Optical noise reduction using partial coherence in spatial filtering for image detail enhancement

Coherent optical spatial filtering can be used to increase the contrast of fine detail in photographs. The images produced, however, contain optical noise blemishes that make the procedure seldom usable in practical photography. A promising method of reducing the optical noise by means of partial coherence in a projection printer has been investigated involving the use of a plurality of point sources. It has been demonstrated, using pictorial enlargements, that subjective sharpness levels may be obtained which are similar to those obtained by using specular illumination while greatly reducing the amount of coherent noise on the image. Enlargements of a sine wave negative have demonstrated the contrast enhancement produced by spatially filtering the zero-order diffraction pattern of the point source array