Source: https://patents.google.com/patent/US20070075772A1/en
Timestamp: 2019-09-21 17:44:56
Document Index: 334806999

Matched Legal Cases: ['Application No. 2005', 'art 11', 'art 11', 'art 11', 'art 11', 'art 11', 'art 11', 'art 11', 'art 11', 'art 11', 'art 11']

US20070075772A1 - Semiconductor integrated apparatus and black level correction method for image sensor - Google Patents
Semiconductor integrated apparatus and black level correction method for image sensor Download PDF
US20070075772A1
US20070075772A1 US11/360,673 US36067306A US2007075772A1 US 20070075772 A1 US20070075772 A1 US 20070075772A1 US 36067306 A US36067306 A US 36067306A US 2007075772 A1 US2007075772 A1 US 2007075772A1
US11/360,673
US7920181B2 (en
2005-09-30 Priority to JP2005-288744 priority Critical
2005-09-30 Priority to JP2005288744A priority patent/JP4928765B2/en
2006-02-24 Assigned to FUJITSU LIMITED reassignment FUJITSU LIMITED ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: DAIKU, HIROSHI, FUNAKOSHI, JUN, HIGUCHI, TSUYOSHI, KOKUBO, ASAO
2007-04-05 Publication of US20070075772A1 publication Critical patent/US20070075772A1/en
2011-04-05 Publication of US7920181B2 publication Critical patent/US7920181B2/en
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.
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2005-288744 filed on Sep. 30, 2005, the entire contents of which are incorporated herein by reference.
The image sensor 11 comprises the n by n number of pixels, lets a part 11 a thereof shaded from light (simply “shaded part 11 a” hereinafter), and constitutes an imaging-use sensor by the other part (called “imaging part” hereinafter) 11 b. The pixels of a shaded part 11 a are used for figuring out the reference value for a black level at a black level correction circuit 13 described later.
Shift registers 14 and 15 are circuits for addressing a line and a column of the image sensor 11 and pixel values of the lines and columns addressed by the shift registers 14 and 15 are transmitted in sequence to be output to A/D (analog to digital) converters 12 a and 12 b.
A black level correction circuit 13 figures out an average of black level pixel values for one line output from the shaded part 11 a of the image sensor 11 as a black level reference value, and outputs, to an automatic gain control (AGC) circuit 16 and a color processing block 17, the difference between the pixels value output from the imaging part 11 b and the black level reference value.
FIGS. 3, 4 and 5 show an A/D converted output code of a black level pixel value output from the shaded part 11 a , that (at a pre-correction black level) of a value of valid pixels of the imaging part 11 b after A/D converting and an output code of a post-correction valid pixel of a black level, which are all shown by a frame, in the case of imaging the same image by the image sensor 11.
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.
In the semiconductor integrated apparatus according to the present invention, the black level correction circuit comprises a gain storage circuit for storing gains of the variable gain amplifier relating to plural frames of images detected by the 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 a gain 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.
In the semiconductor integrated apparatus according to the present invention, the black level correction circuit comprises a gain storage circuit for storing gains of the variable gain amplifier relating to plural frames of images detected by the 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 changes 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.
In the semiconductor integrated apparatus according to the present invention, the black level correction circuit at least comprises a first gain storage circuit for storing a gain of the 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 amounts of changes 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.
In the semiconductor integrated apparatus according to the present invention, the variable gain amplifier comprises a first variable gain amplifier for amplifying a black level value output from a shaded pixel, from light, of the image sensor, and a second variable gain amplifier for amplifying a value of a valid pixel of the image sensor; and the 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.
FIG. 1 shows a conventional image sensor and black level correction circuit;
The following is a detailed description of the preferred embodiment of the present invention while referring to the accompanying drawings. FIG. 6 shows a fundamental comprisal of a semiconductor integrated apparatus according to the present embodiment.
A black level pixel value output from a shaded part from light 11 a (simply a “shaded part 11 a” hereinafter) of an image sensor 11 (refer to FIG. 1) is amplified by a variable gain amplifier 22 and converted to digital image data by an A/D converter 23. Meanwhile, a pixel value of a valid pixel output from an imaging part 11 b of the image sensor 11 is amplified by a variable gain amplifier 24 and converted to digital valid image data by an A/D converter 25.
The condition judgment circuit 34 retains the past gains of the variable gain amplifiers 22 and 24 for a frame to be judged by a number which is stored by the register 30, judges as to which condition it applies to by judging whether or not amounts of changes in gains of other frames vis-à-vis a gain of a specific frame is equal to or greater than a preset threshold value and output the judgment result to the black reference data calculation circuit 35.
For example, in the case of a number of frames to be judged is “2” when the condition judgment circuit 34 judges an amount of change in a gain, a signal is output for making the average of the black level data of the current frame selected as new black reference data if the amount of change in gains (i.e., the absolute value of the gain a minus the gain c) which is a result of subtracting the gain of the second previous frame (i.e., the gain c) from the current gain (i.e., the gain a) is equal to or greater than a threshold value and also if an amount of change in gains (i.e., the absolute value of the gain b minus gain c) which is a result of subtracting the gain of the second previous frame (i.e., the gain c) from the first previous frame (i. e., the gain b) is equal to or greater than a threshold value.
And in the case of a number of frames to be judged being “L (≧3) ”, judged are whether or not an amount of change in gains (i.e., the gain a minus the gain L plus 1) which is a result of subtracting the gain of the L plus one previous frame (i.e., the gain L+1) from the current gain (i.e., the gain a) is equal to or greater than a threshold value, an amount of change in gains (i.e., the gain b minus the gain L+1) which is a result of subtracting the gain of the L− previous frame from that of the first previous frame (i.e., the gainb) is equal to or greater than a threshold value, omitting frames in between, and an amount of change in gains (i.e., the gain L minus the gain L+1) which is a result of subtracting the gain of the L− previous frame (i.e., the gain L+1) from that of the L−1 previous frame (i.e., the gain L) is equal to or greater than a threshold value.
The weighted average calculation circuit 52 comprises a multiplication circuit 59 for multiplying an average value of black level data calculated at the average calculation circuit 51 by a weighting value N stored by the register 31, a multiplier 60 for multiplying new black reference data latched by the latch circuit 54 by a weighting value M stored by the register 32, an adder 62 for adding the multiplication result of the multiplication circuit 59 and that of the multiplier 60, an adder 63 for adding the weighing values N and M, and a divider 64 for dividing the addition result of the adder 62 by the “N+M”.
In the weighted average calculation circuit 52, an average is calculated by dividing, by weighting values “N+M”, a result of adding a value obtained by multiplying the average value of the black level date for one line by the weighting value N and that obtained by multiplying the black reference data by the weighting value M.
First is to obtain black level data output from the A/D converter 23 (S11 shown in FIG. 11). Next is to calculate an average value of black level data for one line (S12). Next is to judge whether or not a gain difference is equal to or greater than a threshold value based on a number of frames to be judged. For example, in the case of the number of frames to be judged being “3”, what is judged is whether or not an absolute value (abs) of the difference (i.e., a gain a minus gain d) between the current gain (i.e., the gain a) and gain of the third previous frame (i.e., the gain d) of the variable gain amplifiers 22 and 24 is equal to or greater than a threshold value, that is, whether or not an amount of change in gains of the current frame vis-à-vis a gain of the third previous frame is equal to or greater than the threshold value (S13).
If the amount of change in gains of the current frame is judged as being equal to or greater than the threshold value in the step S13 (“yes” for S13), proceed to the step S14 to judge whether or not the absolute value of the difference between a gain (i.e., a gain b) of the first previous frame and that of the third previous frame (i.e., the gain b minus the gain d) is equal to or greater than a threshold value, that is, whether or not the amount of change in gains of the first previous frame is equal to or greater than the threshold value.
If the step S14 judges that the amount of change in gains of the first previous frame is equal to or greater than the threshold value (“yes” for S14), proceed to the step S15 to judge whether or not the absolute value of the difference between a gain (i.e., a gain c) of the second previous frame and that of the third previous frame (i.e., the gain c minus the gain d) is equal to or greater than a threshold value, that is, whether or not the amount of change in gains of the second previous frame is equal to or greater than the threshold value.
If the step S15 judges that the amount of change in gains of the second previous frame is equal to or greater than the threshold value (“yes” for S15), proceed to the step S16 to set the average value of black level data of the current frame as new black reference data.
Meanwhile, if the step S13 judges that the difference between the gain of the current variable gain amplifiers 22 and 24 and that of the third previous frame is smaller than the threshold value (“no” for S13), proceed to the step S17 to judge whether or not the absolute value of the difference in gains of the first previous frame and third previous frame is smaller than the threshold value, that is, whether or not an amount of change in gains of the first previous frame is smaller than the threshold value.
If the step S17 judges that the amount of change in gains of the first previous frame is smaller than the threshold value (“yes” for S17), proceed to the step S18 to judge whether or not the absolute value of the difference in gains of the second previous frame and third previous frame is smaller than a threshold value, that is, whether or not an amount of change in gains of the second previous frame is smaller than the threshold value.
If the step S18 judges that the amount of change in gains of the second previous frame is smaller than the threshold value (“yes” for S18), proceed to the step S19 to divide, by an “N+M”, an added value of a value which is the result of multiplying the average value of the current black level by the N and value which is the result of multiplying the previous black reference data by the M, followed by setting the value obtained by the division as new black reference data.
FIG. 12 shows results of judging, with a threshold value of judgment reference for an amount of change in gains being “6”, as “condition one” if a frame of an amount of change in gains being equal to or greater than a threshold value continues for the number of frames to be judged or more, as “condition two” if a frame of an amount of change in gains being equal to or greater than a threshold value does not exist and as “condition three” if a frame of an amount of change in gains being equal to or greater than a threshold value does not continue for the number of frames to be judged or more. Also shown here are the case of the number of frames to be judged are “1”, “2” and “3”.
Note that the “condition one” is defined as the case of selecting an average value of black level data of the current frame as new black reference data. The “condition two” is defined as the case of a value, which is an added value of a value multiplying the current black level data by a predetermined value N and a value multiplying black reference data by a predetermined value M, then divided by an “N+M” and selecting, and outputting, the division result value as black reference data. The “condition three” is defined as the case of selecting, and outputting, the previous black reference data in lieu of updating it.
Let it describe the case of a gain a of the current frame being “0”, a gain b of the first previous frame being “0”, a gain c of the second previous frame being “0”, and a gain d of the third previous frame being “0” as shown by FIG. 12 (1).
In this case, amounts of changes in gains of the current frame, first previous frame, second previous frame are all smaller than the threshold value “6”. Accordingly the judgment results are all “condition two.”
Next, let it describe the case of a gain a of the current frame being “11” and gains b, c and d of the other frames being “0” as shown by FIG. 12 (2). In this case, the amount of change in gains of the gain a of the current frame with the gain d being the reference is “11” which is more than the threshold value “6”.
In this case, when the number of frames to be judged is “1”, the number of frames of an amount of change in gains being equal to or greater than the threshold value “6” is “1”, satisfying a judgment condition for the number of frames and accordingly the judgment result of the condition judgment circuit 34 resulting in a “condition one”.
When the number of frames to be judged is “2”, the number of frames of an amount of change in gains being equal to or greater than the threshold value “6” is “1”, falling short of the number of frames to be judged as “2”, hence the judgment result in a “condition three”.
Likewise when the number of frames to be judged is “3”, the number of frames of an amount of change in gains being equal to or greater than the threshold value “6” falls short of the number of frames to be judged as “3”, hence the judgment resulting in a “condition three”.
Let it then describe the case of a gain a of the current frame being “13”, a gain b of the first previous frame being “11”, a gain c of the second previous frame being “11”, and a gain d of the third previous frame being “0” as shown by FIG. 12 (3).
In this case, when the number of frames to be judged is “1”, the difference in gains between the gain a of the current frame and gain b of the first previous frame is “1” and therefore the amount of change in gains is smaller than the threshold value “6”, hence the judgment resulting in a “condition two”.
When the number of frames to be judged is “2”, the difference in gains between the gain a of the current frame and gain c of the second previous frame is “2”, and the difference in gains between the gain b of the first previous frame and gain c of the second previous frame is “1” and therefore both of the amount of change in gains is smaller than the threshold value “6”, hence the judgment resulting in a “condition two”.
When the number of frames to be judged is “3”, the difference in gains between the gain a of the current frame and gain d of the third previous frame is “13”, the gain difference between the gain b and gain d is “12”, the gain difference between the gain c and gain d is “11” and therefore the frames of the amount of change in gains being equal to or greater than the threshold value “6” continue for the three frames or more, hence the judgment resulting in a “condition one”.
FIG. 13 shows another example of a condition judgment circuit, specifically showing a circuit diagram of a condition judgment circuit 71 with the number of frames to be judged being “2”.
The AND circuit 83 acquires the logic product of the comparison result of the comparator 81 and that of the comparator 82, and outputs a high level signal for indicating an establishment of a “condition one” if the mounts of changes in gains of the comparators 81 and 82 are judged as being equal to or greater than a threshold value, that is, the amounts of changes in gains are equal to or greater than the threshold value for consecutive two frames.
The AND circuit 84 acquires the logic product of the inverted output of the comparators 81 and 82, and outputs a high level signal for indicating an establishment of a “condition two” if both the gain a of the current frame and gain b of the first previous frame are smaller than a threshold.
Referring to FIG. 14, an average calculation circuit 51 (refer to FIG. 9) calculates the average value of black level data (simply called a “black level a” hereinafter) of the current frame which is detected by a shaded part 11 a of an image sensor 11 and A/D converted.
If a frame of an amount of change in black level data being equal to or greater than a threshold value is judged to continue for three frames or more, the condition judgment unit 106 outputs a selection signal for a “condition one” to the selection circuit 53 (refer to FIG. 9). And, if a frame of an amount of change in black level data being equal to or greater than a threshold value is judged not to exist, the condition judgment unit 106 outputs a selection signal for a “condition three” to the selection circuit 53. Furthermore, if a frame of an amount of change in black level data being equal to or greater than a threshold value is judged to continue for one frame or more, and yet less than three, then the condition judgment unit 106 outputs a selection signal for a “condition two” to the selection circuit 53.
The selection circuit 53 selects and outputs the current black level data as new black reference data if it receives a selection signal for the “condition one” from the condition judgment unit 106. Or, the selection circuit 53 selects and outputs the weighted average data, which weights the current black level data and the black reference data for up to this event respectively, as new black reference data if it receives a selection signal for the “condition three”. Furthermore, the selection circuit 53 selects and outputs the previous black reference data in lieu of updating black reference data if it receives a selection signal for the “condition two”.
This example has applied with weighting the current black level value and black reference data respectively, showing the case of “1” for the multiplier “N” to the current black level data, “7” for the multiplier “M” to the black reference data, and “10 (code value)” for the threshold value. In FIG. 15, the vertical axis shows the code values and the horizontal axis shows the frame numbers.
Referring to FIG. 15, the round black dots show codes of black level data, indicating that the code value of the number 10 frame is “15”, the code value rapidly increases from the number 11 frame to “50”, the next number 12 frame stays at approximately the same value and then the next number 13 frame rapidly decreases approximately to “10”.
Applying the black level correction method according to the second embodiment to the above described black data when the number of frames to be judged is “1” and when the black level value becomes “50” at the number 11 frame, the amount of change in the black level value is “50 minus 15”, hence the value exceeding the threshold value of “10” and accordingly black reference data is changed to “50” which is the current black level value. The next number 12 frame indicates the black level value at “50”, hence the amount of change in the black level value being smaller than the threshold value of “10” and accordingly the previous black reference data (i.e., the immediate previous value “50” in this case) is used, in lieu of updating the black reference.
As the black level value changes to “10” in the next number 13 frame, the amount of change in the black level value exceeds the threshold value “10” and accordingly the black reference data is changed to “10” which is the black level value at this event.
Next description is on the case of the number of frames to be judged being “2”. In this case, when the black level values become “50” continuously in the numbers 11 and 12 frames, thus the amount of change in the black level value exceeding the threshold value for two consecutive frames and accordingly the black reference data at this time is changed to the current black level value “50”. Then, when the black level value changes to “10” in the next number 13 frame, the number of frame of the amount of change in black level being equal to or greater than the threshold value becomes “1” and accordingly the black reference data up to now is maintained (i.e., the immediate previous value “50” in this case).
Then, when the black level value becomes “10” in the next number 14 frame, the black level value of the current frame being “10”, that of the first previous frame being “10” and that of the second previous frame being “50”, and therefore the amount of change in the black level value becomes equal to or greater than the threshold value of “10” for two consecutive frames, hence changing the black reference data to “10” that is the current black level value.
The “x” dots on the dotted line f shown by FIG. 15 indicate a change of the value of the black reference data in the case of the number of frames to be judged being “2”.
Next description is on the case of the number of frames to be judged being “3”. In this case, the change in the black levels for the numbers 11 and 12 frames only continues for two frames, and therefore the black reference value is not updated.
Referring to FIG. 15, as the black level value becomes no less than “50” for continuous three frames at the number 16 frame and thereafter, the amount of change in the black level exceeds the threshold of “10” for three consecutive frames or more when the black level value becomes no less than “50” at the number 19 frame that is three frames after the number 16 frame at which the black level value rapidly changes at first, and accordingly a value of the black reference data is changed to “50” that is the black level value at this event.
As the black level value becomes no less than “50” at the number 19 frame and thereafter, the number of frames of the amount of change in the black level value being equal to or greater than the threshold value becomes smaller than “3” and therefore the previous black reference data (i.e., “50” in this case) is maintained, in lieu of updating it. Then, as all of the amount of change in the black level values for the current frame, first previous frame and second previous frame become smaller than the threshold value, then a weighted average value of a value which is the current black level value multiplied by N and a value which is the black reference data multiplied by M is calculated and the calculated value is set as the black reference data.
The “x” dots on the solid line curve g shown by FIG. 15 indicate a change of the value of the black reference data in the case of the number of frames to be judged being “3”. When an amount of change in a black level value becomes equal to or greater than a threshold value for consecutive three frames, the black reference data is changed to the black level value at that event in the case of the number of frames to be judged being “3”.
In the case of setting the number of frames to be judged at “3”, if a change in a black level value is in a short period (i.e., a period of two frames or less), the previous black reference data is retained as understood from FIG. 15, thereby preventing a flicker in brightness of a photographed image otherwise as a result of the black reference data being changed by an instantaneous fluctuation of brightness in an image as the subject of photographing.
The curve h shown by FIG. 15 indicates a convergence characteristic of black reference data in the case of the number of frames to be judged being “0” that is applicable to the conventional black level correction method in which a data weighting is applied even if a black level value changes drastically and therefore the black referenced at a changes merely gradually, resulting in taking a long time for the black reference data to converge at an appropriate value.
Note that a combined configuration of the first and second embodiments maybe possible to calculate both an amount of change in gains and that in black level data, and perform a condition judgment based on these amounts thereof.
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
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
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 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 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
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
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.
US11/360,673 2005-09-30 2006-02-24 Semiconductor integrated apparatus and black level correction method for image sensor Expired - Fee Related US7920181B2 (en)
JP2005-288744 2005-09-30
JP2005288744A JP4928765B2 (en) 2005-09-30 2005-09-30 Black level correction method of a semiconductor integrated device and an image sensor
US20070075772A1 true US20070075772A1 (en) 2007-04-05
US7920181B2 US7920181B2 (en) 2011-04-05
ID=37901313
US11/360,673 Expired - Fee Related US7920181B2 (en) 2005-09-30 2006-02-24 Semiconductor integrated apparatus and black level correction method for image sensor
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