JP4403873B2 - Clamp level adjusting device and electronic camera - Google Patents

Description

  The present invention relates to a clamp level adjustment circuit that performs black level correction on the output of an image sensor in an electronic camera or the like.

It has been conventionally known that the output of an image pickup device of an electronic camera includes noise corresponding to a black level due to a dark current component of a light receiving device. As such a black level correction method, a method is known in which a black level is detected from a light shielding area where a part of the image sensor is shielded, and a black level is subtracted from the image level of an effective pixel area which is not shielded from light.
In Patent Document 1, a correction value is calculated by comparing a horizontal average value of a digital signal in a light shielding area and a target value of a black level, and the correction value is fed back after D / A conversion to correct a black level. A black level correction apparatus that performs the above is disclosed.
JP 2003-209713 A

However, the upper Symbol Patent Document 1, since the information at the time of black level correction in the corrected image data is not left, it is very difficult to determine what the black level correction has been performed from the image data . In particular, when adjusting the brightness of the image by processing the corrected image data, if there is information at the time of correcting the black level, it becomes an adjustment reference for the brightness of the image, and the correctable range becomes clear. However, since the information at the time of black level correction is not recorded in the image data in Patent Document 1, the user has to repeat trial and error at the time of black level recorrection. Therefore, the actual situation is that the user's request to adjust the fine brightness of the image data by image processing of the computer is not sufficiently satisfied.

The present invention has been made to solve the above problems of the prior art, its object can Yu Za acquires the information of the black level correction, convenience is high clamping level adjustment during the image processing Is to provide a device.

A clamp level adjusting apparatus according to a first aspect of the present invention is an imaging device including an effective pixel region that generates an image signal, and a light shielding region that is formed on the outer periphery of the effective pixel region and generates a black level reference signal.
  A clamp level calculation unit that generates a clamp level value corresponding to each row in the horizontal direction of the effective pixel area based on the black level reference signal or a preset clamp fixed value;
  A clamp unit for correcting a black level of the image signal based on the clamp level value;
  An output unit that outputs the clamp level value output from the clamp level calculation unit in association with each row in the horizontal direction of the effective pixel area to the image data after black level correction output from the clamp unit; It is characterized by having.
  According to a second invention, in the first invention,
  The clamp level calculation unit extracts the black level reference signal from an extraction range extending across a plurality of horizontal rows of the light shielding region, and calculates the effective pixel region from the vertical moving average value of the black level reference signal of the extraction range. A clamp level value corresponding to each row in the horizontal direction is generated.

According to a third invention, in the second invention, the clamp level calculation unit includes a low-pass filter that reduces a high-frequency component of the black level reference signal for each horizontal row of the light-shielding region;
The output value of the low-pass filter is added up to the number of rows in the extraction range to output the integrated value of the extraction range, and when the output value of the low-pass filter is input exceeding the number of rows in the extraction range, An integrating unit that sequentially updates and outputs the integrated value by reducing the output value of the first row of the extraction range;
A division unit that divides the integrated value by a predetermined value to generate the moving average value in the vertical direction.

In a fourth aspect based on the third aspect , the accumulator adds an output value of the low-pass filter up to at least the number of rows in the extraction range, and outputs an addition unit;
A register unit for storing the output value of the low-pass filter in a first-in first-out manner up to the number of rows in the extraction range and sequentially outputting;
A subtracting unit that subtracts the output value of the register unit from the output value of the adding unit to calculate the integrated value and outputs the integrated value to the dividing unit;
The integrated value is re-input to the adding unit, and the integrated value sequentially output becomes the vertical direction movement added value of the extraction range.

According to a fifth invention, in any one of the first to fourth inventions, the clamp level calculation unit sets a clamp level value corresponding to the top row in the horizontal direction of the effective pixel region above the top row. It generates from the said extraction range set to the said light-shielding area | region of a part, It is characterized by the above-mentioned.
According to a sixth invention, in any one of the first to fifth inventions, a fixed value storage unit that stores a clamp fixed value set in advance to correct the black level of the image signal;
And a selection unit that selects either the clamp fixed value or the vertical moving average value based on a user input and outputs the clamp level value.

An electronic camera according to a seventh aspect of the invention includes the clamp level adjusting device according to any one of the first to sixth aspects of the invention .

In the present invention, the clamp level value used for correcting the black level of the image signal is output in association with each row in the horizontal direction of the effective pixel region. Therefore, the user can adjust the brightness of the image based on the clamp level value data for each row in the horizontal direction of the image, and more fine image processing can be easily performed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Description of Configuration of First Embodiment)
Figure 1 is Ru block diagram der clamp level adjusting device of the first embodiment. The clamp level adjusting apparatus according to the first embodiment is incorporated in an electronic camera, and includes an image sensor 1, a clamp unit 2, an A / D conversion unit 3, a signal output switching unit 4, a clamp level calculation unit 5, It has a D / A conversion unit 6, a first selector unit 7 as an output unit, and a CPU 8.

  As shown in FIG. 2, light receiving elements (photodiodes) that perform photoelectric conversion are two-dimensionally arranged on the light receiving surface of the image sensor 1, and each light receiving element constitutes one pixel. A vertical readout line (not shown) is provided for each column of the light receiving elements. A horizontal readout line 9 is provided at an output end of these vertical readout lines, and an output of the horizontal readout line is connected to the clamp unit 2.

  As shown in FIG. 2, the region where the light receiving elements of the image sensor 1 are arranged is partitioned into an effective pixel region 10 and a light shielding region (optical black region) 11 formed adjacent to the outer periphery of the effective pixel region 10. Has been. In the effective pixel region 10, signal charges are accumulated in each light receiving element in accordance with the brightness of a subject image formed by a photographing optical system (not shown), and an image signal for generating a photographed image based on the signal charges. Generated.

On the other hand, the surface of the light shielding region 11 is shielded by a light shielding film. The output of the light shielding area 11 can be regarded as data corresponding to the portion where the subject light is not incident, that is, the black color of the subject image. In the light shielding region 11, the charge (dark current component) accumulated in the light receiving element due to a temperature change or the like is detected, and a black level reference signal is generated based on this charge.
Here, signal reading of the image sensor 1 is performed as follows. First, signals in the uppermost row of the image sensor 1 are read in order from the left end to the right end, and then signals in the next lower row are read in order from the left end to the right end. Thereafter, the same process is repeated to sequentially read out signals for one screen by scanning. As shown in FIGS. 2 and 5, k rows (provided that k ≧ 2) of only the light-shielding region 11 are formed above the effective pixel region 10 of the image sensor 1. Therefore, the output of only the black level reference signal from the image sensor 1 continues for k rows until the signal of the row including the effective image area 10 is output from the image sensor 1.

The clamp unit 2 performs black level correction of the output of the image sensor 1 by subtracting a clamp level value described later from the image signal and black level reference signal of the image sensor 1. The A / D conversion unit 3 performs A / D conversion of the output of the clamp unit 2 to convert the image signal and the black level reference signal into digital signals.
The signal output switching unit 4 is connected to the clamp level calculation unit 5 and the first selector unit 7. The signal output switching unit 4 switches the output destination of the digital signal input from the A / D conversion unit 3 in accordance with an instruction from the CPU 8 and outputs a black level reference signal for a predetermined portion (for m pixels in the horizontal direction) of the light shielding region 11. Extract.

The clamp level calculation unit 5 calculates the moving average value in the vertical direction of the extraction range (m × n pixels) obtained by collecting the black level reference signals for the m pixels for n rows (where n ≧ 2, n ≦ k). . The total number of vertical moving average values output by the clamp level calculation unit 5 corresponds to the number of horizontal rows of the effective pixel region 10.
As shown in FIG. 3, the clamp level calculation unit 5 includes an LPF (Low Pass Filter) 12, an integration unit 13, a division unit 14, a fixed value storage unit 15, and a second selector unit 16 as a selection unit. , Is composed of.

The LPF 12 calculates an average value of m pixels of the black level reference signal for each row in the horizontal direction, and reduces a high frequency component of the black level reference signal due to an output of a defective pixel or the like. Note that the LPF 12 may calculate the weighted average value of the black level reference signal for each row in the horizontal direction, or may calculate the added value of the black level reference signal for m pixels for each row in the horizontal direction.
The accumulating unit 13 calculates the vertical movement addition value (integrated value) of the extraction range based on the output value for each row in the horizontal direction of the LPF 12. As shown in FIG. 4, the integration unit 13 includes an addition unit 13a, a register unit 13b, and a subtraction unit 13c. The output of the LPF 12 is input to the adding unit 13a and the register unit 13b, respectively, and the outputs of the adding unit 13a and the register unit 13b are input to the subtracting unit 13c. One of the outputs of the subtractor 13c is sequentially input to the divider 14 and the other is re-input to the adder 13a.

The adder 13a adds the output values of the LPF 12 up to at least n rows in accordance with instructions from the CPU 8, and outputs the result to the subtractor 13c. When there is re-input from the subtractor 13c, the adder 13a adds the output value of the LPF 12 to the re-input value from the subtractor 13c and outputs the result to the subtractor 13c.
The register unit 13b stores up to n rows of output values of the LPF 12 with a first-in first-out data structure. Then, the register unit 13b sequentially outputs the output values of the LPF 12 exceeding n rows to the subtracting unit 13c. Note that the initial value of the register unit 13b is set to zero.

The subtractor 13c calculates the integrated value by subtracting the output value of the register unit 13b from the output value of the adder 13a.
The dividing unit 14 calculates the integrated value input from the subtracting unit 13c as a predetermined value (for example, the value of n when the LPF 12 outputs an average value, or mx when the LPF 12 outputs an added value for m pixels. The vertical moving average value of the extraction range is generated by dividing by the value of n).

The fixed value storage unit 15 stores a clamp fixed value set by the user for correcting the black level of the image signal.
The second selector unit 16 is either one of the vertical moving average value of the division unit 14 and the clamp fixed value of the fixed value storage unit 15 based on a user input from a camera operation member (not shown). To output the clamp level value.

The clamp level value output from the second selector unit 16 is converted into an analog signal by the D / A conversion unit 6 and then input to the clamp unit 2. The clamp level value output from the second selector unit 16 is also input to the first selector unit 7 via an input delay unit (not shown).
The first selector unit 7 switches the output of the image signal and black level reference signal from the signal output switching unit 4 and the clamp level value from the second selector unit 16 in accordance with an instruction from the CPU 8, thereby A clamp level value is output in association with each row in the direction. The output of the second selector unit 16 is connected to a digital signal processing unit and a memory (both not shown) of the electronic camera.

  The CPU 8 controls the operation of each part of the electronic camera, such as an instruction for the charge accumulation time of the image sensor 1, and executes various arithmetic processes necessary for focus control, exposure control, and the like. For example, the CPU 8 instructs the charge accumulation time of the image sensor 1. Further, the CPU 8 holds position information (height and width of the effective pixel area 10 and the light shielding area 11) of the effective pixel area 10 and the light shielding area 11 of the image sensor 1. The CPU 8 controls the output switching timing of the signal output switching unit 4, the clamp level calculation unit 5, and the first selector unit 7 based on the clock count.

(Description of functions and effects of the first embodiment)
The clamp level adjusting apparatus according to the first embodiment is configured as described above. Hereinafter, the operation and effect thereof are “when a clamp level value is generated from a light shielding region” and “when a clamp fixed value is a clamp level value”. Separately described.
(When generating the clamp level value from the shading area)
In this case, the user sets the output of the second selector unit 16 as the input from the division unit 14.

First, the CPU 8 controls the image sensor 1 to perform photoelectric conversion of the subject image by the user's shutter release. From the image sensor 1, the output signals of the light receiving elements are sequentially read out row by row from the top row.
The output signal read from the image sensor 1 is input to the signal output switching unit 4 via the clamp unit 2 and the A / D conversion unit 3 in the order of reading. The signal output switching unit 4 outputs an output from the pixel at the left end of the screen of the image sensor 1 to the pixel at the right end position of the effective pixel region 10 to the first selector unit 7 in accordance with an instruction from the CPU 8. Then, the signal output switching unit 4 outputs the output of the pixel at the right end of the screen (for m pixels) from the pixel right next to the right end position of the effective pixel region 10 to the clamp level calculation unit 5 and the first selector unit 7. That is, only the black level reference signal of the light shielding region 11 located on the right side of the effective pixel region 10 is input to the clamp level calculation unit 5.

  The LPF 12 of the clamp level calculation unit 5 calculates the average value of the black level reference signals for m pixels and inputs the average value to the addition unit 13a and the register unit 13b of the integration unit 13. The adding unit 13a adds n rows of average values output from the LPF 12, and outputs the added value of the extraction range (m × n pixels) to the subtracting unit 13c. On the other hand, the register unit 13b outputs an initial value of 0 until there is an input exceeding the nth row. Therefore, the subtraction unit 13c outputs the total addition value of the extraction range as it is to the addition unit 13a and the division unit 14 as an integrated value.

  When the integration unit 13 receives the average value of the LPF 12 corresponding to the (n + 1) th row, the addition unit 13a adds the previous integration value and the average value of the (n + 1) th row and outputs the result to the subtraction unit 13c. To do. The register unit 13b outputs the average value of the first row (the output value of the first row in the previous extraction range) to the subtraction unit 13c in response to the input of the average value of the (n + 1) th row. The subtractor 13c subtracts the average value of the first row from the output value of the adder (m × (n + 1) range), and adds the integrated value obtained by moving the extraction range downward by one row to the adder 13a. Output to the division unit 14. Thereafter, by repeating the same operation, the integration unit 13 sequentially outputs the vertical direction movement addition value of the extraction range as the integration value.

  The division unit 14 divides the integration value of the integration unit 13 by the number of rows in the extraction range (n value), and sequentially outputs the vertical moving average value of the extraction range that becomes the clamp level value. One of the clamp level values is input to the clamp unit 2 via the D / A conversion unit 6, and the other is input to the first selector unit 7 via an input delay unit (not shown). The clamp unit 2 starts black level correction based on the clamp level value from the output signal of the (n + 1) th row of the image sensor 1.

Here, as shown in FIG. 5, when the (n + 1) th row is the uppermost row of the effective pixel region 10, the image signal and the black level reference signal in the (n + 1) th row are m × n pixels including the immediately preceding nth row. Black level correction is performed with the average value of minutes. Therefore, in the first embodiment, it is possible to perform highly accurate black level correction with very little influence of defective pixels or the like in the light shielding region.
Further, among the output signals of the (n + 1) th row subjected to the black level correction, the black level reference signal of the light shielding region 11 corresponding to the extraction range is input to the signal output switching unit 4 to generate the clamp level value of the (n + 2) th row. Is done. That is, the black level correction of the immediately preceding row is always reflected in the clamp level value. Therefore, in the first embodiment, gentle black level correction is performed on the entire effective pixel region 10 without the clamp level value changing rapidly between the upper and lower rows.

Further, the output signal of the (n + 1) th row subjected to the black level correction is input to the first selector unit 7. The first selector unit 7 switches the output in the following manner according to an instruction from the CPU 8.
That is, the first selector unit 7 outputs a signal from the signal output switching unit 4 in the range from the left end of the screen of the (n + 1) th row to the right end of the effective pixel region 10.
On the other hand, the first selector unit 7 switches the output to the clamp level calculation unit 5 at the right end position of the light shielding region 11 on the right side of the screen, and outputs the clamp level value corresponding to the (n + 1) th row. As a result, the clamp level value used for black level correction of the row is output at a predetermined position in the light shielding region 11 (see FIG. 6).

  Thereafter, the first selector unit 7 switches the output to the signal output switching unit 4 again when the output of the clamp level value is completed, omits the signal in the range in which the clamp level value is recorded, and the right end of the screen of the (n + 1) th row. The signal up to is output. Thereafter, by repeating the same operation for each row, the clamp level value used for the black level correction is output in association with each row of the effective image area 10.

  Therefore, in the first embodiment, the user can know the correctable range of the black level of the image data from the clamp level value data for each row of the effective image area 10. Then, when the user processes the image data on the computer, it becomes easy to adjust the fine brightness of the image by using the data of the clamp level value. In particular, the effect is remarkable when RAW data (raw data output from the clamp level adjusting device) of the first embodiment is processed by software on a computer.

  Note that the CPU 8 samples a clamp level value generated from the black level reference signal according to a user setting or the like, and stores the sampled clamp level value in the fixed value storage unit 15 as a clamp fixed value. In this case, for example, it is possible for the user to appropriately select a clamp fixed value suitable for the shooting situation from the fixed value storage unit 15 according to a change in the shooting optical system or the like.

  Of course, the clamp level value generated from the black level reference signal can be further processed by the user to generate the clamp fixed value. For example, if the sampled clamp level value is 200 LSB, the clamp fixed value is processed to 100 LSB if the user wants a brighter image, and the clamp fixed value is processed to 300 LSB if a darker image is desired. And set. In this case, since the clamp fixed value is customized based on the sampled clamp level value, the black level correction setting imaged by the user can be realized relatively easily.

(When the clamp fixed value is the clamp level value)
In this case, the user sets the output of the second selector unit 16 as the input from the fixed value storage unit 15. In this case, the output destination of the signal output switching unit 4 is fixed to the first selector unit 7 side. The clamp level calculation unit 5 outputs the clamp fixed value stored in the fixed value storage unit 15 as a clamp level value. The clamp unit 2 performs black level correction on the output signal of the image sensor 1 based on the clamp fixed value.

  The first selector unit 7 outputs a signal from the signal output switching unit 4 in the range from the left end of the screen to the right end of the effective pixel region 10, while calculating the clamp level at the right end position of the light shielding region 11 on the right side of the screen. The output is switched to the unit 5 side, and a clamp fixed value corresponding to the row is output. Thereafter, the first selector unit 7 switches the output to the signal output switching unit 4 again when the output of the clamp fixed value is completed, omits the signal in the range in which the clamp fixed value is recorded, and reaches the right end of the screen of the row. The signal is output. Thereafter, by repeating the same operation for each row, the clamp level value (clamp fixed value) used for the black level correction is output in association with each row of the effective image area 10, and the same effect as described above is obtained. Obtainable.

(Description of Second Embodiment)
Figure 7 is Ru block diagram der clamp level adjusting device of the second embodiment. The clamp level adjusting apparatus according to the second embodiment is an example in which black level correction is performed based on an average value for one row of the light shielding region 11. That is, in the second embodiment, the clamp level value is generated for each row of the effective pixel region 10 based on the average value (m pixels) of one row of the light shielding region 11 output from the LPF 12. In addition, since the other structure and operation | movement of 2nd Embodiment are common in 1st Embodiment, the detailed description is abbreviate | omitted.

Also according to the second embodiment, the clamp level value used for the black level correction is output in association with each row of the effective image region 10, so that information on the clamp level value for each row of the effective image region 10 is obtained. The used image can be processed.
(Supplementary items of the embodiment)
As mentioned above, although this invention has been demonstrated by said embodiment, the technical scope of this invention is not limited to the said embodiment. For example, in the above embodiment, the clamp level value is generated from the light shielding area on the right side of the screen. However, an extraction range may be set in the light shielding area on the left side of the screen, and the vertical moving average value of the extraction range may be used as the clamp level value. . In this case, it is also possible to generate the clamp level value by including in the extraction range the light-shielding region of the same row as the row of the effective pixel region to be corrected.

  In the above embodiment, the clamp level value is output in association with each row at the right end position of the light shielding region 11 on the right side of the screen. However, the output method of the clamp level value is not limited to this. For example, a memory (not shown) that temporarily stores a clamp level value for each row is provided in the clamp level calculation unit 5 or the like, and a predetermined shading area portion below the effective pixel area and a final image data tag are predetermined. The correspondence between each row of the effective pixel area and the clamp level value may be written in the area. The setting of the extraction range shown in FIG. 5 is merely an example, and it goes without saying that the number m of horizontal pixels and the number n of rows in the extraction range can be changed as appropriate.

  In the above embodiment, an example of the image sensor 1 of the XY address method (CMOS, LBCAST, etc.) is shown, but the image sensor 1 of charge sequential transfer method (CCD, etc.) may be used.

  The present invention can be applied to a clamp level adjusting device that performs black level correction such as an electronic camera.

Block diagram of the clamp level adjusting device of the first embodiment The figure which shows the structure of the light-receiving surface side of an image sensor Block diagram of the clamp level calculation unit of FIG. Block diagram of the integration unit of FIG. The figure which shows the correspondence of the row | line | column of an effective pixel area | region, and an extraction range The figure which shows the output of the clamp level value by a 1st selector part Block diagram of clamp level adjusting device of 2nd Embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image pick-up element 2 Clamp part 3 A / D conversion part 4 Signal output switching part 5 Clamp level calculating part 6 D / A conversion part 7 1st selector part 8 CPU
9 Horizontal readout line 10 Effective pixel area 11 Shading area (optical black area)
12 LPF (Low Pass Filter)
13 Accumulator 13a Adder 13b Register 13c Subtractor 14 Divider 15 Fixed Value Storage 16 Second Selector

Claims (7)

An image pickup device comprising an effective pixel region for generating an image signal, and a light-shielding region formed on the outer periphery of the effective pixel region for generating a black level reference signal;
  A clamp level calculation unit that generates a clamp level value corresponding to each row in the horizontal direction of the effective pixel area based on the black level reference signal or a preset clamp fixed value;
  A clamp unit for correcting a black level of the image signal based on the clamp level value;
  An output unit that outputs the clamp level value output from the clamp level calculation unit in association with each row in the horizontal direction of the effective pixel area to the image data after black level correction output from the clamp unit; A clamp level adjusting device comprising: In the clamp level adjustment device according to claim 1,
  The clamp level calculation unit extracts the black level reference signal from an extraction range extending across a plurality of horizontal rows of the light shielding region, and calculates the effective pixel region from the vertical moving average value of the black level reference signal of the extraction range. A clamp level adjusting device that generates a clamp level value corresponding to each row in a horizontal direction. In the clamp level adjusting device according to claim 2,
  The clamp level calculation unit, a low-pass filter that reduces a high-frequency component of the black level reference signal for each row in the horizontal direction of the light-shielding region;
  The output value of the low-pass filter is added up to the number of rows in the extraction range to output the integrated value of the extraction range, and when the output value of the low-pass filter is input exceeding the number of rows in the extraction range, An integrating unit that sequentially updates and outputs the integrated value by reducing the output value of the first row of the extraction range;
  A clamp level adjusting apparatus comprising: a division unit that divides the integrated value by a predetermined value to generate the vertical moving average value. In the clamp level adjusting device according to claim 3,
The integrating unit adds an output value of the low-pass filter up to at least the number of rows in the extraction range, and outputs the addition unit;
  A register unit for storing the output value of the low-pass filter in a first-in first-out manner up to the number of rows in the extraction range and sequentially outputting;
  A subtracting unit that subtracts the output value of the register unit from the output value of the adding unit to calculate the integrated value and outputs the integrated value to the dividing unit;
  The integrated value is re-inputted to the adding unit, and the integrated value sequentially output becomes a vertical movement added value of the extraction range. In the clamp level adjustment device according to any one of claims 1 to 4,
The clamp level calculation unit generates a clamp level value corresponding to the top row in the horizontal direction of the effective pixel region from the extraction range set in the light shielding region above the top row. Clamp level adjustment device. In the clamp level adjustment device according to any one of claims 1 to 5,
A fixed value storage for storing a clamp fixed value set in advance to correct the black level of the image signal;
  A clamp level adjusting apparatus, further comprising: a selection unit that selects either the clamp fixed value or the vertical moving average value based on a user input and outputs the clamp level value.   An electronic camera comprising the clamp level adjusting device according to any one of claims 1 to 6.

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