Quote:
Originally posted by Wilbert
Pure yellow (or green, blue, red, etc ...) has an value (lightness) of 1. This implies that reducing the saturation turns it into white.
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Ah, I see. Based solely on the diagram I must agree with you. But those diagrams and links are all about computer graphics. Maybe it works differently in the video world?
Honestly, "Hue" and "Value" (or "Intensity") I couldn't care less about. I only want the "Saturation" control.
In my mind (not getting too technical), I've always thought about it like the "Color" knob on a TV set. You turn it up and colors bloom and people's faces turn red. You turn it down and it's just like watching a B&W set. The "saturation" slider in Donald Graft's filter seems to accomplish a similar effect for digital video, but is "saturation" really the proper term for it?
Just to confuse you more, here's something I noticed: Try desaturating the same BlankClip in VirtualDub, first using Donald's "H/S/I" filter, and then using VirtualDub's internal "HSV adjust" filter. The results are quite different.
Since DG is currently unavailable, perhaps you can ask Avery Lee if he has any thoughts on this.
EDIT:
Just thought of something else. IIRC in video there is the concept of colors being "NTSC safe." (There may also be a similar concept in PAL video.) A vectorscope is a device used to measure the color saturation of broadcast video, and determine if it is "safe" or not. The colors must fall within certain fixed boundaries. Therefore it may not be possible to represent "pure yellow" (or any other pure color) in the video world, i.e., it's always less than Value=1. Perhaps the VirtualDub filters are using formulas customized to reflect this concept...