What causes chroma to shift away from the picture?

The chroma and luma signals go through different filters and delays. If the delay lines that align them are mismatched, or the chroma path is much narrower, color arrives later than brightness and appears displaced to one side. The size of the shift depends on how mismatched the two paths are, so a longer cable chain or a worn deck usually makes it larger.

Is chroma shift the same as chromatic aberration?

No. Chromatic aberration is an optical fault in a lens, where wavelengths focus in slightly different positions, and it grows toward the edges of the frame. Chroma shift is an electronic timing offset that is uniform across the picture. A quick check is position: aberration grows toward the corners, while chroma shift is the same on the left, center, and right of the frame.

Can chroma shift be corrected?

Yes. A time base corrector or a capture device with a chroma delay adjustment can realign it, and in editing software you can offset the color channel against the luma by a few pixels. Doing so at capture time keeps your options open.

How is chroma shift different from chroma bleed?

Chroma bleed is a smear caused by low chroma bandwidth, which spreads color past the edge. Chroma shift is a displacement of the color against the picture. They often occur together on tape, so the shifted color is also smeared.

Chroma shift: what it is and how to make it in After Effects

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.

WHAT CAUSES IT

Chroma shift is the horizontal misregistration of the color information against the brightness information in an analog video picture. Luma and chroma travel through separate circuits, with different bandwidths and different filters, and each filter delays its signal by an amount that depends on its bandwidth. A narrow chroma filter, such as the roughly 400 kHz band of VHS color-under, delays the color by much more than the wide luma path does. A designer adds a delay line to the luma path to bring the two back together, and any mismatch leaves the color displaced by some tens or hundreds of nanoseconds. At a sampling rate of 13.5 MHz, one pixel is about 74 nanoseconds, so a delay of 200 nanoseconds is nearly three pixels. Cable length, a worn deck, a dub, a mismatched comb filter, or an incorrectly aligned decoder shifts it further. In digital video, chroma subsampling and codec processing can offset color by half a pixel or a pixel. Lens chromatic aberration also displaces color, but optically, not in the signal.

WHAT IT LOOKS LIKE

Color that sits slightly to one side of the object it belongs to. A red shirt has its pink fill drifting to the right of the black outline, and a white title has a cyan fringe on one side and a red fringe on the other. The black and white picture is sharp, with a ghost of color floating nearby. Faces look slightly off register, with the lips and cheeks displaced from the shape underneath. The shift is the same for the whole picture and constant for a given source, unlike wobble, and it is most visible on high contrast edges.

WHERE YOU SEE IT

VHS and Betamax playback, composite connections with a mismatched path, early camcorders, security tapes, SCART and RF chains, and old game consoles over composite. It is also seen in broadcast monitors with poor alignment. Editors use a small chroma shift to put a gentle color fringe on modern footage, which gives a tape-era feel without much noise or damage, and a larger shift for a malfunctioning display.

RECREATE IT

PHANTOM CORRUPT

CONTROLS COLOR TEAR, PHANTOM BLEED, CORRUPT COMPOSITE

COLOR TEAR moves the color away from the picture, so raise it until edges show a fringe offset to one side. PHANTOM BLEED adds the soft smear that normally accompanies the shift on tape. Use CORRUPT COMPOSITE to keep the effect subtle. Start small, because a shift of a few pixels is plenty at HD and larger values quickly look like a broken file.

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HOW TO MAKE IT IN AFTER EFFECTS

1. Pre-compose the footage and apply PHANTOM CORRUPT. 2. Leave CORRUPT WARP, CORRUPT SHRED, and CORRUPT RAINBOW at their minimum. 3. Raise COLOR TEAR slowly while you look at a high contrast edge, such as a white title or a dark object against a bright wall. 4. Stop as soon as a colored fringe is visible on one side of the edge, and compare at 100 percent zoom. 5. Add PHANTOM BLEED to soften the shifted color, so it spreads past the outline the way tape chroma does. 6. Use CORRUPT COMPOSITE to blend the effect back until faces look natural. 7. Keep the amount constant across a shot, because a real misalignment is a property of the signal path and does not change from frame to frame. 8. For a failing display, keyframe COLOR TEAR upward over a few seconds so the color drifts away from the picture. 9. Check on a still, then on motion; the fringe should follow the edges of the moving objects.

QUESTIONS

What causes chroma to shift away from the picture?: The chroma and luma signals go through different filters and delays. If the delay lines that align them are mismatched, or the chroma path is much narrower, color arrives later than brightness and appears displaced to one side. The size of the shift depends on how mismatched the two paths are, so a longer cable chain or a worn deck usually makes it larger.
Is chroma shift the same as chromatic aberration?: No. Chromatic aberration is an optical fault in a lens, where wavelengths focus in slightly different positions, and it grows toward the edges of the frame. Chroma shift is an electronic timing offset that is uniform across the picture. A quick check is position: aberration grows toward the corners, while chroma shift is the same on the left, center, and right of the frame.
Can chroma shift be corrected?: Yes. A time base corrector or a capture device with a chroma delay adjustment can realign it, and in editing software you can offset the color channel against the luma by a few pixels. Doing so at capture time keeps your options open.
How is chroma shift different from chroma bleed?: Chroma bleed is a smear caused by low chroma bandwidth, which spreads color past the edge. Chroma shift is a displacement of the color against the picture. They often occur together on tape, so the shifted color is also smeared.

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

LOOKS THAT USE IT

VHS rental tape look The VHS rental tape look: a worn, dubbed cassette with tracking lines, soft color and dropouts, rebuilt in After Effects for trailers, title cards and horror.
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.
Y2K webcam look The Y2K webcam look: low-resolution video with blocky compression, washed color and a choppy frame rate, recreated in After Effects.
camcorder night shot look The camcorder night shot look: green-tinted infrared video with glowing eyes, heavy grain and lag, recreated in After Effects for found footage and horror.
video feedback tunnel look The video feedback tunnel look: infinite spiraling echoes from a camera aimed at its own monitor, recreated in After Effects with loop and decay.