Radiation image read-out method and apparatus

Claim 1

A radiation image read-out method in which, prior to final read-out for exposing a stimulable phosphor sheet exposed to a radiation passing through an object to have a radiation image of the object stored thereon to stimulating rays which cause the stimulable phosphor sheet to emit light in proportions to the stored radiation energy, and photoelectrically detecting the emitted light to obtain an electric image signal for reproducing a visible image, preliminary read-out for approximately detecting the radiation image stored on the stimulable phosphor sheet is conducted by use of stimulating rays of a level lower than the level of stimulating rays used in the final read-out, read-out conditions in the final read-out and/or image processing conditions are adjusted on the basis of the information obtained by the preliminary read-out, and the final read-out is conducted by use of the adjusted conditions, wherein the improvement comprises the steps of: (i) creating a histogram of frequencies of preliminary read-out image signals obtained by said preliminary read-out versus levels of said preliminary read-out signals, (ii) detecting prospective edge point signals, which are considered to be signals representing edge portions of an irradiation field on said stimulable phosphor sheet, from said preliminary read-out image signals, (iii) removing a region of a level lower than the level of a characteristic value representing said prospective edge point signals from said histogram, and (iv) adjusting said read-out conditions in the final read-out and/or said image processing conditions on the basis of said histogram outside of said lower level region.

Claim 6

A method as defined in any of claims 1 to 4 wherein said prospective edge point signals are detected by digitizing said preliminary read-out image signals and conducting a differentiation processing of the digitized preliminary read-out image signals.

Claim 13

An apparatus as defined in any of claims 7 to 10 further comprising a switch for controlling the operation of said histogram correction means so that histogram correction is conducted only when said irradiation field is limited in an image recording step.