etaylor@wilkins.iaims.bcm.tmc.edu (Eric Taylor) (12/15/90)
Here is a question that has always bothered me: Why is the formula for a gray level = .3 * red + .6 * green + .1 * blue (approximately) It seems to me that you REALLY want : sqrt((red * red + green * green + blue * blue) / 3) since gray is a measure of intensity. -- Eric Taylor Baylor College of Medicine etaylor@wilkins.bcm.tmc.edu (713) 798-3776
cflatter@ZIA.AOC.NRAO.EDU (Chris Flatters) (12/15/90)
Eric Taylor writes: > Here is a question that has always bothered me: > > Why is the formula for a gray level = > .3 * red + .6 * green + .1 * blue (approximately) > > It seems to me that you REALLY want : > > sqrt((red * red + green * green + blue * blue) / 3) > > since gray is a measure of intensity. The first formula reflects the fact that human eye is not equally sensitive to the brightness of red, green and blue light. In particular the eye's response to blue light is much less than that to red or green (note that most people perceive saturated blue as a dark colour and saturated green as a dark colour). If you want the full details on this take at look at Foley, van Dam, Feiner and Hughes [%], p574ff or any other good text on computer graphics. Chris Flatters -------------------- [%] "Computer Graphics, Principles and Practice", 2nd Edn., Foley et al., Addison-Wesley, 1990.