Standard Primaries and Chromaticity Illumination and Color Models 1 Light Properties • What is light? – “light” = narrow frequency band of electromagnetic spectrum • The Electromagnetic Spectrum – Red: 3.8x10 14 hertz – Violet: 7.9x10 14 hertz Illumination and Color Models 2 Spectrum of Light Illumination and Color Models 3 Spectrum of Light • Monochrome light can be described by frequency f and wavelength λ – c = λ f (c = speed of light) • Normally, a ray of light contains many different waves with individual frequencies • The associated distribution of wavelength intensities per wavelength is referred to as the spectrum of a given ray or light source Illumination and Color Models 4 Psychological Characteristics of Color • Dominant frequency (hue, color) • Brightness (area under the curve), total light energy • Purity (saturation), how close a light appear to be a pure spectral color, such as red – Purity = E D − E W • ED = dominant energy density • EW = white light energy density • Chromaticity, used to refer collectively to the two properties describing color characteristics: purity and dominant frequency Illumination and Color Models 5 The CIE Chromaticity Diagram • A tongue-shape curve formed by plotting the normalized amounts x and y for colors in the visible spectrum – Points along the curve are spectral color (pure color) – Purple line, the line joining the red and violet spectral points – Illuminant C, plotted for a white light source and used as a standard approximation for average daylight Illumination and Color Models 6 The CIE Chromaticity Diagram • Color gamuts – All color along the straight line joining C1 and C2 can be obtained by mixing colors C1 and C2 – Greater proportion of C1 is used, the resultant color is closer to C1 than C2 – Color gamut for C3, C4, C5 generate colors inside or on edges • No set of three primaries can be combined to generate all colors Illumination and Color Models 7 The CIE Chromaticity Diagram Illumination and Color Models 8.