JP2006121386A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus without increase of a noise even if it performs processing of both a shading compensation and an adaptive gamma correction. <P>SOLUTION: The imaging apparatus includes a configuration of dividing a photography image into a plurality of blocks, performing the adaptive gamma correction by detecting the density distribution of each block, detecting the correction condition by the shading compensation by the density distribution of an image peripheral block with large influence of shading, and controlling the amount of the shading compensation so that the noise does not increased beyond a predetermined range. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an imaging apparatus that generates a histogram of an output signal from an imaging device, applies adaptive gamma correction from the histogram, and corrects shading of an optical system and the imaging device.

  As proposed in (Patent Document 1) and the like, adaptive gamma correction by taking a histogram selects a gamma characteristic that increases the contrast by signal processing when the subject image contrast is low, and the subject When the contrast of the image is high, a gamma characteristic that lowers the contrast by signal processing is selected.

In addition, as in Patent Document 2, there is a proposal for performing adaptive gamma correction on a signal subjected to shading correction.
JP 09-224174 A JP 2003-304399 A

  However, in an imaging apparatus having an optical system and an image sensor, shading (brightness and color shading) possessed by the optical system and the image sensor is conspicuous in low-contrast subjects. When the type gamma correction is performed, shading of brightness and color becomes more conspicuous.

  In addition, by correcting the shading of the optical system and the image sensor, it is possible to reduce the adverse effects of shading on the captured image in the low-contrast subject as described above. As a result, the amount of gain increase due to both the adaptive gamma characteristic and the luminance increases and the noise of the color increases.

  In the present invention, even if a histogram of a subject image is generated, and luminance and color shading correction is performed while selecting an adaptive gamma characteristic from the histogram, noise increase is caused at the location where the correction is applied. An object of the present invention is to provide a non-imaging device.

  In order to achieve the above object, in the present invention, a captured image is divided into a plurality of areas, density distribution is detected for each divided area, and an appropriate gamma characteristic is selected as the adaptive gamma characteristic from the density distribution status of all areas. At the same time, the density distribution situation of the plurality of areas in the peripheral part of the captured image that is easily affected by the shading of the optical system and the image sensor is detected, and the plurality of areas are applied from the predetermined range of density and the selected gamma characteristic. A typical gamma correction Gain is detected, while a shading correction table provided in the optical system and the image sensor is provided to detect the Gain UP amount due to the shading correction applied to a plurality of areas around the selected photographed image. A white balance correction coefficient is detected, and a plurality of correction amounts (gamma correction Ga) applied to the predetermined areas. n, and calculates the maximum Gain amplification amount as the shading correction Gain, results WB correction Gain) multiplied by. The gain amplification amount is compared with a predetermined limit value. When the gain amplification amount by various corrections exceeds the limit value, shading is performed so that the gain amplification amount by the correction is within the limit value. By suppressing the correction amount and performing shading correction of the optical system and the image sensor with the suppressed shading correction amount, an increase in noise due to various corrections can be kept within a predetermined range.

  Further, the first invention of the present invention will be described as follows.

  (1) An optical system and an image sensor that converts light that has passed through the optical system into an electric signal, a dividing unit that divides an image signal output from the image sensor into a plurality of areas, and an image sensor output signal in the divided area Means for detecting the density distribution of the image, gamma correction means, means for storing the shading correction amount for correcting the shading characteristics of the optical system and the image sensor, and the shading correction means. Means for calculating a suppression amount with respect to the stored shading correction amount, and performing shading correction on the image sensor output signal by applying the suppression calculated above to the shading correction amount. Imaging device.

  In the present invention, even if a histogram of a subject image is generated, and luminance and color shading correction is performed while selecting an adaptive gamma characteristic from the histogram, noise increase is caused at the location where the correction is applied. An object of the present invention is to provide a non-imaging device.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

  FIG. 1 is a block diagram showing an embodiment of a digital camera to which the present invention is applied. 1 is a lens having a zoom mechanism and a focus mechanism, a mechanism for driving the lens, and 2 is a light collected by the lens 1. An aperture mechanism 3 for controlling the amount of light is an image pickup device (hereinafter referred to as a CCD) having a plurality of color filters for converting an image that has passed through the lens 1 and the aperture mechanism 2 into an electrical signal, and 4 is an output signal from the CCD. A CDS / AD circuit which removes the CCD drive pulse component and converts it into a digital signal, 5 is a timing generator (hereinafter referred to as TG) for generating a pulse signal for driving the CCD 3, 6 is a data bus, and 7 is a digital signal. It is a memory for storing.

  Reference numeral 8 denotes a shading correction circuit that corrects a peripheral light amount drop and color shading caused by optics from the lenses 1 to 4 to the CCD output or caused by the CCD.

Reference numeral 9 denotes a white balance circuit (hereinafter referred to as a WB circuit) that gives a gain for each color in order to balance the output of the CDS / AD circuit 4 or the output signal of the memory 7 storing the output of the CDS / AD circuit 4. ). For example, when the CCD 3 has a multi-color filter (R, G ₁ , G ₂ , B),
A ′ = WB_R ^* R, B ′ = WB_G ₁ ^* G ₁ , C ′ = WB_G ₂ ^* G ₂ , D ′ = WB_B ^* B
Coefficient _{(WB_R, WB_G 1, WB_G 2} , WB_B) over (Ca ', Cb', Cc ', Cd') outputs a.

Reference numeral 10 denotes a matrix circuit (hereinafter referred to as MTX) that converts each color by applying a predetermined coefficient to an RGB signal.
R1 = a1 ^* Ca ′ + b1 ^* Cb ′ + c1 ^* Cc ′ + d1 ^* Cd ′
G1 = a2 ^* Ca ′ + b2 ^* Cb ′ + c2 ^* Cc ′ + d2 ^* Cd ′
B1 = a3 ^* Ca ′ + b3 ^* Cb ′ + c3 ^* Cc ′ + d3 ^* Cd ′
(A1, b1, c1, d1, a2, b2, c2, d2, a3, b3, c3, d3) are coefficients.

  Reference numeral 11 denotes a gamma circuit (hereinafter referred to as γ circuit) for making the MTX output signal an appropriate gradation characteristic as an image, and the output of the comma circuit 10 is (R ′, G ′, B ′).

Reference numeral 12 denotes an RGB to YUV1 conversion circuit that converts the output signal of the WB2 circuit 11 of RGB type into a YUV (luminance / color difference signal) form.
Y = j1 ^* R "+ k1 ^* G" + m1 ^* B ", U = j2 ^* R" + k2 ^* G "+ m2 ^* B", V = j3 ^* R "+ k3 ^* G" + m3 ^* B " To do.

13 is a UV Gain circuit that applies a gain to each of the U signal and the V signal.
It is assumed that Y ′ = Y, U ′ = u1 ^* U, V ′ = v1 ^* V.

14 is a hue adjustment circuit for adjusting the hue of the UV signal,
Y ″ = Y ′, U ″ = n1 ^* U ′ + (p1 + q1) ^* V ′, V ″ = (p2 + q2) ^* U ′ + n2 ^* V ′
It shall be represented by Of the hue adjustment coefficients (n1, p1, q1, n2, p2, q2),
q1 is q1 = 0 when U '> 0, and q2 is q2 = 0 when V'> 0.
It is assumed to have the following characteristics.

  Reference numeral 15 denotes an exposure amount detection circuit for detecting the light amounts from 1 to 3, which detects the exposure amount from the signal after the shading correction circuit 8 performs the shading correction on the output signal of the CCD 3. is there. Reference numeral 17 denotes a controller for controlling the system of the present invention.

  Reference numeral 18 denotes a compression circuit that compresses the video signal that has undergone the processes 9 to 14, and 19 denotes a recording medium that records the compressed video signal. Reference numeral 20 denotes display means for displaying a video signal that has undergone the processes 8 to 14. Further, reference numeral 21 denotes a release button for photographing an image by the system of the present invention.

FIG. 2 is a flowchart showing the operation at the time of still image shooting of the present invention, and the operation of the present invention will be described along the flowchart.
The still image shooting flowchart of FIG. 2 starts when the still image shooting operation is performed by operating the release button 21 in FIG. 1. At 100, the zoom stop position of the lens 1 in FIG. The subject brightness is measured, an appropriate exposure time and an aperture value of the aperture mechanism 2 are calculated, and the aperture mechanism 2 is controlled to be the aperture value. In 102, the subject distance is measured and the focus mechanism of the lens 1 is moved to an appropriate position.

  Subsequently, at 103, an electronic shutter value output from the TG 5 is set so that the CCD 3 is exposed for the exposure time obtained in 101, and a still image is exposed by the CCD 3 for a desired exposure time. In 104, the image exposed on the CCD 3 is read out and processed by the CCD / AD circuit 4, and then stored in the memory 7 via the data bus 6.

  At 105, the still image stored in the memory 7 is input to the WB detection circuit 15, and the color temperature of the subject is detected from the still image and the WB correction amount is calculated.

  In 106, the WB correction amount calculated in 105 is set in the WB circuit 8, and the MTX coefficient corresponding to the detected color temperature is set in the MTX circuit 9. In addition, each coefficient set in the UV Gain circuit / hue adjustment circuit is calculated to be appropriate for the previously detected color temperature, and each coefficient is set in each circuit.

  In 107, the color temperature / WB correction amount detected and calculated in 105, the zoom position information detected in 100, and the shading so that an appropriate image is obtained from the photometric result (subject brightness, aperture amount, shutter speed) in 101. A correction amount and a gamma correction amount are calculated. Details of the calculation method of the shading correction amount and the gamma correction amount will be described later.

  In 108, the shading correction amount calculated in 107 is set in the shading correction circuit 8 of FIG.

  In 109, the gamma correction amount calculated in 107 is set in the γ circuit 11 of FIG.

  At 110, the still image data stored in the memory 7 at 104 is read out and subjected to processes 8 to 14 to obtain desired video data. In 111, the video data obtained in 110 is compressed in the compression circuit 18 and then recorded on the recording medium, and the video data is displayed on the display means 20.

As shown in FIG. 4A, the exposure amount detection circuit 15 in FIG. 1 divides the photographing screen into a plurality of areas, and the color components (R, G ₁ , G ₂ ,. B) has a function of measuring the density distribution (histogram), and histograms as shown in FIG. 4 [b-1], [c-1], and [d-1] are output for all areas. The controller 17 shown in FIG. 2 multiplies the color components (R, G1, G2, B) for each area by a weighting factor (3, 3, 3, 1), and displays a histogram of luminance signals in each area and each The average luminance value of the area ([b-2], [c-2], [d-2] and Ave_Y [1],..., Ave_Y [x],..., Ave_Y [n] in FIG. 4) is calculated. The exposure value is obtained by multiplying the average luminance value of each area by a weight according to the area position. It is assumed that the aperture amount of the aperture 2 shown in FIG. 1 and the exposure time of the CCD 3 shown in FIG.

  The exposure amount detection circuit 15 performs the above-described operation, and a histogram of color components (R, G1, G2, B) constituting the image pickup device CCD3 for each area that is an output of the exposure detection circuit 15 (FIG. 4). [B-1], [c-1], and [d-1]), the controller 17 shown in FIG. 1 generates a histogram of the color components (R, G1, G2, B) in the entire shooting screen. The contrast of the captured image is determined from the histogram of the captured image (contrast is determined from the brightness histogram of the entire captured image as shown in FIG. 4 [e-2]). For example, the density distribution is wide and the average value is higher. 5 is selected such as the gamma characteristic C shown in FIG. 5 that suppresses the contrast of the image, and conversely, the density distribution width of the photographed image is narrow and seems to be closer to the low luminance side. In the case, by operating to select a gamma characteristic as to increase the image contrast, such as a gamma characteristic A referred in Fig. 5, it operates to output an image is proper contrast.

  The plurality of gamma characteristics are stored as a table in the controller 17 of FIG.

  The operation of gamma characteristic selection and shading correction coefficient selection will be described with reference to FIG. 3 which explains the flow of gamma characteristic selection and shading correction amount determination from the contrast of the photographed image. In 213 of FIG. 3, a table of a plurality of gamma characteristics as shown in FIG. 5 is stored in the adaptive gamma correction table in the controller 17 of FIG. 1, and the exposure amount detection of FIG. The gamma characteristic that optimizes the contrast of the photographed image is selected by the gamma selection 214 in FIG. 3 from the histogram (density distribution information 204 in FIG. 3) that is output by the circuit 15.

  Also, from the density distribution information 204 in FIG. 3, density information of areas at predetermined positions such as the divided areas (1), (2), (3), and (4) in [a] in FIG. 4 (in FIG. 4). Density information for each color component such as [b-1] and [d-1] is acquired, and an average value and a standard deviation are created for each area / color component in the gamma correction Max coefficient extraction 215 of FIG. Then, the maximum value as the gamma correction coefficient is calculated by applying the density value corresponding to the range of the average value ± standard deviation for each area / color component to the gamma characteristic selected by the gamma selection 214. Here, it is assumed that the maximum value of the gamma correction coefficient is Γ_max.

  The luminance shading_Zoom Position correction table 206 and the color shading_Zoom Position correction table 207 in FIG. 3 are luminances for horizontal and vertical pixel positions as shown in [a], [b], [c], and [d] in FIG. This means that the shading correction Gain and the color shading correction Gain for the R signal and the B signal for the horizontal and vertical pixel positions are stored in the controller 17 of FIG. 1 as a table corresponding to the Zoom Position. 3 outputs the luminance shading correction coefficient and the color shading correction coefficient corresponding to the zoom position from the zoom lens position information 201, and multiplies the luminance shading correction coefficient selected by the multiplication means 208 and the color shading. Calculates CCD color components (R, G1, G2, B) the shading correction coefficient for each.

For example, when the selected luminance shading correction coefficient is represented by the function ShY [x, y] and the color shading correction coefficient is represented by the function ShR [x, y], ShB [x, y], the output of the multiplication unit 208 is output. _{{ShR_1 [x, y],} ShG 1 _1 [x, y], ShG 2 _1 [x, y], ShB_1 [x, y]} is ShR_1 [x, y] = ShY [x, y] * ShR [ x, y];
ShG _{1 —} 1 [x, y] = ShG _{2 —} 1 [x, y] = ShY [x, y];
ShB_1 [x, y] = ShY [x, y] ^* ShB [x, y];
Is calculated as follows. The above x means the horizontal pixel position, and y means the vertical pixel position.

The aperture information 202 in FIG. 3 means information on the aperture amount in the aperture 2 in FIG. 1, and the luminance / color shading amount changes depending on the aperture amount. Therefore, the aperture correction coefficient 209 in FIG. The output is multiplied by the shading correction coefficient previously obtained by the multiplication means 210. When the aperture correction coefficient at 209 is expressed by the function F [x, y], the output {ShR2 [x, y], ShG2 [x, y], ShB2 [x, y]} of the multiplication unit 210 is ShR_2 [ x, y] = F [x, y] ^* ShR_1 [x, y];
^{ShG_2 [x, y] = F} [x, y] * ShG 1 _1 [x, y];
ShB_2 [x, y] = F [x, y] ^* ShB_1 [x, y];
Can be expressed as

  In the shading correction Max coefficient extraction 211 in FIG. 3, the maximum value for each color is extracted from the shading correction coefficient for each color output from the multiplication unit 210.

  This result is set as {ShR_2 [x, y] _max, ShG_2 [x, y] _max, ShB_2 [x, y] _max}.

The WB correction coefficient in FIG. 3 means that the controller 17 obtains the result of calculating the WB correction coefficient from the detection result from the WB detection circuit 16 in FIG. 1, and here, the WB correction coefficient is expressed as {WB_R, WB_G ₁ , Let WB_G ₂ , WB_B}.

  3 multiplies the results of the shading correction Max coefficient extraction 211, the WB correction coefficient 203, and the gamma correction Max coefficient extraction.

As a result, {R_max, G ₁ _max, G ₂ _max, B_max} is R_max = WB_R ^* Γ_max ^* ShR_2 [x, y] _max;
G ₁ _max = WB_G ₁ ^* Γ_max ^* ShG_2 [x, y] _max;
G ₂ _max = WB_G ₂ ^* Γ_max ^* ShG_2 [x, y] _max;
B_max = WB_B ^* Γ_max ^* ShB_2 [x, y] _max;
It is calculated by the following formula.

In the comparison 217 in FIG. 3, a predetermined correction coefficient limit value 205 and a maximum value ({R_max, G ₁ _max) among the outputs {R_max, G ₁ _max, G ₂ _max, B_max} of the multiplication unit 216. , G ₂ _max, B_max} _max),
If {R_max, G ₁ _max, G ₂ _max, B_max} _max ≦ (correction coefficient limit value),
K = 1;
If {R_max, G ₁ _max, G ₂ _max, B_max} _max> (correction coefficient limit value),
K = (correction coefficient limit value) / {R_max, G ₁ _max, G ₂ _max, B_max} _max;
The coefficient K obtained in the above is calculated.

In the correction 218 of the shading correction amount in FIG. 3, the outputs from the multiplication unit 210 and the comparison 217 are used.
The final shading correction amount {ShRf [x, y], ShG ₁ f [x, y], ShG ₂ f [x, y], ShBf [x, y]} is set to ShRf [x, y] = K ^* ShR_2 [X, y];
ShG ₁ f [x, y] = K ^* ShG_2 [x, y];
^{_{ShG 2 f [x, y]}} = K * ShG_2 [x, y];
ShBf [x, y] = K ^* ShB2 [x, y];
3 and set in the shading correction circuit of FIG. 3 at the stage of setting 219, the shading correction amount {ShRf [x, y], ShG ₁ f [x, y], obtained in the shading correction circuit 8 of FIG. Set ShG ₂ f [x, y], ShBf [x, y]}.

Block diagram of the present invention Flow chart of the present invention The flowchart explaining the flow which calculates the shading correction amount in the present invention Diagram explaining concentration distribution detection Illustration explaining the gamma characteristics Diagram explaining the characteristics of shading correction

Explanation of symbols

1 Lens 2 Aperture mechanism 3 Image sensor (CCD)
4 CDS / AD circuit 5 Timing generator (TG)
6 Data bus 7 Memory 8 Shading correction circuit 9 White balance circuit (WB circuit)
10 Matrix circuit (MTX)
11 Gamma circuit (γ circuit)
12 RGB to YUV1 conversion circuit 13 UV Gain circuit 14 Hue adjustment circuit 15 Exposure amount detection circuit 17 Controller 18 Compression circuit 19 Recording medium 20 Display means 21 Release button

Claims (2)

An optical system and an image sensor that converts light that has passed through the optical system into an electrical signal. Detecting means, gamma correction means, means for storing a shading correction amount for correcting shading characteristics of the optical system and the image sensor, and shading correction means,
Means for calculating a suppression amount with respect to the stored shading correction amount from the gamma characteristic and the density distribution state of the predetermined region, and performing the shading correction obtained by applying the above-described suppression to the shading correction amount. An imaging device characterized in that the imaging device is performed. A means for calculating an average value and a standard deviation from a density distribution of the predetermined area, a means for calculating a representative gamma correction amount in the predetermined area from the average value, the standard deviation, and a gamma characteristic, and a white balance correction amount; And means for calculating a total correction amount of various corrections from the representative gamma correction amount of the predetermined region and the shading correction amount applied to the predetermined region, and means for determining whether the total correction amount is within a predetermined range; And means for calculating a suppression amount with respect to the correction amount so as to be within a predetermined range,
The imaging apparatus according to claim 1, wherein the shading correction amount is suppressed by a suppression amount.

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