Positive Process

the combination of operations by which a positive image is obtained from a negative. The positive process consists of exposing the material, such as photographic paper, a positive film, or diapositive plate, and processing it with photographic chemicals. The emulsions used in this process, whether for motion-picture or still photography, are less sensitive to light and more contrasty than those of negatives; moreover, the emulsions of black-and-white materials usually have not been color-sensitized.

Prints may be produced from a negative by either the contact or the projection method. In contact printing, the emulsion of the positive material is tightly pressed against the emulsion of the negative and is exposed to light passing through the negative. Therefore, the positive image produced is the same size as the negative image and possesses the sharpness and resolution of small details inherent in the negative. The printing is done in printing frames, printing machines, and motion-picture film printers.

Projection printing consists of projecting a negative image by a lens onto the emulsion of a positive material located at some distance from the negative. This makes it possible to vary widely the size of the image, to print only part of the negative, to eliminate distortions in perspective, and to make photomontages, combining several images in one positive. Projection printing uses enlargers of various designs. As far as the actual physical and chemical processes involved are concerned, the processing of exposed positive materials does not differ from the processing of negative materials. Positives are sometimes additionally subjected to toning.

A positive image with colors close to the natural colors of the photographed object is obtained by printing from color negatives onto multilayer color positive materials. A feature of color printing is the use of corrective filters to eliminate color distortions.