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Quality is the best policy >> Video The basic parameters of video are simple and well known. White in the picture should be represented by the peak white level and black by peak black. You need to understand what is happening to the video levels in each of the three colour channels. Colour gamut is also a very important consideration. It may sound improbable but, because of the way the television system is defined, there are some colours in the visible spectrum which are outside the gamut of colours which can be reliably broadcast. You may ask why colours could be outside gamut or levels outside the defined limits, if the original video is shot properly. The answer is that any post production process can change the levels, which can cause problems. Colour correction – now built in to editors as a standard tool – is the obvious example, but graphics overlays can cause problems, too. On the other hand, if you are concentrating on creating a great programme, you really do not want to keep your eyes on a row of test instruments rather than the picture monitor. To give the post artist the right support there needs to be a way of illustrating problems – out of gamut colours or peak black and white excursions – on the picture monitor itself, usually by putting a dotted line around the error. What happens if you do not take care to keep video levels and colours within limits? Either the broadcaster will reject the content and you have to rework it, or it will accept it and put it through a device called a legaliser. This is a box of electronics which squeezes the signal back into specification. Unfortunately, it does it in a way which is rarely subtle, so is likely to result in colour shifts. If you have spent hours with the colourist getting the pack shot precisely right, the last thing you want is an unattended piece of electronics in the transmission suite changing it again. PSE Photo-sensitive epilepsy (PSE) is a pretty devastating condition. Flashing lights, or certain colour combinations, can trigger an epileptic episode which is dangerous for the sufferer and unpleasant, at best, for those around who offer care. The best estimate is that PSE afflicts about one in 5000 of the population. Over the last decade healthcare professionals have worked closely with broadcast engineers and others to determine precisely what circumstances are likely to trigger a PSE episode. This knowledge is now implemented in ITU recommendation 1702, and devices built using its algorithms can determine which sequences may be likely to cause a problem. The editor will need to work closely with the producer to determine how much of a PSE sequence to remove 70 | TV-BAY MAGAZINE and how much can be covered with warnings before transmission. A documentary about clubbing, for example, could be very short if you take out all the flashing lights, whereas a programme with just a short sequence involving flashing colours could probably be re-edited. This is a serious problem, and major broadcasters certainly check for PSE. One in 5000 potential sufferers means a thousand people for a programme reaching five million. 3D If you are making a stereoscopic 3D programme then getting it right on set is very important. While the core parameters like inter-axial distance and convergence can be faked in post, to a certain degree, the best results come when you shoot it right first (and we sell specialist tools to make sure that happens). The rules with regard to video levels and colour gamut apply in stereo 3D, of course, but doubly so because it is vital that the two eyes are precisely matched. Graphic placement is another unique consideration in 3D post. The general consensus is that graphics have to sit in front of all other 3D objects, but they have to live within the broadcaster’s defined depth budget. In general, objects a long way in front of the screen plane do not work well in the home. It may be that for graphics sequences – titles and credits, for example – you have to flatten the 3D effect in the content to be able to put the graphics in a comfortable place. In conclusion, there are many technical issues which need to be addressed in post if the finished content is going to look and sound as good as it possibly can. Post, though, is primarily a creative process, handled by artists who do not want to look at dull test displays. At Hamlet we try to bridge the gap, with tools and displays that make it obvious if there is a problem. Avoiding technical errors is a win all round: the programme looks great and there is no costly reworking, which is why an emphasis on quality control is the best policy.