Method of reducing flicker noises of X-Y address type solid-state image pickup device

• US 20020158971A1
• Filed: 12/12/2001
• Published: 10/31/2002
• Est. Priority Date: 04/26/2001
• Status: Active Grant

• Current Assignee: Socionext Inc.
• Original Assignee: Fujitsu Limited
• Inventors: Daiku, Hiroshi, Sugiyama, Iwao
• Granted Patent: US 7,106,368 B2
• Time in Patent Office: Days
• US Class Current: 348/226.1
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/73 by influencing the exposure time
• CPC Class Codes: H04N 23/745 Detection of flicker frequency or suppression of flicker wherein the flicker is caused by illumination, e.g. due to fluorescent tube illumination or pulsed LED illumination

Abstract

It is an object of the invention to provide a method of reducing flicker noises in an X-Y address type solid-state image pickup device for reducing flicker noises generated by a fluorescent light for room illumination when taking a picture in door.

A configuration is provided in which signal storage time ts resulting in no flicker noise under a fluorescent lamp having an emission frequency of 120 Hz is preset (step S1); average luminance of image data is calculated for each frame in a predetermined average luminance detection area allocated in the frame (step S2); a difference in average luminance is calculated between frames (step S3); and the signal storage time ts is changed based on the difference in luminance (steps S4, S5 and S6).

Claims

1. A method of reducing flicker noises attributable to the emission frequency of illumination light generated in an X-Y address type image pickup device having a plurality of pixels for performing photoelectric conversion of incident light in a predetermined signal storage time and outputting image data, the method comprising the steps of:

calculating average luminance of the image data for each frame in a predetermined average luminance detection area allocated in the frame;

calculating a difference in the average luminance between frames; and

changing the signal storage time based on the difference in luminance.

2. A method of reducing flicker noises in an X-Y address type solid-state image pickup device according to claim 1, wherein the average luminance detection area is constituted by a plurality of pixels connected to a predetermined number of horizontal selection lines adjacent to each other.

3. A method of reducing flicker noises in an X-Y address type solid-state image pickup device according to claim 2, wherein the predetermined number is set at a value that does not coincide with an integral multiple of the period of irregularities of luminance generated by the flicker noises.

4. A method of reducing flicker noises in an X-Y address type solid-state image pickup device according to claim 3, wherein the predetermined number is set at a value other than 3/10 times, 6/10 times or 9/10 times the total number of horizontal selection lines in one frame in the case of a frame frequency of 30 Hz.

5. A method of reducing flicker noises in an X-Y address type solid-state image pickup device according to claim 4, wherein the average luminance detection area is set in one, two or three locations in one frame at an interval that is 3/10 times the total number of horizontal selection lines.

10. A method of reducing flicker noises in an X-Y address type solid-state image pickup device according to claim 1 or 6, comprising the steps of:

presetting a first signal storage time which allows reduction of flicker noises under illumination light having a first emission frequency; and

changing the signal storage time to a second signal storage time which allows reduction of flicker noises under illumination light having a second emission frequency when the difference in luminance or sum-of-product calculation value exceeds a predetermined threshold value.

11. A method of reducing flicker noises in an X-Y address type solid-state image pickup device according to claim 10, wherein the first emission frequency is 120 Hz and the second emission frequency is 100 Hz.

12. A method of reducing flicker noises in an X-Y address type solid-state image pickup device according to claim 11, wherein the first signal storage time is set at any of {fraction (1/120)}, {fraction (2/120)}, {fraction (3/120)} or {fraction (4/120)} sec. and wherein the second signal storage time is set at any of {fraction (1/100)}, {fraction (2/100)} or {fraction (3/100)} sec.

14. A method of reducing flicker noises in an X-Y address type solid-state image pickup device according to claim 1 or 6, wherein the alteration of the signal storage time based on the difference in luminance or sum-of-product calculation value is carried out at least when the power supply of the X-Y address type solid-state image pickup device is turned on.

6. A method of reducing flicker noises attributable to the emission frequency of illumination light generated in an X-Y address type image pickup device having a plurality of pixels for performing photoelectric conversion of incident light in a predetermined signal storage time and outputting image data, the method comprising the steps of:

providing two average luminance detection areas in each frame and calculating average luminance of the image data in the two average luminance detecting areas of a plurality of frames;

performing a sum-of-product calculating process on the plurality of values of average luminance to calculate a sum of products; and

changing the signal storage time based on the sum of products.

7. A method of reducing flicker noises in an X-Y address type solid-state image pickup device according to claim 6, wherein one horizontal selection line is allocated as each of the two average luminance detection areas.

8. A method of reducing flicker noises in an X-Y address type solid-state image pickup device according to claim 7, wherein the interval between the two average luminance detection areas is set as V×

(½

−

(remainder of A/B))/(A/B) where A represents the emission frequency (Hz);

B represents the frame frequency (Hz) of the X-Y address type solid-state image pickup device; and

V represents the total number of horizontal selection lines.

9. A method of reducing flicker noises in an X-Y address type solid-state image pickup device according to claim 8, wherein the interval between the two average luminance detection areas is set at 1/20 times the total number V of horizontal selection lines where A=100 Hz and B=30 Hz.

13. A method of reducing flicker noises in an X-Y address type solid-state image pickup device according to claim 6, wherein sum-of-product coefficients used in the sum-of-product calculating process are determined such that each group of coefficients total at 0 (zero) for both of sine terms and cosine terms.