Vectorscope

Drop in any photo or video frame and see its colour the way a colourist does: hue as an angle, saturation as distance from the centre. Drag a box over a face and the scope shows just the skin, with the skin tone line to check it against.

Drag a box over a face to measure just the skin. Without one, the whole image is plotted.

Average hue

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Saturation

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Against the skin line

Too close to neutral to read.

Hue is measured counter-clockwise from three o'clock (the B−Y axis), the convention scopes use; the skin tone line sits at 123°. Saturation is the distance from the centre as a share of the scope's radius. Your image never leaves your browser.

What a vectorscope shows

A vectorscope throws away brightness and plots only colour. Every pixel becomes a point on a circle: the direction from the centre is its hue and the distance is its saturation. That makes it the scope for questions your eyes are bad at answering, such as whether a white wall is really neutral, or whether a face has picked up a green cast from the trees behind it. Your eyes adapt to a colour cast within seconds. The scope does not.

How to read a vectorscope

The centre

Neutral: whites, greys and blacks. A trace that sits off-centre where you expected neutral is a colour cast.

The angle

Hue. Red, magenta, blue, cyan, green and yellow each sit at their own angle, marked by the small target boxes.

The distance from the centre

Saturation. The further out, the more intense the colour. A trace reaching past the target boxes is very saturated.

The dashed line

The skin tone line, at 123°, between red and yellow. Where a face sits against it tells you whether skin has drifted pink or yellow-green.

The target boxes mark where 75% colour bars land, the broadcast test signal scopes are calibrated against. They are reference points, not limits, but a trace that pushes well past them in one direction usually looks overcooked.

The skin tone line

The skin tone line runs from the centre up and to the left, between the red and yellow targets, at 123°. It comes from analogue television: it is the I axis of the NTSC colour system, which was placed along the direction of flesh tones. Skin of every complexion falls close to it, because the hue of skin barely changes from person to person; darker and lighter skin differ in brightness and saturation, which moves the trace along the line rather than off it.

To use it, measure the skin alone. A whole frame mixes skin with clothes, walls and sky, so box just the face (this tool lets you drag a box; in Resolve or Premiere you would use a window or a qualifier). Then read where the trace points:

The skin trace	What it usually means
Along the line	Natural-looking skin for the light it was shot in.
Turned towards red and magenta	Skin reads pink or flushed. Common under tungsten corrected too far towards cool, or a warm grade pushed into the reds.
Turned towards yellow and green	Skin reads sallow or ill. Common under fluorescent light, or green spill from grass and leaves.
Very short, close to the centre	Washed-out, grey skin. Often a heavy desaturating look, or a strong colour cast cancelling it out.
Very long, past the red target	Oversaturated, orange skin. The classic sign of a teal-and-orange grade taken too far.

To fix a face that has drifted, rotate its hue back towards the line rather than changing the whole image: a hue shift on the skin range with an HSL qualifier, or white balance if the cast is everywhere. The HSL Secondary panel in Luttie's editor does the first; Basic Correction does the second.

Vectorscope, waveform or histogram?

They answer different questions. The histogram and waveform are about brightness: is anything clipped, where in the frame is the problem. The vectorscope is about colour: is it neutral, how saturated is it, is the skin right. Colourists keep both on screen. In the Luttie editor all four sit in the left panel, and they update as you grade.

Frequently asked questions

Is this vectorscope free?

Yes, and it needs no account. The image is measured in your browser and is never uploaded. The same scope is built into the Luttie editor's left panel, also free, next to the histogram, waveform and RGB parade.

Why is everything bunched in the middle?

Because most images are not very saturated. A vectorscope's edge is the most saturated colour a video signal can carry, and skin, sky and foliage sit well inside it. That is normal, not a problem. Switch to 2x to magnify the centre, which is what colourists do for everyday footage.

Does skin have to sit exactly on the skin tone line?

No. The line is a guide for spotting a cast, not a target. Warm sunset light or a deliberate grade will move skin off it, and that can be the point. What the line tells you is which direction the skin has drifted, so if a face looks wrong you know whether it has gone too pink or too yellow-green.

Do darker skin tones sit on a different line?

No. Skin of every complexion has much the same hue, because the pigments involved are the same; what changes is brightness and how saturated it is. On a vectorscope that shows up as distance along the line, not as a different angle, which is why one line works for everyone.

Where is the vectorscope in Premiere Pro or DaVinci Resolve?

In Premiere Pro it is in the Lumetri Scopes panel: click the wrench icon at the bottom of the panel and choose Vectorscope YUV, which draws the skin tone line on its own. In DaVinci Resolve it is one of the scopes on the Color page, and the skin tone indicator is switched on in the scope's settings. Both draw the line at the same angle as this one.