Gradation processing method and apparatus for radiation image recording system

Claim 1

In a method of processing the gradation of a radiation image recorded in a stimulable phosphor in a pattern of radiation energy stored therein where the stimulable phosphor is scanned by a stimulating ray to emit light of the amount proportional to the level of the radiation energy stored, the emitted light is converted to an electric signal having a level corresponding to the emitted amount of the light, and a visible image corresponding to said radiation image is reproduced on a recording material by use of the electric signal, the method of processing the gradation of the radiation image comprising; processing the electric signal at the minimum and maximum levels thereof so that the radiation image of the density corresponding to the minimum level of the electric signal is reproduced on the recording material in the optical density within the range of the fog density to the fog density plus 0.3 in terms of optical density, and the radiation image of the density corresponding to the maximum level of the electric signal is reproduced on the recording material in the optical density within the range of 1.5 to 2.8 in terms of optical density, and processing the electric signal of the level in the range between the minimum and maximum levels so that the derivative ##EQU7## of a density curve (D=f(S)) drawn in a coordinate in which the ordinate represents the optical density (D) of the reproduced image on the recording material and the abscissa represents the level of the electric signal (S) is always positive (γ>0).

Claim 6

A method as defined in any one of claims 2 to 4 wherein said predetermined level Sp satisfies the formula of ##EQU8##

Claim 8

A method as defined in any one of claims 2 to 4 wherein the second derivative of said density curve is positive or zero ##EQU10## at least in the range below said predetermined level (S<Sp).

Claim 10

A method as defined in any of claims 2 to 4 wherein the derivative of said density curve is continuous at least in the range below said predetermined level (S<Sp).

Claim 12

An apparatus for processing the gradation of a radiation image in a radiation image recording system which comprises radiation image read-out means including scanning means for scanning a stimulable phosphor carrying a radiation image stored therein with a stimulating ray, a reading means for reading out the radiation image stored therein by detecting the light emitted from the stimulable phosphor upon stimulation thereof and converting the light to an electric signal having a level corresponding to the amount of the emitted light, a signal processing means for processing the electric signal, a modulating means controlled by the processed electric signal, and a recording means controlled by the modulating means for reproducing on a recording material an image corresponding to the radiation image recorded in the stimulable phosphor, said signal processing means comprising a signal converting means which converts the electric signal of the minimum level corresponding to the minimum amount of the light emitted from the stimulable phosphor to the level which results in the optical density in the image reproduced on the recording material within the range from the fog density of the recording material to the fog density plus 0.3 in terms of optical density, converts the electric signal of the maximum level corresponding to the maximum amount of the light emitted from the stimulable phosphor to the level which results in the optical density in the image reproduced on the recording material within the range from 1.5 to 2.8 in terms of optical density, and converts the electric signal of the level between the minimum level and the maximum level to a level which results in the optical density in the image reproduced on the recording material that monotonously increases as the level of the electric signal rises.

Claim 13

An apparatus for processing the gradation of a radiation image in a radiation image recording system which comprises radiation image read-out means including scanning means for scanning a stimulable phosphor carrying a radiation image stored therein with a stimulating ray, a reading means for reading out the radiation image stored therein by detecting the light emitted from the stimulable phosphor upon stimulation thereof and converting the light to an electric signal having a level corresponding to the amount of the emitted light, a signal processing means for processing the electric signal, a modulating means controlled by the processed electric signal, and a recording means controlled by the modulating means for reproducing on a recording material an image corresponding to the radiation image recorded in the stimulable phosphor, said signal processing means comprising a signal converting means which converts the electric signal of the minimum level corresponding to the minimum amount of the light emitted from the stimulable phosphor to the level which results in the optical density in the image reproduced on the recording material within the range from the fog density of the recording material to the fog density plus 0.3 in terms of optical density, converts the electric signal of the maximum level corresponding to the maximum amount of the light emitted from the stimulable phosphor to the level which results in the optical density in the image reproduced on the recording material within the range from 1.5 to 2.8 in terms of optical density, and converts the electric signal of the level between the minimum level and the maximum level to a level which results in the optical density in the image reproduced on the recording material that monotonously increases as the level of the electric signal rises.