Waveform Monitor

The Exposure Map

The Waveform Monitor is one of the two most essential video scopes used in filmmaking, from on-set monitoring to final color grading. While the human eye is easily fooled by optical illusions or the ambient lighting in a room, the waveform provides a purely objective, mathematical representation of the image’s luminance (brightness). It is an indispensable tool for setting correct exposure, balancing shots, and ensuring technical standards are met.

How to Read a Waveform

A waveform display translates the image into a 2D graph:

• The Horizontal Axis of the graph corresponds directly to the horizontal position in the image. A spike on the far left of the waveform represents a bright object on the far left of the camera’s frame.
• The Vertical Axis represents brightness. The scale typically runs from 0 at the bottom to 100 at the top (measured in IRE) or from 0 to 1023 (for a 10-bit video signal). A value of 0 represents pure, absolute black, and a value of 100/1023 represents pure, absolute white.

The result is a ‘trace’ of light intensity across the frame. A flat, dark image will have a trace bunched up near the bottom of the scope. A bright, high-contrast image will have a trace that is spread out across the entire vertical range.

Primary Uses

1. Setting Exposure: The primary use is to judge exposure. A properly exposed shot will typically have its main subject matter falling in the middle of the waveform, with a good distribution of values. If the entire trace is pushed up against the top, the shot is overexposed. If it’s all crushed at the bottom, it’s underexposed.
2. Setting Black and White Points: The waveform makes it easy to set true black and white. A colorist will adjust the Lift control until the very lowest parts of the trace are just touching the ‘0’ line (a process called ‘setting the black point’). They will then adjust the Gain until the brightest parts are just touching the ‘100’ line (‘setting the white point’). This ensures the image has a full, rich contrast range without ‘crushing’ blacks or ‘clipping’ whites, which results in a loss of detail.
3. Shot Matching: When cutting between two shots in a scene, a colorist can use the waveform to ensure they match perfectly. By comparing the waveforms of the two shots, they can adjust the brightness and contrast until the traces have a similar distribution and sit at similar levels on the scope.

The RGB Parade

A powerful variation of the waveform is the RGB Parade. This displays three waveforms side-by-side: one showing only the Red channel, one for Green, and one for Blue. This view is the go-to tool for judging color balance. If an image has a blue color cast, the blue waveform will be sitting noticeably higher than the red and green waveforms. The colorist’s job is to use the color wheels to ‘balance’ the parade, aligning the three waveforms to similar levels to achieve a neutral white or gray.