Bleach bypass

Bleach bypass, also known as skip bleach or silver retention, is an optical effect which entails either the partial or complete skipping of the bleaching function during the processing of a color film. By doing this, the silver is retained in the emulsion along with the color dyes. The result is a black-and-white image over a color image. The images usually have reduced saturation and exposure latitude, along with increased contrast and graininess. It usually is used to maximum effect in conjunction with a one-stop underexposure.

Bleach bypass can be done to any photochemical step in the process, be it original camera negative, interpositive, internegative, or release print. For motion pictures, it is usually applied at the internegative stage, as insurance companies usually are reluctant to have the camera negative bleach bypassed, or the interpositive (a "protection"/"preservation" element), in the event that the look is agreed to be too extreme, and the cost of the process for each individual release print is most often cost-prohibitive. The effect, however, will render slightly differently at each stage, especially between the camera negative and interpositive stages.

Bleach bypass generally refers to a complete circumvention of the bleach stage of development, and is the most commonly offered service among labs. Technicolor's ENR and OZ and Deluxe Labs' ACE and CCE processes are proprietary variants which allow the film to be only partially bleached, giving the cinematographer a more finely tuned control over the effect rendered by the process.

While originally a laboratory technique, a similar effect can now be achieved digitally through digital intermediate color grading.

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