To stay well within the limits of television transmitters, cable systems, satellite links, DVD encoders, and so on, broadcasters or distributors often issue safe color limits for video levels. Video levels outside safe color limits are generally known as "illegal." Of course, no law is broken if you exceed the specified limits, but the program might be rejected on technical grounds or the image quality might suffer with further processing. If you know that your delivery master is a VHS tape that does not handle high chroma well, set some reasonable limits by yourself.

In Y (luma only) waveforms, reference white of 100% corresponds to a digital level of 235, an NTSC level of 100 IRE, and a PAL level of 700ámV. White excursions up to 108% are technically possible.

In Y (luma only) waveforms, reference black of 0% corresponds to a digital level of 16, an NTSC level of 7.5 IRE, and a PAL level of 0 mV. Black excursions down to –8% are technically possible.

Use Y Waveform to see the black and white levels of your image. Sometimes, particularly with white levels, keeping the white peaks within the 100% limit will not produce a pleasing level for the rest of the image. This is particularly common with backlit subjects, where the sky or a window is in the background and the lighting on the foreground is insufficient. In these cases, you might want to adjust for the foreground and leave the background too bright.

Chroma peaks are easiest to see on the vectorscope. The theoretical maximum is the circle around the outer edge, but to be safe you might like to keep vectors closer to the center than the 75% color bar squares.

Saturated bright or dark colors might have very low or high luma values, together with a lot of chroma. Even if neither luma nor chroma alone is excessive, the combination can be illegal. For example, vivid yellow and cyan in an image can produce composite levels that are too high, and those from vivid blue might be unacceptably low. The YC Waveform is a good way to see how far these levels extend. In general, avoid levels above approximately 120 IRE or 850 mV, and those below –20 IRE or –200 mV.

The Y Waveform, YC Waveform, and RGB Parade displays incorporate any safe color limits you have set. The following table describes the colors used to represent various conditions. "Legal" means the value is within the safe color limits. "Illegal" means the value is outside (either above or below) the safe color limits.