Photosensor system and drive control method thereof

• US 6,879,344 B1
• Filed: 10/31/2000
• Issued: 04/12/2005
• 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:
  US09/703,025
• Time in Patent Office: 1,624 Days
• Field of Search: 348/302, 348/308, 348/246, 348/362, 348/364, 348/365, 348/367, 348/297, 348/221.1, 348/301, 382/124
• US Class Current: 348/362
• CPC Class Codes: H04N 23/71 Circuitry for evaluating the brightness variation
• CPC Class Codes: H04N 25/53 Control of the integration time
• CPC Class Codes: H04N 25/533 by using differing integration times for different sensor regions
• CPC Class Codes: H04N 25/683 by defect estimation performed on the scene signal, e.g. real time or on the fly detection

Abstract

A photosensor system is provided which includes a photosensor array constituted by two-dimensionally arraying a plurality of photosensors, a driver circuit for supplying a drive signal to the photosensors, and a controller for controlling a reading operation of a subject image and a sensitivity setting. Before the start of normal reading operation of a subject image, a pre-reading operation of changing the image reading sensitivity at a plurality of stages for respective rows is executed. A row in an optimal image reading state is easily determined based on the dynamic range distribution of the lightness data of read image data or a dynamic range distribution from which an abnormal value deviating from the main change trend of lightness data is removed, and the linearly differentiated value of the dynamic range. An image reading sensitivity set for this row is set as an optimal sensitivity.

Claims

1. A photosensor system comprising:

a photosensor array including a plurality of photosensors in a two-dimensional array;

image reading means for reading a subject image at a predetermined reading sensitivity by the photosensor array;

pre-reading means for causing the subject image to be read by different regions of the photosensor array using different image reading sensitivities in a plurality of stages, prior to an image reading operation by the image reading means;

optimal 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 relate to image patterns of the subject image read by said pre-reading means and which correspond to the different regions of the photosensor array; and

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

2. The system according to claim 1, wherein the image reading operation is executed by setting the different image reading sensitivities stepwise for respective rows of the photosensor array and reading the subject image.

3. 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 a pre-reading operation of the pre-reading means.

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

5. The system according to claim 1, effective voltage adjustment means for applying to each photosensor a correction signal for setting effective voltages of signal voltages applied to each photosensor to optimal values.

6. The system according to claim 1, wherein said 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 pre-reading means;

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 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.

7. The system according to claim 6, wherein said measurement amount comparison means extracts the maximum and minimum values of the measurement amount in a predetermined column range of each row.

8. The system according to claim 1, wherein said reading sensitivity extraction means comprises:

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 pre-reading means; and

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.

9. The system according to claim 8, wherein said displacement calculation means calculates a differentiated value of the measurement amount on predetermined columns of each row in the different regions.

10. The system according to claim 1, wherein said 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 pre-reading means;

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 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.

11. The system according to claim 1, further comprising 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 pre-reading means, for each of the different image sensitivities.

12. The system according to claim 11, wherein said 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.

13. 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 pre-reading means;

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

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

14. 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.

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

executing a pre-reading operation of causing a subject image to be read by different regions of the photosensor array using different image reading sensitivities in a plurality of stages, prior to an image reading operation;

extracting an image reading sensitivity suitable for the image reading operation of the subject image based on a comparison of predetermined measurement amounts which relate to mage patterns of the subject image read by the pre-reading operation and which correspond to the different regions of the photosensor array;

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.

16. The method according to claim 15, wherein the pre-reading operation is executed by the setting different image reading sensitivities stepwise for respective rows of the photosensor array and reading the subject image.

17. The method according to claim 15, wherein the predetermined measurement amounts comprise lightness data corresponding to the image pattern of the subject image read by the pre-reading operation.

18. The method according to claim 15, wherein the image reading sensitivity of the photosensor array is set by adjusting a photosensor charge accumulating period.

19. The method according to claim 15, wherein 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 pre-reading operation;

calculating a dynamic range of the measurement amount based on the maximum and minimum values of the measurement amount extracted for 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 image reading sensitivities.

20. The method according to claim 15, wherein 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 pre-reading operation; and

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

21. The method according to claim 15, wherein 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 pre-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.

22. The method according to claim 15, wherein the step of extracting the image reading sensitivity comprises the steps of:

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 pre-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, 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

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

23. The method according to claim 15, 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.

24. The method according to claim 23, 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.

25. The method according to claim 15, 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 plate 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.