CompuServe Thread

Mike: It has been my experiance that 255,255,255 is 100% NTSC Video and conversly 0,0,0 is 7.5 IRE there is NO WAY to create a graphic with the toaster that has 0 IRE video in it. However if you select a video source 1,2,3,or4 that has no source actualy conected to it you can get 0 IRE. Brad Hayes Hayes Visual Communication

Mike, Well, yes and no. First, lets eliminate any package that may do NTSC filtering/limiting automatically. Now, you also have to consider the base "black" that is under the color to begin with. For example, if 000 gives you 15 IRE, then 195 195 195 might be your limit. OK. Lets take TPaint (I'm using v 3.1 for this since my WF/VS is already connected to this version – 4.0 may differ) on a VT4000 card. 000 gives 7.5 IRE. Now, if I use 208 0 0 the level out is 75 IRE. 0 208 0 give 95 IRE and 0 0 208 gives 49 IRE. Each of the primary colors has a different luma level. Now, when you start combining colors, it gets difficult. Cyan at 0 208 208 is too hot (108 IRE) where as magenta (208 0 208) is fine comming in at 81 IRE. Yellow is again, too hot at 109 IRE (208 208 0). But a 208 208 208 white is only 85 IRE! In fact you can go 255 255 255 in toasterpaint to get a nice 100 IRE signature. But, if you used a 0 255 0 green you'd be over the top at about 115 IRE. If I go to Alpha Paint, 000 give 7.5 IRE again, but 255, 255, 255 give 95 IRE. 210 0 0 results in 80 IRE, 0 210 0 gives 100 IRE and 0 0 210 gives 70 IRE. In the case of a paint program all that matters are your colors but it can vary from program to program. Now, lets get to 3D. Here's where it really gets interesting, because now it depends on the lights you have in the scene, how each color is illuminated with those lights and how your lights are relflected etc. Then there is the issue of the output buffer. You can take a graphic that was well within limits when it was built, transfer it to another system and it displayes through the roof. The reason being that one output buffer device was not properly tuned for correct color levels before it was used. So, this is really the long winded way of saying there ain't no substitute for a Waveform monitor to check the levels of, first, the output buffer, then the grahics themselves. With a little practice you can look at the WF display and go to the element of the graphic that may need toning down. Now for the good news – very rarely does one worry about "too low". It is very hard on most correctly tuned systems to get below 7.5 IRE. Some systems even add 7.5 IRE to any "0" portion of a signal before it goes out the program spigot. And, about the only time "low" is a problem is when you are trying to luma key at the low end of the scale. Then you might want the darkest part of the picture you do not want keyed out to be 20 IRE or so to give some head-room above 7.5 IRE in which to key, for example. wmc – via Autopilot!