What it does
Reduces the image to two colors with a hard cutoff between light and dark, with optional outlined edges.
Thresholding is older than digital imaging. Lith film pushed photographs to pure black and white for platemaking, photocopiers did it to everything by accident, and stencil artists have always worked in it, because a stencil physically cannot hold a gradient. The single decision that matters is where the cutoff sits: slide it down and highlights survive as thin white shapes, slide it up and the shadows flood the frame. The same photograph becomes a dozen different images along the way.
The classic failure mode is speckle. Around the cutoff, noise and film grain flip neighboring pixels to opposite sides, and a clean silhouette dissolves into confetti. The fix is smoothing the image upstream of the cutoff, melting the noise before it is judged, so shapes come out solid with honest edges. And the two colors are choices, not constants: black on white is only the default, and swapping in ink and paper colors turns any photo into a two-color print in one move.
Past the fill, threshold has a second life as a line-drawing machine. Instead of filling the two regions, it can draw a contour along the boundary where the image crosses the cutoff, then repeat that line at additional brightness levels above and below. The image becomes a topographic map of its own light, rings of elevation lines tracing every gradient, floating on flat color or blended back over the source.
Signature looks
Stencil
One cutoff, two flat colors, silhouettes with spray-paint edges. The street-stencil read, instantly graphic.
Photocopy
The cutoff pushed until highlights blow out and shadows flood solid. A photograph run through the office machine twice.
Contour map
The fill turned off and lines drawn at stepped brightness levels, so the image becomes a topographic chart of its own lighting.
Try it on your own footage
This effect runs live in the Modulate editor, with layers, effect chains, masks, and keyframes. Free, no signup, nothing to install.
Common questions
What does the threshold effect do?
It compares every pixel’s brightness against a single cutoff level and assigns one of two colors: one for everything above, one for everything below. The result is a hard-edged, two-tone image with no gradients, the digital equivalent of a stencil or a lith print.
What is the difference between threshold and posterize?
Posterize keeps a ladder of tonal bands, usually several, and can preserve the image’s colors within them. Threshold takes the ladder to its floor: one rung, two flat colors, everything decided by a single cutoff. Posterize simplifies an image; threshold turns it into a silhouette.
Why does my thresholded image look speckled?
Noise. Around the cutoff level, grain and sensor noise push neighboring pixels to opposite sides of the line, which renders as salt-and-pepper confetti. Smoothing the image before the cutoff is judged melts that noise away and leaves solid shapes with clean edges.
Can the threshold effect draw contour lines?
Yes. Instead of filling the two regions, it can trace the boundary where brightness crosses the cutoff, and repeat that line at several levels above and below it. The result reads as a topographic map of the image’s light, and the lines can float on flat color or sit over the original.
Does threshold work on video?
Yes, and the silhouettes track motion, which is most of the appeal: a figure moving through changing light becomes a living stencil. In Modulate the Threshold effect runs live on images and video in the editor and stacks with halftone, grain, and blur.
Related effects
Posterize effect
Collapses smooth gradients into a few flat tonal bands for a screen-printed, cel-shaded look. Band per channel or by brightness, with a gamma bias to push the steps toward shadows or highlights.
Invert colors
Flips colors to their opposites, like a photo negative. Invert everything, just the brightness, or individual channels.
Halftone effect
Turns the image into printed dot patterns, from single-color newspaper dots to full four-ink color screens.
Dither effect
Early computer graphics look: the image is rebuilt from tiny dot patterns and a limited color palette.