[vision][colour blindness][blindness][perception][photography]
	Photography: method of recording the image of an object by the action of light, or related radiation, on a sensitive material. The term photography usually refers to the formation of optical images projected by a lens in a camera onto a film or other material carrying a layer of light-sensitive silver salts and the duplication and reproduction of such images by light action (printing); in an extended sense it also includes the formation of images by certain invisible radiations (ultraviolet and infrared rays) and images recorded in other sensitive materials not containing silver by means of chemical or physical processes or both. Related processes include the recording of images by X rays, electron beams, and nuclear radiations (radiography) and the recording and transmission of light images in the form of electromagnetic signals (television and videotape). As a means of visual communication and expression, photography has marked aesthetic capabilities. In order to understand them, the characteristics of the process itself must first be understood. Of these the first is immediacy. Usually, but not necessarily, the image that is recorded is formed by a lens in a camera. Upon exposure to the light forming the image, the sensitive material undergoes changes in its structure;a latent image is formed, which becomes visible by development and permanent by fixing. With modern materials, the processing may take place immediately or may be delayed for weeks or months.But, either way, the elements of the final image are determined at the time of exposure.