In its most straightforward implementation, this operator takes as input two identically sized images and produces as output a third image of the same size as the first two, in which each pixel value is the sum of the values of the corresponding pixel from each of the two input images.
More sophisticated versions allow more than two images to be combined with a single operation.
A common variant of the operator simply allows a specified constant to be added to every pixel. The addition of two images is performed straightforwardly in a single pass. If the image format being used only supports, say 8-bit integer pixel values , then it is very easy for the result of the addition to be greater than the maximum allowed pixel value. The effect of this depends upon the particular implementation. The overflowing pixel values might just be set to the maximum allowed value, an effect known as saturation .