What is Cross Processing

Cross-Processing is the name given to the technique of processing film in the wrong chemistry (i.e. processing print film in slide chemistry or vice versa).
Traditionally, cross processing color slide film in C-41 process chemicals is most common. Some commercial-level photography/darkroom merchants will perform this developing process. However, cross processing can take place in many other forms, such as negative color print film and/or positive color reversal film in a black and white developer.

Color cross processed photographs are often characterized by unnatural colors and high contrast. The results of cross processing differ from case to case, as the results are determined by many factors such as the make and type of the film used, the amount of light exposed onto the film and the chemical used to develop the film.
Cross processing effects can be simulated in digital photography by a number of techniques involving the manipulation of contrast/brightness, hue/saturation and curves in image editors such as Adobe Photoshop or GIMP; however, they lack the unpredictable nature of regular cross processed images.