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 would have reduced saturation and exposure latitude, along with increased contrast and graininess. It usually is used to maximal 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 original negative bleach bypassed in the event that the look is agreed to be too extreme, and the cost of the process for each individual release print is usually cost-prohibitive. The effect, however, will render slightly differently at each stage, especially between the negative and positive 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.
Use in movies 
Bleach bypass was first used in Japanese filmmaker Kon Ichikawa's 1960 film Her Brother. Kazuo Miyagawa as Daiei Motion Picture Company's cameraman invented bleach bypass for Ichikawa's film, inspired by the color rendition in the 1956 release of Moby-Dick, printed using Technicolor, and was achieved through the use of an additional black and white overlay. Despite this early foray into the technique, it remained overlooked for the most part until its use by Roger Deakins in 1984. The effect has subsequently become a regular development tool in labwork, and has remained in widespread usage ever since. Some notable practitioners include cinematographers Rodrigo Prieto, Remi Adefarasin, Darius Khondji, Dariusz Wolski, Oliver Stapleton, Newton Thomas Sigel, Park Gok-ji, Shane Hurlbut, Steven Soderbergh (as "Peter Andrews"), Tom Stern, Vittorio Storaro, and Janusz Kamiński (notably at Steven Spielberg's Saving Private Ryan ).
- "Kon Ichikawa Retrospective Part 1" (in Japanese). National Film Center. Retrieved 2008-04-20.
- "日刊スポーツ・訃報・宮川一夫氏" (in Japanese). Retrieved 2008-04-20.
- "東京現像所：the 50th Anniversary：TOGENの歴史" (in Japanese). Archived from the original on 2007-11-14. Retrieved 2008-04-20.
- "Combat Footage". Saving Private Ryan Online Encyclopedia. Retrieved 2008-09-08.
|Wikimedia Commons has media related to: Bleach bypass|
- "Soup du Jour: Bleach Bypass", American Cinematographer, November 1998.
- Bleach Bypass effect with Gimp.