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Re: Color space Police!



All color monitors, TV sets and CRT projectors (and that is what 95% of all
material is viewed on) are RGB devices and the only color space they can
handle is RGB.  Because we can only add colors in those devices (and not
subtract) negative RGB values are a very big sin.  However, these negative
RGB values could also not be displayed on the broadcast monitor used to
commit the sin.

Going over the maximum values for RGB is where the biggest problem is.
 Display devices are calibrated using 10% and 100% white (or 100% R,G,B).  As
soon as one applies RGB signals over 100% on such a device you wonder into
unknown territory.  At any moment one or more of the guns can start clipping.
 The problem is that every display device will start clipping for different
RGB values.  Those values are determined by the type of CRT's used, but also
the age of the CRT's.

The only guarantee for true color reproduction is to stay within the RGB
color space.  Remember that a color may be legal in one color space and
become illegal when transcoded to another color space.  Therefore it is
better to use the term "valid" color.  A color in any color space is a valid
color if and only if it is legal when transcoded to the RGB format.

Barco has an invalid color detector built in to their serial digital monitors
(the invalid part of the screen flashes).  I don't know of any customer
actually using it because 90% of the time the screen flashes so badly that
the customer can't work with it, and they simply switch the feature off.
 Imagine what is left of the creative color work once it gets to the viewer
at home.

Is everyone aware that our trusted SMPTE bars have invalid colors in them?

Dan Desmet
Barco Communication Systems

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