Dithering, halftone, ASCII: retro effects explained

Why these effects exist

For a long time, reproducing an image was expensive: printing had only a few inks, the first screens two, four or sixteen colors, terminals nothing but characters. To suggest shades all the same, printers and programmers invented ingenious techniques. What was a constraint has become an aesthetic, found today on posters, album covers, websites and social media.

Dithering

Dithering simulates shades with a limited number of colors. Instead of a gray, it places black and white pixels in proportion: from a distance, the eye blends them. There are two big families:

• Error diffusion (Floyd–Steinberg, Atkinson, Serpentine): each pixel is rounded to the nearest color, and the error is passed on to its neighbors. The result is organic and detailed. Floyd–Steinberg is the most faithful; Atkinson, more contrasty, recalls the first personal computers; Serpentine passes the error along a curve that winds through the image, for a texture with no preferred direction.
• Ordered dithering (Bayer 2×2, 4×4, 8×8 matrices, clustered dots, diagonal lines): a regular pattern of thresholds. Bayer produces the crosshatch grids typical of 1980s video games and screens; clustered dots form round dots that grow in the shadows, like a newspaper halftone; diagonal lines thicken like an engraving. Very graphic, it goes well with a palette of two to four colors.

Dithering really comes into its own with a reduced palette: black and white, phosphor green on black, or the sixteen colors of old computers.

Halftone (print screen)

Halftone comes from offset printing and newspapers. The image is turned into a grid of dots whose size varies: big dots in the shadows, small ones in the highlights. In color, four screens (cyan, magenta, yellow and black) are overlaid at different angles, creating the little rosettes you can see through a magnifying glass on a magazine page.

Deliberately enlarged, the screen becomes a strong graphic effect, very “pop art” or “comic book”. It is also an effect that exports as vectors: each dot is a circle, sharp at any size.

Dithering or halftone? Halftone keeps a regular grid and varies the size of the dots; dithering keeps identical pixels and varies how they are spread.

ASCII art

ASCII art draws an image with text characters. Each area of the image is replaced by a more or less “dense” character: a space for white, a period for light gray, an @ or a # for black. Born on the terminals and printers of the 1960s and 1970s, it now evokes code, hacker culture and the computers of yesteryear.

The choice of character set changes everything: a few simple signs for a clean, readable result, a long range of characters for more detail, blocks (░▒▓█) for a pixel effect, 0s and 1s for a binary feel. ASCII art can be exported as an image, as SVG or as a plain text file.

Other retro effects

• Light net, in the Geometry tool: a 3D scene made of points of light, where lines go from solid to dotted with depth, built from abstract shapes or from your photo.
• VHS: offset color bands, interference lines and a wavering image, like a worn tape.
• CRT screen: scanlines, glow around light areas, chromatic aberration (colors shifting at the edges) and a slight screen curvature.
• Pixel sorting: trails of pixels sorted by brightness, the “glitch” effect of digital art.
• Hatching and wavy lines: the image redrawn in lines, like an engraving or a banknote.

From photos to lines: geometric art

In the same spirit, a photo can be reinterpreted as contour lines (like a topographic map of the light), as engraving-style flow lines or as a network of connected points. These more contemporary looks share with retro effects a taste for images built from a reduced vocabulary.

A graphic designer’s tips

• Choose a simple image. A sharp subject on an uncluttered background, with good contrast, survives color reduction much better than a busy scene.
• Set the contrast before the effect. A little more contrast and brightness on the starting photo avoids undefined gray areas.
• Play with scale. A deliberately large screen or large characters turn the technical effect into a graphic statement. Conversely, a very fine screen gives a subtle texture.
• Limit the palette. Two well-chosen colors (an ink, a paper) often have more impact than the original colors. Our guide to creating a color palette will help you choose them.
• Export in the right format. In PNG, avoid any later resizing: pixel art enlarged by software turns blurry. Prefer the ×2 or ×4 export, or SVG for the vector effects.

For a more photographic retro look, with grain and film colors, read our guide to the film look.