What causes rainbow patterns on striped clothing on TV?

A composite decoder cannot always separate fine luma detail from the color subcarrier. Stripes at a frequency near 3.58 MHz look like color information, so the decoder produces false hues. S-Video and component connections avoid the problem. The effect is purely a decoding mistake, since the original scene contained only black, white, and gray stripes. That is why it vanishes with a better connection.

Is rainbow banding the same as dot crawl?

They share a cause, the mixing of luma and chroma in composite video. Dot crawl is the moving dot pattern at color edges, while rainbow banding is false color on fine patterns inside areas. You can usually tell them apart by looking at the location of the artifact: along a boundary it is dot crawl, and inside a patterned area it is rainbow banding.

Does it affect digital video?

A digital file does not make it by itself, but a transfer from a composite source can carry it permanently. Once it is baked in, only specialized comb filter processing can reduce it. Digital cameras avoid it entirely, but a capture made from a composite output records the decoded result as is, rainbows included.

Why do rainbows move when the subject moves?

The false color depends on the phase between the pattern and the subcarrier. Movement changes that phase, so the bands slide and change color as the subject shifts. That sliding is a good test for authenticity: a static colored stripe pattern looks like a texture, while a rainbow that swims across a moving shirt looks like a decoder error.

Rainbow banding: what it is and how to make it in After Effects

Rainbow banding is the swirling color fringes on fine patterns in composite video. Understand the cause and recreate it with PHANTOM CORRUPT.

WHAT CAUSES IT

Rainbow banding is the false color that appears when fine luma detail is misread by a composite decoder as chroma. In NTSC composite video, the 3.58 MHz color subcarrier is added on top of the luma signal in the same bandwidth. A decoder separates the two with notch or comb filters, but patterns whose spatial frequency is close to the subcarrier, such as a striped shirt, a fine grille, or a herringbone jacket, look to the decoder like a modulated color signal. It demodulates them, producing colored stripes that did not exist in the scene. Because the subcarrier phase advances by a fixed amount along the line, the false color cycles through the hues of the spectrum across a repeating pattern, which gives the rainbow look. In PAL, with its 4.43 MHz subcarrier, the phase alternates line to line, so the artifacts differ and partly cancel, but they exist too. A better comb filter, S-Video, or component transmission keeps the luma and chroma apart and removes it.

WHAT IT LOOKS LIKE

Colored stripes, in red, green, blue and magenta, that run across fine patterns such as pinstripes, venetian blinds, brickwork, and tweed. They flow and shimmer as the subject moves, because small shifts change the phase relationship with the subcarrier. The false color is soft and iridescent, and its bands are roughly the width of the underlying pattern. On solid color areas nothing appears, so it is localized to fine detail. At the edges of high contrast text on a news broadcast you can see a thin colored fringe as well.

WHERE YOU SEE IT

Composite-video broadcast and consumer sources: television news from the 1980s and 1990s, VHS captured over composite, early game consoles, and security video with striped clothing. Newscasters were told to avoid fine patterns for this reason. In editing, rainbow banding marks a composite video source and is also the signature of a deliberately broken decoder in glitch art. Watch for it on fine fabric in archival interviews and on broadcast graphics with thin colored rules.

RECREATE IT

PHANTOM CORRUPT

CONTROLS CORRUPT RAINBOW, PHANTOM NOISE, CORRUPT COMPOSITE

CORRUPT RAINBOW is the control for the false-color cycling. Raise it until fine detail sprouts colored banding, then add a little PHANTOM NOISE so the color fringes do not look too clean. Use CORRUPT COMPOSITE to blend the effect back. The result reads best on footage with fine pattern, so choose the test frame accordingly.

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HOW TO MAKE IT IN AFTER EFFECTS

1. Pick a shot with fine pattern, such as clothing, a fence, or a window blind. If your footage has none, expect a subtle result. 2. Apply PHANTOM CORRUPT. 3. Leave CORRUPT WARP and CORRUPT SHRED at minimum so you isolate the rainbow behavior. 4. Raise CORRUPT RAINBOW slowly and watch the fine detail. Colored stripes should appear on the patterned areas first. 5. Add PHANTOM NOISE to break up the color so it does not look digitally perfect. 6. Reduce CORRUPT COMPOSITE if the banding overwhelms the picture. 7. Keyframe CORRUPT RAINBOW to rise during camera movement, because moving the pattern is what makes real rainbows swim. 8. Add chroma bleed or generation loss in a separate pass to match the rest of the signal path. 9. Check that skin and large solid colors stay clean, as a real decoder keeps them.

QUESTIONS

What causes rainbow patterns on striped clothing on TV?: A composite decoder cannot always separate fine luma detail from the color subcarrier. Stripes at a frequency near 3.58 MHz look like color information, so the decoder produces false hues. S-Video and component connections avoid the problem. The effect is purely a decoding mistake, since the original scene contained only black, white, and gray stripes. That is why it vanishes with a better connection.
Is rainbow banding the same as dot crawl?: They share a cause, the mixing of luma and chroma in composite video. Dot crawl is the moving dot pattern at color edges, while rainbow banding is false color on fine patterns inside areas. You can usually tell them apart by looking at the location of the artifact: along a boundary it is dot crawl, and inside a patterned area it is rainbow banding.
Does it affect digital video?: A digital file does not make it by itself, but a transfer from a composite source can carry it permanently. Once it is baked in, only specialized comb filter processing can reduce it. Digital cameras avoid it entirely, but a capture made from a composite output records the decoded result as is, rainbows included.
Why do rainbows move when the subject moves?: The false color depends on the phase between the pattern and the subcarrier. Movement changes that phase, so the bands slide and change color as the subject shifts. That sliding is a good test for authenticity: a static colored stripe pattern looks like a texture, while a rainbow that swims across a moving shirt looks like a decoder error.

RELATED EFFECTS

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.
Chroma bleed Chroma bleed is the soft color smear on analog video where hue spills past object edges. Learn the cause and how to dial it with PHANTOM CORRUPT.
Chroma shift Chroma shift is the sideways offset of color from the black and white image on analog video. See what causes it and how to dial it with PHANTOM CORRUPT.

LOOKS THAT USE IT

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.
1987 camcorder look The 1987 camcorder look: soft Video8 and VHS-C picture, smeared color, date stamp and wobbling timebase, built in After Effects with a repeatable recipe.
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.
analog horror look The analog horror look: broadcast and VHS signal failure as dread, with static, tracking loss and color collapse, built in After Effects.