Digital Image Fundamentals

– Nearly a sphere with an average diameter of approximately 20mm – Enclosed by various membranes – Cornea and sclera outer cover ∗ Cornea: Transparent convex anterior portion of the outer fibrous coat of the eyeball that covers the iris and the pupil and is continuous with the sclera ∗ Sclera: Tough white fibrous outer envelope of tissue covering all of the eyeball except the cornea – Choroid ∗ Dark-brown vascular coat of the eye next to sclera towards the interior of the eye ∗ Network of blood vessels to provide nutrition to eye ∗ Heavily pigmented to reduce the amount of extraneous light entering the eye, and backscatter within optical globe ∗ Divided into ciliary body and iris diaphragm ∗ Iris expands or contracts to control the amount of light entering the eye ∗ Central opening of iris (pupil) varies from 2 to 8 mm in diameter ∗ Front of iris contains the visible pigment of the eye whereas the back contains the black pigment – Lens ∗ Made up of concentric layers of fibrous cells ∗ Suspended by fibers attached to the ciliary body ∗ Colored by slightly yellow pigmentation that increases with age ∗ Excessive clouding of lens, called cataract, leads to poor color discrimination and loss of clear vision ∗ Absorbs about 8% of visible light, and most of IR and UV waves, possibly causing damage in excessive amounts – Retina ∗ Delicate, multilayered, light-sensitive membrane lining the inner eyeball and connected by the optic nerve to the brain ∗ Distribution of discrete light receptors allows for pattern discrimination ∗ Cones · 6 to 7 million photoreceptors, packed at about 150,000 cones per sq mm in the center of fovea · Located in central portion of retina (fovea) · Highly sensitive to color · Each one is connected to its own nerve end, allowing for fine resolution detail · Responsible for photopic or bright light vision ∗ Rods · 75 to 150 million over the retinal surface with several rods connected to a single nerve end, providing coarse resolution · General overall view of the scene · Not involved in color vision and sensitive to low levels of illumination · Responsible for scotopic or low light vision