JP2007281812A - Imaging apparatus, video signal processing circuit, video signal processing method, and computer program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology of realizing correction of a drop in peripheral light quantity by using a computational expression wherein the computational complexity is suppressed. <P>SOLUTION: In the case of applying the correction of a drop in the peripheral light quantity to image data obtained by imaging an optical image passing through an optical system including a lens and an aperture section and made incident on an imaging section, a correction gain of a pixel value of an optional pixel of the image data is calculated by using a correction formula that is expressed by only terms proportional to an even-ordered distance from an optical center of the optical system to the pixel depending on an aperture position of the aperture section, and the pixel value of the pixel is corrected by the calculated correction gain. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a video signal processing circuit, an imaging device, a video signal processing method, and a computer program that correct a decrease in the amount of light at a peripheral portion of image data that occurs according to a distance from the optical center in an optical system including a lens and a diaphragm. .

  2. Description of the Related Art Conventionally, in an optical system such as a lens and a diaphragm used in a video camera or the like, a reduction in the amount of light in the peripheral portion that occurs according to the distance from the optical center has been a problem. In particular, the amount of change in the amount of light is large depending on the aperture position (aperture amount) of the aperture section, and the more the aperture section is opened, the more conspicuous the image quality becomes. It was causing deterioration.

  In order to solve this problem, various methods for correcting the peripheral light amount drop have been considered. As a method that has been realized so far, in addition to a method of accurately obtaining the distance from the optical center to a specific pixel of the image sensor and correcting the light loss in the peripheral part according to the distance, for example, from the center of the screen There are a method of obtaining the distance to the center by approximating the polygon, and a patterning for giving a predetermined gain to an appropriate interval on the screen.

In Patent Document 1, in order to correct the peripheral dimming characteristics of the captured image data by the lens, the peripheral dimming is performed using a quadratic, cubic, or quaternary expression relating to the image height (distance from the center of the light receiving surface). An image processing method for performing correction is described.
JP 11-164194 A

  However, when the distance from the optical center is accurately obtained, correction can be performed with the highest accuracy, but on the other hand, the circuit scale tends to increase because square root calculation is required. On the other hand, near the polygon, there is a problem that when the gain conversion point appears in the image, the corner of the polygon is recognized. In addition, when the area to which gain is applied is patterned, there is a problem that it is difficult to smoothly connect the areas to which gain is applied.

  The present invention has been made in view of such a point, and an object of the present invention is to realize peripheral light amount drop correction by a calculation formula that suppresses the calculation amount.

In order to solve the above-described problems, the present invention is configured to correct the peripheral light amount drop for image data obtained by capturing an optical image incident on the imaging unit through an optical system including a lens and a diaphragm unit. A pixel value in an arbitrary pixel is corrected by using a correction formula expressed only by a term proportional to an even-numbered distance from the optical center of the optical system to the pixel in accordance with the stop position of the stop portion. It is characterized by.
It is more preferable to set a correction formula in consideration of the zoom value of the lens in addition to the aperture position.

  According to the above configuration, the square root calculation is performed without applying the correction according to the distance from the optical center to the pixel value of the pixel to be corrected based on the size (zoom value) of the stop at the stop. Peripheral light loss correction can be performed.

  According to the present invention, since the square root calculation is not performed according to the aperture position, and the peripheral light amount drop correction can be realized using a simple calculation formula with a small calculation amount, compared with the case involving the square root calculation. The circuit scale can be reduced to a fraction, and the processing time can be reduced to a fraction. Further, by using a correction formula that also takes into account the zoom value, a more accurate peripheral light amount drop correction process can be performed.

  Hereinafter, examples of embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing a basic configuration example of a video camera to which an imaging apparatus of the present invention is applied.

  The video camera shown in FIG. 1 includes a lens optical system including a lens 1a on which a light beam (optical image) is incident at a predetermined zoom position, a diaphragm unit 1b for adjusting a diaphragm, and the like, red (R), green (G), Image pickup means including image sensors 1, 2, and 3 that are provided corresponding to blue (B) and perform photoelectric conversion for each color are arranged along the optical axis (optical center). A color separation optical system (filter) (not shown) that separates color information of an optical image into red, green, and blue is disposed on the front surface of the image sensors 1, 2, and 3. The video camera further includes video amplifiers 4, 5, 6 to which signals from the image sensor are input, A / D converters 7, 8, 9, a video signal processing unit 16 that performs predetermined signal processing, A microcomputer 17 and an operation unit 18 are provided.

  The zoom position of the lens 1 a and the stop position of the stop blades of the stop 1 b are detected by a zoom position detection device and a stop position detection device (not shown), respectively, and these detected signals are output to the microcomputer 17. The lens 1a and the diaphragm unit 1b are driven by a lens driving device and a diaphragm unit driving device (not shown), respectively. The lens driving device and the diaphragm driving device are driven and controlled by a control signal from the microcomputer 17.

  In FIG. 1, the lens 1a and the diaphragm 1b are described so as to act only on the image sensor 1 for red. However, the lens 1a is actually shared with the image sensors 2 and 3, and therefore the lens 1a. The diaphragm portion 1b acts in the same manner on all the image sensors 1, 2, and 3. In this example, the color separation optical system and the image sensor for red, green, and blue are provided. However, for example, a color separation optical system and an image sensor for four colors may be provided. It is not a thing.

  In general, an image sensor (imaging unit) is provided with a micro lens (not shown) for each pixel on which light rays from a lens optical system are incident on the front surface of a color separation optical system arranged on the image sensor. Light rays incident on the microlens are received by the image sensors 1, 2, and 3 via the color separation optical system. The image sensors 1, 2, and 3 are configured by an image pickup device using a CCD (Charge Coupled Device) or the like, and R, G, and B primary color images incident through a color separation optical system are photoelectrically converted to R, G, and B. G and B primary color signals (R signal, G signal, and B signal) are generated, and these three primary color signals are supplied to video amplifiers 4, 5, and 6, respectively. The video signal can be applied not only to moving images but also to still images.

  The video amplifiers 4, 5, and 6 are gain adjusting means, and an AGC (Automatic Gain Control) circuit or the like can be applied as an example. The video amplifiers 4, 5, 6 adjust the gains of the primary color signals and supply the primary color signals whose gains have been adjusted to the A / D converters 7, 8, 9, respectively. The A / D converters 7, 8, 9 convert the input analog signals into digital signals and supply them to the video signal processing unit 16.

  The video signal processing unit 16 of this example includes a correction circuit 10, a gain adjustment circuit 11, a color adjustment circuit 12, a luminance adjustment circuit 13, a gamma correction circuit 14, and an output signal generation circuit 15, and the video amplifier 4, 5, 6, the R, G, B primary color signals that are adjusted to an appropriate level by the A / D converters 7, 8, 9 and quantized are first input to the correction circuit 10 of the video signal processing unit 16. .

  The correction circuit 10 is an example of the video signal processing circuit described in the claims. The correction circuit 10 performs a correction process of a decrease in the amount of peripheral light in the image data with respect to the input three primary color signals, and the gain adjustment circuit 11. To supply. In this correction circuit 10, signal processing such as predetermined interpolation processing, accompanying filter processing, and shading processing may be performed in addition to the above-described peripheral light amount drop correction processing to further improve the image quality.

  The gain adjustment circuit 11 adjusts the gain so that the three primary color signals input from the correction circuit 10 are at appropriate levels, and supplies the gain to the color adjustment circuit 12.

  The color adjustment circuit 12 adjusts (corrects) the color tones of the three primary color signals input from the gain adjustment circuit 11 to a required color tone and supplies the adjusted color tone to the luminance adjustment circuit 13.

  The luminance adjustment circuit 13 extracts a luminance signal from each primary color signal input from the color adjustment circuit 12 in order to keep the video signal within a specified range, and suppresses the amplitude characteristic of the luminance signal in the high luminance region. The dynamic range of the image sensor output is compressed and supplied to the gamma correction circuit 14.

  The gamma correction circuit 14 corrects each of the three primary color signals input from the luminance adjustment circuit 13 according to the gamma characteristics of a monitor (receiver) such as a CRT (Cathode Ray Tube), and each gamma corrected The primary color signal is supplied to the output signal generation circuit 15.

  The output signal generation circuit 15 converts the three primary color signals input from the gamma correction circuit 14 into a final video signal output format and outputs it to the outside. As an example, the output signal generation circuit 15 converts primary color signals of three colors into color difference signals so as to comply with a signal standard such as NTSC (National Television System Committee) or PAL (Phase Alternating Line), and subcarriers (not shown). It functions as an encoder circuit that modulates using a signal. Furthermore, when the video signal to be output is an analog signal, a D / A converter is provided that converts the quantized color difference signal output from the encoder circuit into an analog signal.

  The microcomputer 17 is an example of a control unit, receives detection signals of the zoom position of the lens 1a and the stop position of the stop 1b, and performs peripheral light amount drop correction based on the detection signals. Further, the microcomputer 17 controls each circuit constituting the video signal processing unit 16, and controls the operation of each unit such as the optical system such as the lens 1a and the diaphragm unit 1b, and the video amplifiers 4, 5, and 6. The microcomputer 17 performs a predetermined calculation and control of each circuit in accordance with a computer program recorded in a nonvolatile storage unit such as a built-in ROM (Read Only Memory).

  Further, a drive circuit (not shown) is connected to the microcomputer 17 as necessary, and a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory, or the like is appropriately mounted, and a computer program read from them is If necessary, it may be installed in a RAM or the like built in the microcomputer 17.

  The operation unit 18 includes button keys arranged on the video camera, soft keys assigned to icons displayed on a monitor screen mounted on the video camera, and the like, and an operation signal corresponding to a user operation is received. Input from the operation unit 18 to the microcomputer 17 via an interface (not shown).

  In the video camera configured as described above, the subject image is photoelectrically converted by the image sensors 1, 2, and 3 to generate primary color signals of red (R), green (G), and blue (B), and then the video The amplifiers 4, 5 and 6 and the A / D converters 7, 8 and 9 adjust the analog signals to appropriate levels, quantize them and convert them into digital signals. The quantized primary color signals (image data) are subjected to peripheral light amount drop correction and gain adjustment processing by the correction circuit 10 and gain adjustment circuit 11 and then input to the color adjustment circuit 12. Each primary color signal input to the color adjustment circuit 12 is adjusted to a desired color tone based on an instruction from the microcomputer 17 and input to the luminance adjustment circuit 13. Then, after appropriate luminance compression processing is performed by the luminance adjustment circuit 13, each primary color signal that is input to the gamma correction circuit 14 and is gamma corrected is converted into a final video signal output format by the output signal generation circuit 15. Is output.

  Here, the relationship between the size of the diaphragm and the light capture amount of the pixels arranged in the image sensor will be described. The same applies to the image sensors 2 and 3.

FIG. 2 is a diagram illustrating the relationship between the diaphragm and the light incident on the pixels in the diaphragm unit 1b and the image sensor 1. In the drawing, the light beam 22 that has passed through the opening 21 of the diaphragm 1 b is incident on the light receiving surface of the image sensor 1. On the light receiving surface of the image sensor 1, the intersection of the optical center and the image sensor 1 is defined as O ₁ point, and the position of an arbitrary pixel arranged in the image sensor 1 is defined as O ₂ point. A region 23 indicated by a broken line indicates a range in which a light beam can be incident on the pixel at the O ₂ point, and a region 24 indicated by a solid line indicates a range of light rays incident on the O ₂ point from the opening 21 of the aperture 1b. Represents.

FIG. 3 is a diagram for explaining the amount of light taken in according to the relationship between the aperture and the pixel. In FIG. 3, the radius 26 of the circle 25 formed around the O ₁ point by the aperture (opening 21) of the aperture 1a is set to r ₁ , and the circle 27 formed by the light capturing range of the pixel at the O ₂ point is set as the aperture. Assume that the radius 28 when projected onto the position 1b is r ₂ , the distance 29 from the optical center to the pixel is d, and the two intersections of the two circles 25 and 27 are A and B, respectively. At this time, the amount of incident light (overlap of the two circles 25 and 27) S incident on the pixel located at the point O ₂ is obtained as follows.

The area of the overlapping region of circle 25 and 27, the area obtained by subtracting the triangle _O 1 AB from sector _O 1 AB in circle 25, the sum of the area obtained by subtracting the triangle _O 2 AB from sector _O 2 AB in circle 27 Is. That is,
S = (πr ₁ ² × θ ₁ / π- r ₁ ² sinθ ₁ cosθ ₁ ) + (πr ₂ ² × θ ₂ / π- r ₂ ² sinθ ₂ cosθ ₂ )
^{_{= (R 1 2 θ 1 -}} r 1 2 sinθ 1 cosθ 1) + (r 2 2 θ 2 - r 2 2 sinθ 2 cosθ 2) ···· (1) formula

On the other hand, from the trigonometric formula,
d = r ₁ cosθ ₁ + r ₂ cosθ ₂ ··· Equation (2)
r ₂ sinθ ₂ = r ₁ sinθ ₁ ··· Equation (3) Also,
sin ² θ ₁ + cos ² θ ₁ = 1 (4)
sin ² θ ₂ + cos ² θ ₂ = 1 (5)

Solving equations (2), (3), (4), (5)
cosθ ₁ = (r ₁ ² + d ² -r ₂ ² ) / 2r ₁ d (6)
sinθ ₁ = √ [1-{(r ₁ ² + d ² -r ₂ ² ) / 2r ₁ d} ² ] (7)
cosθ ₂ = (r ₂ ² + d ² -r ₁ ² ) / 2r ₂ d (8)
sinθ ₂ = √ [1 − {(r ₂ ² + d ² −r ₁ ² ) / 2r ₂ d} ² ] (9)

Therefore, the incident light quantity S is
S = (r ₁ ² × arccos {(r ₁ ² + d ² -r ₂ ² ) / 2r ₁ d}-r ₁ ² × √ (1-((r ₁ ² + d ² -r ₂ ² ) / 2r ₁ d} ² ]
× {(r ₁ ² + d ² -r ₂ ² ) / 2r ₁ d}]
+ [R ₂ ² × arccos {(r ₂ ² + d ² -r ₁ ² ) / 2r ₂ d}-r ₂ ² × √ [1-((r ₂ ² + d ² -r ₁ ² ) / 2r ₂ d} ² ]
× {(r ₂ ² + d ² -r ₁ ² ) / 2r ₂ d}]... (10)

here,
F = (r ₁ ² + d ² -r ₂ ² ) / 2r ₁ d (11)
L = (r ₂ ² + d ² -r ₁ ² ) / 2r ₂ d (12)

If the replacement formulas (11) and (12) are used, the incident light quantity S can be finally expressed as follows.
S = [r ₁ ² × arccosF-r ₁ ² × √ (1-F ² ) × F] + (r ₂ ² × arccosL- r ₂ ² × √ (1-L ² ) × L)
.... (13) Formula

Here, in a pixel having image data, the change in the amount of incident light S with respect to the radius r ₁ of the stop (opening 21) is as shown in the graph of FIG. In the figure, the horizontal axis indicates the distance d from the screen center (optical center) to the pixel, and the vertical axis indicates the incident light quantity S. The radius r ₂ depending on the light capturing range of the pixel is fixed to “1”, and the radius r ₁ of the diaphragm is set to “1”, “3/4”, “1/2”, “1/4”, “1/8”. "5 levels." For each setting, the relationship between the distance d from the optical center to the pixel and the amount of incident light S was measured, and characteristic curves 31, 32, 33, 34, and 35 were obtained.

As can be seen from this result, the change in the amount of incident light S according to the distance d from the optical center depends on the size of the diaphragm (radius r ₁ ), and in particular when r ₁ = 1, that is, the diaphragm opens wide. If it is (open end), show the biggest drop.

  In order to correct such a peripheral light amount drop phenomenon, the present applicant proposes a method of applying a correction according to the distance from the optical center according to the size of the stop. However, in order to actually obtain the distance from the optical center, a square root calculation is required, and the burden on the circuit is large.

  The square root operation is an algorithm for obtaining an approximate value by a square root fraction of a positive real number that cannot be represented by a rational number, and recalculates iteratively using a result calculated once using approximate expansion or polynomial expansion. Usually, infinite terms are truncated at the appropriate point and calculated. The calculation results are temporarily stored in a memory and output at any time. In image processing, there are many cases where arithmetic processing is performed near the limit of processing capacity in accordance with clock synchronization of an arithmetic processing device such as the microcomputer 17, and real-time performance may be lacking. If the time required for the iterative calculation exceeds a predetermined calculation time for one pixel, the real-time property cannot be maintained.

Therefore, it is considered that all pixels on the screen are corrected by an expression that is proportional to the square of the distance from the screen center (optical center). For example, the corrected value of the amount of incident light at any pixel on the screen data (or image sensor) is expressed by the following equation, where Din is the pixel data before correction and Dout is the pixel data after correction. . This pixel data is data expressed by luminance values.

Dout = {a (d ² -c) + 1} × Din (d ² > c)
= Din (d ² <= c)
here,
d: Distance from the screen center (optical center)
a: Correction coefficient
c: Radius that is not corrected from the center of the screen (gain is 1 time).

  The correction coefficients a and c are parameters that are greatly influenced by the aperture position (aperture amount) and zoom position of the lens 1a. For example, c is a coefficient determined in consideration of a distance where the incident light amount S shown in FIG. 4 is a constant value (flat). Since the correction coefficient related to the radius that is not corrected from the optical center (gain is 1 time) is set, the correction gain is set with high accuracy according to the distance from the optical center, and correction with higher accuracy is possible.

  When the above correction formula is used, for example, the characteristics of the lens 1a are measured in advance, and at the time of shooting, the microcomputer 17 acquires information on the aperture position and zoom position of the lens 1a and interlocks with the aperture position and zoom position. Then, by setting an appropriate value, it is possible to correct the light amount drop at the periphery of the image sensor in real time.

  In this example, the correction coefficients a and c are determined in consideration of the zoom position in addition to the aperture position for the following reason. When the zoom position of the lens is changed, the angle of view changes, and the incident angle of the light beam transmitted through the lens with respect to the image sensor changes. If it does so, the circle which the light taken in in a stop part forms will become small, and the amount of light taking in will decrease. Therefore, as a preferred embodiment, when the zoom position is taken into consideration in addition to the aperture position, more accurate peripheral light amount drop correction is realized.

  When the pixel near the optical center of the image data is bright, that is, when the luminance value is larger than a predetermined threshold value, the correction coefficient a is negative, and the corrected luminance value is smaller than the luminance value before correction. Then, the pixel may be darkened.

Here, a graph in which the square of the distance d in the graph of FIG. 4 is taken on the horizontal axis and the maximum value (maximum gain) of the incident light amount of each characteristic curve is normalized to 1 time is plotted on the vertical axis in FIG. Show. In the figure, characteristic curve 41,42,42,44,45 the radius r ₁ of the aperture respectively (opening 21) is "1", "3/4", "1/2", "1/4", The peripheral light amount drop characteristic at “1/8” is shown. The reciprocal of each characteristic curve in this graph is an ideal correction gain.

  FIG. 6 shows an ideal correction gain for the peripheral light amount drop characteristic of FIG. In the figure, the horizontal axis indicates the square of the distance d from the screen center (optical center) to an arbitrary pixel, and the vertical axis indicates the correction gain. That is, when the normalized characteristic curve shown in FIG. 5 is multiplied by the correction gain characteristic curve shown in FIG. 6, “1” is obtained.

  As can be seen from this graph, the correction gain is approximated by a substantially monotonically increasing curve. However, it is conceivable that the error between the corrected value and the ideal value increases only by the correction related to the square term of the distance d from the center of the screen as described above. Accordingly, correction using not only a term proportional to the square of the distance d but also a term proportional to the fourth power of the distance d is considered. This is expressed by the following equation, where Din is pixel data before correction in a pixel and Dout is pixel data after correction. This pixel data is data expressed by luminance values.

Dout = {a (d ² -c _a ) ² + b (d ² -c _b ) + 1} × Din (d ² > c _a , c _b )
= {a (d ² -c _a ) ² + 1} × Din (d ² > c _a , d ² <c _b )
= {b (d ² -c _b ) + 1} × Din (d ² > c _b , d ² <c _a )
= Din (d ² <= c _a , c _b )
here,
d: Distance from the screen center (optical center)
b: Correction coefficient
c _a : Radius that is not corrected from the optical center in the fourth power term (gain is 1 time)
c _b : Radius that is not corrected from the optical center in the squared term (gain is 1 time).

With the above correction equation, the correction curve can be made closer to an ideal one without performing a large circuit scale calculation such as square root extraction. For the correction coefficients a, b, c _a , and c _b , the correction curve as shown in FIG. 6 is measured in advance according to the aperture position and the zoom position, and the correction coefficient in each case is measured. The value is obtained by approximate calculation such as the least square method and stored in the ROM. Then, the microcomputer 17 selects an appropriate coefficient corresponding to the aperture position at the time of shooting, and the correction circuit 10 corrects the pixel value at an arbitrary pixel of the screen data by a correction formula using the coefficient instructed to the microcomputer 17. , Etc. can be considered. It should be noted that a and b can take not only positive values but also negative values depending on the peripheral light amount drop characteristics depending on the aperture position and zoom position. Similarly, c _a and c _b may be the same value depending on the peripheral light amount drop characteristic.

  FIG. 7 shows an example of the circuit configuration of the correction circuit 10 that realizes the peripheral light amount drop correction process. In this example, the peripheral light amount drop correction circuit is configured by combining an adder and a multiplier.

  In the correction circuit of FIG. 7, the adder 61 adds the data indicating the input horizontal address value of the pixel to be corrected and the data indicating the value obtained by inverting the sign of the horizontal center value of the screen. That is, a process of subtracting the horizontal center value of the screen from the horizontal address value of the pixel is performed. Next, the multiplier 63 squares the value calculated by the adder 61 and supplies it to the adder 65.

  Similarly, the adder 62 adds the input data indicating the vertical address value of the pixel to be corrected and the data indicating the value obtained by inverting the sign of the vertical center value of the screen. That is, a process of subtracting the vertical center value of the screen from the vertical address value of the pixel is performed. Next, the multiplier 64 squares the calculated value calculated by the adder 62 and supplies it to the adder 65.

  The adder 65 adds the data output from the multipliers 63 and 64, and outputs the result to the adders 66 and 67, respectively.

In the adder 66, to data supplied from the adder 65, the microcomputer 17 selects, is not applied correction from the center in the fourth power term (gain 1 times) subtracts the data indicating the radius c _a And output to the clip processing unit 66a.

  The clip processing unit 66a is set to perform a clip operation at the clip level 0. When the value of the input data is greater than 0, the input data is output to the multiplier 68 as it is, and when the input data is 0 or less, it is discarded and 0 is output to the multiplier 68.

  Next, in the multiplier 68, the value of the data output from the clip processing unit 66 a is squared and output to the multiplier 69. Subsequently, the multiplier 69 multiplies the output of the multiplier 68 by a predetermined correction coefficient a selected by the microcomputer 17 and outputs the result to the adder 71.

On the other hand, in the adder 67, the data supplied from the adder 65 is data indicating the radius c _b that is not corrected from the center of the screen in the square term selected by the microcomputer 17 (gain is 1 time). Subtract and output to the clip processing unit 67a.

  The clip processing unit 67a is set to perform the clip operation at the clip level 0, similarly to the clip processing unit 66a. When the value of the input data is greater than 0, the input data is output to the multiplier 70 as it is, and when the input data is 0 or less, it is discarded and 0 is output to the multiplier 70.

  Next, the multiplier 70 multiplies the output of the clip processing unit 67 a by a predetermined correction coefficient b selected by the microcomputer 17 and outputs the result to the adder 71.

  The adder 71 adds the data output from the multipliers 69 and 70 and outputs the result to the adder 72. In the adder 72, a constant of a value representing a 1 × gain, for example, 1 is added to the output of the adder 71 and supplied to the multiplier 73. The multiplier 73 multiplies the pixel data Din representing the pixel value of the correction target pixel by the data output from the adder 72 and supplies the result to the rounding operation unit 74. Then, the rounding calculation unit 74 performs rounding calculation for a predetermined number of digits of the quantized data based on the rounding calculation code, and then outputs the pixel data Dout subjected to the peripheral light amount drop correction processing to the outside. As an example, the pixel value is expressed in 256 gradations from 0 to 255 based on 8-bit information.

The operation of the peripheral light amount drop correction circuit having the above configuration will be described with reference to FIG. In FIG. 8, in the coordinate system in which the upper left corner of the image data (image sensor) is the origin O (0, 0), the coordinates of the center of the screen are (C _H , C _V ), and the coordinates of the pixel to be corrected are (X _H, and _{Y V).}

First, the coordinate data with the pixel data Din of the pixel to be corrected is input to the adder 61 and 62 of the correction circuit 10, a horizontal address values X _H and the vertical address value X _V pixels, the horizontal center value of the window C _H and vertical address value C _V are respectively divided. Next, the data “(X _H −C _H )” and “(X _V −C _V )” calculated by the adders 61 and 62 by the multipliers 63 and 64 are squared by the multipliers 63 and 64, respectively. Then, the adder 65 adds the two data to obtain “(X _H −C _H ) ² + (X _V −C _V ) ² ”. ^{_{(X H -C H) 2 +}} (X V -C V) is a 2 = ^{d 2.} Then, the data “d ² ” calculated by the adder 65 is output to the adders 66 and 67, respectively.

The data “d ² ” input to the adder 66 is subtracted from the data c _a selected by the microcomputer 17 and indicating _a radius that is not corrected from the center of the screen in the fourth power term (gain is 1 time). , Output to the multiplier 68. Then, the multiplier 68 performs a calculation of squaring “(d ² −c _a )”, and the calculation result is output to the multiplier 69. In the multiplier 69, “(d ² −c _a ) ² ” is multiplied by the correction coefficient a selected by the microcomputer 17 and output to the adder 71.

On the other hand, the data “d ² ” supplied to the adder 67 is subtracted by the data c _b selected by the microcomputer 17 and indicating the radius that is not corrected from the center of the screen in item 2 (the gain is 1). Is done. The calculation result “(d ² −c _b )” is output to the multiplier 70, multiplied by the correction coefficient b selected by the microcomputer 17, and output to the adder 71.

In the adder 71, “a (d ² −c _a ) ² ” supplied from the multiplier 69 and “b (d ² −c _b )” supplied from the multiplier 70 are added, and the result is obtained. It is supplied to the adder 72. Then, a constant of a value representing a 1 × gain, for example, 1 is added by the adder 72 to obtain “a (d ² −c _a ) ² + b (d ² −c _b ) +1”. This calculation result is output to the multiplier 73, multiplied by the pixel data Din, subjected to a predetermined rounding operation by the rounding operation unit 74, and then output as pixel data Dout. As shown in the above formula, the clip processing units 66a and 67b perform the clip operation according to the values of (d ² −c _a ) and (d ² −c _b ), and the calculated value of the pixel data Dout differs. . This correction processing is performed for all the pixels of the image data based on each primary color signal.

Similarly, by adding higher-order even-order terms such as the 6th power term ((d ² -c) to the 3rd power) and 8th power terms ((d ² -c) to the 4th power) It is also possible to approach an ideal correction curve. Although correction with a higher degree of freedom is possible by using an odd-numbered term such as the third power (d ³ ), it is a trade-off relationship with circuit scale such as the need for square root calculation, and is not used in the present invention. .

  According to the peripheral light amount drop correction process described above, square root calculation is performed by applying correction according to the distance from the optical center based on the aperture position (zoom position) on the pixel value in an arbitrary pixel of the image data. Therefore, the peripheral light amount drop correction can be performed using a simple calculation formula.

  In addition to the term proportional to the square of the distance from the center of the screen (optical center), a term proportional to a higher-order even-order term such as the fourth power of the distance is used, so that the peripheral light amount drop correction can be performed with higher accuracy. Is possible. By approximating only the even-order term of the distance, highly accurate peripheral light amount drop correction can be realized with a simple circuit configuration (logic). Compared to the case involving square root extraction, the circuit scale can be reduced to a fraction, and the processing time can be reduced to a fraction.

  Furthermore, by using a correction formula that takes into account not only the aperture position but also the zoom value, a more accurate peripheral light amount drop correction process can be performed.

  In the above-described embodiment, the screen center and the optical center have been described as being coincident. However, the screen center and the optical center are not necessarily coincident, and in this case, the optical center is located at any position ( The peripheral light amount drop correction process is performed using the distance from the coordinate to the correction target pixel. Further, the shape of the aperture 21 of the aperture 1b and the light receiving portions of the image sensors 1, 2, and 3 has been described as a circle. However, even if this is a rectangle or the like, the video signal processing method of the present invention can be applied, and the same effect Can be obtained.

  In addition, the correction circuit 10 includes a storage unit such as a ROM that stores a diaphragm position (and zoom position) and a correction expression including a coefficient corresponding to the diaphragm position (and zoom position), and a diaphragm position (and You may provide the control part which selects a pattern (correction formula) according to a zoom position. In this case, the correction circuit 10 obtains information related to the aperture position (and zoom position) from the microcomputer 17, reads an appropriate correction formula based on the information, and uses the read correction formula for each pixel of the screen data. You may make it perform peripheral light amount fall correction | amendment.

  The processing of the video signal processing unit 16 (see FIG. 1) including the correction circuit 10 described above can be executed by hardware, but can also be executed by software. When a series of processing is executed by software, program codes constituting the software are stored in a storage unit such as a ROM built in the microcomputer 17. In particular, when the video signal processing (peripheral light intensity drop correction processing) according to the present invention is executed by software, a program code for executing the processing is newly installed in the storage unit, so that the video signal processing unit 16 On the other hand, the peripheral light amount drop correction function according to the present invention can be expanded.

  According to the present invention, a recording medium recording software program codes for realizing the functions of the above-described exemplary embodiments is supplied to a system or apparatus, and a computer (arithmetic processing unit) of the system or apparatus is stored in the recording medium. Needless to say, this can also be achieved by reading and executing the program code.

  As a recording medium for supplying the program code in this case, for example, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like is used. Can do.

  Further, by executing the program code read out by the computer, not only the functions of the above-described embodiment example are realized, but also an OS running on the computer is actually executed based on the instruction of the program code. This includes a case where part or all of the processing is performed and the functions of the above-described exemplary embodiments are realized by the processing.

  In the above-described embodiment, the example in which the imaging device according to the present invention is applied to a video camera has been described. However, the present invention is not limited to this, and may be, for example, a digital still camera or another device having an equivalent function. It can be widely applied to various devices. Furthermore, a receiver that receives a video signal from the imaging apparatus may be provided with the video signal processing function of the present invention, and this video signal processing, that is, peripheral light amount drop correction processing may be performed on the receiver side.

It is a block diagram which shows the structural example of the video camera which concerns on one Embodiment of this invention. It is a figure explaining the relationship between the position of a stop part, and the light which injects into a pixel. It is a figure explaining the taking-in light quantity by the relationship between an aperture stop and a pixel. It is a diagram which shows the relationship between the aperture radius and incident light quantity which concern on one Embodiment of this invention. It is a diagram which shows the relationship (after normalization) of the square of the distance and incident light quantity which concern on one Embodiment of this invention. It is a diagram which shows the relationship between the square of the distance which concerns on one Embodiment of this invention, and a peripheral light quantity fall correction gain. It is a figure which shows the example of the peripheral light amount fall correction | amendment circuit which concerns on one Embodiment of this invention. It is a figure where it uses for description of the coordinate of a pixel.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1a ... Lens, 1b ... Aperture part, 1, 2, 3 ... Image sensor, 10 ... Correction circuit, 17 ... Microcomputer, 18 ... Operation part, 61, 62, 65, 66, 67, 71, 72 ... Adder, 63, 64, 68, 69, 70, 73... Multiplier, 66a, 67a... Clip processing unit, 74.

Claims (8)

In an imaging apparatus that has an optical system including a lens and a diaphragm and an imaging unit, and performs peripheral light amount drop correction for image data obtained by the imaging unit,
Using a correction formula that represents a pixel value at an arbitrary pixel of the image data only by a term proportional to an even order of the distance from the optical center of the optical system to the pixel in accordance with the stop position of the stop portion. An image pickup apparatus comprising: a video signal processing circuit for correcting the image signal. The video signal processing circuit selects an appropriate correction formula from a storage unit in which the stop position and the correction formula are stored in association with each other according to the stop position of the stop portion, and based on the selected correction formula The imaging apparatus according to claim 1, wherein the pixel value of the pixel is corrected. When the pixel value before correction in any pixel of the image data input to the video signal processing circuit is Din, and the pixel value after correction is Dout, the correction formula is
Dout = {a (d ² -c) + 1} × Din (d ² > c)
= Din (d ² <= c)
However,
d: Distance from the optical center to the pixel
a: Correction coefficient determined according to the aperture position
The imaging apparatus according to claim 1, wherein c is expressed by a radius that is not corrected from the optical center. When the pixel value before correction in any pixel of the image data input to the video signal processing circuit is Din, and the pixel value after correction is Dout, the correction formula is
Dout = {a (d ² -c _a ) ² + b (d ² -c _b ) + 1} × Din (d ² > c _a , c _b )
= {a (d ² -c _a ) ² + 1} × Din (d ² > c _a , d ² <c _b )
= {b (d ² -c _b ) + 1} × Din (d ² > c _b , d ² <c _a )
= Din (d ² <= c _a , c _b )
However,
d: Distance from the optical center to the pixel
a, b: Correction factors determined according to the aperture position
c _a : Radius that is not corrected from the optical center in the fourth power term
The imaging apparatus according to claim 1, wherein the imaging device is represented by a radius that is not corrected from the optical center in the term of c _b : square. The imaging apparatus according to claim 1, wherein correction of a pixel value in an arbitrary pixel of the image data is performed in accordance with a zoom position of the lens, in addition to a diaphragm position of the diaphragm unit. In a video signal processing circuit that performs peripheral light amount drop correction on image data obtained by imaging an optical image incident on an imaging unit through an optical system including a lens and a diaphragm unit,
The video signal processing circuit is a term in which a pixel value in an arbitrary pixel of the image data is proportional to an even order of a distance from the optical center of the optical system to the pixel according to a stop position of the stop portion. A video signal processing circuit characterized in that correction is performed using a correction formula represented. In a video signal processing method for performing peripheral light amount drop correction on image data obtained by imaging an optical image incident on an imaging unit through an optical system including a lens and a diaphragm unit,
Detecting the aperture position of the aperture section;
Selecting an appropriate correction formula from the storage unit that stores the aperture position and the correction formula in association with each other according to the detected aperture position;
Correcting a pixel value at an arbitrary pixel of the image data using the selected correction formula,
The video signal processing method, wherein the correction formula is expressed only by a term proportional to an even order of the distance from the optical center of the optical system to the pixel. In a computer program for causing a computer to perform a peripheral light amount drop correction process on image data obtained by imaging an optical image incident on an imaging unit through an optical system including a lens and a diaphragm unit,
A process for detecting a diaphragm position of the diaphragm unit;
In accordance with the detected aperture position, a process for selecting an appropriate correction formula from the storage unit that stores the aperture position and the correction formula in association with each other;
Processing to correct a pixel value in an arbitrary pixel of the image data using the selected correction formula,
The computer program according to claim 1, wherein the correction formula is expressed only by a term proportional to an even order of a distance from the optical center of the optical system to the pixel.

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