Naturally, the color range available for transmission and recording is bounded at the upper level by white and at the lower level by black. Anything else falls somewhere in-between.
Consider what happens if you gradually raise the brightness control on your television. Beyond a certain point (and unlike claims made for laundry detergent) your whites do not become whiter. They can’t – the upper limit (white) is firmly fixed. Instead, parts of the image that are nearly white are boosted, eventually also becoming white. Meanwhile, black portions of the picture are tending towards gray. Since white cannot become whiter, and black has become gray, we could say that the dynamic range of the image has been narrowed. The net result is a less vibrant image.
The same thing is true for video from your cameras. If the black and white levels from the camera are incorrect, you are effectively losing either shadow or highlight detail. For this reason, the first thing many do is calibrate their camera for correct levels.
From days of old, for video engineering purposes the scale between black and white was defined in IRE units (IRE being an acronym for “Institute of Radio Engineers”). White was pegged at 100 IRE. For PAL (and NTSC-J) countries, black was defined as 0 IRE. For NTSC lands, black properly sat at 7.5 IRE.
Thankfully, the day of strict adherence to these analog video concepts has virtually disappeared. Today, confirming that the black and white levels your camera is sending TriCaster are correct is as simple as sending first black, and then white (or the brightest past of your scene, and reading values from the scale alongside TriCaster’s Waveform scope.
Connect your camera to the correct TriCaster input, block the lens so it receives no illumination, and check the level shown in the Waveform monitor. Generally, it should be 16 on the 8bit scale.
To check white, use either the brightest part of your scene or a white card, ensuring that it is evenly illuminated with the same lighting your main subject will receive. Move in or zoom to fill the viewfinder with this, and confirm that the Waveform monitor is showing 235 on the same scale. Otherwise, you might try using your camera’s Auto White Balance feature with the white card – your camera manual will provide instructions. Afterwards, check the black level again.
Some more professional cameras offer full manual controls for white balance and/or black level. Use these as instructed to ensure your camera is providing the correct white and black levels.
If you cannot make source adjustments, or can’t get it quite right by these means alone, you can use the Brightness and Contrast controls in the Proc Amp TriCaster provides for that input to tweak black and white levels. (Of course it is always best to perform adjustments at the source if possible.)
For more information please download the entire document at new.tk/rt-m