Method of and apparatus for reading out radiation image

1. A method of reading out a radiation image from a radiation image sensor, which stores electric charges corresponding to the amount of radiation exposed onto the radiation image sensor upon exposure of radiation carrying thereon a radiation image and thereby stores the radiation image, by causing the radiation image sensor to output an electric signal corresponding to the stored electric charges and by amplifying the output electric signal by a reading amplifier, wherein the improvement comprises that

a part of the stored electric charges are read before reading the radiation image, and

an offset is determined according to an amount of electric charges of the part of the stored electric charges which has been read before reading the radiation image and the determined offset is added to the electric signal obtained by reading the radiation image.

2. A method as defined in claim 1 in which the gain of the reading amplifier is changed on the basis of the amount of electric charges of the part of the stored electric charges which has been read before reading the radiation image so that the range of the electric signal obtained by reading the radiation image matches the conversion range of an A/D converter which digitizes the electric signal.

3. A method as defined in claim 2 in which the gain of the reading amplifier and the offset are determined on the basis of the amount of electric charges of the part of the stored electric charges which has been read before reading the radiation image so that the range of the electric signal obtained by reading the radiation image matches the conversion range of an A/D converter which digitizes the electric signal.

4. A method as defined in claim 1 in which the gain of the reading amplifier when reading the part of the stored electric charges is determined on the basis of the exposure condition when the radiation image is recorded.

5. A method as defined in claim 1 in which when erasing light is exposed onto the radiation image sensor to erase the residual image of the radiation image sensor after the image on the radiation image sensor is read out, the amount of the erasing light is changed on the basis of the amount of electric charges of the part of the

stored electric charges which has been read before reading the radiation image.

6. An apparatus for reading out a radiation image comprising:

a radiation image sensor which stores electric charges corresponding to the amount of radiation exposed onto the radiation image sensor upon exposure of radiation carrying thereon a radiation image, thereby storing the radiation image and outputs an electric signal corresponding to the stored electric charges and

a reading means which is provided with a reading amplifier which amplifies and outputs the electric signal output by the radiation image sensor and causes the radiation image sensor to output the electric signal corresponding to the stored electric charges and the reading amplifier to amplify and output the electric signal output from the radiation image sensor, wherein the improvement comprises that

the reading amplifier is a variable gain amplifier, and

the reading means reads a part of the stored electric charges before reading the radiation image,

wherein the apparatus further comprises:

an offset adding means which determines an offset according to an amount of electric charges of the part of the stored electric charges which has been read before reading the radiation image and adds the determined offset to the electric signal obtained by reading the radiation image.

7. An apparatus as defined in claim 6 in which the reading means changes the gain of the reading amplifier on the basis of the amount of electric charges of the part of the stored electric charges which has been read before reading the radiation image so that the

range of the electric signal obtained by reading the radiation image matches the conversion range of an A/D converter which digitizes the electric signal.

8. An apparatus as defined in claim 7 in which the reading

means changes the gain of the reading amplifier on the basis of the amount of electric charges of the part of the stored electric charges which has been read before reading the radiation image so that the range of the electric signal obtained by reading the radiation image matches the conversion range of an A/D converter which digitizes

the electric signal and

the offset adding means changes the offset on the basis of the amount of electric charges of the part of the stored electric charges which has been read before reading the radiation image so that the range of the electric signal obtained by reading the

radiation image matches the conversion range of the A/D converter which digitizes the electric signal.

9. An apparatus as defined in claim 6 in which the reading means determines the gain of the reading amplifier when reading the part of the stored electric charges on the basis of the exposure condition when the radiation image is recorded.

10. An apparatus as defined in claim 6 further comprising a residual image erasing means which exposes erasing light onto the radiation image sensor to erase the residual image of the radiation image sensor after the image on the radiation image sensor is read out, the residual image erasing means changing the amount of the

erasing light on the basis of the amount of electric charges of the part of the stored electric charges which has been read before reading the radiation image.

11. A method as defined in claim 1 , wherein a gain of the reading amplifier is changed on the basis of the amount of electric charges of the part of the stored electric charges which has been read before reading the radiation image.

12. An apparatus as defined in claim 6 , wherein the reading means changes a gain of the reading amplifier on the basis of the amount of electric charges of the part of the stored electric charges which has been read before reading the radiation image.