JP2001245313A - Digital camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital camera that can reduce moire caused by level fluctuations in color difference components between two adjacent pixels. SOLUTION: A complementary color filter 14 is mounted on a light receiving plane of a CCD imager 16, and each pixel of the CCD imager 16 outputs a pixel signal having a color component of G, Mg, Ye or Cy. The pixel signal from the CCD imager 16 is given to an arithmetic circuit 28 after subjected to A/D conversion, interpolation and serial/parallel conversion. The arithmetic circuit 28 receives the pixel signal resulting from the pixels having all G, Mg, Ye and Cy color components. The arithmetic circuit 28 converts the components of the received pixel signal into Y, Cr and Cb components, gives the Y and Cr components to an RGB conversion circuit 32 without modification, and gives the Cb component to the RGB conversion circuit after passing it through a moire reduction circuit 30. The moire reduction circuit 30 reduces the level of the received Cb component corresponding to a Cb difference between two adjacent pixels.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital camera, and more particularly, to a digital camera for photographing a subject using an image sensor provided with a complementary color filter.

[0002]

2. Description of the Related Art When a complementary color filter as shown in FIG. 2 is mounted on a light receiving surface of an image sensor, the image sensor outputs Ye (yellow), Cy (cyan), G (green) and Mg (magenta). A pixel signal corresponding to any one of the color components is output. This pixel signal is
After the interpolation processing, the luminance signal Y and the color difference signals Cr and C
b, the luminance signal Y and the color difference signals Cr and C
b is further converted into an R signal, a G signal and a B signal.

[0003]

Here, FIG.
When attention is paid to a color block B _C of pixels × 2 lines, each pixel signal generated from this color block is G, M
It corresponds to only one color component of g, Ye and Cy. Such interpolation processing to a pixel signal by Hodokosuru, pixel signals corresponding to all of the four color components are generated in the middle of the color blocks B _C (closed circles position). further,
The color difference signals Cr and C are obtained from the pixel signals subjected to the interpolation processing.
When generating b, an operation according to Equation 1 is performed.

[0004]

[Formula 1] Cr = Mg + Ye−Cy−G Cb = Mg + Cy−Ye−G According to the formula 1, the color difference signal Cr is obtained by adding the result of adding two pixels located on one diagonal of the color block B _C and the other diagonal. It is generated by performing a subtraction process between the addition result of the two pixels located above. On the other hand, the color difference signal Cb is generated by performing a subtraction process between the addition result of the two pixels located on the right side of the color block B _C and the addition result of the two pixels located on the left side.

When the brightness of the subject changes rapidly in the horizontal direction, the color difference signal Cr is
As shown in FIG. 6D, the color difference signal Cb has a flat characteristic of always taking a zero level, but the color difference signal Cb has a characteristic in which the polarity alternates as shown in FIG. As described above, since the color difference signal Cb takes a level different from the zero level, moire occurs at the horizontal edge of the subject image. In the vertical direction, as shown in FIG.
Both of the color difference signals Cr and Cb show flat characteristics, and as a result, a level change appears only in the horizontal characteristics of the color difference signal Cb.

However, this is a characteristic when the complementary color filters having the arrangement shown in FIG. 2 are used. As long as a complementary color filter composed of Ye, Cy, Mg and G filter elements is used, the horizontal direction of the color difference signal Cr or Cb is obtained. Alternatively, a level change appears in the characteristics in the vertical direction, and as a result, moire occurs at any edge.

Therefore, a main object of the present invention is to provide a digital camera capable of reducing moire.

[0008]

According to the present invention, there is provided a complementary color filter in which a plurality of color filter elements are arranged, a complementary color filter mounted on a light receiving surface, and each pixel having one of a plurality of color components. An image sensor that outputs one pixel signal; a first generation unit that generates a second pixel signal in which each pixel has a plurality of color components based on the plurality of first pixel signals;
Second generating means for performing predetermined arithmetic processing on the pixel signal to generate a third pixel signal in which each pixel includes a color difference component, detecting means for detecting a difference in color difference components between two pixels adjacent to each other, and a third pixel A digital camera includes a reduction unit that reduces a level of a color difference component included in a signal according to a difference.

[0009]

A complementary color filter in which filter elements of a plurality of colors are arranged is mounted on the light receiving surface of the image sensor, and the first pixel signal of each pixel output from the image sensor is any one of a plurality of color components. have. The first generation unit generates a second pixel signal in which each pixel has a color component of a plurality of colors based on the plurality of first pixel signals output from the image sensor. The second pixel signal is subjected to predetermined arithmetic processing by the second generation unit, whereby a third pixel signal in which each pixel includes a color difference component is generated. The detecting means detects a difference between color difference components between two pixels adjacent to each other,
The reduction unit reduces the level of the color difference component included in the third pixel signal according to the detected difference.

Preferably, the plurality of first pixel signals used for generating a second pixel signal of a certain pixel are partially different from the plurality of first pixel signals used for generating a second pixel signal of a pixel adjacent to this pixel. Common to

More preferably, a part of the plurality of colors belongs to the first column, and another part of the plurality of colors belongs to a second column adjacent to the first column. At this time, the second generation unit obtains a color difference component by subtracting the sum of the first pixel signals having the color components belonging to the second column from the sum of the first pixel signals having the color components belonging to the first column. The detecting means detects a difference between color difference components between two pixels adjacent to each other in a direction orthogonal to the first column and the second column.

The plurality of colors are preferably G, Mg, Y
e and Cy. Among them, G and Ye belong to the first column, and Mg and Cy belong to the second column. The color difference component is preferably a Cb component.

In the reducing means, preferably, the gain generating means generates a gain which changes between "0" and "1" according to the difference. The generated gain is multiplied by a color difference component included in the second pixel signal by the multiplication means. Here, the gain generating means preferably generates the gain “1” when the difference is smaller than the first predetermined value, and sets the gain “0” when the difference is equal to or larger than a second predetermined value larger than the first predetermined value. Is generated, and when the difference is equal to or larger than the first predetermined value and smaller than the second predetermined value, a gain equal to or larger than “0” and smaller than “1” is generated.

In the detecting means, preferably, the first difference between the color difference component of the current pixel and the color difference component of the previous pixel is the first difference.
The second difference between the color difference component of the current pixel and the color difference component of the next pixel is detected by the difference detection unit. The output means outputs one of the first difference and the second difference having a larger absolute value.

[0015]

According to the present invention, the level of the color difference component is reduced in accordance with the difference between the color difference components between two pixels adjacent to each other, so that the level of the color difference component fluctuates between two adjacent pixels. Can be reduced.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

[0017]

Referring to FIG. 1, a digital camera 10 according to this embodiment includes a lens 12, and a light image incident from the lens 12 is applied to a CCD imager 16 via a complementary color filter 14. The complementary color filter 14 has Ye, Cy, G or Mg filter elements as shown in FIG. G and Mg filter elements are alternately arranged for each pixel in odd lines, and Ye and Cy are arranged in even lines.
Are alternately arranged for each pixel. The G filter element is arranged above and below the Ye filter element.
The g filter element is arranged above and below the Cy filter element. Therefore, focusing on a color block B _C of 2 pixels × 2 lines, G and Ye filter elements are present in the left vertical column, and Mg and Cy filter elements are present in the right vertical column. Each of such filter elements corresponds to one light receiving element (pixel) of the CCD imager 16.

The CCD imager 16 outputs a pixel signal generated by photoelectric conversion in each light receiving element in a progressive scan system in response to a timing signal from the timing generator 20. For this reason, pixel signals corresponding to the G or Mg color components are alternately output for each pixel on the odd lines, and pixel signals corresponding to the Ye or Cy color components are alternately output for each pixel on the even lines. Is output. The A / D converter 18 is a CCD imager 1
6 is converted into a digital signal and supplied to the RAM 22. The A / D-converted pixel signal is written to the memory area 22a by the memory control circuit 24 that operates according to the timing signal from the timing generator 20.

Since each pixel has only one color component of Ye, Cy, Gr and Mg, the memory control circuit 24 processes the flow chart shown in FIG. 3 when reading out pixel signals from the memory area 22a. Then, three color components for which each pixel is insufficient are interpolated. FIG.
In step S1, the memory control circuit 24 first calculates a count value x of a counter 24a indicating an address in a row direction (horizontal direction) and a count value y of a counter 24b indicating an address in a column direction (vertical direction). The pixel signal is set to "1", and pixel signals are sequentially read from the addresses (x, y), (x + 1, y), (x, y + 1) and (x + 1, y + 1) in steps S3 to S9. In step S11, it is determined whether or not the count value x is a predetermined value, that is, the number of horizontal pixels minus one. Where "N
If O ", the count value x is incremented in step S13 to process the next four pixels in the row direction,
It returns to step S3. On the other hand, in step S11, "YE
If S "is determined, it is determined in step S15 whether or not the count value y is a predetermined value, that is, the number of vertical pixels -1.
If "NO", in order to process the four pixels located at the left end of the next line, the count value x is returned to "1" in step S17, the count value y is incremented, and the process returns to step S3. “YES” in the step S15
If so, the process ends.

[0020] In this way, the 2 pixels × 2 interpolation processing for each color block B _C line is applied, each pixel G, Mg, Y
A pixel signal having all the color components e and Cy is generated. Pixel signal having the four color components can be considered to have been generated at the center of each color block B _C (closed circles position).

The G, Mg, Ye and Cy color components generated at the same pixel position are output from the RAM 22 in a serial manner. Therefore, every time four color components are input, the serial / parallel conversion circuit 26 performs serial / parallel conversion on the four color components. As a result, the G, Mg, Ye, and Cy color components included in the same pixel signal are output from the serial / parallel conversion circuit 26 at the same time.

The arithmetic circuit 28 performs an arithmetic operation on the Ye, Cy, Mg, and G color components simultaneously output from the serial / parallel conversion circuit 26 according to the following equation (2) to obtain a luminance component Y
And the color difference components Cr and Cb are generated. The components forming each pixel signal are converted from G, Mg, Ye and Cy components to Y, Cr and Cb components.

[0023]

Y = Mg + Ye + Cy + G Cr = Mg + Ye-Cy-G Cb = Mg + Cy-Ye-G Of these, the luminance component Y and the color difference component Cr are R as they are.
The color difference component Cb is supplied to the RGB conversion circuit 32 via the moiré reduction circuit 30. In the RGB conversion circuit 32, a predetermined operation is performed on the luminance component Y and the color difference components Cr and Cb, whereby the components of each pixel signal are converted into the primary color R component, the G component, and the B component.
Converted to components.

The moiré reduction circuit 30 is specifically configured as shown in FIG. C input from the arithmetic circuit 28
The b component is given to the multiplier 30n through a delay process of two pixel periods by the registers 30a and 30b. On the other hand, the subtractor 30c outputs the Cb input from the arithmetic circuit 28.
A subtraction process is performed on the component and the Cb component output from the register 30a, and the absolute value of the subtraction result is compared with the absolute value comparison circuit 30.
e. The subtractor 30d performs a subtraction process on each of the Cb components output from the registers 30a and 30b, and supplies the absolute value of the subtraction result to the absolute value comparison circuit 30e. That is, the subtractor 30d gives the absolute value of the difference between the previous pixel Cb component and the current pixel Cb component to the absolute value comparison circuit 30e, and the subtractor 30c outputs the current pixel Cb component and the next pixel Cb component.
The absolute value of the difference between the b components is given to an absolute value comparison circuit 30e.

The absolute value comparison circuit 30e compares the two absolute values given from the subtracters 30c and 30d with each other, and outputs an absolute value having a larger value (differential absolute value Cb _S ). The output difference absolute value Cb _S is provided to the subtractor 30f, and the subtractor 30f subtracts a predetermined threshold “Cb _TH ” from the difference absolute value Cb _S. The multiplier 30g includes the subtractor 3
The subtracted value output from 0f is multiplied by a predetermined value “−Cb _INC ”, and the multiplied value is given to the adder 30h. In the adder 30h, the multiplied value is added to a predetermined value “1”. Therefore, the added value Cb _A output from the adder 30h satisfies Equation 3.

[0026]

Cb _A = 1−Cb _INC (Cb _S −Cb _TH ) The added value Cb _A is subjected to low-level clipping by the clipping circuit 30j. That is, if the added value Cb _A indicates a numerical value equal to or greater than “0”, the added value Cb _A is output from the clipping circuit 30j as it is, but if the added value Cb _A falls below “0”, the value becomes “0”. Is output from the clip circuit 30j.

The absolute difference value Cb _S output from the absolute value comparison circuit 30e is also supplied to a comparator 30i. The comparator 30i compares the input difference absolute value Cb _S with a predetermined threshold C
compared with b _TH, Cb _S> a high level signal if Cb _TH, and outputs a low level signal if Cb _S ≦ Cb _TH selector 30k. The selector 30k selects the output of the clipping circuit 30j when the output of the comparator 30i is at a high level, and outputs a predetermined value "1" when the output of the comparator 30i is at a low level. The output of the selector 30k, that is, the gain Cb _G, is delayed by one pixel period in the register 30m, is given to the multiplier 30n, and is multiplied by the Cb component from the register 30b by the multiplier 30n. Then, the multiplication result of the multiplier 30n is output to the RGB conversion circuit 32 shown in FIG.

FIG. 5 shows the relationship between the difference absolute value Cb _S output from the absolute value comparison circuit 30e and Cb _{G applied} to the multiplier 30n. Since the absolute difference value Cb _S is a low level signal from the comparator 30i if less than the threshold value Cb _TH is outputted, the selector 30k selects "1" as the gain Cb _G. On the other hand, when the difference absolute value Cb _S exceeds the threshold value Cb _TH, the selector 30k selects the output of the clip circuit 30i as the gain Cb _G. Clip circuit 30i is summed value _{Cb A (= 1-Cb INC} (Cb S -Cb TH)) is "0" or when outputting the added value Cb _A, additional value Cb _A is "0" when below " 0 "is output. Therefore, when the selector 30k selects the output of the clipping circuit 30i, the gain Cb _G gradually decreases from “1” as the difference absolute value Cb _S increases. Then, when the absolute difference value Cb _S exceeds a predetermined value (= Cb _TH + 1 / Cb _INC ), the gain Cb _G becomes “0”.

As can be seen from the arrangement of black circles shown in FIG. 2 and the processing shown in FIG. 3, the four color components used in the pixel signal generation processing (interpolation processing) at a certain black circle position are as follows.
It partially overlaps with the four color components used in the pixel signal generation processing (interpolation processing) at the position of the black circle adjacent to the black circle. For example, the G component and the Ye component forming the color block B _C shown in FIG. 2 are generated by generating a pixel signal at the position of the black dot located at the center of the color block B _C and the position of the black dot located to the left of the black dot. Used for
Mg component and Cy components forming a color block B _C is
It used in generation processing of the pixel signal at the position of the black circle located on one right black circles and the black circles located at the center of the color blocks B _C.

Then, when the luminance of light incident on the filter element corresponding to each color component changes in the horizontal direction,
The level of the Cb component generated by Cb = Mg + Cy-Ye-G fluctuates at the position of each black circle located in the horizontal direction. That is, the luminance of the incident light changes in the horizontal direction as shown in FIG.
When the level of the pixel signal output from the comparator changes as shown in FIG.
The component levels alternate between the positive electrode and the negative electrode as shown in FIG. This causes moiré to occur at the edge portion of the image.

For this reason, in this embodiment, a moiré reduction circuit 30 shown in FIG. 4 is provided so that a gain Cb _G having a characteristic as shown in FIG. 5 is given to the Cb component output from the arithmetic circuit 28. I have. For the Cb component shown in FIG. 6D, the absolute difference value Cb _S shown in FIG.
Gain Cb _G when the difference absolute value Cb _S is equal to or lower than a threshold Cb _TH takes a "1", takes a value less than "0" or "1" when the absolute difference Cb _S exceeds the threshold value Cb _TH. As a result, the Cb component whose level has been reduced is output from the multiplier 30n as shown in FIG. Thereby, it is possible to reduce the moiré generated at the edge portion of the image.

FIG. 6G is a waveform diagram showing the absolute value of the difference output from the subtractor 30c. As can be seen from the comparison with FIG. 6E, the timings at which the difference absolute values become maximum are shifted from each other. FIG. 6G shows the absolute value of the difference between the previous pixel Cb component and the current pixel Cb component, while FIG. 6E shows the absolute value of the difference between the previous pixel Cb component and the current pixel Cb component. This is because the larger value of the difference absolute value between the current pixel Cb component and the previous pixel Cb component is shown. On the other hand, since the Cb component changes at the timing shown in FIG. 6D, the level of the Cb component can be more effectively reduced by using the absolute difference value shown in FIG.

The digital camera of this embodiment includes a so-called digital still camera for recording only a still image and a video movie for recording a moving image. A digital camera that records both still images and moving images is also conceivable.

In this embodiment, a CCD image sensor is used as an image sensor. However, it goes without saying that a CMOS image sensor may be used instead.

Further, in this embodiment, a description has been given using a complementary color filter in which each filter element is arranged as shown in FIG. 2, but the arrangement of the filter elements is not limited to this.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is an illustrative view showing a complementary color filter applied to the embodiment in FIG. 1;

FIG. 3 is a flowchart showing a part of the operation of the embodiment in FIG. 1;

FIG. 4 is a block diagram showing a moiré reduction circuit.

FIG. 5 is a graph showing characteristics of the moiré reduction circuit.

6A is an illustrative view showing a part of an array of complementary color filters, FIG. 6B is a waveform chart showing a change in luminance of incident light, and FIG. 6C is a view showing an output of an A / D converter; FIG.
(D) is a waveform diagram showing the color difference signal Cb before performing the moiré reduction process, (E) is a waveform diagram showing an example of the Cb difference signal, and (F) is a color diagram showing the color difference signal after performing the moiré reduction process. FIG. 9 is a waveform chart showing a signal Cb, and FIG. 9G is a waveform chart showing another example of the Cb differential signal.

7A is an illustrative view showing a part of an array of complementary color filters, FIG. 7B is a waveform chart showing a change in luminance of incident light, and FIG. 7C is a view showing an output of an A / D converter; FIG.
(D) is a waveform diagram showing the color difference signal Cr.

8A is an illustrative view showing a part of an array of complementary color filters, FIG. 8B is a waveform chart showing a change in luminance of incident light, and FIG. 8C is a view showing an output of an A / D converter; FIG.
(D) is a waveform diagram showing the color difference signal Cr.

[Explanation of symbols]

 Reference Signs List 10 digital camera 14 complementary color filter 16 CCD imager 28 arithmetic circuit 30 moiré reduction circuit 32 RGB conversion circuit

Claims (7)

[Claims] A complementary color filter having a plurality of color filter elements disposed thereon, wherein the complementary color filter is mounted on a light receiving surface, and each pixel outputs a first pixel signal having one of the plurality of color components. An image sensor, first generating means for each pixel to generate a second pixel signal having the plurality of color components based on a plurality of the first pixel signals, performing a predetermined arithmetic process on the second pixel signal, A second generation unit that generates a third pixel signal in which a pixel includes a color difference component, a detection unit that detects a difference between the color difference components between two adjacent pixels, and a level of the color difference component included in the third pixel signal A digital camera, comprising: a reduction unit configured to reduce the difference according to the difference. 2. The plurality of first pixel signals used for generating the second pixel signal of a certain pixel are the plurality of first pixel signals used for generating the second pixel signal of a pixel adjacent to the certain pixel. The digital camera according to claim 1, wherein the digital camera is partially common to a signal. 3. A part of the plurality of colors belongs to a first column; another part of the plurality of colors belongs to a second column adjacent to the first column; The color difference component is obtained by subtracting the sum of the first pixel signals having the color components belonging to the second column from the sum of the first pixel signals having the color components belonging to The digital camera according to claim 1, wherein a difference between the color difference components between two pixels adjacent in a direction orthogonal to the second column is detected. 4. The plurality of colors are G, Mg, Ye and Cy, wherein the G and Ye belong to the first column, the Mg and Cy belong to the second column, and the color difference component is The digital camera according to claim 3, which is a Cb component. 5. The method according to claim 1, wherein said reducing means sets "0" in accordance with said difference.
2. A gain generating means for generating a gain that changes between the first and second signals, and a multiplying means for multiplying the color difference component included in the second pixel signal by the gain generated by the gain generating means. A digital camera according to any one of claims 1 to 4. 6. The gain generating means generates a gain “1” when the difference is smaller than a first predetermined value, and sets a gain when the difference is equal to or larger than a second predetermined value larger than the first predetermined value. 6. The digital camera according to claim 5, wherein the digital camera generates "0" and generates a gain of "0" or more and less than "1" when the difference is equal to or more than the first predetermined value and less than the second predetermined value. 7. A first detecting means for detecting a first difference between the color difference component of a current pixel and the color difference component of a previous pixel.
Difference detection means, second difference detection means for detecting a second difference between the color difference component of the current pixel and the color difference component of the next pixel,
7. An output unit for outputting a larger absolute value of the first difference and the second difference.
A digital camera according to any one of the above.