What is an image? An optical searchance; a psychical theatrical performance an idea or conception. The term image may be applied to a exposure such as a photograph a painting or a subject area which has a real physical existence. May also be applied to an idea or concept which has a mental rather than physical existence.
Visual images are of two types; Real Images- those having a real physical existence such as a photographic image. Mental Images; Those generated as a mental picture within our own minds and which are accessible only to natural study.
Real images consist of patterns of airy intensity and possibly variations in colour. The patterns of light are created in one of three ways;
Viewing by reflected light from a surface; Reflected light- ultrasound, RNI, Theatre, thermal imaging paper. (pg7)
Viewing by light transmitted through a semitransparent storey; Radiographs, CT, MRI, DIGITAL, Fluoroscopy, ultrasound.
Viewing by light emitted from a fluorescent layer, Fluoroscopy, ultrasound, CT, RNI, Digital, MRI, anglography, endoscopy.
CONTRAST; To be equal to(p) to identify a feature or an image, must start different from its milieu. On a radiograph, a structure must be of different optical density (Shade of grey) from adjacent structures. If the differences of smartness is great, the structure will stand out well from its surroundings and we say the contrast is HIGH.
HIGH CONTRAST; With a high aim of contrast the image produced appears harsh with lots of dense slows and burnished whites. Detail may be lost in highlighted areas and in the deep shadows but the boundries between the dark and light areas appear sharply defined.
LOW CONTRAST; With the contrast level at minimal the image appears dull, lacking in any true black and whites. However, inspection of the highlighted areas and the shadows reveal detail that was absent in...
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