Standard Primaries and Chromaticity

Illumination and Models 1 Properties

• What is light? – “light” = narrow frequency band of • The Electromagnetic Spectrum – : 3.8x10 14 hertz – : 7.9x10 14 hertz

Illumination and Color Models 2 Spectrum of Light

Illumination and Color Models 3 Spectrum of Light

• 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 (, 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 = 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 in the – Points along the curve are spectral color (pure color) – 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 – 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 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