rows of dots therefore eliminating the potential for creating a Moiré in the screening process.

If using digital images reproducing subjects that have continuous straight lines there is a potential for a morie before the screening process. This type of morie is due to the angle of the continuous straight line and rows of the digital pixels. When encountering this situation refer to Castle Press Digital Tips "Having Moiré Pattern Problems?"

Simulates the appearance of a continuous tone image.

Demonstrating this type of appearance on a web page is impossible. Give your Castle Press representative a call to set an appointment to view the actual printing pieces.