JP4375726B2 - Color filter array and video signal processing circuit - Google Patents

Description

  The present invention relates to a color filter array and a video signal processing circuit of an image sensor, and more specifically, to an improvement of a color filter array and a video signal processing circuit suitable for an all-pixel readout type solid-state image sensor.

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

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

However, the background art as described above has the following disadvantages.
(1) If the frequency of the color subcarrier is fs, a color moire of fs / 2 is mixed in the luminance signal, resulting in deterioration of the horizontal resolution.
(2) Since only a luminance signal obtained by mixing two lines of signals 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, in an image pickup apparatus using a conventional single-plate image pickup device (IL-CCD), an Mg (magenta) color filter is generally used to mix two lines into a luminance signal. Before the color filter array is composed of four colors of Mg, G, Cy (cyan), and Ye (yellow) as in the present, a method using four colors of W (transparent), G, Cy, and Ye is also available. Although devised (see Japanese Patent Application Laid-Open No. Sho 62-108694) and commercially available, there is no such system for making a luminance signal in one line in such a four-color system of W, G, Cy, and Ye. FIG. 8 shows the color filter arrangement of the above publication, in which a line constituted by G and W filters and a line constituted by Cy and Ye filters are alternately arranged. Yes.

  By the way, since the transparent filter W is a system that does not use a color filter, the pixel output of the transparent filter W portion becomes the spectral characteristics of the solid-state imaging device. FIG. 9A shows an example of the characteristics of the transparent filter W, where the horizontal axis represents wavelength and the vertical axis represents relative sensitivity. In FIG. 5B, the characteristics of other filters G, Cy, Ye are shown for reference.

  Here, consider a case where a luminance signal is obtained with one line in the color filter array of FIG. If the luminance signal by the W and G lines is YA and the luminance signal by 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 hatching in FIG.

  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 both levels are matched when imaging a monochrome subject, the subject having a wavelength in the hatched range, that is, B or Flickers in the field period (1/60 second in the case of the NTSC system) occur in the R subject portion due to the level difference of the luminance signal for each field. Furthermore, when printing out based on the luminance signal or displaying on a non-interlace monitor, a line cloaking phenomenon appears.

  The present invention focuses on the above points, reduces the occurrence of flicker during interlace monitoring, reduces line cloaking in printouts based on frame signals in non-interlace monitor printers, and further, shifts between fields. The purpose is to obtain a frame still image without any image.

In order to solve the above-mentioned problems, the present invention comprises means described in the following 1) to 2).
That is,
1) In a color filter array used for a solid-state imaging device of an all-pixel readout method,
Even number, for one line of the odd, with alternately arranged in a W filter and the G filter which is less transparent filter sensitivity at short wavelength side longer wavelength side, to the other line Are arranged so that the average transmittance of the W and G filters in the transmitted light of each color filter and the average transmittance of the Cy and Ye filters are approximately the same. A color filter array characterized by setting spectral characteristics of the filter.
2) A video signal processing circuit comprising luminance signal generating means for generating a luminance signal for each line based on the video signal output from the image sensor of the color filter array described in 1).

  According to the “color filter array and video signal processing circuit” of the present invention, the average transmittance of the W and G color filters and the average transmittance of the Cy and Ye color filters are the same. Alternatively, line flow in a printout based on a frame signal by a non-interlace monitor printer 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.

  The best mode for carrying out the invention of the color filter array and the video signal processing circuit according to the present invention will be described below with reference to preferred embodiments.

  FIG. 1 shows a color filter array according to this reference example. In the figure, luminance filters Y (Y = R + G + B) are arranged in a checkered pattern, and red filters R and blue filters B are arranged in the remaining part. 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 line-sequentially arranged.

  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 such a filter array of color filters. The video signal output from the image sensor is clamped for each line by the OB clamp circuit 10 and then supplied to the color separation circuit 12, the two-line mixing circuit 14, and the trap circuits 16 and 18, respectively.

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

  Of the processed video signals YLr, YLb, RL, and BL, RL and BL are supplied to a WB (white balance) circuit 22 and are supplied to a γ correction circuit 24 after the processing. The video signals YLr and YLb are supplied from the LPF 20 to the γ correction circuit 24 as they are. The video signals YLr, YLb, RL, and BL that have been subjected to the γ correction by the γ correction circuit 24 are supplied to the matrix circuit 26, where they are subjected to matrix processing to obtain color difference signals RL-YLr and BL-YLb. These color-difference signals are processed by the 1H (one-line) delay circuit 30 and the adder 32 and 34 in the upper and lower lines after the false signal such as the folding signal or moire generated in the color component is removed in the color-difference gain circuit 28. Is added. The added color difference signals are output as color difference signals RL-YL and BL-YL after S / N improvement by the base clip circuit 36.

  Next, luminance signal processing will be described. In the two-line mixing circuit 14, signals of two continuous lines are mixed. For example, in the first field, the nth line signal and the (n + 1) th line signal, the n + 2 line signal and the (n + 3) line signal, and so on are mixed. In the second field, The luminance signal YH is generated by mixing 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, and so on. 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, the video signal subjected to the fs / 2 trap processing by the trap circuits 16 and 18 is supplied to the luminance vertical difference circuit 40, where the following processing is performed. When the luminance signal of the first field obtained by the two-line mixing described above is YA 'and the luminance signal of the second field is YB', the following equation (1) is obtained.

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

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

  The output signal of the setup circuit 38 is supplied to the vertical component correction circuit 42 after 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, multiplied by K by the amplifier 46, and supplied to the vertical component correction circuit 42. 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 subjected to horizontal and vertical aperture corrections by the aperture correction circuit 48 and 1H delay circuits 50 and 52, and thereafter coring and luminance gain processing by the coring circuit 54, and a delay signal by the adder 56. After the addition, the final luminance signal YW is output.

  As described above, according to the present reference example, since the two-line addition is performed, the moire of fs / 2 is canceled, and the horizontal resolution is improved. Further, since the vertical component is corrected, the vertical resolution is also improved. Further, since the R and B primary color filters are used, the color reproducibility is excellent.

  Next, Example 1 will be described with reference to FIGS. FIG. 3 shows a color filter arrangement in the first embodiment. As shown in the figure, the basic arrangement itself is the same as the background art of FIG. 8 described above, but the spectral characteristics of the transparent filter W ′ are different. That is, in this embodiment, the spectral characteristic shown in the graph GA in FIG. 4 is used instead of the spectral characteristic shown in FIG. In the figure, the cyan filter Cy is a graph GB, the 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.

なお、この（4）式中、「＋」は、フィルタの重ね合わせではなく、平均透過率を表わす。

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

  As a result, the transparent filter W ′ becomes a filter with low sensitivity on the short wavelength side. Further, the green filter G is generally configured by superimposing the cyan filter Cy and the yellow filter Ye, but may be configured by the green filter G alone shown by the graph GD. A filter array is configured 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. Of the video signal output from the image sensor (not shown) having the color filter array shown in FIG. 3, a luminance signal is composed of one line, and a 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. Further, the luminance signal of the second field, that is, the luminance signal YB of the lines n + 1, n + 3,... Shown in FIG. These are shown in a graph as GE in FIG.

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

  These signals are output from the OB clamp circuit 10 of FIG. Among these, the color signal is supplied to the pixel interpolation circuit 60, and a signal obtained by performing pixel interpolation processing on each pixel output is supplied to the matrix circuit 62. Video signals RL, GL, BL obtained by matrix processing by the matrix circuit 62 are supplied to another matrix circuit 68 after white balance processing by the white balance circuit 64 and γ correction by the γ correction circuit 66. Then, color difference signals RL-YL and BL-YL are obtained by 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 process by the setup circuit 72.
The trap filter 76 performs fs / 2 trap processing, and the processed signal is supplied to the field / frame memory 78 after γ correction by the γ correction circuit 66. In the field / frame memory 78, a field / frame switching process corresponding to the video or the situation is performed. The processed field or frame signal is subjected to aperture correction similar to that of the reference example, and the final luminance signal YW is output from the adder 56.

  By the way, according to the present embodiment, the spectral characteristics of the transparent filter W 'are set as shown in FIG. As a result, the average transmittance of the W ′ and G color filters and the average transmittance of the Cy and Ye color filters are the same, and the spectral sensitivity difference as shown by the oblique lines in FIG. 10 does not occur. For this reason, flicker at the time of interlace monitoring or line flow in printout based on a frame signal by a non-interlace monitor printer is reduced, and an image with about 480 vertical resolutions can be obtained. In addition, as shown in FIG. 5, since a field or frame memory is provided in the imaging device and a luminance signal is configured for each line, it is possible to capture a frame still image with no deviation between fields. Become. Furthermore, according to the present embodiment, signal processing by a matrix is facilitated, so that the configuration of the matrix circuit can be simplified.

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

It is a figure which shows the color filter array of the reference example of this invention. It is a block diagram which shows the signal processing circuit of a reference example. It is a figure which shows the color filter arrangement | sequence of Example 1 of this invention. 6 is a graph illustrating spectral characteristics of the color filter of Example 1. 1 is a block diagram illustrating a signal processing circuit according to a first embodiment. It is a figure which shows the color filter arrangement | sequence of the other Example of this invention. It is a figure which shows an example of the conventional color filter arrangement | sequence. It is a figure which shows an example of the conventional color filter arrangement | sequence. It is a graph which shows the spectral characteristic of the conventional color filter arrangement | sequence. It is a graph which shows the spectral sensitivity difference of the luminance signal between the lines in the conventional color filter arrangement | sequence.

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 ... Two-line mixing circuits 16, 18 ... Trap Circuit 20 ... LPF
22, 64, white balance circuits 24, 66, γ correction circuits 26, 62, 68, matrix circuits 28, 70, color difference gain circuit 30, 1H delay circuits 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 (2)

In the color filter array used for the solid-state image sensor of the all-pixel readout method,
Even number, for one line of the odd, with alternately arranged in a W filter and the G filter which is less transparent filter sensitivity at short wavelength side longer wavelength side, to the other line Are arranged so that the average transmittance of the W and G filters in the transmitted light of each color filter and the average transmittance of the Cy and Ye filters are approximately the same. A color filter array characterized by setting spectral characteristics of the filter.   2. A video signal processing circuit comprising: luminance signal generating means for generating a luminance signal for each line based on a video signal output from an image sensor of a color filter array according to claim 1.

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