The Purposes of Editing

Editing is used to piece together all of the footage into the correct order that is wanted by the editor. The correct order is generally the chronological order but this isn't necessarily the case for everything. For instance, the film Memento is shown backwards. It is made so well that in the viewers eye everything is revealed to them in the right order as when looked at in the chronological order it doesn't create the same impact as it does as being shown this way. The fact that it is shown backwards links very strongly to the storyline which works well. Below is the trailer for Memento.

After filming there would be a lot of footage that isn't needed like different takes of different scenes which wouldn't be used for the film so these would need to be edited out.

Editing is also used to create a certain effect to the film that is wanted by the film maker; you can use different transitions between shots, edit the colour tones of the footage, the brightness etc. You can also see the footage in a much clearer form to see whether any other filming is needed to create the effect that is wanted. It can also be used to edit the timing of the footage, it can be made shorter or longer. This works with the editing of timing of the film itself. It can also be used to create special effects like speeding up a scene or slowing it down. The video below shows both of these effects.