Sony G90 manual Are used in some circumstances, Instrument known as a color analyzer or a spectro

are used in some circumstances.	V I D E O		the test pattern directly from a display
Remember that although the signal lev-			using a sophisticated electro-optical
els are the same, the actual brightness of light from each		instrument known as a color analyzer (or a spectro-
primary is not the same, that is determined by calibrating		radiometer) and plot the results along with the SMPTE C
the reference white color to D65.		standard colors to display the errors.
Changing the signal levels of all primary colors
together does not change the CIE (x,y) chromaticity of a
color. Color bars with 50 percent signal amplitudes would
have the same (x,y) coordinates as color bars with 75 per-
cent signal amplitudes. The difference is that the bright-
ness of the color bars will change with amplitude, but
brightness information is not included in the CIE Chro-
maticity Diagram.
Notice that a complementary color lies on the exten-
sion of a line connecting its missing primary and the refer-
ence white point. This follows from the fact that adding
equal signal levels of a primary and its complementary
color must create the reference white, and the rule that any
color lies on a line between the two colors creating it. That
latter rule also means that the complementary color lies on
the line connecting its two primary components. Hence the
intersection of these two lines geometrically locates the
(x,y) position of the complimentary colors. (See Figure 6)
The (x,y) coordinates can also be calculated using a
mathematical analysis based on the coordinates of the		Fig. 6
phosphors and white point. The (x,y) coordinates for each
color in the color bars based on the SMPTE C phosphors		At this point you might realize that the color accuracy
and the D65 white point is shown in Table 1.		for a display being driven by RGB signals is pretty cut and
We can measure the (x,y) coordinates for each color in		dry. Once the primary colors are determined and the white
			point set, the color accuracy
			is determined. The				variable
			for any display is its variation
			in grayscale color tempera-
			ture, which means the white
			point’s		(x,y)	coordinates
			change with brightness level.
			If the white point moves
			around, we can see from the
			simple		geometric		analysis
			that the complementary col-
			ors will move on the edges of
			the display’s RGB triangle. Of
			course, the (x,y) point for
			other color signals will also
			move	around		proportionally
			inside the color triangle cre-
			ating errors.
			Some of you may wonder
			if it isn’t possible to convert
			the RGB video signals from
			the	SMPTE		standard to
			match a non-standard set of
			display		primaries,		thereby
			avoiding		color errors. The
			answer is yes, within the lim-
			its of the display’s color
			gamut, but it is more complex
			than	one might			expect
			because the RGB signals are
			non-linear. Why they are non-