JohnPartridge Posted February 11, 2006 Share Posted February 11, 2006 Hi , just to let you know , I am no ware near an AV technician , but a Lampie :) The question I am wondering is , when I do a job and AV techs are using screens and projections , I see that they are displaying the Coloured bar screen test. (you will all know what I mean) Can someone explain the purpose for this test and what programme would be used to do the test. I have some idea that it will be to test that each colour is being displayed correctly , and there are no dead pixels etc?? Cheers GuysJohn Partridge Link to comment Share on other sites More sharing options...
bruce Posted February 11, 2006 Share Posted February 11, 2006 Basically, it's just a standard reference signal. I'm sure someone will explain it much more clearly, but basically "colour bars" come from the analogue broadcast TV world. It's a standard image which, when monitored on a Waveform Monitor and Vectorscope will give a well-known (to experienced engineers!) output. So you feed into the transmission/processing system a standard signal, and then can tweak the various parameters to make sure your output is sufficiently similar.... Most pro video setups will have a dedicated "colour bar generator" - typically a 1U rack unit, which is used as a reference signal. Pro cameras will also have built-in generators, to generate a standard signal. This then allows the eq of the processing system to be tweaked to compensate for any variations introduced by the transmission system between cameras and vision mixer. etc etc. More info HERE, although that is for NTSC (north america) rather than PAL (UK). Principles are the same. I believe it tends to be used as a "standard image" in the digital world, simply because it is familiar... Bruce. Link to comment Share on other sites More sharing options...
JohnPartridge Posted February 11, 2006 Author Share Posted February 11, 2006 Ok , so its basically a way of adjusting the colour so that images/video which were designed on another monitor will look the same?? Hope some more people can give me abit more guidence. John Partridge Link to comment Share on other sites More sharing options...
bruce Posted February 11, 2006 Share Posted February 11, 2006 so its basically a way of adjusting the colour so that images/video which were designed on another monitor will look the same?? Not exactly. It's a standard waveform which you send into a system - usually a transmission, recording, or processing system - and you check to make sure that electrically (using the above mentioned waveform monitor, vectorscope, and usually a pro monitor and a good pair of eyes) it isn't corrupted in transit. It's really intended to allow you to compensate for alterations which have been introduced by a recording or transmission system. It's used to make sure that the signal REACHING the monitor is correct, rather than for tweaking individual monitors. Having said that, it is often used as a standard output for comparing different monitors.... Bruce. Link to comment Share on other sites More sharing options...
Brian Posted February 11, 2006 Share Posted February 11, 2006 As Bruce has said it's a standard test signal. However, it has limited use for lining up monitors or projectors. Most AV techs will use it because they haven't been taught any different and it's all they have available. Link to comment Share on other sites More sharing options...
dosxuk Posted February 12, 2006 Share Posted February 12, 2006 The technical name is 'bars' :) We often use them in our AV system for identing video feeds. Bars are easy to spot when tuning video recorders and switching matricies, so when you get a picture with bars up you know you've found the right source and can confirm it by switching them off again. In my work in TV we use bars as has been stated, to ensure that any losses caused by cables / connectors / radio links are 'nulled' out before the picture is fed on. It's very simple to line up a signal when it is showing bars and you have a waveform monitor. A couple of useless facts about colour bars - there is an equal quantity of red, green and blue in the entire image, and when seen on a black and white monitor, you get a nice graduation in shade across the screen. Much more complicated test cards are used for setting up digital systems, and will often include movement in order to make sure that devices haven't frozen. Link to comment Share on other sites More sharing options...
Pete McCrea Posted February 12, 2006 Share Posted February 12, 2006 As most of the others have said. I generally use them to verify that the feed is going to the right places, and to make sure that the kit is set up right. And as the others have said, it's quick and easy. The MX50 for example has a Matte Generator that puts out the colours, and bars. So for checking the colour rendition of a projector you can use the bars, then a Matte for positioning, which is generally how I'll work. Use a Matte to check the fill and keystone, then bars to get the projector color balance sorted. Extron do a test DVD of various images for a whole host of different scenarios. These give grey scales for setting the contrast etc. Link to comment Share on other sites More sharing options...
marky Posted February 12, 2006 Share Posted February 12, 2006 We use them to help set in vision monitors (this is only my experience in a TV environment) Using a colour corrector, by turning the chroma off, you can set the brighness then adjust the chroma and video level so bars look right, then when you see a face on the monitor, you can fine tune it...Testcard is better for this, but sometimes only bars are available... Link to comment Share on other sites More sharing options...
eviljohn2 Posted February 13, 2006 Share Posted February 13, 2006 At a nice basic level, colour bars will enable you to easily see if any colours are missing at the output through dodgy cables. They're easily put into the combined test patterns which also include some geometry hatching too. Not ideal but good "rough & ready" solution for setting up a few plasmas or projectors. :) Link to comment Share on other sites More sharing options...
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