A vectorscope is a video measurement display that plots the chrominance of every pixel on a circular graph, with hue shown as the angle around the center and saturation shown as the distance from it. In color grading and broadcast engineering, it is the standard tool for judging color balance, saturation limits and skin tones objectively, independently of how a particular monitor or the colorist’s eye renders the image.
The vectorscope ignores brightness entirely; luminance is measured by its companion, the waveform monitor. Together with the RGB parade, these scopes form the core set of instruments that colorists rely on in applications such as DaVinci Resolve.
How a vectorscope maps color
A vectorscope maps color by plotting the two color difference signals, usually Cb on the horizontal axis and Cr on the vertical axis, for every pixel. A pixel with no color, any shade of gray from black to white, lands exactly at the center. As saturation increases, the point moves outward, and its direction indicates the hue.
The display carries a graticule with target boxes for the three primaries and three secondaries, arranged around the circle in a fixed order. The table below lists their approximate positions on a conventionally oriented scope.
| Color | Approximate position | Neighbors on the circle |
|---|---|---|
| Red | Upper left, about 11 o’clock | Magenta and yellow |
| Magenta | Upper right, about 1 to 2 o’clock | Red and blue |
| Blue | Right, about 3 to 4 o’clock | Magenta and cyan |
| Cyan | Lower right, about 5 o’clock | Blue and green |
| Green | Lower left, about 7 to 8 o’clock | Cyan and yellow |
| Yellow | Left, about 9 to 10 o’clock | Green and red |
Most graticules provide boxes for both 75 percent and 100 percent color bars. When a camera or playback chain reproduces a color bar test signal correctly, each bar lands inside its box, which makes the vectorscope a quick calibration check for signal paths.
Reading the vectorscope trace
Reading a vectorscope means interpreting the shape, offset and extent of the trace. A typical natural image produces a compact cloud near the center with arms reaching toward the dominant hues. The position of that cloud relative to the center reveals color casts, and its reach reveals saturation.
| Trace pattern | What it indicates | Typical correction |
|---|---|---|
| Cloud centered | Neutral color balance | None needed |
| Whole cloud shifted toward orange | Warm cast, too low white balance setting | Shift balance toward blue |
| Whole cloud shifted toward blue or cyan | Cool cast | Shift balance toward orange |
| Arms extending beyond targets | Oversaturation, possible legal limit issues | Reduce saturation selectively |
| Very small cloud | Low saturation, flat log image | Apply transform or increase saturation |
| Arm along skin tone line | Skin tones in natural hue range | Use as reference for faces |
To check neutral balance, colorists often isolate a white or gray area of the image with a window or qualifier. A correctly balanced neutral collapses into a tight dot at the center; any offset shows the direction of the remaining cast.
The skin tone line
Most vectorscopes display a skin tone line, also called the flesh line, running from the center toward the area between red and yellow. Human skin of every complexion tends to fall close to this line, because skin color is driven mostly by the same pigments and blood beneath it, which vary in density more than in hue.
Darker and lighter complexions differ mainly in brightness and saturation, which change their distance from the center, not their angle. A face whose trace drifts noticeably toward magenta or green usually looks unnatural to viewers, even when the rest of the image looks correct.
| Deviation | Visual effect | Likely cause |
|---|---|---|
| Toward magenta | Flushed, pinkish skin | Lighting gel, white balance tint |
| Toward green | Sickly, sallow skin | Fluorescent or LED spectrum gaps |
| Too far from center | Overly saturated, sunburned look | Heavy saturation or contrast |
| Too close to center | Gray, lifeless skin | Under-saturated or flat grade |
Vectorscope compared with other video scopes
Each video scope answers a different question about the image. The vectorscope answers what hue and how much saturation, but it cannot tell where in the frame or at what brightness a color occurs.
| Scope | Measures | Best for |
|---|---|---|
| Vectorscope | Hue and saturation of chrominance | Color casts, saturation, skin tones |
| Waveform monitor | Luminance across the frame width | Exposure, contrast, black and white levels |
| RGB parade | Red, green and blue levels side by side | Channel balance in shadows and highlights |
| Histogram | Distribution of tonal values | Overall tonal spread |
| CIE chromaticity plot | Color against gamut boundaries | Gamut compliance for Rec. 709 or Rec. 2020 |
A common workflow uses the waveform for exposure first, then the RGB parade to balance channels in shadows and highlights, and finally the vectorscope to confirm overall balance and saturation limits.
Practical tips and pitfalls
The vectorscope is objective but not decisive: it shows where colors fall, while the creative intent decides where they should fall. A stylized look such as teal and orange will deliberately pull the trace away from neutral.
- Use zoom or gain on the scope when grading log footage, whose small trace is hard to read at normal scale.
- Check the color space of the scope; a Rec. 709 graticule does not represent Rec. 2020 limits.
- Do not chase a perfectly centered trace in scenes lit with intentionally colored light.
- Remember brightness is missing: two very different images can produce similar vectorscope traces.
A plain-language summary
A vectorscope is a color compass for video. It draws a circle, and every color in the picture is placed on it. The direction shows which color it is, such as red, blue or green. The distance from the middle shows how strong the color is.
Gray and white sit right in the middle. If the whole pattern leans toward orange, the picture is too warm. Editors use it because their eyes and screens can be fooled, but the scope measures the color honestly.
An example from practice
A colorist receives interview footage shot under mixed window light and LED panels. On the client’s monitor, the speaker’s face looks slightly odd, but nobody can say why. On the vectorscope, the colorist isolates the face with a power window and sees that the skin trace sits noticeably toward green of the skin tone line.
Next, the colorist isolates a white wall and finds that it also drifts toward green, confirming a global tint problem from the LED panels. A small shift toward magenta in the primary correction brings the wall to the center and the face onto the skin tone line. A final check confirms that no saturated colors in the background exceed the targets, and the client approves the shot.