It is difficult to determine where the physiological function of color ends and the psychological aspect begins. This is the subjective part of evaluating and describing color. It is important to remember that the human eye is linked with the brain through a neurological/electrochemical response net work. The sophistication of this human response system allows us process data at phenomenal rates of speed. The human mind, however, is not capable of "remembering" color or tone on an absolute basis: it can only make comparisons under a standard viewing light. The need for densitometry and colorimetry to assist in the evaluation of color thus becomes critical in the verification of standards.
Several conditions that affect a person's ability to view color are listed below:
• Angle of viewing -- the vest angle to view color is at a consistent 90 degrees.
• Angle of illumination -- the standard should be at 45 degrees or in a commercially prepared viewing booth.
• Distance of viewing -- a consistent 14 to 18 inches should be maintained.
• Texture of the surface being viewed.
• Glossy color images versus flat color.
• Size and shape of colored image.
• The health and mental attitude of the observer (rested vs. tired).