JPH09116913A - Color filter array and video signal processing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve horizontal/vertical resolution and to obtain excellent sensitivity. SOLUTION: Brightness filters Y (Y=R+G+B) are arranged checkerwise and a red filter R and a blue filter B are arranged at remaining positions. That is, the red filters R and the green filters G are arranged the same in a line and alternate between lines in line sequencing. Since the brightness signal is added by adding two adjacent lines, moire of fs/2 is cancelled and the horizontal resolution is improved. Since the vertical component is corrected, the vertical resolution is improved. Moreover, since R, B primary color filters are used, excellent color reproducibility is attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color filter array of an image pickup device and a video signal processing circuit, and more specifically, a color filter array and a video signal processing circuit suitable for an all pixel readout type solid-state image pickup device. Regarding the improvement of.

[0002]

2. Description of the Related Art As a filter array of an image pickup device using a solid-state image pickup device such as CCD, an array of R (red), G (green), and B (blue) primary color filters is arranged. is there. FIG. 7 shows an example of a primary color filter array in an image sensor of the all-pixel readout system, in which green filters G are arranged in a checkered pattern, and red filters R and blue filters B are arranged in the remaining portion. ing. In this method, the luminance signal is synthesized from the R, G, and B signals of two rows.

For example, in the first field, a signal of the nth line and a signal of the (n + 1) th line, a signal of the (n + 2) th line and a signal of the (n + 3) th line, ... Is generated. In the second field, the signal of the (n + 1) th line and the signal of the (n + 2) th line, the signal of the (n + 3) th line and the nth line.
The luminance signal is generated by combining the +4 line signal, and so on.

However, the above background art has the following disadvantages. (1) When the frequency of the color subcarrier is fs, the color moire of fs / 2 is mixed in the luminance signal, and the horizontal resolution is deteriorated. (2) Since only the luminance signal in which the signals of two lines are mixed is used, the vertical resolution is insufficient. For example, the vertical resolution is about 350 lines. (3) Since the primary color filter is used, the light utilization rate is poor and the sensitivity is insufficient.

Next, a conventional single plate image pickup device (IL-CC
In the image pickup apparatus using D), since two lines are mixed into a luminance signal, an Mg (magenta) color filter is generally used. In addition, as in the present, the color filter array has four colors of Mg, G, Cy (cyan), and Ye (yellow).
Before being composed of colors, a system using four colors of W (transparent), G, Cy, and Ye was also devised (JP-A-62-108694).
However, the method of using the luminance signal in one line does not exist in such a four-color method of W, G, Cy, and Ye. FIG. 8 shows the color filter array of the above publication, which has a configuration in which a line composed of G and W filters and a line composed of Cy and Ye filters are alternately arranged. There is.

By the way, since the transparent filter W does not use a color filter, the pixel output of the portion of the transparent filter W has the spectral characteristic of the solid-state image pickup device. FIG.
An example of the characteristics of the transparent filter W is shown in (A), where the horizontal axis represents wavelength and the vertical axis represents relative sensitivity. It should be noted that the characteristics of the other filters G, Cy, and Ye are shown for reference in FIG.

Here, in the color filter array of FIG.
Consider the case where a luminance signal is obtained on a line. When the luminance signal of the W and G lines is YA and the luminance signal of the Cy and Ye lines is YB, for example, the characteristics shown in FIG. 10 are obtained, and a spectral sensitivity difference is generated as shown by the shaded areas in the figure.

As a result, when the luminance signal YA is used for the field A and the luminance signal YB is used for the field B,
Even if the levels of both are matched when a black and white subject is imaged, the subject having a wavelength in the shaded range, that is, B or R
The field period (1/60 in the case of NTSC system) due to the level difference of the luminance signal for each field in the subject part of
S) flicker occurs. Further, when the image is printed out or displayed on the non-interlaced monitor based on the luminance signal, a line cloak phenomenon appears.

The present invention focuses on the above points,
The first purpose is to improve the horizontal and vertical resolutions and to obtain good sensitivity. The second purpose is to reduce the occurrence of flicker during interlaced monitoring, reduce line cloak in printouts based on frame signals in non-interlaced monitor printers, and obtain a frame still image with no shift between fields. That is.

[0010]

In order to achieve the above object, the present invention provides a color filter array for use in a solid-state image pickup device of all-pixel readout system, in which filters corresponding to Y spectrum are arranged in a checkered pattern. The R and B filters are arranged so that they are the same within a line and alternate between lines. The luminance signal is adjacent to 2
Generated by the sum and difference signals of the Y filter outputs in the line.

Another aspect of the present invention is a color filter array used for a solid-state image pickup device of the all-pixel readout system, wherein a W filter and a G filter are provided for either even or odd line.
And the Cy and Ye filters are alternately arranged for the other line, and the average transmittance of the W and G filters and the average transmittance of the Cy and Ye filters are , Are set to be substantially the same. The luminance signal is generated for each line.

The above and other objects, features and advantages of the present invention will be apparent from the following detailed description and the accompanying drawings.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to Examples.

Embodiment 1 FIG. 1 shows a color filter array according to this embodiment. In the figure, the luminance filter Y (Y
= R + G + B) are arranged in a checkered pattern, and the red filter R and the blue filter B are arranged in the remaining portion. That is, as compared with the background art, the luminance filter Y is arranged instead of the green filter G, and the red filter R and the green filter G are arranged line-sequentially.

FIG. 2 shows a signal processing circuit for processing a video signal output from an image pickup device (not shown) such as a CCD having a filter array of such a color filter array. The video signal output from the image sensor is O
After each line is clamped by the B clamp circuit 10, the color separation circuit 12, the two-line mixing circuit 14,
It is supplied to the trap circuits 16 and 18, respectively.

First, the color difference signal processing will be described. In the color separation circuit 12, the Yr, Yb, R and B signals are separated from the input signal and supplied to the LPF 20. In addition, Yr is
The luminance signal obtained from the line containing the red filter R, and Yb is the luminance signal obtained from the line containing the blue filter B. The LPF 20 performs filter processing for color signal processing.

Of the processed video signals YLr, YLb, RL, BL, RL, BL are supplied to a WB (white balance) circuit 22, and after processing by this, are supplied to a γ correction circuit 24. The video signals YLr and YLb are directly supplied from the LPF 20 to the γ correction circuit 24. The video signals YLr, YLb, RL and BL which have been subjected to the γ correction by the γ correction circuit 24 are supplied to a matrix circuit 26 where they are subjected to matrix processing to obtain color difference signals RL-YLr and BL-YLb. In these color difference signals, the 1H (1 line) delay circuit 30 and the adder 3 after the aliasing signal generated in the color components or the false signal such as moire is removed in the color difference gain circuit 28.
The signals of the upper and lower lines are added by 2, 34. The color difference signal after addition is S / by the base clip circuit 36.
After N improvement, the color difference signals RL-YL and BL-YL are output.

Next, the luminance signal processing will be described. 2
The line mixing circuit 14 mixes the signals of two consecutive lines. For example, in the first field, the signal of the nth line and the signal of the (n + 1) th line, the signal of the (n + 2) th line and the nth line.
In the second field, the signal of the (n + 1) th line and the signal of the (n + 2) th line, the signal of the (n + 3) th line and the signal of the (n + 4) th line are mixed. , And so on, and the luminance signal YH is generated. The luminance signal YH thus obtained is supplied to the setup circuit 38, where the setup component is added to the luminance signal.

On the other hand, f is generated by the trap circuits 16 and 18.
The video signal subjected to the s / 2 trap processing is supplied to the luminance vertical difference circuit 40, where the following processing is performed. If the luminance signal of the first field and the luminance signal of the second field obtained by the above-described two-line mixing are YA 'and YB', the following equation (1) is obtained.

(Equation 1)

On the other hand, when the vertical component is calculated as YV, the following (2) is obtained.

(Equation 2)

The vertical component YV is added to the luminance signals YA 'and YB' by accumulating a certain coefficient α as in the following equation (3) to obtain final luminance signals YA and YB. Then, the difference YA-YB is output from the luminance vertical difference circuit 40.

(Equation 3)

The output signal of the setup circuit 38 is supplied to the vertical component correction circuit 42 after the γ correction by the γ correction circuit 24. On the other hand, the difference signal from the luminance vertical difference circuit 40 is subjected to base clip processing by the base clip circuit 44, and then multiplied by K in the amplifier 46, so that the vertical component correction circuit 42
Supplied to In the vertical component correction circuit 42, the input signal YH is corrected by the difference signal K × (YA−YB) multiplied by K, and the corrected luminance signal YW is output. The luminance signal YW is supplied to the aperture correction circuit 48 and the 1H delay circuit 5
Aperture corrections in the horizontal and vertical directions are performed by 0 and 52, after which coring and brightness gain processing is performed by the coring circuit 54, delay signal addition is performed by the adder 56, and the final brightness signal YW is output. .

As described above, according to this embodiment, since the addition of two lines is performed, the moire of fs / 2 is canceled out, and the horizontal resolution is improved. Moreover, since the vertical component is corrected, the vertical resolution is also improved. Furthermore, since the R and B primary color filters are used, the color reproducibility is also excellent.

[0023]

Second Embodiment Next, a second embodiment will be described with reference to FIGS.
Will be described. FIG. 3 shows a color filter array in the second embodiment. As shown in the figure, the basic arrangement itself is the same as the background art of FIG. 8 described above,
The spectral characteristics of the transparent filter W'are different. That is, in this embodiment, the spectral characteristics shown in FIG.
The graph shows the spectral characteristics shown by GA. In the figure,
Cyan filter Cy is graph GB, yellow filter Ye
Is a graph GC, and the green filter G is a graph GD. The transparent filter W'of this embodiment is expressed by the following equation (4) with respect to Cy, Ye, and G.

[0024]

(Equation 4) In the equation (4), “+” represents the average transmittance, not the superposition of filters.

As a result, the transparent filter W'becomes a filter having low sensitivity on the short wavelength side. Also, the green filter G
Is generally a cyan filter Cy and a yellow filter Ye.
However, the green filter G shown by the graph GD may be used alone. A filter array is constructed by arranging the filters W ′, G, Cy, and Ye having the above spectral sensitivity characteristics as shown in FIG.

Next, the signal processing circuit of this embodiment will be described with reference to FIG. One of the video signals output from the image sensor (not shown) having the color filter array of FIG.
The luminance signal is composed of lines, and the color signal is composed of two lines. For example, the luminance signal of the first field, that is, the luminance signal YA of the lines n, n + 2, ... Shown in FIG.
It is expressed by equation (5). Further, the luminance signal of the second field, that is, the luminance signal YB of the lines n + 1, n + 3, ... Shown in FIG. 3 is expressed by the equation (6). If these are shown in a graph, it becomes like GE of FIG.

[0027]

(Equation 5)

(Equation 6)

On the other hand, the color signal is obtained by the following equations (7) to (9).

(Equation 7)

(Equation 8)

(Equation 9)

These signals are the OB clamp circuit 1 of FIG.
Output from 0. Of these, the color signal is supplied to the pixel interpolation circuit 60, and the signal obtained by performing pixel interpolation processing on each pixel output here is supplied to the matrix circuit 62. The video signals RL, GL and BL obtained by the matrix processing by the matrix circuit 62 are subjected to white balance processing by the white balance circuit 64 and a γ correction circuit 66.
After the .gamma. Then, the color difference signals RL-YL and BL-YL are obtained by the matrix processing by the matrix circuit 68. These color difference signals are supplied to the base clip circuit 36 after the false signals generated in the color components are removed in the color difference gain circuit 70, and final color difference signals RL-YL and BL-YL are obtained.

On the other hand, the luminance signals YA and YB of each field
Are supplied to the trap filter 76 after the setup processing by the setup circuit 72. The trap filter 76 performs the fs / 2 trap processing, and the processed signal is supplied to the field / frame memory 78 after the γ correction by the γ correction circuit 66. In the field / frame memory 78, field / frame switching processing is performed according to the image or the situation. Then, the aperture correction similar to that in the first embodiment is performed on the processed field or frame signal, and the adder 56
Outputs the final luminance signal YW.

By the way, according to the present embodiment, the spectral characteristic of the transparent filter W'is set as shown in FIG. As a result, the average transmittances of the W ′ and G color filters are the same as the average transmittances of the Cy and Ye color filters, and FIG.
There is no difference in spectral sensitivity as indicated by 0 in FIG. Therefore, flicker during interlaced monitoring, or
Line flow in a printout based on a frame signal by a non-interlaced monitor printer is reduced, and an image with a vertical resolution of about 480 lines can be obtained. Further, as shown in FIG. 5, since the field or frame memory is provided in the image pickup device and the luminance signal is configured for each line, it is possible to pick up a frame still image without a shift between fields. Become. Furthermore, according to the present embodiment, since the signal processing by the matrix is facilitated, the structure of the matrix circuit can be simplified.

[0032]

Other Embodiments The present invention has many embodiments and can be variously modified based on the above disclosure. For example, the following is also included. (1) As an array for combining the filters of W ′, G, Cy, and Ye, the array shown in FIGS. 6 (A) to 6 (C) is considered in addition to the array of the second embodiment. The same effect can be obtained. (2) The present invention can be applied by using an image pickup device of an all-pixel readout system, and is not affected by so-called single-plate system or twin-plate system. (3) The color signal processing method and the processing device shown in the above-mentioned embodiment may be appropriately modified as necessary, and are not limited to the above-mentioned embodiment.

[0033]

As described above, the present invention has the following effects. (1) Since the addition of two lines is performed, the moire of fs / 2 is canceled out, and the horizontal resolution is improved. Also,
Since the vertical component is corrected, the vertical resolution is also improved. Furthermore, since the R and B primary color filters are used, the color reproducibility is also excellent.

(2) Since the average transmittances of the W and G color filters and the average transmittances of the Cy and Ye color filters are the same,
Flicker during interlaced monitoring, or line flow in printouts based on frame signals from non-interlaced monitor printers is reduced. In addition, since the luminance signal is configured for each line, it is possible to capture a frame still image with no shift between fields.

[Brief description of the drawings]

FIG. 1 is a diagram showing a color filter array according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a signal processing circuit according to the first exemplary embodiment.

FIG. 3 is a diagram showing a color filter array according to a second embodiment of the present invention.

FIG. 4 is a graph showing the spectral characteristics of the color filter of Example 2.

FIG. 5 is a block diagram showing a signal processing circuit according to a second embodiment.

FIG. 6 is a diagram showing a color filter array according to another embodiment of the present invention.

FIG. 7 is a diagram showing an example of a conventional color filter array.

FIG. 8 is a diagram showing an example of a conventional color filter array.

FIG. 9 is a graph showing spectral characteristics of a conventional color filter array.

FIG. 10 is a graph showing a spectral sensitivity difference of a luminance signal between lines in a conventional color filter array.

[Explanation of symbols]

 R ... Red filter G ... Green filter B ... Blue filter W, W '... Transparent filter Cy ... Cyan Ye ... Yellow Y ... Luminance filter 10 ... OB clamp circuit 12 ... Color separation circuit 14 ... 2-line mixing circuit 16, 18 ... Trap Circuit 20 ... LPF 22, 64 ... White balance circuit 24, 66 ... Gamma correction circuit 26, 62, 68 ... Matrix circuit 28, 70 ... Color difference gain circuit 30 ... 1H delay circuit 32, 34, 56 ... Adder 36 ... Base clip Circuits 38, 72 ... Setup circuit 40 ... Luminance vertical difference circuit 42 ... Vertical component correction circuit 44 ... Base clip circuit 46 ... Amplifier 48 ... Aperture correction circuit 50, 52 ... 1H delay circuit 54 ... Coring circuit 60 ... Pixel interpolation circuit 76 … Trap filter 78… Field / frame memory

Claims (4)

[Claims] 1. In a color filter array used for a solid-state image pickup device of all-pixel readout system, Y filters are arranged in a checkered pattern, and R and B filters are the same in a line and alternate between lines. A color filter array characterized by being arrayed in. 2. Luminance for generating a luminance signal based on a video signal output from an image sensor including the color filter array according to claim 1 by a sum and difference signal of Y filter outputs in adjacent two lines. A video signal processing circuit comprising a signal generating means. 3. A color filter array used for a solid-state image pickup device of all-pixel readout system, wherein W filters and G filters are alternately arranged for one of even and odd lines, and the other one is arranged. For the line, the Cy and Ye filters are alternately arranged, and the average transmittance of the W and G filters and the average transmittance of the Cy and Ye filters are set to be substantially the same. Characteristic color filter array. 4. A video signal processing comprising: a brightness signal generating means for generating a brightness signal for each line based on a video signal output from the image pickup device of the color filter array according to claim 3. circuit.