Halftoneskärmar

Halftoneskärmar, commonly referred to as halftone screens, are devices or techniques used to convert continuous-tone images into patterns of dots that can be reproduced by printing, photographic or digital processes. They are essential for printing color prints, newspapers, and for generating tonal gradients in digital displays. The fundamental principle of a halftone screen is dot modulation: by varying the size or density of dots in a regular grid, a range of intermediate tones can be simulated. When viewed from a normal viewing distance, the individual dots blend optically to give the impression of continuous tone.

In traditional printing, mechanical halftone screens were attached to hand or computer typesetting machines. Modern halftone screens are typically generated by software such as Adobe Photoshop or Illustrator. The screen specifications—screen angle (usually 45°, 63°, or 78°), frequency (dots per inch), and dot shape (round, elliptical, or custom shapes)—determine the tonal quality and the appearance of the output. Adjusting the screen angle between sub‑processes (cyan, magenta, yellow, black in CMYK) prevents moiré patterns and improves color registration.

Digital halftone techniques include error diffusion, which spreads the quantization error of pixel values across neighboring pixels to preserve edges, and dithering, which creates patterns that emulate intermediate tones. In digital displays, subpixel rendering can be seen as a form of halftone, with each pixel’s RGB subcomponents acting like dots at subpixel precision. The use of halftones is also common in modern data visualization, where discrete color bands are employed to illustrate intensity gradients.