Principal photography

Principal photography is the phase of film production in which the movie is filmed, with actors on set and cameras rolling, as distinct from pre-production and post-production.
Principal photography is usually the most expensive phase of film production, generally due to actor, director, and set crew salaries, the costs of certain shots, including any props or on-set special effects. Its start generally marks a point of no return for the financiers, because until it is complete there is unlikely to be enough material filmed to release a final product needed to recoup costs. While it is common for a film to lose its greenlight status during pre-production (for example, because an important cast member drops out), it is extremely uncommon for finance to be withdrawn once principal photography has commenced, and it is usually regarded as a catastrophe.
Once a film concludes principal photography, it is said to have wrapped, and a wrap party may be organized to celebrate. During post-production, it may become clear that certain shots or sequences are missing or incomplete and are required to complete the film, or that a certain scene is not playing as expected, or even that a particular actor has failed to turn in a performance of the required caliber. In these circumstances, additional material may have to be shot. If the material has already been shot once, or is substantial, the process is referred to as a re-shoot, but if the material is new and relatively minor, it is often referred to as a pick-up.

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