JP2004200888A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device which is capable of correcting images luminance unevenness depending on the luminance level of the photoed image signals. <P>SOLUTION: The imaging device is equipped with an imaging means provided with an imaging element composed of a plurality of pixels for converting light rays incident through a lens into image signals, a recording means for recording correction data calculated on the basis of the image signals of an object which is photographed as a reference by the imaging means, a level detection means for detecting the luminance level of the image signals converted through the imaging means, a correction factor setting means for setting a prescribed correction factor for correcting the luminance level of the image signals converted through the imaging means corresponding to the luminance level of the image signals detected through the level detecting means, and a luminance unevenness correcting means for correcting the luminance level of the image signals converted through the imaging means on the basis of the prescribed correction factor set by the correction factor setting means and the correction data recorded in the recording means. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an imaging device capable of correcting luminance unevenness according to a luminance level of a captured video signal.
[0002]
[Prior art]
2. Description of the Related Art In an imaging device such as a digital still camera or a video camera, light from a subject input via a lens is converted into an electric signal by an imaging device such as a CCD (Charge Coupled Device), and the signal is further converted into a digital signal. The signal processing unit corrects the white balance and gradation and converts it into RGB (red / green / blue) signals, and converts the RGB signals into a luminance signal (Y) and color difference signals (Cb, Cr). ) Is generated for one frame.
[0003]
However, unevenness (hereinafter referred to as uneven brightness) occurs in the distribution of the brightness level in the video signal in one frame due to the characteristics of the lens and the image sensor of the imaging device.
[0004]
The uneven brightness caused by the lens characteristics is caused by a difference in the light amount between the central portion and the peripheral portion of the lens due to a decrease in the amount of incident light as the distance from the center of the lens decreases.
[0005]
FIG. 9 schematically shows the relationship between the distance of the lens from the optical axis center and the luminance level of the video signal. As the distance from the optical axis center of the lens increases, the amount of incident light (video signal level) increases. Is reduced, that is, in a captured one-frame video, the peripheral portion of the frame looks darker than the central portion, which greatly affects the image quality.
[0006]
In addition, luminance unevenness caused by an image sensor is uneven luminance caused by different incident angles of light with respect to a lens attached to an opening of each pixel (cell) constituting an image sensor such as a CCD. When light enters the pixel (cell) perpendicularly, a sufficient amount of light can be obtained, but as the angle of incidence of light changes (the angle increases) as the distance from the center of the lens increases, the pixel (cell) This is caused by a decrease in the amount of light incident on ()).
[0007]
FIG. 10 is a graph showing the relationship between the position of the lens and the luminance level of the video signal at each pixel. The amount of light decreases as the distance from the optical axis center of the lens increases. Since the luminance level decreases, the luminance level of the video signal decreases as the distance from the center of the lens increases, which causes luminance unevenness in the video signal of one frame.
[0008]
Such luminance unevenness can be reduced by improving the lens characteristics, but it is costly and may not be able to be completely corrected, and is usually corrected by the video signal processing unit.
[0009]
Here, a specific operation of the brightness unevenness correction processing of the video signal processing unit in the related art will be described with reference to the drawings.
[0010]
For example, as shown in the block diagram of FIG. 11, the main components related to the video signal processing include an imaging unit 10a, an S / H (Sample / Hold) circuit 20a, an AGC (Automatic Gain Control) circuit 30a, and an A / A It includes a D (Analog / Digital) conversion circuit 40a, a camera signal processing unit 50a, and the like.
[0011]
The camera signal processing unit 50a includes a video signal unevenness correction circuit 510a, a WB (white balance) circuit 511a, a γ correction circuit 512a, a color separation circuit 513a, a YC conversion circuit 514a, a memory 517a, and the like.
[0012]
In such a configuration, light from a subject is input through a lens of the imaging unit 10a, is converted into an electric signal by each pixel constituting an imaging device such as a CCD, and is converted into an S / H circuit 20a, an AGC circuit 30a, A It is converted to a digital video signal via the / D conversion circuit 40a and sent to the camera signal processing unit 50a.
[0013]
Then, the camera signal processing unit 50a corrects the luminance unevenness of the digital video signal input by the video signal correction circuit 510a using the correction data for the luminance correction stored in the memory 517a, and the white balance is output by the WB circuit 511a. Is adjusted (white correction), the tone is corrected by the γ correction circuit 512a, the pixel is interpolated by the color separation circuit 513a, and RGB signals are obtained for all the pixels. Then, the luminance signal (YC) is output by the YC conversion circuit 514a. Y) and color difference signals (Cb, Cr).
[0014]
Here, the correction data stored in the memory 517a is a distribution of luminance levels in a video signal obtained by photographing a colorless and high-luminance subject (white paper, light box, etc.), and measures the measured luminance level. Is calculated by the following equation (A) or (B) according to the distance [d] from the lens center point and the lens position [x, y] based on the distribution state of.
[0015]
Gi [d] = L [0] / L [d] (A)
[0016]
Note that L [0] is the luminance level of the optical axis center point (d = 0), and L [d] is the luminance level of the video signal at a distance [d] from the optical axis center point of the lens.
[0017]
Gi [x, y] = L [0,0] / L [x, y] (B)
[0018]
[X, y]; position corresponding to the lens, L [x, y]; luminance level of the video signal at position [x, y], L [0, 0]; y] = [0,0]).
[0019]
Then, the correction data Gi [d] or the correction data Gi [x, y] obtained using the mathematical formula (A) or the mathematical formula (B) are recorded in the memory 517a in advance at the time of factory shipment or the like.
[0020]
The camera signal processing circuit 50a corrects the luminance level of the photographed video signal using the correction data Gi [d] or the correction data Gi [x, y] recorded in the memory 517a, so that the position with respect to the lens and the position of the lens are corrected. The luminance level is corrected according to the distance from the center point.
[0021]
When the correction of the luminance level is performed according to the distance [d] from the center point of the lens (when the correction data Gi [d] is used), the circuit is simplified as shown in the graph of FIG. By setting the correction data Gi [d] to increase by a predetermined value each time the distance from the center point of the lens increases, it is also possible to correct the luminance without using a memory.
[0022]
In addition, when performing correction according to the position [x, y] of the lens (when using the correction data Gi [x, y]), the characteristics of the color filter on each pixel (cell) constituting the image sensor are not uniform. It is also possible to correct luminance unevenness caused by such factors as variation in characteristics caused in the manufacturing stage of pixels (cells) and luminance unevenness caused by pixel arrangement, so-called fixed pattern noise.
[0023]
In such luminance unevenness correction processing, since the luminance level of the video signal generally decreases more in the peripheral portion of the lens, the correction data in the peripheral portion of the lens is set to a larger value than the correction data in the central portion of the lens. ing. Therefore, the noise is amplified to the luminance level of the noise around the lens.
[0024]
Further, the correction data recorded in the memory is calculated based on a video signal when a colorless and high-luminance subject is photographed. When the brightness is dark (dark), the value of the correction data is too large (too strong), and the image at the peripheral portion of the lens becomes too bright than the central portion, which may result in an unnatural image.
[0025]
This becomes remarkable when an image of a subject whose periphery is dark is to be photographed. The reason for this is that the lower the luminance level, the more the video signal from an image sensor such as a CCD is more susceptible to noise components, and the human eye is more likely to notice noise in darker areas than in bright areas. Because it is.
[0026]
Furthermore, the lower the luminance level of the video signal is, the lower the S / N ratio is, and the more noise components are included. Therefore, the noise components that existed uniformly in the video signal (for one frame) before the correction become the lens components after the correction. In some cases, only the noise component in the peripheral portion is increased, and the noise in the peripheral portion of the lens, which was originally large, is further emphasized, thereby deteriorating the image quality.
[0027]
Further, the variation state of the luminance level in the video signal for one frame also depends on the luminance level of the video signal. When a high-luminance subject is photographed, the variation of the luminance level in the video signal in one frame is large, and the variation decreases as the luminance level of the subject decreases.
[0028]
For example, in the video signal A and the video signal B shown in FIG. 13, since the video signal A has a higher luminance level (the luminance of the subject is higher), the luminance level of the video signal in one frame greatly varies (luminance unevenness occurs). Large), and the video signal B has a lower luminance level (lower luminance of the subject), so that the noise component is larger.
[0029]
Here, the case where the luminance level of the video signal A and the video signal B shown in FIG. 13 is corrected according to the distance [d] from the center point of the lens (when the correction data Gi [d] is used) is referred to FIG. It will be explained while doing so.
[0030]
The video signal A and the video signal B take values of luminance levels as shown in the table of FIG. 14B according to the distance 0 to 10 from the center of the lens (optical axis). 14A, the luminance level decreases as the distance from the center of the lens (optical axis) increases, as indicated by the solid line in FIG.
[0031]
Further, as the value of the correction data (correction coefficient), a value obtained by the above equation (A) based on a video signal obtained by photographing a colorless and high-luminance subject is stored in the memory in advance. .
[0032]
Then, when the luminance levels of the video signal A and the video signal B are corrected by the correction data (correction coefficient), the luminance level of the peripheral portion of the lens that is lower than the center point of the (optical axis) of the lens becomes a dotted line in FIG. The correction is made as shown in the graph shown by.
[0033]
The video signal A is a video signal obtained by capturing a high-luminance subject, and the correction data (correction coefficient) is a value obtained based on the video signal obtained by capturing the colorless and high-luminance subject. The brightness is corrected to a uniform brightness level from the center to the periphery, and brightness unevenness is almost eliminated.
[0034]
On the other hand, since the video signal B is a video signal obtained by photographing a low-luminance subject, the value of the correction data is too large with respect to the luminance level of the peripheral portion of the lens. The brightness level becomes high.
[0035]
In addition, in practice, due to variations in characteristics that occur during the manufacturing stage of each pixel (cell) constituting the image sensor and non-uniform characteristics of the color filters on the pixels (cells), the above-described FIGS. As the distance from the (optical axis) center point of such a lens increases, the luminance level does not decrease, but as shown in FIG. 15, the luminance level varies due to the characteristics and arrangement (position) of each pixel. In addition, a unique pattern for each image sensor (each device), that is, a so-called fixed pattern noise appears.
[0036]
Therefore, since the variation in the luminance level of the video signal is not proportional to the distance from the center of the lens, it is necessary to perform correction for each pixel according to the position [x, y] of the lens.
[0037]
A case where the luminance level is corrected for each pixel according to such a lens position [x, y] (a case where correction data Gi [x, y] is used) will be described.
[0038]
A video signal A and a video signal B (solid line) shown in FIG. 16 are video signals when the effect of fixed pattern noise is added, and a certain one line (one column or one row of pixels) in one frame of the video signal 3 shows the state of the luminance level.
[0039]
The video signal A and the video signal B take luminance level values as shown in the table of FIG. 16B in a range of ± 60 from the center of the lens (optical axis), and are represented by graphs. As shown in the solid line in FIG. 16A, the luminance level varies for each pixel depending on the characteristics of the pixel and the distance from the center of the (optical axis) of the lens.
[0040]
Further, as the value of the correction data (correction coefficient), the value obtained by the above equation (B) based on the video signal obtained by photographing the colorless and high-luminance subject is stored in the memory in advance. .
[0041]
Then, when the luminance levels of the video signal A and the video signal B are corrected by the correction data (correction coefficient), they are corrected as indicated by the dotted lines in the graph of FIG.
[0042]
The video signal A is a video signal obtained by capturing a high-luminance subject, and the correction data (correction coefficient) is a value obtained based on a video signal obtained by capturing a colorless and high-luminance subject. Is corrected to a uniform luminance level, and luminance unevenness is almost eliminated.
[0043]
On the other hand, since the video signal B is a video signal of a low-luminance subject, the value of the correction data for a certain pixel may be too large (for example, when the distance [d] from the lens center is “-20”). (A correction value of a pixel), and the luminance level around this pixel becomes significantly higher than the luminance levels of other pixels, resulting in an unnatural image.
[0044]
Therefore, the correction of the luminance of the central portion and the peripheral portion of the image caused by the lens is corrected by the correction data created based on the image data obtained by photographing the solid white reference subject with uniform brightness over the entire surface. Reference 1) Sensitivity of an image sensor by changing at least one of correction data for columns and rows of an image captured by an image sensor in which pixels are two-dimensionally arranged according to the position of a pixel of interest. (See, for example, Patent Document 2), contour enhancement processing is performed together with shading correction processing, and luminance unevenness is improved by weakening contour enhancement of an image in a peripheral portion of a lens (for example, Patent Document 3). And other methods and devices have been devised.
[0045]
[Patent Document 1]
JP 2001-21456 A (pages 2-4, FIG. 1)
[Patent Document 2]
JP 2001-16509 A (page 5-8, FIG. 1)
[Patent Document 3]
JP 2001-167263 A (page 5-8, FIG. 1)
[0046]
[Problems to be solved by the invention]
As described above, the decrease in the luminance level of the video signal is proportional to the distance from the center of the optical axis of the lens, but is not necessarily symmetrical in the horizontal and vertical directions. For this reason, when the correction is performed only with the distance information from the center of the optical axis of the lens, there is a problem that the brightness of the corrected image differs depending on the direction.
[0047]
On the other hand, for uneven brightness caused by uneven application of color filters during the manufacture of imaging devices such as CCDs, a table with correction coefficients for each pixel is created, and the relationship between each pixel and lens position is checked for each pixel. It is necessary to correct the luminance level, but when using correction data created based on a video signal of a colorless and high-luminance subject at the time of correction, the correction gain is too large in a dark part with relatively much noise As a result, there is a problem that the fixed pattern noise is further emphasized.
[0048]
Further, with the miniaturization of the pixel (cell) size, when a pigment is used as a color filter material, a problem that luminance unevenness caused by the size of the pigment particles cannot be ignored is corrected. Removal) is becoming important.
[0049]
In addition, when the luminance enhancement is improved by performing the contour enhancement processing together with the shading correction processing, two correction data (table) for correcting the luminance unevenness of the video signal and the contour correction are required, so that the circuit scale becomes large and the processing becomes large. Is also complicated.
[0050]
Therefore, there is a method of switching the correction data (table) used for the correction based on the setting information (shutter speed, exposure, etc.) of the imaging device at the time of shooting, but the control is complicated and the captured video signal (1 There is a problem that it is not possible to correct luminance unevenness in accordance with the distribution state of the luminance level in (the frame).
[0051]
Therefore, it is necessary to solve the problem that the luminance level can be adjusted according to the distribution state of the luminance level in the photographed video signal and that the luminance unevenness caused by the lens and the image sensor can be corrected. Have issues that must be met.
[0052]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, an imaging device according to the present invention has the following configuration.
[0053]
(1) Imaging means including an image sensor composed of a plurality of pixels for converting light incident from a lens as a video signal, and a luminance level of the video signal converted by each pixel constituting the image sensor In order to correct the image signal, a recording unit in which correction data calculated based on a video signal obtained by capturing an image of a reference subject by the imaging unit is recorded, and a luminance level of the video signal converted by the imaging unit is detected. Level detecting means for performing, and a correction coefficient setting means for setting a predetermined correction coefficient for correcting the luminance level of the video signal converted by the imaging means according to the luminance level of the video signal detected by the level detecting means. The luminance level of the video signal converted by the imaging means based on the predetermined correction coefficient set by the correction coefficient setting means and the correction data recorded in the recording means. Imaging device, characterized in that it comprises a positive luminance nonuniformity correction unit.
(2) The correction data of the recording means is correction data calculated based on a video signal at the time of capturing an image of the reference subject with reference to a center point of the lens and according to a distance from the center point. The imaging device according to (1), wherein:
(3) The correction data of the recording means is based on a video signal when the subject as the reference is imaged, with the center point of the lens as a reference, and the image sensor based on positional information from the center point. (1). The imaging device according to (1), wherein the correction data is correction data calculated for each of the pixels constituting the image data.
(4) The correction coefficient setting means, when converting the video signal imaged by the imaging means into RGB signals, and processing the converted signals, a predetermined correction coefficient corresponding to each of the R, G, B signals (1). The imaging device according to (1), wherein
(5) The imaging device according to (1), wherein the correction coefficient setting unit can set a predetermined correction coefficient for each pixel constituting the image sensor.
[0054]
With such a configuration, the luminance level of the video signal converted by the imaging unit is detected by the level detection unit, and the correction coefficient setting unit sets a predetermined correction coefficient in accordance with the detected luminance level, thereby correcting the luminance unevenness. Means for correcting the luminance level of the video signal converted by the imaging means based on the correction coefficient set by the correction coefficient setting means and the correction data recorded in the recording means. To correct the luminance level and to correct luminance unevenness caused by the lens and the image sensor.
[0055]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of an imaging device according to the present invention will be described with reference to the drawings. However, the drawings are for explanation only, and do not limit the technical scope of the present invention.
[0056]
First, a first embodiment of an imaging device according to the present invention will be described with reference to FIG.
[0057]
FIG. 1 is a block diagram schematically showing a configuration of a main portion of a video signal for correcting unevenness in luminance of a video signal, and includes an imaging unit 10, an S / H (Sample / Hold) circuit 20, an AGC ( An automatic gain control (AT) circuit 30, an analog / digital (A / D) conversion circuit 40, a timing generator 45, a camera signal processing unit 50, and the like are provided.
[0058]
The imaging unit 10 includes a lens and an imaging element configured by arranging a plurality of pixels (for example, a CCD (Charge Coupled Device)) for converting incident light into an electric signal.
[0059]
Then, each pixel constituting the image sensor converts the light from the subject taken in through the lens into an electric signal, and sequentially takes in the electric signal converted by each pixel according to the timing signal generated by the timing generator 45, and An image in a range (hereinafter, referred to as a frame) captured through a lens in time is transmitted to the S / H circuit 20 as an analog video signal for one frame.
[0060]
The S / H circuit 20 has an input side connected to the imaging unit 10 and an output side connected to the AGC circuit 30, samples an analog video signal sent from the imaging unit 10, sends it to the AGC circuit 30, and outputs the sampled value. The data is held until the processing of the A / D conversion circuit 40 ends, and when this processing ends, the next sampling value is sent to the AGC circuit 30.
[0061]
The AGC circuit 30 has an input side connected to the S / H circuit 20 and an output side connected to the A / D conversion circuit 40, amplifies the analog video signal sampled by the S / H circuit 20, and Send to
[0062]
The A / D circuit 40 has an input side connected to the AGC circuit 30 and an output side connected to the camera signal processing unit 50, converts an analog video signal amplified by the AGC circuit 30 into a digital video signal, and sends the digital video signal to the camera signal processing unit 50. Send out.
[0063]
The timing generator 45 generates a timing signal serving as a reference for taking in the electric signal converted by each pixel constituting the image sensor of the image pickup unit 10 and sends it to the image pickup unit 10, and at the same time, an address counter of the camera signal processing unit 50. The same timing signal is sent to 518.
[0064]
The camera signal processing unit 50 includes a video signal correction circuit 510, a WB (white balance) circuit 511, a γ (gamma) correction circuit 512, a color separation circuit 513, a YC conversion circuit 514, a level detection circuit 515, a correction coefficient setting circuit 516, It is composed of a memory 517, an address counter 518, a multiplier 519, an LPF (Low Pass Filter) 520, an optical axis distance calculation circuit 521, etc., and a predetermined signal for a digital video signal sent from the A / D conversion circuit 40. The signal is processed, converted into a luminance signal (Y signal) and a color difference signal (Cb signal, Cr signal) and output.
[0065]
The circuits 510 to 521 constituting the camera signal processing unit 50 have the following functions.
[0066]
The video signal correction circuit 510 corrects the unevenness of the luminance signal level in the digital video signal sent from the A / D circuit 40 based on a shading correction coefficient G [d] (described later) and sends it to the WB circuit 511. .
[0067]
A WB (white balance) circuit 511 can correctly photograph white of the digital video signal subjected to the luminance unevenness correction processing by the video signal correction circuit 510 according to the color temperature that changes depending on the state of the light source in the photographing environment. That is, the so-called white balance correction is performed, and the result is sent to the γ correction circuit 512.
[0068]
The γ (gamma) correction circuit 512 corrects the gradation of the digital video signal subjected to the white balance correction processing in the WB circuit 511, that is, performs so-called γ correction, and sends the signal to the color separation circuit 513.
[0069]
The color separation circuit 513 performs interpolation of the digital video signal that has been subjected to the γ correction processing by the γ correction circuit 512, and is provided at a position where pixel data of R (red), G (green), and B (blue) does not exist. , And performs an interpolation process on the RGB signals in step (1), and sends the result to the YC conversion circuit 514.
[0070]
Specifically, for example, when an image sensor having a primary G color checkerboard and an R / B line sequential color filter array is used, only one of R, G, and B color signals exists at each pixel position. . In order to generate a luminance signal and a color difference signal for each pixel, R, G, and B signals are required at all pixel positions. This is a circuit for performing processing for obtaining RGB signals for pixels.
[0071]
The YC conversion circuit 514 converts the RGB signals interpolated by the color separation circuit 513 into a luminance signal (Y signal) and color difference signals (Cb signal, Cr signal) and outputs them.
[0072]
The level detection circuit 515 detects the luminance level of the digital video signal sent from the A / D circuit 40 and sends it to the correction coefficient setting circuit 516.
[0073]
The correction coefficient setting circuit 516 sets a correction coefficient Gh [In] for correcting luminance according to the luminance level of the digital video signal detected by the level detection circuit 515, and multiplies by the set correction coefficient Gh [In]. To the device 519.
[0074]
The memory 517 stores an image of a reference subject (for example, a colorless subject having a high luminance level and a colorless subject) based on the distribution of luminance levels in a video signal obtained from the image signal. The correction data Gi [d] of the luminance level calculated according to the distance is stored, and the correction data Gi [d corresponding to the distance [d] from the optical axis center of the lens indicated by the optical axis distance calculation circuit 521 is stored. ] To the multiplier 519.
[0075]
The address counter 518 fetches and counts the timing signal of the timing generator 45, and sends the count value to the optical axis distance calculation unit 521.
[0076]
The count value is a value that can determine at which position in the video (signal) of one frame captured by the imaging unit 10 the video signal has been processed by the pixel arranged, that is, the pixel value The value is a value corresponding to the arranged position.
[0077]
The optical axis distance calculation circuit 521 calculates the distance [d] from the optical axis center of the lens of the imaging unit 10 based on the count value from the address counter 518, and corresponds to the distance [d] calculated for the memory 517. To output the correction data Gi [d] to be output.
[0078]
The multiplier 519 multiplies the correction coefficient Gh [In] set by the correction coefficient setting circuit 516 by the correction data Gi [d] output from the memory 517, and calculates a correction value and a shading correction coefficient G. [d] is output to the LPF 520.
[0079]
An LPF (Low Pass Filter) 520 is sent from the multiplier 519 to remove the influence of noise and the like and to prevent the luminance of the video signal photographed by the correction using the shading correction coefficient G [d] from changing abruptly. The incoming shading correction coefficient G [d] is adjusted to a predetermined value and sent to the video signal correction circuit 510.
[0080]
A process of correcting uneven brightness of a video signal by the imaging device having the above configuration will be described with reference to the drawings.
[0081]
First, each pixel constituting the image sensor converts light from a subject captured through the lens of the imaging unit 10 into an electric signal, and converts the electric signal converted by each pixel according to a timing signal generated by the timing generator 45. The video is sequentially captured, and a video in a range (hereinafter, referred to as a frame) captured via a lens within a predetermined time is transmitted to the S / H circuit 20 as an analog video signal for one frame.
[0082]
The S / H circuit 20 samples the analog video signal sent from the imaging unit 10, sends it to the AGC circuit 30, and holds the sampled value until the processing of the A / D conversion circuit 40 is completed. Is completed, the next sampling value is sent to the AGC circuit 30.
[0083]
The AGC circuit 30 amplifies the analog video signal sampled by the S / H circuit 20, converts the analog video signal amplified by the AGC circuit 30 by the A / D circuit 40 into a digital video signal, and converts the analog video signal into a digital video signal. Send to
[0084]
The camera signal processing unit 50 sends the digital video signal from the A / D circuit 40 to the video signal correction circuit 510 and the level detection circuit 515.
[0085]
The level detection circuit 515 detects the luminance level of the transmitted digital video signal and sends it to the correction coefficient setting circuit 516. The correction coefficient setting circuit 516 outputs the correction coefficient Gh [In] according to the detected luminance level. Set and send to multiplier 519.
[0086]
More specifically, the correction coefficient setting circuit 14 divides the luminance level of the digital video signal into several stages, and has a table in which a predetermined correction coefficient Gh [In] is set in each stage. A predetermined correction coefficient Gh [In] is set with reference to this table according to the luminance level detected in 515.
[0087]
For example, as shown in FIG. 2, when the luminance level of the digital video signal detected by the level detection circuit 515 is in the range of 0 to 255, and when the luminance level is “0 to 64”, the correction coefficient Gh [In ] Is “5/8”, the correction coefficient Gh [In] is “6/8” when the luminance level is “65 to 128”, and the correction coefficient Gh [In] is “6/8” when the luminance level is “129 to 192”. When “7/8” and the luminance level are “193 to 255”, the correction coefficient Gh [In] is set to “8/8”. It is to be noted that more detailed control is possible by having a large table in which the level is divided more finely.
[0088]
On the other hand, the address counter 518 fetches the timing signal from the timing generator 45 and sends the counted value to the optical axis distance calculation circuit 521, and the image (for one frame) captured by the imaging unit 10 by the optical axis distance calculation circuit 521. Signal), and the distance [d] from the optical axis center point of the lens (frame) of the imaging unit 10 as shown in FIG. 3 is calculated based on the determined position information. Then, it instructs the memory 517 to transmit the correction data Gi [d] corresponding to the distance [d] to the multiplier 519.
[0089]
Then, the multiplier 519 multiplies the correction coefficient Gh [In] set by the correction coefficient setting circuit 516 by the correction data Gi [d] sent from the memory 517 to obtain a shading correction coefficient G [d]. Is calculated.
[0090]
Here, the value of the correction data Gi [d] stored in the memory 517 is closer to “1” toward the center of the lens and becomes larger than “1” toward the periphery of the lens. When the luminance unevenness occurs due to the color filter described above, the luminance may be higher (brighter) than the central portion of the lens which is the reference for the correction, and the value of the correction data Gi [d] is “1” or less. It may be.
[0091]
In consideration of such a case, the multiplier 519 calculates the equation 1 when the value of the correction data Gi [d] is smaller than “1”, and sets the equation 1 when the value of the correction data Gi [d] is larger than “1”. The shading correction coefficient G [d] is calculated by Expression 2.
[0092]
(Equation 1)
G [d] = (1-Gi [d]) × Gh [In]; When Gi [d] <1
[0093]
(Equation 2)
G [d] = (Gi [d] −1) × Gh [In]; When Gi [d]> 1
[0094]
The shading correction coefficient G [d] calculated by the multiplier 519 is sent to the LPF 520 to remove the influence of noise and the like by the LPF 520 and to prevent a sudden change in the entire video signal due to the shading correction coefficient G [d]. Is adjusted and sent to the video signal correction circuit 510.
[0095]
The video signal correction circuit 510 corrects luminance unevenness of the digital video signal sent from the A / D circuit 40 based on the shading correction coefficient G [d] from the LPF 520 and sends the corrected signal to the WB circuit 511.
[0096]
The digital video signal that has been subjected to the luminance unevenness correction processing by the video signal correction circuit 510 is subjected to white balance correction by the WB circuit 511, and then subjected to gradation correction by the γ correction circuit 512, The RGB signals interpolated by the color separation circuit 513 are converted into a luminance signal (Y signal) and a color difference signal (Cb signal, Cr signal) by a YC conversion circuit 514 and output to a subsequent circuit.
[0097]
In this way, based on the luminance level of the captured video signal, it is possible to appropriately correct the luminance unevenness according to the distance [d] from the center of the optical axis of the lens.
[0098]
Next, a second embodiment will be described with reference to FIG.
[0099]
Similar to the first embodiment (see FIG. 7), the same is true in that the luminance unevenness of the video signal is corrected in accordance with the distance [d] from the center of the lens, but it is provided in a general imaging device. A description will be given of a case where unevenness of luminance is corrected by using a shooting parameter setting circuit that automatically sets parameters required for shooting, such as a shutter speed and an exposure.
[0100]
As shown in FIG. 4, main parts for correcting uneven brightness in such an imaging device include an imaging unit 10, an S / H (Sample / Hold) circuit 20, an AGC (Automatic Gain Control) circuit 30, and an A / It includes a D (Analog / Digital) conversion circuit 40, a timing generator 45, a camera signal processing unit 50, a subject detection circuit 60, a shooting parameter setting circuit 70, and the like.
[0101]
Next, functions of each circuit and the like will be described. The imaging unit 10, an S / H (Sample / Hold) circuit 20, an AGC (Automatic Gain Control) circuit 30, an A / D (Analog / Digital) conversion circuit 40, a timing The function of the generator 45 is the same as that of the first embodiment, and the description thereof is omitted.
[0102]
The camera signal processing unit 50 includes a video signal correction circuit 510, a WB (white balance) circuit 511, a γ (gamma) correction circuit 512, a color separation circuit 513, a YC conversion circuit 514, a correction coefficient setting circuit 516, a memory 517, and an address counter. 518, a multiplier 519, an LPF (Low Pass Filter) 520, an optical axis distance calculation circuit 521, and the like.
[0103]
Next, the function of each of the circuits 510 to 521 constituting the camera signal processing unit 50 will be described. The video signal correction circuit 510 other than the correction coefficient setting circuit 516, the WB circuit 511, the γ correction circuit 512, and the color separation circuit 513 , The YC conversion circuit 514, the memory 517, the address counter 518, the multiplier 519, the LPF 520, and the optical axis distance calculation circuit 521, which have the same functions as those of the above-described first embodiment, and a description thereof will be omitted.
[0104]
The correction coefficient setting circuit 516 of the camera signal processing unit 50 controls the entire digital video signal based on the distribution state of the luminance level of the video signal (for one frame) detected by the subject detection circuit 60 under the control of the shooting parameter setting circuit 70. A correction coefficient Gh [all] for appropriately correcting the luminance of is set.
[0105]
As shown in FIG. 5, the value of the correction coefficient Gh [all] is set by decreasing the value of Gh [all] when photographing a subject with low luminance and increasing the value of Gh [all] when photographing a subject with high luminance. In addition, it is possible to suppress an increase in noise when the luminance is low, that is, when photographing a dark subject, and an increase in the luminance around the lens more than necessary.
[0106]
The subject detection circuit 60 detects the distribution state of the luminance level of the video signal (for one frame) sent from the A / D circuit 40 and sends it to the imaging parameter setting circuit 70.
[0107]
The photographing parameter setting circuit 70 controls the AGC circuit 30 and the WB circuit 511 to automatically set parameters necessary for photographing, such as a shutter speed and an exposure, and also sets an entire digital video signal detected by the subject detecting circuit 60 ( The distribution state of the luminance level (for one frame) is sent to the correction coefficient setting circuit 516.
[0108]
A process of correcting uneven brightness of a video signal by the imaging device having the above configuration will be described with reference to the drawings.
[0109]
First, each pixel constituting the image sensor converts light from a subject captured through the lens of the imaging unit 10 into an electric signal, and converts the electric signal converted by each pixel according to a timing signal generated by the timing generator 45. The video is sequentially captured, and a video in a range (hereinafter, referred to as a frame) captured via a lens within a predetermined time is transmitted to the S / H circuit 20 as an analog video signal for one frame.
[0110]
The S / H circuit 20 samples the analog video signal sent from the imaging unit 10, sends it to the AGC circuit 30, and holds the sampled value until the processing of the A / D conversion circuit 40 is completed. Is completed, the next sampling value is sent to the AGC circuit 30.
[0111]
The AGC circuit 30 amplifies the analog video signal sampled by the S / H circuit 20, converts the analog video signal amplified by the AGC circuit 30 by the A / D circuit 40 into a digital video signal, and converts the analog video signal into a digital video signal. Is sent to the subject detection unit 60.
[0112]
The subject detection unit 60 detects the distribution state of the luminance level of the digital video signal (for one frame) and sends it to the photographing parameter setting circuit 70. The photographing parameter setting circuit 70 converts the distribution state of the luminance level into a camera signal processing unit. 50 to the correction coefficient setting circuit 516.
[0113]
In the camera signal processing unit 50, the digital video signal from the A / D circuit 40 is sent to the video signal correction circuit 510, and the timing signal sent from the timing generator 45 is fetched and counted by the address counter 518. It is determined which position of the image (signal) of one frame captured by the imaging unit 10 is being processed, and a lens (frame) of the imaging unit 10 as shown in FIG. 3 based on the determined position information. Is calculated from the center of the optical axis, and the memory 517 is instructed to transmit the correction data Gi [d] corresponding to the distance [d] to the multiplier 519.
[0114]
The correction coefficient setting circuit 516 of the camera signal processing unit 50 sets a correction coefficient Gh [all] according to the luminance level distribution state of the digital video signal (photographed subject) sent from the photographing parameter setting circuit 70. Is sent to the multiplier 519.
[0115]
Then, the multiplier 519 performs shading by multiplying the correction coefficient Gh [all] set by the correction coefficient setting circuit 516 by the correction data Gi [d] sent from the memory 517 as shown in Expression 3. A correction coefficient G [d] is calculated.
[0116]
[Equation 3]
G [d] = Gi [d] × Gh [all]
[0117]
The shading correction coefficient G [d] calculated by the multiplier 519 is sent to the LPF 520 to remove the influence of noise or the like by the LPF 520, or to perform a sudden change due to the shading correction coefficient G [d] on the entire video signal. The signal is adjusted to prevent it from being sent to the video signal correction circuit 510.
[0118]
The video signal correction circuit 510 corrects luminance unevenness of the digital video signal sent from the A / D circuit 40 based on the shading correction coefficient G [d] from the LPF 520 and sends the corrected signal to the WB circuit 511.
[0119]
The digital video signal that has been subjected to the luminance unevenness correction processing by the video signal correction circuit 510 is subjected to white balance correction by the WB circuit 511, and then subjected to gradation correction by the γ correction circuit 512, The RGB signals interpolated by the color separation circuit 513 are converted into a luminance signal (Y signal) and a color difference signal (Cb signal, Cr signal) by a YC conversion circuit 514 and output to a subsequent circuit.
[0120]
As described above, it is also possible to perform correction using an existing circuit such as a subject detection circuit and a shooting parameter setting circuit.
[0121]
Next, a third embodiment will be described with reference to FIG. In the first and second embodiments described above, the uneven brightness of the video signal is corrected according to the distance [d] from the center of the lens. However, as described above, the image sensor of the image pickup unit 10 is configured. Each pixel has variations in characteristics that occur during the manufacturing stage, and furthermore, uneven brightness occurs due to the positional relationship between the lens and the pixel.
[0122]
Therefore, a case in which luminance unevenness is corrected based on the positional relationship between the lens and the pixel will be described.
[0123]
FIG. 6 is a block diagram schematically showing a configuration of a main part of luminance unevenness correction in an imaging device. The imaging unit 10, an S / H (Sample / Hold) circuit 20, an AGC (Automatic Gain Control). The circuit 30 includes an A / D (Analog / Digital) conversion circuit 40, a timing generator 45, a camera signal processing unit 50, and the like.
[0124]
The imaging unit 10 includes a lens and an imaging element configured by arranging a plurality of pixels (for example, a CCD (Charge Coupled Device)) for converting incident light into an electric signal.
[0125]
Then, each pixel constituting the image sensor converts the light from the subject captured through the lens of the imaging unit 10 into an electric signal, and converts the electric signal converted by each pixel according to the timing signal generated by the timing generator 45. The video is sequentially captured, and a video in a range (hereinafter, referred to as a frame) captured via a lens within a predetermined time is transmitted to the S / H circuit 20 as an analog video signal for one frame.
[0126]
The S / H circuit 20 has an input side connected to the imaging unit 10 and an output side connected to the AGC circuit 30, samples an analog video signal sent from the imaging unit 10, sends it to the AGC circuit 30, and outputs the sampled value. The data is held until the processing of the A / D conversion circuit 40 ends, and when this processing ends, the next sampling value is sent to the AGC circuit 30.
[0127]
The AGC circuit 30 has an input side connected to the S / H circuit 20 and an output side connected to the A / D conversion circuit 40, amplifies the analog video signal sampled by the S / H circuit 20, and Send to
[0128]
The A / D circuit 40 has an input side connected to the AGC circuit 30 and an output side connected to the camera signal processing unit 50, converts an analog video signal amplified by the AGC circuit 30 into a digital video signal, and sends the digital video signal to the camera signal processing unit 50. Send out.
[0129]
The timing generator 45 generates a timing signal serving as a reference for taking in the electric signal converted by each pixel constituting the image sensor of the image pickup unit 10 and sends it to the image pickup unit 10, and at the same time, an address counter of the camera signal processing unit 50. The same timing signal is sent to 518.
[0130]
The camera signal processing unit 50 includes a video signal correction circuit 510, a WB (white balance) circuit 511, a γ (gamma) correction circuit 512, a color separation circuit 513, a YC conversion circuit 514, a level detection circuit 515, a correction coefficient setting circuit 516, It comprises a memory 517, an address counter 518, a multiplier 519, an LPF (Low Pass Filter) 520, etc., performs predetermined signal processing on the digital video signal sent from the A / D conversion circuit 40, and outputs a luminance signal ( (Y signal) and color difference signals (Cb signal, Cr signal).
[0131]
Each of the circuits 510 to 520 constituting the above-described camera signal processing unit 50 has the following functions.
[0132]
The video signal correction circuit 510 corrects unevenness of the luminance signal level in the digital video signal sent from the A / D circuit 40 based on a shading correction coefficient G [x, y] (described later) and sends the corrected signal to the WB circuit 511. Send out.
[0133]
A WB (white balance) circuit 511 can correctly photograph white of the digital video signal subjected to the luminance unevenness correction processing by the video signal correction circuit 510 according to the color temperature that changes depending on the state of the light source in the photographing environment. That is, the so-called white balance correction is performed, and the result is sent to the γ correction circuit 512.
[0134]
The γ (gamma) correction circuit 512 corrects the gradation of the digital video signal subjected to the white balance correction processing in the WB circuit 511, that is, performs so-called γ correction, and sends the signal to the color separation circuit 513.
[0135]
The color separation circuit 513 performs interpolation of the digital video signal that has been subjected to the γ correction processing by the γ correction circuit 512, and is provided at a position where pixel data of R (red), G (green), and B (blue) does not exist. , And performs an interpolation process on the RGB signals in step (1), and sends the result to the YC conversion circuit 514.
[0136]
Specifically, for example, when an image sensor having a primary G color checkerboard and an R / B line sequential color filter array is used, only one of R, G, and B color signals exists at each pixel position. . In order to generate a luminance signal and a color difference signal for each pixel, R, G, and B signals are required at all pixel positions. This is a circuit for performing processing for obtaining RGB signals for pixels.
[0137]
The YC conversion circuit 514 converts the RGB signals interpolated by the color separation circuit 513 into a luminance signal (Y signal) and color difference signals (Cb signal, Cr signal) and outputs them.
[0138]
The level detection circuit 515 detects the luminance level of the digital video signal sent from the A / D circuit 40 and sends it to the correction coefficient setting circuit 516.
[0139]
The correction coefficient setting circuit 516 sets a correction coefficient Gh [In] for correcting luminance according to the luminance level of the digital video signal detected by the level detection circuit 515, and multiplies by the set correction coefficient Gh [In]. To the device 519.
[0140]
The memory 517 performs processing (conversion) for each pixel constituting the image sensor of the imaging unit 10 based on a video signal obtained when an image of a reference subject (for example, a colorless subject having a high luminance level) is captured. The luminance level of the video signal is obtained, and correction data Gi [x, y] for each pixel calculated based on the luminance level is stored, and correction data Gi [x corresponding to the position information indicated by the address counter 518 is stored. , y] to the multiplier 519.
[0141]
The address counter 518 fetches and counts the timing signal of the timing generator 45, and sends the count value to the memory 517.
[0142]
This count value can be used to determine where in the video (signal) of one frame captured by the imaging unit 10 the video signal has been processed by the pixel disposed, that is, the pixel is located. It has a value corresponding to the position information (position [x, y]).
[0143]
The multiplier 519 multiplies the correction coefficient Gh [In] set by the correction coefficient setting circuit 516 by the correction data Gi [x, y] output from the memory 517 and calculates a correction value for each pixel. The shading correction coefficient G [x, y] is output to the LPF 520.
[0144]
An LPF (Low Pass Filter) 520 is sent from the multiplier 519 to remove the influence of noise and the like and to prevent the luminance of the video signal photographed by the correction using the shading correction coefficient G [d] from changing abruptly. The incoming shading correction coefficient G [x, y] is adjusted to a predetermined value and sent to the video signal correction circuit 510.
[0145]
A process of correcting uneven brightness of a video signal by the imaging device having the above configuration will be described with reference to the drawings.
[0146]
First, each pixel constituting the image sensor converts light from a subject captured through the lens of the imaging unit 10 into an electric signal, and converts the electric signal converted by each pixel according to a timing signal generated by the timing generator 45. The video is sequentially captured, and a video in a range (hereinafter, referred to as a frame) captured via a lens within a predetermined time is transmitted to the S / H circuit 20 as an analog video signal for one frame.
[0147]
The S / H circuit 20 samples the analog video signal sent from the imaging unit 10, sends it to the AGC circuit 30, and holds the sampled value until the processing of the A / D conversion circuit 40 is completed. Is completed, the next sampling value is sent to the AGC circuit 30.
[0148]
The AGC circuit 30 amplifies the analog video signal sampled by the S / H circuit 20, and the A / D circuit 40 converts the analog video signal amplified by the AGC circuit 30 into a digital video signal, and converts the analog video signal into a digital video signal. Send to 50.
[0149]
The camera signal processing unit 50 sends the digital video signal from the A / D circuit 40 to the video signal correction circuit 510 and the level detection circuit 515.
[0150]
The level detection circuit 515 detects the luminance level of the transmitted digital video signal and sends it to the correction coefficient setting circuit 516. The correction coefficient setting circuit 516 outputs the correction coefficient Gh [In] according to the detected luminance level. Set and send to multiplier 519.
[0151]
On the other hand, the address counter 518 takes in the timing signal from the timing generator 45 and sends the counted value to the memory 517. The memory 517 uses the lens (frame) as shown in FIG. 7 based on the sent count value. Is instructed to transmit the correction data Gi [x, y] of the pixel corresponding to the position [x, y] to the multiplier 519.
[0152]
Here, the value of the correction data Gi [x, y] stored in the memory 517 is closer to “1” toward the center of the lens and becomes larger than “1” toward the periphery of the lens. When luminance unevenness occurs due to the color filter of the image sensor, the luminance may be larger (brighter) than the central portion of the lens that is the reference for correction, and the value of the correction data Gi [x, y] may be smaller. It may be "1" or less.
[0153]
Therefore, in consideration of such a case, when the value of the correction data Gi [x, y] is smaller than “1”, the multiplier 519 sets the value of Expression 3 and the value of the correction data Gi [x, y] to “1”. If it is larger, the shading correction coefficient G [x, y] is calculated by Expression 4.
[0154]
(Equation 4)
G [x, y] = (1-Gi [x, y]) × Gh [In]; When Gi [x, y] <1
[0155]
(Equation 5)
G [x, y] = (Gi [x, y] −1) × Gh [In]; When Gi [x, y]> 1
[0156]
The shading correction coefficient G [x, y] calculated by the multiplier 519 is sent to the LPF 520 to remove the influence of noise or the like by the LPF 520, or to use the shading correction coefficient G [x, y] for the entire video signal. Adjustments are made to prevent abrupt changes and sent to the video signal correction circuit 510.
[0157]
The video signal correction circuit 510 corrects luminance unevenness of the digital video signal sent from the A / D circuit 40 based on the shading correction coefficient G [x, y] from the LPF 520 and sends the corrected signal to the WB circuit 511.
[0158]
The digital video signal that has been subjected to the luminance unevenness correction processing by the video signal correction circuit 510 is subjected to white balance correction by the WB circuit 511, and then subjected to gradation correction by the γ correction circuit 512, The RGB signals interpolated by the color separation circuit 513 are converted into a luminance signal (Y signal) and a color difference signal (Cb signal, Cr signal) by a YC conversion circuit 514 and output to a subsequent circuit.
[0159]
As described above, since the uneven brightness is corrected based on the positional relationship between the lens and the pixel according to the brightness level of the captured video signal, the uneven brightness due to the fixed pattern noise caused by the pixels constituting the image sensor is included. Corrections can be made.
[0160]
Next, a fourth embodiment will be described with reference to FIG.
[0161]
Similar to the third embodiment (see FIG. 6) described above, the method is the same in that luminance unevenness is corrected for each pixel constituting an image sensor, but the shutter speed, exposure, and the like provided in a general image capturing device are used. A description will be given of a case where luminance unevenness is corrected by using a shooting parameter setting circuit that automatically sets parameters required for shooting.
[0162]
As shown in FIG. 8, the main parts for correcting the uneven brightness in such an imaging device include an imaging unit 10, an S / H (Sample / Hold) circuit 20, an AGC (Automatic Gain Control) circuit 30, and an A / It includes a D (Analog / Digital) conversion circuit 40, a timing generator 45, a camera signal processing unit 50, a subject detection circuit 60, a shooting parameter setting circuit 70, and the like.
[0163]
Next, the function of each circuit will be described. The imaging unit 10, an S / H (Sample / Hold) circuit 20, an AGC (Automatic Gain Control) circuit 30, an A / D (Analog / Digital) conversion circuit 40, a timing generator 45 has the same function as the above-described first to third embodiments, and a description thereof will be omitted.
[0164]
The camera signal processing unit 50 includes a video signal correction circuit 510, a WB (white balance) circuit 511, a γ (gamma) correction circuit 512, a color separation circuit 513, a YC conversion circuit 514, a correction coefficient setting circuit 516, a memory 517, and an address counter. 518, a multiplier 519, an LPF (Low Pass Filter) 520, and the like.
[0165]
Next, the function of each of the circuits 510 to 520 constituting the camera signal processing unit 50 will be described. The video signal correction circuit 510 other than the correction coefficient setting circuit 516, the WB circuit 511, the γ correction circuit 512, and the color separation circuit 513 , The YC conversion circuit 514, the memory 517, the address counter 518, the multiplier 519, and the LPF 520 have the same functions as those of the third embodiment described above, and thus the description thereof will be omitted.
[0166]
The correction coefficient setting circuit 516 of the camera signal processing unit 50 controls the entire video signal based on the luminance level distribution of the video signal (for one frame) detected by the subject detection circuit 60 under the control of the imaging parameter setting circuit 70. A correction coefficient Gh [all] for appropriately correcting the luminance is set.
[0167]
Note that, as in the description of the second embodiment, the value of the correction coefficient Gh [all] is set to a small value for Gh [all] when a subject with low luminance is photographed, as shown in FIG. When a high-luminance subject is photographed, by increasing the luminance, it is possible to suppress an increase in noise at the time of photographing a low-luminance, or dark subject, and an increase in luminance around the lens more than necessary.
[0168]
The subject detection circuit 60 detects the distribution state of the luminance level of the video signal (for one frame) sent from the A / D circuit 40 and sends it to the imaging parameter setting circuit 70.
[0169]
The shooting parameter setting circuit 70 controls the AGC circuit 30 and the WB circuit 511 to automatically set parameters required for shooting, such as shutter speed and exposure, and also sets a digital video signal (1) detected by the subject detection circuit 60. The distribution state of the luminance level (for the frame) is sent to the correction coefficient setting circuit 516.
[0170]
A process of correcting uneven brightness of a video signal by the imaging device having the above configuration will be described with reference to the drawings.
[0171]
First, each pixel constituting the image sensor converts light from a subject captured through the lens of the imaging unit 10 into an electric signal, and converts the electric signal converted by each pixel according to a timing signal generated by the timing generator 45. The video is sequentially captured, and a video in a range (hereinafter, referred to as a frame) captured via a lens within a predetermined time is transmitted to the S / H circuit 20 as an analog video signal for one frame.
[0172]
The S / H circuit 20 samples the analog video signal sent from the imaging unit 10, sends it to the AGC circuit 30, and holds the sampled value until the processing of the A / D conversion circuit 40 is completed. Is completed, the next sampling value is sent to the AGC circuit 30.
[0173]
The AGC circuit 30 amplifies the analog video signal sampled by the S / H circuit 20, converts the analog video signal amplified by the AGC circuit 30 by the A / D circuit 40 into a digital video signal, and converts the analog video signal into a digital video signal. Is sent to the subject detection unit 60.
[0174]
The subject detection unit 60 detects the distribution state of the luminance level of the digital video signal (for one frame) and sends it to the photographing parameter setting circuit 70. The photographing parameter setting circuit 70 converts the distribution state of the luminance level into a camera signal processing unit. 50 to the correction coefficient setting circuit 516.
[0175]
The camera signal processing unit 50 sends the digital video signal from the A / D circuit 40 to the video signal correction circuit 510, and also takes in the timing signal from the timing generator 45 and sends the count value counted by the address counter 518 to the memory 517. The correction data Gi [x, y] of the pixel corresponding to the position [x, y] in the frame as shown in FIG. 5 is transmitted to the multiplier 519 based on the count value transmitted from the memory 517. Instruct.
[0176]
Further, the correction coefficient setting circuit 516 of the camera signal processing unit 50 sets a correction coefficient Gh [all] according to the distribution state of the luminance level sent from the imaging parameter setting circuit 70 and sends it to the multiplier 519.
[0177]
Then, the multiplier 519 multiplies the correction coefficient Gh [all] set by the correction coefficient setting circuit 516 and the correction data Gi [x, y] sent from the memory 517 as shown in Expression 4. The shading correction coefficient G [x, y] is calculated.
[0178]
(Equation 6)
G [x, y] = Gi [x, y] × Gh [all]
[0179]
The shading correction coefficient G [x, y] calculated by the multiplier 519 is sent to the LPF 520 to remove the influence of noise or the like by the LPF 520, or to use the shading correction coefficient G [x, y] for the entire video signal. Adjustments are made to prevent abrupt changes and sent to the video signal correction circuit 510.
[0180]
The video signal correction circuit 510 corrects luminance unevenness of the digital video signal sent from the A / D circuit 40 based on the shading correction coefficient G [x, y] from the LPF 520 and sends the corrected signal to the WB circuit 511.
[0181]
The digital video signal that has been subjected to the luminance unevenness correction processing by the video signal correction circuit 510 is subjected to white balance correction by the WB circuit 511, and then subjected to gradation correction by the γ correction circuit 512, The color separation circuit 513 interpolates the pixels to obtain RGB signals for all the pixels. The RGB signals are converted into a luminance signal (Y signal) and a color difference signal (Cb signal, Cr signal) by a YC conversion circuit 514, and the subsequent stage. Output to the circuit.
[0182]
As described above, using the existing circuits such as the subject detection circuit and the shooting parameter setting circuit, the correction including the brightness unevenness due to the fixed pattern noise by the pixels constituting the image sensor is performed according to the brightness level of the captured video signal. It can be carried out.
[0183]
In the above-described first to fourth embodiments, in a device that captures a color image, a color filter is used for an image sensor such as a CCD, and the color filter is R (red) / G (green) / Since B (blue) color is applied and one pixel corresponds to each color, for example, even when a white subject is photographed, these three color filters have different spectral characteristics, so that the three color filters have different spectral characteristics. The distribution state of the luminance level is not the same for the pixels corresponding to the filters of the respective colors, and the luminance level of the video signal is generally higher in the order of G (green) → R (red) → B (blue). That is, the luminance level of the pixel corresponding to each color filter is high.
[0184]
Therefore, the correction data Gi [d] or the correction data Gi [x, y] corresponding to the filters of R (red) / G (green) / B (blue) are stored in the memory, and the correction coefficient setting circuit is provided. By setting a correction coefficient G [d] or a correction coefficient G [x, y] corresponding to the luminance level of the video signal of each color, the shading correction coefficient G [d] for the RGB video signal or A shading correction coefficient G [x, y] is calculated, and the luminance level and the luminance unevenness of the R (red) / G (green) / B (blue) video signal are corrected.
[0185]
In addition, not only the CCD but also a CMOS (Complementary Metal Oxide Semiconductor) sensor as the imaging device in the first to fourth embodiments can perform the same brightness unevenness correction as described above.
[0186]
【The invention's effect】
As described above, the luminance level of the captured video signal is detected, the luminance level correction coefficient is set according to the detected luminance level, and the set correction coefficient and the luminance level correction stored in a memory or the like in advance are set. Since the luminance level of the photographed video signal is corrected based on the data, the luminance level can be corrected according to the photographed video signal, and the luminance unevenness caused by a lens, an image sensor, and the like can be effectively reduced. This is an extremely excellent effect that it can be removed to a great extent.
[0187]
Furthermore, it is possible to prevent the noise in the peripheral portion of the lens caused by the correction of the unevenness of the video signal from being emphasized, and when a subject having a low luminance level is photographed, the image in the peripheral portion of the lens becomes too bright. Unnatural images can be prevented.
[0188]
In addition, since uneven brightness can be corrected according to the brightness level of the video signal, there is no need to separately prepare correction data according to shooting conditions such as shutter speed, reducing the memory capacity and circuit scale. can do.
[0189]
In addition, since the S / N ratio when the illuminance of the subject is dark is improved, there is a merit that shooting with a darker illuminance of the subject becomes possible.
[Brief description of the drawings]
FIG. 1 is a block diagram schematically illustrating a main part of luminance unevenness correction in an imaging device according to a first embodiment of the present invention.
FIG. 2 is an explanatory diagram for describing a table of a correction coefficient Gh included in the imaging device illustrated in FIG. 1;
FIG. 3 is an explanatory diagram for describing a distance [d] from a center of an optical axis of a lens (frame) in the imaging device illustrated in FIG. 1;
FIG. 4 is a block diagram schematically illustrating a main part of luminance unevenness correction in an imaging device according to a second embodiment of the present invention.
FIG. 5 is an explanatory diagram for describing setting of a correction coefficient Gh [all] in the imaging device shown in FIG. 4;
FIG. 6 is a block diagram schematically illustrating a main part of luminance unevenness correction in an imaging device according to a third embodiment of the present invention.
7 is an explanatory diagram for describing a position [x, y] on a lens (frame) in the imaging device shown in FIG. 6;
FIG. 8 is a block diagram schematically illustrating a main part of luminance unevenness correction in an imaging device according to a fourth embodiment of the present invention.
FIG. 9 is a graph schematically showing a relationship between a distance from a center of an optical axis of a lens and a luminance level of a video signal.
FIG. 10 is a graph showing a relationship between a lens position and a luminance level of a video signal in each pixel.
FIG. 11 is a block diagram schematically showing a main part of luminance unevenness correction in a conventional imaging device.
FIG. 12 is an explanatory diagram for describing setting of correction data when correcting a luminance level according to a distance [d] from a center point of a lens in the imaging device illustrated in FIG. 11;
FIG. 13 is an explanatory diagram schematically showing a comparison between a video signal having a large luminance level (the luminance of the subject is high) and a video signal having a low luminance level (the luminance of the subject is low).
14 is an explanatory diagram in a case where the luminance level of the video signal shown in FIG. 13 is corrected according to the distance [d] from the center point of the lens.
FIG. 15 is a graph showing a relationship between a lens position and a luminance level of a video signal in each pixel when fixed pattern noise is considered.
FIG. 16 is an explanatory diagram of a case where a video signal having a large luminance level (subject luminance is high) and a video signal having a low luminance level (subject luminance is low) are corrected in consideration of fixed pattern noise.
[Explanation of symbols]
Reference numeral 10: imaging unit, 20; S / H (Sample / Hold) circuit, 30; AGC (Automatic Gain Control) circuit, 40; A / D (Analog / Digital) conversion circuit, 45; timing generator, 50; camera signal processing 510; WB (white balance) circuit, 512; γ correction circuit, 513; color separation circuit, 514; YC conversion circuit, 515; level detection circuit, 516; 517; memory, 518; address counter, 519; multiplier, 520; LPF (Low Pass Filter), 521; distance calculation circuit, 60; subject detection circuit, 70; shooting parameter setting circuit
10a; imaging unit, 20a; S / H (Sample / Hold) circuit, 30a; AGC (Automatic Gain Control) circuit, 40a; A / D (Analog / Digital) conversion circuit, 50a; camera signal processing unit, 510a; Signal unevenness correction circuit, 511a; WB (white balance) circuit, 512a; γ correction circuit, 513a; color separation circuit, 514a; YC conversion circuit, 515a; level detection circuit, 517a;

Claims (5)

Imaging means including an imaging element composed of a plurality of pixels for converting light incident from the lens as a video signal,
In order to correct the luminance level of the video signal converted by each pixel constituting the image sensor, correction data calculated based on a video signal obtained when an image of a reference subject is captured by the imaging unit is recorded. Recording means;
A level detecting means for detecting a luminance level of the video signal converted by the imaging means, and correcting a luminance level of the video signal converted by the imaging means according to the luminance level of the video signal detected by the level detecting means. Correction coefficient setting means for setting a predetermined correction coefficient of
Brightness unevenness correction means for correcting the brightness level of the video signal converted by the imaging means based on the predetermined correction coefficient set by the correction coefficient setting means and the correction data recorded in the recording means. An imaging device characterized in that: The correction data of the recording unit is correction data calculated based on a video signal obtained when the reference subject is imaged, based on a center point of the lens and based on a distance from the center point. The imaging device according to claim 1, wherein: The correction data of the recording unit configures the image sensor according to position information from the center point with reference to the center point of the lens based on a video signal obtained when the reference subject is imaged. 2. The imaging apparatus according to claim 1, wherein the correction data is correction data calculated for each pixel. The correction coefficient setting means can set a predetermined correction coefficient corresponding to each of the R, G, and B signals when the video signal imaged by the imaging means is converted into RGB signals and processed. The imaging device according to claim 1, wherein: 2. The imaging apparatus according to claim 1, wherein the correction coefficient setting unit can set a predetermined correction coefficient for each pixel constituting the image sensor.

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