1. A method of compensation for the thickness of an organ in an X-ray machine, of the type comprising a source of X-rays and a means of detection of the X-ray beam after it has passed through the said organ, the detection means being capable of converting the X-ray beam into a digital electronic signal in which, from a digitized image there is calculated an image of the radiologic thicknesses of the organ traversed by the X-ray beam, comprising the steps of: defining a thickness threshold; deriving an algebraic compensation image to bring the pixels of lower or higher level back to the said threshold to the value of the threshold; and summing the thickness image and a proportion of the compensation image to obtain a compensated thickness image.