Photosensor system and drive control method thereof

• US 20020085109A1
• Filed: 10/30/2001
• Published: 07/04/2002
• Est. Priority Date: 11/08/1999
• Status: Active Grant

• Current Assignee: Casio Computer Company Limited
• Original Assignee: Casio Computer Company Limited
• Inventors: Nakamura, Yoshiaki, Koshizuka, Yasuo
• Granted Patent: US 6,867,811 B2
• Time in Patent Office: Days
• US Class Current: 348/302
• CPC Class Codes: H04N 23/71 Circuitry for evaluating the brightness variation

Abstract

A photosensor system performs a sensitivity-adjusting reading operation with respect to a subject image, while simultaneously changing the image reading sensitivity stepwise for each of rows of a photosensor array or for specific rows thereof. The dynamic ranges of the lightness data on the read subject image are checked to see how they are distributed in relation to the image reading sensitivities. On the basis of this distribution, an image reading sensitivity that contributes to an optimal image reading state is extracted as an optimal image reading sensitivity.

Claims

1. A photosensor system comprising

a photosensor array constituted by two-dimensionally arraying a plurality of photosensors,

an image reader which reads a subject image at a predetermined reading sensitivity by the photosensor array:

sensitivity-adjusting reader which reads the subject image while changing an image reading sensitivity of the photosensor array at a plurality of stages;

optimal image reading sensitivity extraction means for extracting an optimal image reading sensitivity suitable for the image reading operation on the basis of a predetermined measurement amount relating to an image pattern of the subject image read by the sensitivity-adjusting reader; and

reading sensitivity setting means for setting the optimal image reading sensitivity to a reading sensitivity of the image reader.

2. A system according to claim 1, wherein the sensitivity-adjusting reader reads the subject image by setting different image reading sensitivities stepwise for respective rows of the photosensor array.

3. A system according to claim 1, wherein the sensitivity-adjusting reader reads the subject image by setting different image reading sensitivities stepwise for photosensors of a specific row section of one to several specific rows of the photosensor array.

4. A system according to claim 3, the photosensors of the specific row section of the photosensor array are photosensors of one specific row.

5. A system according to claim 3, further comprising abnormal pixel determining means for determining whether the specific row section contain an abnormal pixel by checking whether the measurement amount corresponding to one column of the specific row section has changed each time the image reading sensitivities are switched from one to another.

6. A system according to claim 5, further comprising sensitivity-adjusting read controlling means for executing the sensitivity-adjusting reading operation with respect to a specific row section other than the specific row section if the abnormal pixel determining means determines that the abnormal pixel exists in the specific row section.

7. A system according to claim 1, wherein the predetermined measurement amount in the optimal reading sensitivity extraction means is lightness data corresponding to the image pattern of the subject image read by the sensitivity-adjusting reader.

8. A system according to claim 1, wherein the image reading sensitivity of the photosensor array is set by adjusting a charge accumulating period of the photosensor.

9. A system according to claim 1, which further comprises, in the image reader and the sensitivity-adjusting reader in the photosensor array, an effective voltage adjuster which applies to each photosensor a correction signal for setting to optimal values effective voltages of signal voltages applied to each photosensor.

10. A system according to claim 1, wherein the optimal reading sensitivity extraction means comprises:

measurement amount comparison means for extracting maximum and minimum values of the measurement amount relating to the image pattern of the subject image for each image reading sensitivity on the basis of the subject image read by a the sensitivity-adjusting reader;

dynamic range calculation means for calculating a dynamic range of the measurement amount on the basis of the maximum and minimum values of the measurement amount extracted for each image reading sensitivity; and

maximum dynamic range extraction means for extracting an image reading sensitivity having a maximum dynamic range among dynamic ranges of measurement amounts calculated for each image reading sensitivity.

11. A system according to claim 10, wherein the measurement amount comparison means extracts the maximum and minimum values of the measurement amount in a predetermined column range of each row.

12. A system according to claim 1, wherein the optimal reading sensitivity extraction means comprises:

displacement calculation means for calculating a displacement of the measurement amount relating to the image pattern of the subject image between image reading sensitivities on the basis of the subject image read by the sensitivity-adjusting reader; and

maximum displacement extraction means for extracting an image reading sensitivity having a maximum displacement among displacements of measurement amounts between image reading sensitivities.

13. A system according to claim 12, wherein the displacement calculation means calculates a differentiated value of the measurement amount on predetermined columns of each row.

14. A system according to claim 1, wherein the optimal reading sensitivity extraction means comprises:

measurement amount comparison means for extracting maximum and minimum values of the measurement amount relating to the image pattern of the subject image for each image reading sensitivity on the basis of the subject image read by the sensitivity-adjusting reader;

dynamic range calculation means for calculating a dynamic range of the measurement amount on the basis of the maximum and minimum values of the measurement amount extracted for each image reading sensitivity; and

maximum dynamic range extraction means for extracting an image reading sensitivity at which the dynamic range of the measurement amount for each image reading sensitivity maximizes and a displacement of the dynamic range between image reading sensitivities minimizes.

15. A system according to claim 1, which further comprises abnormal value removing means for removing an abnormal value deviating from a main change trend of the measurement amount, from the measurement amount relating to the image pattern of the subject image read by the sensitivity-adjusting reader.

16. A system according to claim 15, wherein the abnormal value removing means removes the abnormal value by performing Fourier transformation for the measurement amount and removing a predetermined high-frequency component from the frequency-converted measurement amount.

17. A system according to claim 1, which further comprises:

measurement amount comparison means for extracting maximum and minimum values of the measurement amount relating to the image pattern of the subject image for each image reading sensitivity on the basis of the subject image read by the sensitivity-adjusting reader;

a dynamic range calculation means for which calculating a dynamic range of the measurement amount on the basis of the maximum and minimum values of the measurement amount extracted for each image reading sensitivity;

specific value extraction means for extracting for each image reading sensitivity a specific value at which the dynamic range of the measurement amount for each image reading sensitivity maximizes and a displacement of the dynamic range between image reading sensitivities maximizes; and

abnormality determination means for which determining presence/absence of an abnormality contained in the subject image on the basis of the specific value.

18. A system according to claim 1, wherein

each of the photosensors has a source electrode and drain electrode formed via a channel region made from a semiconductor layer, and a top gate electrode and bottom gate electrode formed at least on and below the channel region via insulating films,

either of the top gate electrode and bottom gate electrode 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.

20. A method according to claim 19, wherein the sensitivity-adjusting reading operation is executed by setting different image reading sensitivities stepwise for respective rows of the photosensor array and reading the subject image.

21. A method according to claim 19, wherein the sensitivity-adjusting reading operation is performed by reading the subject image at different image reading sensitivities that are set stepwise for photosensors of a specific row section of one to several specific rows of the photosensor array.

22. A method according to claim 21, wherein the photosensors of the specific row section of the photosensor array are photosensors of one specific row.

23. A method according to claim 21, further comprising determining whether the specific row section contain an abnormal pixel by checking whether the measurement amount corresponding to one column of the specific row section has changed each time the image reading sensitivities are switched from one to another.

24. A method according to claim 23, further comprising executing the sensitivity-adjusting reading operation with respect to a specific row section other than the specific row section if the abnormal pixel determining step determines that the abnormal pixel exists in the one specific row section.

25. A method according to claim 19, wherein the predetermined measurement amount is lightness data corresponding to the image pattern of the subject image read by the sensitivity-adjusting reading operation.

26. A method according to claim 19, wherein the image reading sensitivity of the photosensor array is set by adjusting a charge accumulating period of the photosensor.

27. A method according to claim 19, wherein the extracting the image reading sensitivity comprises:

extracting maximum and minimum values of the measurement amount relating to the image pattern of the subject image for each image reading sensitivity on the basis of the subject image read by the sensitivity-adjusting reading operation;

calculating a dynamic range of the measurement amount on the basis of the maximum and minimum values of the measurement amount extracted for each image reading sensitivity; and

extracting an image reading sensitivity having a maximum dynamic range among dynamic ranges of measurement amounts calculated for each image reading sensitivity.

28. A method according to claim 19, wherein the extracting the image reading sensitivity comprises:

calculating a displacement of the measurement amount relating to the image pattern of the subject image between image reading sensitivities on the basis of the subject image read by the sensitivity-adjusting reading operation; and

extracting an image reading sensitivity at which a displacement of the measurement amount between image reading sensitivities maximizes.

29. A method according to claim 19, wherein the extracting the image reading sensitivity comprises:

extracting maximum and minimum values of the measurement amount relating to the image pattern of the subject image for each image reading sensitivity on the basis of the subject image read by the sensitivity-adjusting reading operation;

calculating a dynamic range of the measurement amount on the basis of the maximum and minimum values of the measurement amount extracted for each image reading sensitivity; and

extracting an image reading sensitivity at which the dynamic range of the measurement amount for each image reading sensitivity maximizes and a displacement of the dynamic range between image reading sensitivities minimizes.

30. A method according to claim 19, wherein the extracting the image reading sensitivity comprises:

extracting maximum and minimum values of the measurement amount relating to the image pattern of the subject image for each image reading sensitivity on the basis of the subject image read by the sensitivity-adjusting reading operation;

calculating a dynamic range of the measurement amount on the basis of the maximum and minimum values of the measurement amount extracted for each image reading sensitivity;

extracting a specific value at which the dynamic range of the measurement amount for each image reading sensitivity maximizes and a displacement of the dynamic range between image reading sensitivities maximizes; and

determining presence/absence of an abnormality contained in the subject image on the basis of the specific value.

31. A method according to claim 19, wherein the extracting the image reading sensitivity comprises:

removing an abnormal value deviating from a main change trend of the measurement amount, from the measurement amount relating to the image pattern of the subject image for each image reading sensitivity.

32. A method according to claim 31, wherein the removing the abnormal value from the measurement amount comprises:

performing Fourier transformation for the measurement amount and removing a predetermined high-frequency component from the frequency-converted measurement amount.

33. A method according to claim 19, wherein

each of the photosensors has a source electrode and drain electrode formed via a channel region made from a semiconductor layer, and a top gate electrode and bottom gate electrode formed at least on and below the channel region via insulating films,

either of the top gate electrode and bottom gate electrode 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.

19. A drive control method for a photosensor system having a photosensor array constituted by two-dimensionally arraying a plurality of photosensors comprising:

executing a sensitivity-adjusting reading operation of reading a subject image while changing an image reading sensitivity of the photosensor array at a plurality of stages;

extracting an image reading sensitivity suitable for reading operation of the subject image on the basis of a predetermined measurement amount relating to an image pattern of the subject image read by the sensitivity-adjusting 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.