Why do CRTs show scanlines at all?

The beam draws one line at a time with a spot narrower than the line pitch, so the gaps between lines stay dark. Interlacing fills those gaps with the second field. A progressive 240-line signal leaves them open. Progressive 240p video, as used by many consoles and early computers, is the case where the gaps are widest.

Do all CRT monitors have the same scanlines?

No. Spot size, focus, brightness, and the line standard all change how pronounced they are. Computer monitors at high resolutions hide them, and professional monitors can look sharper, while small consumer sets show them more strongly. A sharp professional monitor and a tired thirty year old set can look like different technologies when they show the same signal.

Why do scanlines look different on bright and dark images?

A brighter beam makes a larger spot, so lines grow wider and fill their gaps, while dim lines stay narrow. This brightness-dependent thickness is why a simple overlay of black stripes looks fake. Matching that behavior, even roughly with a glow, is the difference between a believable tube and a flat striped filter.

Is a scanline overlay enough to look like a CRT?

Rarely. A stripe overlay cuts brightness evenly and adds no bloom. A convincing result adds glow, brightness-dependent line thickness, slight softness, and in some cases the red, green, and blue structure of the mask. Looking at a photograph of a real screen before you start helps you decide which of those details matter for your shot.

CRT scanlines: what it is and how to make it in After Effects

CRT scanlines are the dark gaps between the lit lines of a tube display. Learn how the beam makes them and how to build them with WIRE WRAITH in After Effects.

WHAT CAUSES IT

CRT scanlines are the visible line structure of a picture drawn by a moving electron beam on a phosphor-coated tube. An NTSC signal carries 525 lines per frame, drawn as two fields of 262.5 lines at 59.94 fields per second, and about 480 of them are visible picture. The beam is a focused spot with a roughly Gaussian brightness profile, so each line is brightest at its center and falls off above and below. When the lines of one field are separated by more than the width of the spot, dark gaps open between them. A console or computer that outputs 240 lines in a progressive mode draws every field in the same place, so there is no second field to fill the gaps, and the structure stays visible. Brightness also changes the spot size, since a stronger beam spreads wider, so bright lines swell and nearly close their gaps while dim lines stay thin. Behind the line structure sits the shadow mask or aperture grille, which divides each line into red, green, and blue phosphor stripes.

WHAT IT LOOKS LIKE

Evenly spaced horizontal lines across the picture, with dark gaps that run the full width of the screen. The lines are soft at the edges, not hard bars, and they vary in thickness with image brightness: bright areas look nearly solid, while shadows reveal the gaps. Up close the lines resolve into a fine red, green, and blue stripe or dot structure. The picture has a slight bloom around bright shapes and a subtle curvature. Pixel art on a CRT looks smoother and warmer than on a flat panel, because each pixel is a vertically stretched glow instead of a hard square.

WHERE YOU SEE IT

Retro games on CRT displays, arcade cabinets, broadcast monitors in control rooms, old computer terminals, and any footage of a television in a scene. Players and collectors value scanlines for pixel art, since the games were designed around them. In post, scanlines are added to retro style graphics, game trailers, and sci-fi screens. They are used together with curvature, glow, and color fringes to sell a believable display.

RECREATE IT

WIRE WRAITH

CONTROLS LINE SPACING, GLOW, DISPLACE

WIRE WRAITH draws the picture as a field of lines, so LINE SPACING sets how far apart they sit. Keep DISPLACE at its minimum so the lines stay straight and do not bend with brightness, then raise GLOW until the lines soften and bloom around bright areas. WIRE WRAITH is a scan processor, so treat this as a stylized scanline look and not a pixel-accurate tube model. Adjust LINE SPACING to your frame height.

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HOW TO MAKE IT IN AFTER EFFECTS

1. Place the footage in a composition at its final resolution, since the line count depends on the height of the frame. 2. Apply WIRE WRAITH. 3. Set DISPLACE to its minimum so the lines remain straight. 4. Adjust LINE SPACING until the line count reads like a tube: for a convincing look at 1080p, try a spacing that gives a few hundred visible lines rather than a thousand. 5. Raise GLOW until the lines soften and bright areas swell, which mimics beam spread. 6. Zoom to 100 percent and compare dark and bright regions; the gaps should be more visible in shadows. 7. For a game screen, scale the footage up with nearest neighbor sampling first, then apply the effect, so the line structure matches the pixel grid. 8. Keep the settings constant through a scene, because scanlines are a fixed property of the display. 9. Check the result on a different monitor, since fine lines can alias or produce moire when the video is scaled for delivery.

QUESTIONS

Why do CRTs show scanlines at all?: The beam draws one line at a time with a spot narrower than the line pitch, so the gaps between lines stay dark. Interlacing fills those gaps with the second field. A progressive 240-line signal leaves them open. Progressive 240p video, as used by many consoles and early computers, is the case where the gaps are widest.
Do all CRT monitors have the same scanlines?: No. Spot size, focus, brightness, and the line standard all change how pronounced they are. Computer monitors at high resolutions hide them, and professional monitors can look sharper, while small consumer sets show them more strongly. A sharp professional monitor and a tired thirty year old set can look like different technologies when they show the same signal.
Why do scanlines look different on bright and dark images?: A brighter beam makes a larger spot, so lines grow wider and fill their gaps, while dim lines stay narrow. This brightness-dependent thickness is why a simple overlay of black stripes looks fake. Matching that behavior, even roughly with a glow, is the difference between a believable tube and a flat striped filter.
Is a scanline overlay enough to look like a CRT?: Rarely. A stripe overlay cuts brightness evenly and adds no bloom. A convincing result adds glow, brightness-dependent line thickness, slight softness, and in some cases the red, green, and blue structure of the mask. Looking at a photograph of a real screen before you start helps you decide which of those details matter for your shot.

RELATED EFFECTS

Interlace combing Interlace combing is the toothed edge on moving objects when interlaced video is shown as full frames. See why it happens and how to approximate it.
Rescan Rescan is the look of a camera filming a CRT screen: refresh bars, moire and soft glow. Learn what it does to a picture and how to build it with ECHO PARASITE.
Dot crawl Dot crawl is the line of moving dots along colored edges in composite video. See what causes it and how to dial it in with PHANTOM CORRUPT in After Effects.
Vertical roll Vertical roll is the picture scrolling up or down when a display loses vertical sync. See how it works and how to recreate it with STATIC DRIFT.

LOOKS THAT USE IT

Rutt-Etra scan look The Rutt-Etra scan look: video displaced into glowing raster lines by brightness, as on the 1972 scan processor, built in After Effects with Wire Wraith.
public access TV look The public access TV look: a low-budget cable studio picture with tube cameras, bad chroma keys, hum bars and tape wear, recreated in After Effects.
dead channel static look The dead channel static look: the snow of a tuner with no signal, recreated in After Effects with controllable noise, bars and rolling.