RGB Models human visual system? Gives an absolute color description? Models color similarity? Linear model? Convenient for color displays?

RGB Models human visual system Gives an absolute color description Models color similarity Linear model Convenient for color displays

Spectra Light reaching the retina is characterized by spectral distribution, i.e. (relative) amount of power at each wavelength. Each kind of cone (S,M,L) responds differently.

Sources of colored light used in modern fireworks. Yellow Sodium D-line589 nm OrangeCaCl nm nm RedSrCl nm nm nm Green BaCl nm nm nm Blue CuCl nm,

Cornea Lens Pupil Iris Retina Fovea Optic nerve

Ganglion Bipolar Amacrine Rod Cone Epithelium Optic nerve Retinal cross section Light Horizontal

Photoreceptors Cones - –respond in high (photopic) light –differing wavelength responses (3 types) –single cones feed retinal ganglion cells so give high spatial resolution but low sensitivity –highest sampling rate at fovea

Photoreceptors Rods –respond in low (scotopic) light –none in fovea –one type of spectral response –several hundred feed each ganglion cell so give high sensitivity but low spatial resolution

Optic nerve 130 million photoreceptors feed 1 million ganglion cells whose output is the optic nerve. Optic nerve feeds the Lateral Geniculate Nucleus approximately 1-1 LGN feeds area V1 of visual cortex in complex ways.

Rods and cones Rods saturate at 100 cd/m 2 so only cones work at high (photopic) light levels All have same spectral sensitivity Low light condition is called scotopic Three cone types differ in spectral sensitivity and somewhat in spatial distribution.

Cones L (long wave), M (medium), S (short) –describes sensitivity curves. “Red”, “Green”, “Blue” is a misnomer. See spectral sensitivity.