Patent EA-004170-B1 (EA)
Title: Photosensor system and drive control method thereof
Inventor: NAKAMURA YOSHIKI
IPC: H04N5/335
Filed: 2000-10-19
Abstract: 1. A photosensor system comprising: a photosensor array (100) constituted by two-dimensionally arraying a plurality of photosensors (10); and image reading means for reading a subject image made up of pixels corresponding to the plurality of photosensors at a predetermined image reading sensitivity by said photosensor array (100), characterized by further comprising: pre-reading means for reading the subject image prior to image reading operation while changing an image reading sensitivity of said photosensor array (100) at a plurality of stages; reading sensitivity extraction means for extracting an image reading sensitivity having a maximum absolute difference value among absolute difference values between adjacent pixels in a predetermined measurement amount relating to an image pattern of the subject image read by said pre-reading means; and reading sensitivity setting means for setting the image reading sensitivity extracted by said reading sensitivity extraction means to a reading sensitivity of said image reading means. 2. A system according to claim 1, characterized in that pre-reading operation by said pre-reading means is executed by setting different image reading sensitivities stepwise for respective rows of said photosensor array and reading the subject image. 3. A system according to claim 1, characterized in that the predetermined measurement amount in said reading sensitivity extraction means is lightness data corresponding to the image pattern of the subject image read by pre-reading operation. 4. A system according to claim 1, characterized in that the image reading sensitivity of said photosensor array (100) is set by adjusting a charge accumulating period of the photosensor. 5. A system according to claim 1, characterized in that said reading sensitivity extraction means comprises: absolute difference value calculation means for calculating an absolute difference value between adjacent pixels for each image reading sensitivity in the predetermined measurement amount relating to the image pattern of the subject image read by said pre-reading means; representative difference value extraction means for extracting a maximum absolute difference value as a representative difference value for each image reading sensitivity from the absolute difference values calculated by said absolute difference value calculation means; and optimal reading sensitivity extraction means for extracting an image reading sensitivity corresponding to the maximum representative difference value from the representative difference values for respective image reading sensitivities extracted by said representative difference value extraction means. 6. A system according to claim 5, characterized in that said absolute difference value calculation means calculates the absolute difference value of the predetermined measurement amount in predetermined row and column ranges of the subject image by said pre-reading means. 7. A system according to claim 1, characterized by further comprising, in said image reading means and said pre-reading means of said photosensor array (100), effective voltage adjusting means for applying to each photosensor (10) a correction signal for setting an effective voltage of a signal voltage from said photosensor (10) to an optimal value which minimizes a change in a threshold voltage of said photosensor (10). 8. A system according to claim 1, characterized in that each photosensor (10) has a semiconductor layer (11) having a channel region, a source electrode (12) and drain electrode (13) formed on the semiconductor layer via the channel region, a top gate electrode (21) and bottom gate electrode (22) formed at least on and below the channel region, and insulating films (15, 16) respectively formed between the channel region and the top gate electrode and bottom gate electrode, either of the top gate electrode (21) and bottom gate electrode (22) is used as a light irradiation side, and charges corresponding to a light quantity irradiated from the light irradiation side are generated and accumulated in the channel region. 9. A drive control method for a photosensor system having a photosensor array (100) constituted by two-dimensionally arraying a plurality of photosensors (10), characterized by comprising the steps of: executing pre-reading operation of reading a subject image made up of pixels corresponding to the plurality of photosensors (10) while changing an image reading sensitivity of the photosensor array (100) at a plurality of stages; extracting an image reading sensitivity having a maximum absolute difference value among absolute difference values between adjacent pixels for each image reading sensitivity in a predetermined measurement amount relating to an image pattern of the subject image read in the pre-reading operation; setting the extracted image reading sensitivity as a reading sensitivity in the reading operation of the subject image; and executing image reading operation of reading the subject image at the set reading sensitivity. 10. A method according to claim 9, characterized in that the step of executing the pre-reading operation comprises executing the pre-reading operation by setting different image reading sensitivities stepwise for respective rows of the photosensor array (100) and reading the subject image. 11. A method according to claim 9, characterized in that the predetermined measurement amount is lightness data corresponding to the image pattern of the subject image read by the pre-reading operation. 12. A method according to claim 9, characterized in that the image reading sensitivity of the photosensor array (100) is set by adjusting a charge accumulating period of the photosensor (10). 13. A method according to claim 9, characterized in that the step of extracting the image reading sensitivity comprises the sub-steps of: calculating an absolute difference value between adjacent pixels for each image reading sensitivity in the predetermined measurement amount relating to the image pattern of the subject image read by the pre-reading operation; extracting a maximum absolute difference value as a representative difference value for each image reading sensitivity from calculated absolute difference values; and extracting an image reading sensitivity corresponding to the maximum representative difference value from the extracted representative difference values for respective image reading sensitivities. 14. A method according to claim 13, characterized in that the sub-step of calculating the absolute difference value comprises calculating the absolute difference value of the predetermined measurement amount in predetermined row and column ranges of the subject image read by the pre-reading operation. 15. A method according to claim 9, characterized by further comprising the step of, in the image reading operation and the pre-reading operation of the photosensor array (100), applying to each photosensor (10) a correction signal for setting an effective voltage of a signal voltage from the photosensor (10) to an optimal value which minimizes a change in a threshold voltage of the photosensor (10). 16. A method according to claim 15, characterized in that each photosensor (10) has a semiconductor layer (11) having a channel region, a source electrode (12) and drain electrode (13) formed on the semiconductor layer via the channel region, a top gate electrode (21) and bottom gate electrode (22) formed at least on and below the channel region, and insulating films (15, 16) respectively formed between the channel region and the top gate electrode and bottom gate electrode, either of the top gate electrode (21) and bottom gate electrode (22) is used as a light irradiation side, and charges corresponding to a light quantity irradiated from the light irradiation side are generated and accumulated in the channel region.