1. An image processing apparatus comprising: input means for inputting image data represented by multi-density level pixel data; detecting means for detecting density levels of each pixel; transposing means for transposing a density of a first pixel to a density of a second pixel neighboring the first pixel, wherein a transposition ratio corresponding to the first pixel changing adaptively according to the density levels of the first and second pixels detected by said detecting means; and output means for outputting the image data processed by said transposing means.