white balance card

[Stephen Mann]

White balance and exposure are not the same. You can white balance on any color of white… Thinking 8-bit, white is 255,255,255 in the RGB channels. Black is 0,0,0. Everything in-between, as long as the R=G=B, is ashade of gray. All that color balancing on the camera does is to adjust the offset of each channel (usually just Red and Blue because DV cameras usually take their luminosity from th Green channel)so that what you told it is white, has the same value in R,G and Blue. So if you are looking at a 127,127,127 gray card and tell the camera to WB on it, then it will come pretty close to setting the outputs to 127,127,127 – and for that lighting situation, you are “balanced”.

Photographers use an 18% gray card for exposure because the light reflected by an 18% gray card is very close to the light reflected by the average caucasion face.

Hope this helps.

Steve Mann
MannMade Digital Video
http://www.mmdv.com