Photosensor system and drive control method thereof

• US 6,867,811 B2
• Filed: 10/30/2001
• Issued: 03/15/2005
• Est. Priority Date: 11/08/1999
• Status: Expired due to Fees

• Current Assignee: Casio Computer Company Limited
• Original Assignee: Casio Computer Company Limited
• Inventors: Nakamura, Yoshiaki, Koshizuka, Yasuo
• Primary Examiner(s): Christensen, Andrew
• Assistant Examiner(s): Ye, Lin
• Application Number:
  US10/013,979
• Publication Number:
  US 20020085109A1
• Time in Patent Office: 1,232 Days
• Field of Search: 348/302, 348/308, 348/246, 348/362, 348/364, 348/365, 348/367, 348/297, 348/221.1, 382/124
• US Class Current: 348/362
• 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 including a plurality of photosensors in a two-dimensional array;

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

a sensitivity-adjusting reader which causes the subject image to be read by a specific region of the photosensor array to read the subject image at a plurality of different image reading sensitivities at a corresponding plurality of stages for the specific region of the photosensor array;

optimal image reading sensitivity extraction means for extracting an optimal image reading sensitivity suitable for the image reading operation based on a comparison of predetermined measurement amounts which correspond to the plurality of different image reading sensitivities and which relate to an image pattern of the subject image corresponding to the specific region of the photosensor array and 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. The 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 at least one specific row of the photosensor array.

3. The system according to claim 2, wherein the photosensors of the specific row section of the photosensor array are photosensors of one specific row.

4. The system according to claim 2, further comprising abnormal pixel determining means for determining whether the specific row section contains 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 changed.

5. The system according to claim 4, further comprising sensitivity-adjusting read controlling means for executing the sensitivity-adjusting reading operation with respect to a different specific row section if the abnormal pixel determining means determines that an abnormal pixel exists in the specific row section.

6. The system according to claim 1, wherein the predetermined measurement amounts comprise lightness data corresponding to the image pattern of the subject image read by the sensitivity-adjusting reader.

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

8. The system according to claim 1, further comprising an effective voltage adjuster which applies to each photosensor a correction signal for setting effective voltages of signal voltages applied to each photosensor to optimal values.

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

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

dynamic range calculation means for calculating a dynamic range of the measurement amount based on the maximum and minimum values of the measurement amount extracted for said each of the different image reading sensitivities; and

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

10. The system according to claim 9, wherein the measurement amount comparison means extracts the maximum and minimum values of the measurement amount in a predetermined column range of each row in the specific region.

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

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

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

12. The system according to claim 11, wherein the displacement calculation means calculates a differentiated value of a measurement amount on predetermined columns of each row in the specific region.

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

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

a dynamic range calculation means for calculating a dynamic range of the measurement amount based on the maximum and minimum values of the measurement amount extracted for said each of the different image reading sensitivities; and

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

14. The system according to claim 1, further comprising an abnormal value removing means for removing an abnormal value deviating from a main change trend of a measurement amount, from a measurement amount relating to the image pattern of the subject image read by the sensitivity-adjusting reader for each of the different image reading sensitivities.

15. The system according to claim 14, 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.

16. The system according to claim 1, which further comprises:

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

dynamic range calculation means for calculating a dynamic range of the measurement amount based on the maximum and minimum values of the measurement amount extracted for said each of the different image reading sensitivities;

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

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

17. The system according to claim 1, wherein:

each of the photosensors comprises;

(i) a source electrode and drain electrode, (ii) a channel region made from a semiconductor layer formed between the source electrode and drain electrode, and (ii) a top gate electrode and bottom gate electrode formed respectively on and below the channel region with insulating films provided between the top gate electrode and bottom gate electrode and the channel region,

one of the top gate electrode side and bottom gate electrode side is 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.

18. A drive control method for a photosensor system including a plurality of photosensors in a two-dimensional array, said method comprising:

executing a sensitivity-adjusting reading operation of causing a subject image to be read by a specific region of the photosensor array at a plurality of different image reading sensitivities at a corresponding plurality of stages for the specific region of the photosensor array;

extracting an image reading sensitivity suitable for an image reading operation of the subject image based on a comparison of predetermined measurement amounts which correspond to the plurality of different image reading sensitivities and which relate to an image pattern of the subject image corresponding to the specific region of the photosensor array and 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 the image reading operation of reading the subject image at the set reading sensitivity.

19. The method according to claim 18, 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 at least one specific row of the photosensor array.

20. The method according to claim 19, wherein the photosensors of the specific row section of the photosensor array are photosensors of one specific row.

21. The method according to claim 19, further comprising determining whether the specific row section contains 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 changed.

22. The method according to claim 21, further comprising executing the sensitivity-adjusting reading operation with respect to a different specific row section if an abnormal pixel exists in the specific row section.

23. The method according to claim 18, wherein the predetermined measurement amounts comprise lightness data corresponding to the image pattern of the subject image read by the sensitivity-adjusting reading operation.

24. The method according to claim 18, wherein the image reading sensitivity of the photosensor array is set by adjusting a photosensor charge accumulating period.

25. The method according to claim 18, wherein the extracting the image reading sensitivity comprises:

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

calculating a dynamic range of the measurement amount based on the maximum and minimum values of the measurement amount extracted for said each of the different image reading sensitivities; and

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

26. The method according to claim 18, wherein the extracting the image reading sensitivity comprises:

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

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

27. The method according to claim 18, wherein the extracting the image reading sensitivity comprises:

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

calculating a dynamic range of the measurement amount based on the maximum and minimum values of the measurement amount extracted for said each of the different image reading sensitivities; and

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

28. The method according to claim 18, wherein the extracting the image reading sensitivity comprises:

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

calculating a dynamic range of the measurement amount based on the maximum and minimum values of the measurement amount extracted for said each of the different image reading sensitivities;

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

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

29. The method according to claim 18, wherein the extracting the image reading sensitivity comprises removing an abnormal value deviating from a main change trend of a measurement amount, from a measurement amount relating to the image pattern of the subject image for each of the different image reading sensitivities.

30. The method according to claim 29, 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.

31. The method according to claim 18, wherein:

each of the photosensors comprises;

(i) a source electrode and drain electrode, (ii) a channel region made from a semiconductor layer formed between the source electrode and drain electrode, and (ii) a top gate electrode and bottom gate electrode formed respectively on and below the channel region with insulating films provided between the top gate electrode and bottom gate electrode and the channel region,

one of the top gate electrode side and bottom gate electrode side is 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.