1. A method of reconstructing an image from compression-processed image signals, in which an image signal presented for reconstruction is comprised of transform image signals obtained by carrying out irreversible compression encoding processing of input image signals, and then carrying out decoding processing. wherein the improvement comprises the steps of: (i) carrying out said irreversible compression encoding processing and said decoding processing on input training image signals representing a predetermined training image, to obtain transformed training image signals prior to image reconstruction, comparing said transformed training image signals with said input training image signals, and calculating differences between said transformed training image signals and said input training image signals at respective picture elements, (ii) generating noise signals having a signal value distribution in accordance with the distribution of said differences, and (iii) reconstructing said input image by randomly adding said noise signals to said transform image signals.