Moseley, Robert Zach (1986, ASQC) General Scanning Incorporated, Watertown, MA
Despite the expansion of machine vision technology, the human eye is still the sensor of choice for many inspection operations. The eyes are themselves very complex and, when combined with the analysis of information performed in the brain, the intricacy of vision becomes staggering.
The data processing within the human visual system enables the eye to respond to moving targets, to sort and highlight areas of interest, to discriminate minuscule angles, to enhance the capabilities of its optical system, to adapt to incredible ranges of light intensity and color and sort a huge number of colors. It is hard to imagine what we would see were it not for the sorting of the complex input signals from the eye. We would be aware of every motion of our body, and head and eye. We would lose our sight with each blink. Colors would disappear at different portions. Moving in a car or watching a moving conveyor belt would present a meangingless stream of blurs. All of these sensation s (along with all others) are modified in the eye and in the brain to create order from chaos. This goal is not always achieved. In inspection where every operation can be crucial, the difference between sight and perception can be the difference between excellence and failure.
This paper examines vision as a physiological and psychological process. The incoming light is traced through the cornea, lens and vitreous humor until it reaches the retina. This tissue contains light sensitive cells which turn the light energy into nerve impulses. Cones (the color sensors) are crammed in the center of the visual field; rods which sense black and white only dominate the periphery.
Data from over 100 million sensor cells in each eye feed to other cells within the retina which perform data reduction of these signals for transfer through the approximately 1 million fibers of each optic nerve to the brain. The brain maps the visual image enabling the inspector to see. Long before this occurs the brain has applied a variety of functions that fill in the blanks in the data. These data modifications will be examined in relation to inspection of color, motion, short lived phenomena, contrast and other important functions.
Without an understanding of this important factor in the quality equation we cannot expect to achieve the highest levels of performance.