TV Gamut - here is a bit I wrote for our work email newletter that we send to clients periodically.

A lot of the standards we adhere to in television today have their origins in the methods established in the dark days of early colour in the sixties. Back then there were no digital pictures, all images were sourced through analogue tubed cameras, telecine and slide scanners. Our world was either RGB (the red, green and blue colour component signals that came out of a camera) or composite (typically the output of VTRs and studios and what was sent to the viewer at home). The relationships were well defined and the graceful behaviour of analogue electronics meant that keeping pictures within the range that the VTR (and hence the transmission chain) could handle wasn't hard.
In the mid seventies the digital framestore started to make an appearance making possible digital video effects (DVE), electronic caption generators and painting systems (Paintbox, Matisse etc.). By the late eighties Silicon Graphics et al ensured that a lot of what we saw on screen was digitally originated rather than coming from 'real world' pictures. Now - properly designed digital systems are more than able to capture the full range of analogue colours (the gamut of the system) but a lot of strange un-analogue things can go on in the digital domain if care isn't taken. A digital signal can go from zero to full level in the space of a single pixel which could never happen in the analogue domain - the size of the scanning spot on an analogue telecine or the spot aperture in a studio camera ensure a more graceful response. You can also get very bizarre combinations of colours in the digital domain that would not equate to colours that came out of a camera. If you consider that the majority of the permutations of the ten-bit digital Y, Cr, Cb colour component signals that most contemporary TV systems store give rise to illegal colours then the pervasive nature of the problem becomes apparent. Add into the mix prosumer DV cameras where the pictures haven't had the caring eyes of a racks engineer looking at them as the were acquired and you'd be forgiven for thinking that getting your master tape past the broadcaster's QC department was well nigh impossible. Well there are two kinds of gadgets that allow us to avoid the pitfalls of bad gamut - waveform monitors and legalisers. With a waveform monitor you can keep an eye on the various parameters that make up a video signal. The best of breed come from Tektronics who have devised various display modes that make gamut errors very clear. The Diamond and Arrowhead modes are only found on Tek units and show clearly when pictures are getting near to gamut limits. The newer rasterised models allow several displays to be shown on screen simultaneously. They will also keep an automated eye on dozens of aspects of your video (and audio) and record them to a log file for later reference. Go for lunch and glance through the tape log when you get back!
If you mention legalisers to those online editors who remember the early models from fifteen years ago you'd be forgiven for imagining such devices only exist to make pictures look bad! It is true that initially they dealt with gamut errors in a very brutal 'digital' style but the last decade has seen much more subtle methods and now a lot of broadcast television (particularly fast-turnaround shows with lots of DV or other domestic content) goes via a legaliser before transmission. They hardly ever effect the looks of pictures (so long as you don't go for particularly garish red captions!) but your pictures are now guaranteed to be 'street legal'. The models we've found to be most effective are from Eyeheight whom we sell for.
Root6 has spent time researching both legalisers and waveform monitors and we believe we offer best-of-breed examples of both at standard and high definition. Please call for details, a demo or advice on both of these.