In film editing, a dissolve is a gradual transition from one image to another. In film, this effect is created by controlled double exposure from frame to frame; transiting from the end of one clip to the beginning of another. In video editing, the effect is created by interpolating voltages of the video signal. In non-linear video editing, a dissolve is done in software, by interpolating gradually between the RGB values of each pixel of the image. The cut and the dissolve are used differently. A camera cut changes the perspective from which a scene is portrayed. It's as if the viewer suddenly and instantly moved to a different place, and could see the scene from another angle. Often this is done without missing any action (a seamless cut). Even though a dissolve is "softer" than a cut, it draws more attention to the change in the image than a "hard" cut. The reason is that the "mixed" images during the transition are unnatural and unfamiliar from usual vision. So, dissolves are mostly used on the borders of sequences, when a break in the continuity is desired. Usually, the purpose is constructive, and it's done slowly enough to portray the passage of time. As such, it replaces the old silent film convention of showing a slide with a caption, like "Later that evening". On the other hand, poorly done hard cuts startle the viewer even more than a dissolve; so dissolves are often used to "soften up" jump cuts or similar problematic cuts.
