Normalized RGB tristimulus value can be plotted on an rg chromaticity diagram. Every RGB monitor has its own color gamut, bounded in chromaticity by a color triangle. RGB color matching serve as the base for rg chromaticity. The inverse calculation, from color temperature to corresponding chromaticity coordinates, is discussed in . The contour of the ellipse therefore represents the just noticeable differences of chromaticity. Mathematically the colors of the chromaticity diagram occupy a region of the real projective plane. In chromaticity space, the gamut is a plane convex polygon with corners at the primaries. The tristimulus values are , and the chromaticity coordinates using the standard observer are . It decreases its lightness while nearly conserving its chromaticity. PNG can store gamma and chromaticity data for improved color matching on heterogeneous platforms. The figure to the side is a plotted rg chromaticity diagram. However, the concept of color can be divided into two parts&colon; brightness and chromaticity. The white point of the rg chromaticity diagram is defined by the point (1/3,1/3). This is why the rg chromaticity diagram extends in the negative r direction. Early LED lamps varied greatly in chromaticity from the incandescent lamps they were replacing.