Chroma bleed
Also called: color bleed, color smear, chroma smear
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.
WHAT CAUSES IT
Chroma bleed occurs because analog video carries color at a far lower bandwidth than brightness, so color detail is spread over a wider area than the luma edge it belongs to. On VHS the luma is frequency modulated on a carrier between roughly 3.4 and 4.4 MHz, while the chroma is heterodyned down to a color-under carrier at 629 kHz and is limited to about 400 kHz of bandwidth. That is a fraction of the horizontal resolution of the luma. When the signal is decoded back to the 3.58 MHz NTSC subcarrier, color transitions smear horizontally over many luma pixels, and any small timing mismatch between the chroma and luma paths shifts the smear to one side. Dubbing, long cables, and composite connections add more low-pass filtering and delay. Saturated colors at high contrast edges, especially reds, show the effect most. The luma edge stays crisp, so the eye sees a sharp black and white drawing with a soft colored wash laid slightly off register.
WHAT IT LOOKS LIKE
Hard-edged shapes with color that overshoots them. A red jacket on a gray wall grows a pink halo that reaches several pixels past the sleeve, usually to the right. Skin tones look slightly detached from the face, with the pink tint sitting under the lips and eyes rather than on them. Thin colored lines such as text or wires lose their color entirely, leaving a gray line with a faint color cloud nearby. Bright saturated edges show a ghost fringe, and quick motion drags the color slightly behind the luma. The picture keeps a sharp outline but looks hand-tinted.
WHERE YOU SEE IT
Any VHS, Video8, or composite captured video, and especially dubbed copies, early camcorders, and television recordings made at long-play speed. It is part of the standard look of 1980s and 1990s home video, early console gameplay over composite, and broadcast graphics seen through poor connections. Editors add it to modern footage to fake a tape source, and to deliberately soften skin tone and neon signs in a period piece.
RECREATE IT
PHANTOM CORRUPT
CONTROLS PHANTOM BLEED, COLOR TEAR, CORRUPT COMPOSITE
PHANTOM BLEED is the main control for the smear. Raise it until saturated edges spill over their outlines, but stop before colors lose all shape. Add COLOR TEAR in small amounts for line-to-line displacement of the color, which sells the idea of an unstable chroma path. Use CORRUPT COMPOSITE to blend the result back, so the picture does not feel fully replaced.
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HOW TO MAKE IT IN AFTER EFFECTS
1. Work on the final graded footage, not on raw log, so the saturated colors that bleed match what the viewer will see. 2. Apply PHANTOM CORRUPT to the layer. 3. Leave CORRUPT WARP, CORRUPT SHRED, and CORRUPT RAINBOW at their minimum for now. 4. Raise PHANTOM BLEED until colored edges spread past the edges of objects. 5. Add a little COLOR TEAR if the color should wander slightly line to line. 6. Use CORRUPT COMPOSITE to pull the effect back until faces still look natural. 7. Check on a shot with strong reds and neon signs, since these show the bleed best, and on a shot with skin, since skin shows when you have gone too far. 8. For a camcorder look, keep PHANTOM BLEED constant. For a failing tape, keyframe it upward over the shot. 9. Combine with a slight softening of the footage itself if the original is very sharp, because real tape also softens luma.
QUESTIONS
- Why is chroma bleed worst with red?
- Red often has the highest saturation and strong contrast against typical backgrounds, so the low-bandwidth chroma channel has the most visible error there. The smear is the same for every hue, but pure red is where the eye notices it first.
- Is chroma bleed the same as color fringing from a lens?
- No. Lens fringing comes from optical dispersion and affects edges by wavelength. Chroma bleed comes from the electronics, where color is stored at lower resolution than brightness, and it spreads horizontally. Both put color slightly outside an edge, so they are easy to confuse, but only chroma bleed is limited to horizontal spreading and comes with sharp luma.
- Can chroma bleed be reduced?
- Using S-Video or component connections avoids some of it, because the chroma and luma are kept separate. A good time base corrector and a short cable help. After capture the smear can only be partly corrected. Capturing through a deck with a good comb filter and a digital noise reduction stage also tightens the color, but nothing restores resolution that tape never stored.
- Does digital video have chroma bleed?
- Highly compressed digital formats use chroma subsampling, such as 4:2:0, which blurs color similarly but on a block basis. The analog effect is smoother and mostly horizontal. Lossy codecs and 4:2:0 sampling also spread color, though the result looks blockier than the smooth horizontal tape smear, and it is rarely a one-sided shift.