1. A tone transformation apparatus transforming a tone of an original image, the apparatus comprising: a signal obtaining unit which extracts or generates a first signal Z[i, j] that changes according to a pixel value of a pixel [i, j] of the original image or to a pixel value of an immediate neighborhood of the pixel [i, j]; a neighborhood processing unit which extracts or generates a second signal ZL[i, j] that changes according to a pixel value of a neighborhood area of the pixel [i, j], the neighborhood area being larger than the immediate neighborhood; a gain generator which determines a transformation gain k for the pixel [i, j] according to the first signal Z[i, j] and the second signal ZL[i, j]; and a tone transformation unit which performs tone transformation by multiplying, by the transformation gain k for said pixel [i, j], a color component of said pixel [i, j] or a signal component generated from the color component.