Image sensor drive control unit and image readout apparatus using the same
An image sensor drive control unit capable of preventing the degradation in image quality due to smearing or blooming with a minimum system change. The drive control unit includes a clock generator that outputs an effective pixel transfer clock during an effective pixel transfer period, and a dummy pixel transfer clock having a higher clock frequency than that of the effective pixel transfer clock during a dummy pixel transfer period following the effective pixel transfer period. The dummy pixel transfer period is set equal to a time period required for outputting a number of clocks corresponding to the number of dummy pixels when the clock frequency of the dummy pixel transfer clock is set equal to that of the effective pixel transfer clock.
1 . A drive control unit for driving an image sensor having a plurality of effective pixels and a plurality of dummy pixels disposed linearly to cause a signal charge stored in each of the effective pixels to be shift transferred from a CCD, wherein:
the drive control unit includes a clock generator that outputs:
an effective pixel transfer clock to the CCD during an effective pixel transfer period, and
a dummy pixel transfer clock having a higher clock frequency than that of the effective pixel transfer clock to the CCD during a dummy pixel transfer period following the effective pixel transfer period; and
the dummy pixel transfer period is set equal to a time period required for outputting a number of clocks corresponding to the number of dummy pixels when the clock frequency of the dummy pixel transfer clock is set equal to that of the effective pixel transfer clock.
2 . The image sensor drive control unit according to claim 1 , wherein the clock frequency of the dummy pixel transfer clock is set twice as high as that of the effective pixel clock.
3 . The image sensor drive control unit according to claim 1 , wherein the clock frequency of the dummy pixel transfer clock is determined based on the time constant obtained from the number of pixels on which a false signal, which is to be produced when signal charges are spilled out due to blooming, may appear.
4 . An image readout apparatus in which excitation light is irradiated on a storage phosphor sheet, on which radiation irradiated on a subject from a radiation source and transmitted through the subject is recorded as a radiation image, to cause stimulated luminescence to be emitted from the storage phosphor sheet, and the stimulated luminescence emitted therefrom is detected by a line sensor to obtain the radiation image, wherein:
the line sensor includes an image sensor having a plurality of effective pixels and a plurality of dummy pixels disposed linearly, and a CCD for shift transferring signal charges from the plurality of effective pixels; and a drive control unit for driving the image sensor to cause the signal charge stored in each of the effective pixels to be shift transferred from the CCD;
the drive control unit includes a clock generator that outputs:
an effective pixel transfer clock to the CCD during an effective pixel transfer period, and
a dummy pixel transfer clock having a higher clock frequency than that of the effective pixel transfer clock to the CCD during a dummy pixel transfer period following the effective pixel transfer period; and
the dummy pixel transfer period is set equal to a time period required for outputting a number of clocks corresponding to the number of dummy pixels when the clock frequency of the dummy pixel transfer clock is set equal to that of the effective pixel transfer clock.
5 . The image readout apparatus according to claim 4 , wherein the line sensor comprises a plurality of image sensors.