Density correcting method and apparatus for subtraction image

Claim 1

A method of correcting the density of a subtraction image in a gradation processing in an energy subtraction processing which includes the steps of exposing two or more stimulable phosphor sheets to radiations having different levels of energy passing through the same object to have radiation images of said object stored in said stimulable phosphor sheets, at least a part of image information being different between said radiation images, scanning the respective stimulable phosphor sheets by stimulating rays to sequentially release the radiation energy stored in said stimulable phosphor sheets as light emission, photoelectrically detecting and converting the amounts of the emitted light into digital image signals, obtaining a difference signal for forming an image of a specific structure of said object by carrying out a subtraction processing of said digital image signals between corresponding picture elements of said radiation images, and then subjecting said difference signal to a gradation processing, the method of correcting the density of a subtraction image comprising the steps of: calculating a characteristic value in said difference signal, and making said characteristic value correspond to a predetermined density of a reproduced image.

Claim 2

A method of correcting the density of a subtraction image in a gradation processing in an energy subtraction processing which includes the steps of exposing two or more stimulable phosphor sheets to radiations having different levels of energy passing through the same object to have radiation images of said object stored in said stimulable phosphor sheets, at least a part of image information being different between said radiation images, scanning the respective stimulable phosphor sheets by stimulating rays to sequentially release the radiation energy stored in said stimulable phosphor sheets as light emission, photoelectrically detecting and converting the amounts of the emitted light into digital image signals, obtaining a difference signal for forming an image of a specific structure of said object by carrying out a subtraction processing of said digital image signals between corresponding picture elements of said radiation images, and then subjecting said difference signal to a gradation processing, the method of correcting the density of a subtraction image comprising the steps of: calculating a characteristic value in said difference signal, and making said characteristic value correspond to a predetermined density of a reproduced image.

Claim 15

A method as defined in any of claims 8 to 13 wherein said maximum signal value and said minimum signal value of said difference signal are made to correspond to said predetermined maximum density value and said predetermined minimum density value of said reproduced image by uniformly converting said difference signal prior to said gradation processing.

Claim 16

A method as defined in any of claims 8 to 13 wherein said maximum signal value and said minimum signal value of said difference signal are made to correspond to said predetermined maximum density value and said predetermined minimum density value of said reproduced image by correcting a gradation conversion table used for said gradation processing.

Claim 17

An apparatus for correcting the density of a subtraction image which comprises: (i) an image read-out means for scanning stimulable phosphor sheets carrying radiation images stored therein by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, and photoelectrically detecting and converting the emitted light into digital image signals, (ii) a subtraction operation means for obtaining a difference signal for forming an image of a specific structure by conducting a subtraction processing of said digital image signals between the corresponding picture elements of said radiation images, said digital image signals being detected by said image read-out means from two or more stimulable phosphor sheets carrying said radiation images stored therein by exposure to radiations having different levels of energy passing through the same object, at least a part of the image information being different between said radiation images, (iii) an image processing means for conducting a gradation processing on said difference signal on the basis of a gradation conversion table, (iv) an operation means for calculating a predetermined characteristic value of said difference signal, and (v) a signal correcting circuit for making said characteristic value of said difference signal correspond to a predetermined density of a reproduced image by uniformly converting said difference signal prior to said gradation processing.

Claim 18

An apparatus for correcting the density of a subtraction image which comprises: (i) an image read-out means for scanning stimulable phosphor sheets carrying radiation images stored therein by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, and photoelectrically detecting and converting the emitted light into digital image signals, (ii) a subtraction operation means for obtaining a difference signal for forming an image of a specific structure by conducting a subtraction processing of said digital image signals between the corresponding picture elements of said radiation images, said digital image signals being detected by said image read-out means from two or more stimulable phosphor sheets carrying said radiation images stored therein by exposure to radiations having different levels of energy passing through the same object, at least a part of the image information being different between said radiation images, (iii) an image processing means for conducting a gradation processing on said difference signal on the basis of a gradation conversion table, (iv) an operation means for calculating a predetermined characteristic value of said difference signal, and (v) a signal correcting circuit for making said characteristic value of said difference signal correspond to a predetermined density of a reproduced image by uniformly converting said difference signal prior to said gradation processing.

Claim 24

An apparatus for correcting the density of a subtraction image which comprises: (i) an image read-out means for scanning stimulable phosphor sheets carrying radiation images stored therein by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, and photoelectrically detecting and converting the emitted light into digital image signals, (ii) a subtraction operation means for obtaining a difference signal for forming an image of a specific structure by conducting a subtraction processing of said digital image signals between the corresponding picture elements of said radiation images, said digital image signals being detected by said image read-out means from two or more stimulable phosphor sheets carrying said radiation images stored therein by exposure to radiations having different levels of energy passing through the same object, at least a part of image information being different between said radiation images, (iii) an image processing means for conducting a gradation processing on said difference signal on the basis of a gradation conversion table, (iv) an operation means for calculating a predetermined characteristic value of said difference signal, and (v) a gradation conversion table correcting circuit for making said characteristic value of said difference signal correspond to a predetermined density of a reproduced image by correcting said gradation conversion table.

Claim 25

An apparatus for correcting the density of a subtraction image which comprises: (i) an image read-out means for scanning stimulable phosphor sheets carrying radiation images stored therein by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, and photoelectrically detecting and converting the emitted light into digital image signals, (ii) a subtraction operation means for obtaining a difference signal for forming an image of a specific structure by conducting a subtraction processing of said digital image signals between the corresponding picture elements of said radiation images, said digital image signals being detected by said image read-out means from two or more stimulable phosphor sheets carrying said radiation images stored therein by exposure to radiations having different levels of energy passing through the same object, at least a part of image information being different between said radiation images, (iii) an image processing means for conducting a gradation processing on said difference signal on the basis of a gradation conversion table, (iv) an operation means for calculating a predetermined characteristic value of said difference signal, and (v) a gradation conversion table correcting circuit for making said characteristic value of said difference signal correspond to a predetermined density of a reproduced image by correcting said gradation conversion table.