Dissolve

In chemistry, to dissolve a substance is to cause that substance to pass into a solution. For example: common salt (sodium chloride) can dissolve in water. See Solvation.

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In film, 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 the effect is created by interpolating voltages of the video signal.