Semiconductor integrated apparatus and black level correction method for image sensor

• US 20070075772A1
• Filed: 02/24/2006
• Published: 04/05/2007
• Est. Priority Date: 09/30/2005
• Status: Active Grant

• Current Assignee: Socionext Inc.
• Original Assignee: Fujitsu Limited
• Inventors: Higuchi, Tsuyoshi, Funakoshi, Jun, Daiku, Hiroshi, Kokubo, Asao
• Granted Patent: US 7,920,181 B2
• Time in Patent Office: Days
• US Class Current: 330/250
• CPC Class Codes: H04N 25/63 applied to dark current

Abstract

The challenge of the present invention is to suppress a variation in brightness of an image and make a reference value of a black level converge at an appropriate value in a short time. Acondition judgment circuit judges whether or not a frame of an amount of change in gains of a variable gain amplifier being equal to or greater than a threshold continues for a predefined frames or more. If a frame of an amount of change in the gains being equal to or greater than the threshold continues for the predefined frames, a black level value of the current frame is set for new black level reference. If not continues for the predetermined number, the previous black level reference value is retained in lieu of correcting the black level.

Claims

1. A semiconductor integrated apparatus, comprising:

a variable gain amplifier for amplifying a pixel value detected by an image sensor;

a black level correction circuit for judging whether or not a period of an amount of change in gains of the variable gain amplifier being equal to or greater than a predetermined value continues for a predefined period or more,

making a black level value of the image sensor which is output from the variable gain amplifier as new black level reference value if a period of an amount of change in gains of the variable gain amplifier being equal to or greater than a predetermined value continues for a predefined period or more,

correcting a black level of a valid pixel of the image sensor based on the black level reference value, or

correcting a black level of the valid pixel based on the previous black level reference value in lieu of updating it if a period of an amount of change in gains of the variable gain amplifier being equal to or greater than a predetermined value does not continue for a predefined period or more; and

an automatic gain control circuit for controlling a gain of the variable gain amplifier based on a value of a valid pixel which is corrected for a black level by the black level correction circuit.

2. The semiconductor integrated apparatus according to claim 1, wherein said black level correction circuit makes said black level value which is output from said variable gain amplifier as new black level reference value if a period of an amount of change in gains being equal to or greater than a predetermined value continues for a predefined period or more and corrects a black level of a valid pixel of said image sensor based on the black level reference value, or makes a calculated value based on the current black level value and the current black level reference value as new black level reference value if an amount of changes is less than a predetermined value and corrects a black level of the valid pixel based on the new black level reference value.

3. The semiconductor integrated apparatus according to claim 1, wherein

said black level correction circuit makes a black level value which is output from said variable gain amplifier as new black level reference value if a frame of an amount of change in gains being equal to or greater than a predetermined value continues for a predefined number of frames or more, makes a calculated value based on a black level value and said black level reference value as new black level reference value if an amount of changes is less than a predetermined value, or retains the previous black level reference value in lieu of updating it if a frame of an amount of change in a gain being equal to or greater than a predetermined value does not continue for a predefined number of frames or more.

4. The semiconductor integrated apparatus according to claim 1, wherein

said black level correction circuit comprises a gain storage circuit for storing gains of said variable gain amplifier relating to plural frames of images detected by said image sensor, a judgment circuit for calculating amounts of changes in gains of other frames vis-à

-vis a gain of a specific frame which is stored by the gain storage circuit and judging whether or not a frame of the amount of change in gains being equal to or greater than a predetermined value continues for a predefined number of frames or more, and a selection circuit for selecting a black level value output from the variable gain amplifier as new black level reference value if the judgment circuit judges that a frame of an amount of change in gains being equal to or greater than a predetermined value continues for a predefined number of frames or more, or selecting the previous black level reference value in lieu of updating it if the judgment circuit judges that a frame of an amount of change in gains being equal to or greater than a predetermined value does not continue for a predefined number of frames or more.

5. The semiconductor integrated apparatus according to claim 1, wherein

said black level correction circuit comprises:

a gain storage circuit for storing gains of said variable gain amplifier relating to plural frames of images detected by said image sensor;

a judgment circuit for calculating amounts of changes in gains of other frames vis-à

-vis a gain of a specific frame which is stored by the gain storage circuit to judge whether or not a frame of the amount of change in gains being equal to or greater than a predetermined value continues for a predefined number of frames or more; and

a selection circuit for selecting a black level value output from the variable gain amplifier as new black level reference value if the judgment circuit judges that a frame of an amount of change in gains being equal to or greater than a predetermined value continues for a predefined number of frames or more, selecting a calculated value from a black level value output from the variable gain amplifier and a black level reference value as new black level reference value if the judgment circuit judges that a frame of an amount of change in gains being equal to or greater than a predetermined value does not exist, or selecting the previous black level reference value in lieu of updating it if the judgment circuit judges that an amount of change in gains is equal to or greater than a predetermined value and that a frame of an amount of change in gains being equal to or greater than a predetermined value does not continue for a predefined number of frames or more.

6. The semiconductor integrated apparatus according to claim 1, wherein

said black level correction circuit at least comprises a first gain storage circuit for storing a gain of said variable gain amplifier of the current frame, a second gain storage circuit for storing a gain of a first previous frame, a third gain storage circuit for storing a gain of a second previous frame, a fourth gain storage circuit for storing a gain of a third previous frame, and a judgment circuit for calculating an amount of change in gains of other frames vis-à

-vis a specific frame stored by the first through fourth gain storage circuits and judging whether or not a frame of the amount of change in gains being equal to or greater than a predetermined value continues for a predefined number of frames.

7. The semiconductor integrated apparatus according to claim 1, wherein

said variable gain amplifier comprises a first variable gain amplifier for amplifying a black level value output from a shaded pixel, from light, of said image sensor, and a second variable gain amplifier for amplifying a value of a valid pixel of the image sensor;

and

said black level correction circuit at least comprises a gain storage circuit for storing gains of the first and second variable gain amplifiers relating to the current, a first previous frame, a second previous frame and a third previous frame, and a judgment circuit for calculating amounts of changes in gains of other frames vis-à

-vis a specific frame stored by the gain storage circuit and judging whether or not a frame of the amount of change in gains being equal to or greater than a predetermined value continues for a predefined number of frames or more.

8. A semiconductor integrated apparatus, comprising:

a variable gain amplifier for amplifying a pixel value detected by an image sensor;

a black level correction circuit for judging whether or not a period in which an amount of changes in black level values output from the variable gain amplifier is equal to or greater than a predetermined value continues for a predefined period or more,

making a black level value which is output from the variable gain amplifier as new black level reference value and correcting a black level of a valid pixel of the image sensor based on the black level reference value if a period in which an amount of changes in black level values output from the variable gain amplifier is equal to or greater than a predetermined value continues for a predefined period or more, or

making a calculated value from the current black level value and the current black level reference value as new black level reference value if an amount of changes in black level values is less than a predetermined value and correcting a black level of the valid pixel based on the black level reference value; and

an automatic gain control circuit for controlling a gain of the variable gain amplifier based on a value of a valid pixel which is corrected for a black level by the black level correction circuit.

9. The semiconductor integrated apparatus according to claim 8, wherein

said black level correction circuit calculates amounts of changes in black level values of a plurality of frames detected by said image sensor,

judges whether or not a period in which an amount of changes in black level values is equal to or greater than a predetermined value continues for a predefined period or more,

makes the black level value which is output from said variable gain amplifier as new black level reference value and correcting a black level of a valid pixel of the image sensor based on the black level reference value if a period in which an amount of changes in black level values is equal to or greater than a predetermined value continues for a predefined period or more, or

corrects a black level of the valid pixel based on the previous black level reference value in lieu of updating it if a period in which an amount of changes in black level values is equal to or greater than a predetermined value does not continue for a predefined period or more.

10. The semiconductor integrated apparatus according to claim 8, wherein

said black level correction circuit makes a black level value which is output from said variable gain amplifier as new black level reference value if a frame of an amount of change in black level values being equal to or greater than a predetermined value continues for a predefined number of frames or more, makes a calculated value based on a black level value and said black level reference value as new black level reference value if an amount of change in black level values is less than a predetermined value, and retains the previous black level reference value in lieu of updating it if a frame of an amount of change in black level values being equal to or greater than a predetermined value does not continue for a predefined number of frames or more.

11. The semiconductor integrated apparatus according to claim 8, wherein

said black level correction circuit comprises a storage circuit for storing black level values of a plurality of frames output from said variable gain amplifier,

a judgment circuit for calculating amounts of changes in black level values of other frames vis-à

-vis a black level value of a specific frame stored by the storage circuit and judging whether or not a frame of the amount of change being equal to or greater than a predetermined value continues for a predefined number of frames or more, and

a selection circuit for selecting a black level value which is output from the variable gain amplifier as new black level reference value if the judgment circuit judges that a frame of an amount of change in black level values being equal to or greater than a predetermined value continues for a predefined number of frames or more, or selecting the previous black level reference value in lieu of updating it if the judgment circuit judges that a frame of an amount of change in black level values being equal to or greater than a predetermined value does not continue for a predefined number of frames or more.

12. The semiconductor integrated apparatus according to claim 8, wherein

said black level correction circuit comprises a first storage circuit for storing a black level value of the current frame, a second gain storage circuit for storing a black level value of a first previous frame, a third gain storage circuit for storing a black level value of a second previous frame, a fourth gain storage circuit for storing a black level value of a third previous frame, and a judgment circuit for calculating an amount of changes in black level value of other frames vis-à

-vis a specific frame stored by the first through fourth gain storage circuits and judging whether or not a frame of the amount of changes in black level values being equal to or greater than a predetermined value continues for a predefined number of frames or more.

13. A black level correction method for an image sensor, comprising the steps of

amplifying a pixel value detected by an image sensor by using a variable gain amplifier;

and

judging whether or not a period of an amount of change in gains of the variable gain amplifier being equal to or greater than a predetermined value continues for a predefined period or more, making a black level value of the image sensor which is output from the variable gain amplifier as new black level reference value if a period of an amount of change in gains of the variable gain amplifier being equal to or greater than a predetermined value continues for a predefined period or more, correcting a black level of a valid pixel of the image sensor based on the black level reference value,

correcting a black level of the valid pixel based on the previous black level reference value in lieu of updating it if a period of an amount of change in gains of the variable gain amplifier being equal to or greater than a predetermined value does not continue for a predefined period or more.

14. The black level correction method for an image sensor according to claim 13, wherein

said step of correcting a black level is to make a black level value which is output from said variable gain amplifier as new black level reference value if a frame of an amount of change in gains being equal to or greater than a predetermined value continues for a predefined number of frames or more, make a calculated value based on a black level value and said black level reference value as new black level reference value if an amount of change in gains of each frame is less than a predetermined value ;

and

retain the previous black level reference value in lieu of updating it if a frame of an amount of change in gains being equal to or greater than a predetermined value does not continue for a predefined number of frames or more.

15. The black level correction method for an image sensor according to claim 13, wherein

said step of correcting a black level is to store a gain of said variable gain amplifier relating to plural frames of images detected by said image sensor, calculate an amount of changes in gains of other frames vis-à

-vis a gain of a specific frame which is stored, and judge whether or not a frame of the amount of changes in gain being equal to or greater than a predetermined value continues for a predefined number of frames or more ; and

select a black level value output from the variable gain amplifier as new black level reference value if a frame of an amount of change in gains being equal to or greater than a predetermined value is judged as continuing for a predefined number of frames or more, or select the previous black level reference value in lieu of updating it if a frame of an amount of change in gains being equal to or greater than a predetermined value is judged as not continuing for a predefined number of frames or more.

16. The black level correction method for an image sensor according to claim 13, wherein

said step of correcting a black level is to store, in a gain storage circuit, gains of said variable gain amplifier relating to plural frames of images detected by said image sensor, calculate amounts of changes in gains of other frames vis-à

-vis a gain of a specific frame which is stored by the gain storage circuit and judge whether or not a frame of the amount of change in gains being equal to or greater than a predetermined value continues for a predefined number of frames or more; and

select a black level value which is output from the variable gain amplifier as new black level reference value if a frame of an amount of change in gains being equal to or greater than a predetermined value is judged as continuing for a predefined number of frames or more,

select a calculated value from a black level value output from the variable gain amplifier and a black level reference value as new black level reference value if a frame of an amount of change in gains being equal to or greater than a predetermined value is judged as not existing;

or

select the previous black level reference value in lieu of updating it if an amount of change in gains is judged as being equal to or greater than a predetermined value and that a frame is judged as not continuing for a predefined number of frames or more.

17. A black level correction method for an image sensor, comprising the steps of

amplifying a pixel value detected by an image sensor by using a variable gain amplifier;

and

judging whether or not a period of an amount of change in gains of the variable gain amplifier being equal to or greater than a predetermined value continues for a predefined period or more, making a black level value of the image sensor which is output from the variable gain amplifier as new black level reference value if a period of an amount of change in gains of the variable gain amplifier being equal to or greater than a predetermined value continues for a predefined period or more; and

correcting a black level of a valid pixel of the image sensor based on the black level reference value;

or making a calculated value based on the current black level value and a black level reference value as new black level reference value if an amount of change in gains is less than a predetermined value, and correcting a black level of the valid pixel based on the black level reference value.

18. The black level correction method for an image sensor according to claim 17, wherein

said step of correcting a black level is to make a black level value which is output from said variable gain amplifier as new black level reference value if a frame of an amount of change in gains being equal to or greater than a predetermined value continues for a predefined number of frames or more, make a calculated value based on a black level value which is output from the variable gain amplifier and said black level reference value as new black level reference value if an amount of change in gains of each frame is less than a predetermined value, and retain the previous black level reference value in lieu of updating it if a frame of an amount of change in gains being equal to or greater than a predetermined value does not continue for a predefined number of frames or more.

19. The black level correction method for an image sensor according to claim 17, wherein

said step of correcting a black level is to store gains of said variable gain amplifier relating to plural frames of images detected by said image sensor, calculate amounts of changes in gains of other frames vis-à

-vis a gain of a specific frame which is stored and judge whether or not a frame of the amount of change in gains being equal to or greater than a predetermined value continues for a predefined number of frames or more; and

select a black level value which is output from the variable gain amplifier as new black level reference value if a frame of an amount of change in gains being equal to or greater than a predetermined value is judged as continuing for a predefined number of frames or more;

or select the previous black level reference value in lieu of updating it if a frame of an amount of change in gains being equal to or greater than a predetermined value is judged as not continuing for a predefined number of frames or more.