JP2013201723A - On-chip color filter alignment for image pick-up device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple on-chip color filter alignment with less moire and false color.SOLUTION: An on-chip color filter alignment for an image pic-up device comprises a basic filter array pattern including 16 RGB filters. The basic filter array pattern is configured by four unit filter arrays, each of which includes two lines and two columns of: G-filters in upper left and lower right; an R-filter in upper right; and B-filter in lower left. Four of the unit filter arrays rotate respectively in 0 degrees, 90 degrees, 180 degrees, and 270 degrees, and are arranged two in vertical and two in horizontal positions in the basic filter array pattern. The unit filter arrays are arranged, for example, in order from upper left, upper right, lower right, and lower left, in 0 degrees, 90 degrees, 270 degrees, and 180 degrees, to be the basic filter array pattern. The basic filter array patterns are repeatedly arranged vertically and horizontally so as to be an on-chip color filter for an image pick-up device.

Description

  The present invention relates to a method for arranging on-chip color filters mounted on, for example, a single-plate color image sensor.

  As a method for acquiring a color image using one image sensor, a method using a color filter array with each pixel of the image sensor as a unit is common. As the color filter array, a Bayer array in which RGB color filters are arranged in a checkered pattern is widely used (Patent Document 1). In the Bayer array, a grid-like 2 × 2 pixel filter array is used as a unit, which is repeatedly arranged in the vertical and horizontal directions. One unit (2 × 2 pixels) is composed of two G filters, one R filter, and one B filter. The G filter is along one diagonal, and the R and B filters are the other. Arranged along a diagonal.

  However, the filter array configured with the Bayer array has high periodicity in the spatial arrangement of each of the RGB filters, so when an image including a regular pattern with a high frequency is captured, moire is generated or a false color is generated at the edge portion. There is a problem. In order to solve such a problem, a configuration in which an optical low-pass filter is disposed in front of the image sensor is generally employed. However, when an optical low-pass filter is used, the resolution and sharpness are inevitably lowered. Further, in the Bayer array, not all the RGB filters are included in each row and each column, which causes a false color.

  On the other hand, an attempt to deal with this problem by adopting an RGB filter array different from the Bayer array, for example, the Yamanaka array in FIG. 12 and the Lukac array in FIG. 13 (Patent Document 2, Non-Patent Document 1) An attempt has been made to break the periodicity of the filter array by randomly arranging RGB filters over the entire surface of the image sensor (Patent Document 3). Further, a method for adding a color other than RGB has also been proposed (Patent Document 4).

Japanese Patent Laid-Open No. 51-112228 U.S. Pat. No. 4,054,906 JP 2000-308071 A JP 2000-316169A

R. Lukac and K. N. Plataniotis, “Colorfilter arrays: Design and performance analysis”, IEEE Transactions on Consumer Electronics vol. 51 No.4, pp. 1260-1267, 2005.

  According to the arrangements of Patent Document 2 and Non-Patent Document 1, the problem of periodicity is solved to some extent. However, in the Yamanaka arrangement of FIG. 12, since a column including only the G filter and a column including only the R filter and the B filter are alternately generated, a false color is generated (FIG. 9 (b) of Non-Patent Document 1). Further, in the Lukac array in FIG. 13, the occurrence of false colors is less than that in the Yamanaka array. However, rows including only the G filter and the R filter and rows including only the G filter and the B filter are alternately generated. From the viewpoint of suppressing false colors, it is desirable that all the components of RGB are included in all rows and columns. Further, in the configuration of Patent Document 3 in which RGB filters are arranged at random, the calculation for constructing a full-color image by interpolating RGB components becomes complicated, and in the configuration of Patent Document 4 in which the color of the filter is increased, the manufacturing cost is increased. Compared with the case where only the RGB filter is used, the calculation for constructing the image with the increased number of colors is more complicated.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a filter arrangement with less moiré and false colors with a simple configuration.

  The on-chip color filter of the image pickup device of the present invention includes a filter array in which a basic filter array pattern composed of 4 × 4 filters is vertically and horizontally arranged. The basic filter array pattern includes a G filter on the upper left and a lower right, and an upper right The unit filter array of 2 rows and 2 columns in which the R filter is arranged in the lower left and the B filter in the lower left is composed of a combination of four unit filter arrays rotated clockwise by 0 degrees, 90 degrees, 180 degrees and 270 degrees. In the upper left, upper right, lower right, and lower left of the filter array pattern, the unit filter array is rotated by 0, 90, 270, and 180 degrees, or rotated by 0, 180, 90, and 270 degrees, or It is characterized in that those rotated by 0 degrees, 90 degrees, 180 degrees, and 270 degrees are arranged in this order.

  In the upper left, upper right, lower right, and lower left of the basic filter array pattern, the unit filter array is rotated by 0, 90, 270, and 180 degrees, or rotated by 0, 180, 90, and 270 degrees. By arranging in this order, the G filters are more evenly distributed and the resolution is further improved.

  The imaging device of the present invention is characterized by mounting the above-described on-chip color filter. In addition, an electronic endoscope according to the present invention is characterized in that the image pickup device is mounted.

  According to the present invention, it is possible to provide a filter arrangement with less moiré and false colors with a simple configuration.

It is a general-view figure of an imaging device carrying an image sensor using an on-chip color filter which is one embodiment of the present invention. It is a top view which shows arrangement | positioning when RGB arrangement | positioning of a unit filter array is rotated 90 degree | times, 180 degree | times, and 270 degree | times. 4 shows an arrangement of four unit filter arrays in the basic filter array pattern of the first embodiment of the present invention. FIG. 4 is a layout diagram of a filter array in which two basic filter array patterns shown in FIG. 3 are arranged vertically and horizontally. 4 shows an arrangement of four unit filter arrays in a basic filter array pattern according to a second embodiment of the present invention. FIG. 6 is a layout diagram of a filter array in which two basic filter array patterns shown in FIG. 5 are arranged vertically and horizontally. 4 shows an arrangement of four unit filter arrays in a basic filter array pattern according to a third embodiment of the present invention. FIG. 8 is a layout diagram of a filter array in which two basic filter array patterns shown in FIG. 7 are arranged vertically and horizontally. An arrangement of four unit filter arrays in a basic filter array pattern other than the embodiment is shown. An example of a basic filter array pattern based on a unit other than the unit filter array 20A is shown. FIG. 11 is a layout diagram of a filter array in which two basic filter array patterns shown in FIG. 10 are arranged vertically and horizontally. It is a figure which shows the Yamanaka arrangement | sequence which is a prior art example. It is a figure which shows the Lukac arrangement | sequence which is a prior art example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of an imaging apparatus equipped with an imaging device using an on-chip color filter according to an embodiment of the present invention.

  The imaging device is, for example, an electronic endoscope device 10 and includes an electronic scope 11, a processor device 12, a monitor device 13, and the like. An imaging device 14 such as a CCD or CMOS is disposed at the distal end of the insertion portion of the scope 11, and the on-chip color filter 15 of this embodiment is mounted on the imaging device 14.

  FIG. 2 shows an array of unit filter arrays (FIG. 2 (a)) constituting the filter array of the on-chip color filter 15 of this embodiment, and 90 ° (FIG. 2 (b)) and 180 ° clockwise. (FIG. 2C) is a plan view showing an arrangement rotated by 270 degrees (FIG. 2D). In this specification, it is assumed that the unit filter array shown in FIG. 2A is rotated by 0 degrees and is indicated by 20A, and the unit filter arrays rotated by 90 degrees, 180 degrees, and 270 degrees are 20B and 20C, respectively. , 20D.

  As shown in FIG. 2A, the unit filter array 20A of the present embodiment forms a Bayer array, and is composed of two rows and two columns, for a total of four RGB filters. That is, two G filters are arranged in one diagonal direction, and one R filter and one B filter are arranged in the other diagonal direction. In the example of FIG. 2A, the G filter is arranged at the upper left and the lower right, the R filter is arranged at the upper right, and the B filter is arranged at the lower left.

  In the present embodiment, the four unit filter arrays 20A to 20D respectively rotated in the directions of 0 degrees, 90 degrees, 180 degrees, and 270 degrees shown in FIGS. A basic pattern (basic filter array pattern) is arranged in a 2 × 2 square lattice, and this basic pattern is repeatedly arranged vertically and horizontally to construct the entire filter array of the on-chip color filter 15.

When one of the unit filter arrays 20A to 20D is defined as a reference (for example, 20A) and the position of the unit filter array in the basic pattern is fixed, the type of the basic pattern obtained is 6 (= _(4-1) P _{( 4-1)} It becomes as follows. The other patterns ( ₄ P ₄ −6 = 18 types) are represented by any one of these 6 types of patterns, as will be described later, and the description thereof is omitted. In the following description, six types of basic patterns obtained when the unit filter array 20A is determined on the basis and arranged at the upper left of the basic pattern will be described with reference to FIGS.

  FIG. 3 shows the arrangement of the unit filter arrays 20A to 20D in the basic filter array pattern 21A according to the first embodiment of the present invention. In FIG. 3, the unit filter array 20A rotated by 0 degrees, 90 degrees, 270 degrees, and 180 degrees is arranged in this order on the upper left, upper right, lower right, and lower left of the basic filter array pattern 21A. FIG. 4 shows the state of the filter array when two basic filter array patterns 21A shown in FIG. 3 are arranged vertically and horizontally. 4 indicate the upward direction in the unit filter array 20A. The upward arrow is 20A (0 degrees), the right arrow is 20B (90 degrees), the downward arrow is 20C (180 degrees), and the left arrow is It corresponds to 20D (270 degrees).

  As shown in FIG. 4, in the array of the first embodiment, the periodicity of the Bayer array is reduced, and all rows, columns, and R filters, G filters, and B filters are all included, so moire and false colors are included. Occurrence is suppressed. Also, the G filters are arranged relatively evenly distributed.

  FIG. 5 shows the arrangement of the unit filter arrays 20A to 20D in the basic filter array pattern 21B of the second embodiment of the present invention. In FIG. 5, the unit filter array 20A is rotated by 0 degrees, 180 degrees, 90 degrees, and 270 degrees. Are arranged in this order on the upper left, upper right, lower right, and lower left of the basic filter array pattern 21A. FIG. 6 shows the state of the filter array when the basic filter array pattern 21B shown in FIG. In addition, the description method of a figure is the same as that of FIG. As shown in FIG. 6, also in the arrangement of the second embodiment, the periodicity of the Bayer arrangement is reduced, and all rows and columns include R filters, G filters, and B filters. Occurrence is suppressed. Also, the G filters are arranged relatively evenly distributed.

  FIG. 7 shows the arrangement of the unit filter arrays 20A to 20D in the basic filter array pattern 21C of the third embodiment of the present invention. In FIG. 7, the unit filter array 20A is rotated by 0 degrees, 90 degrees, 180 degrees, and 270 degrees. Are arranged in this order on the upper left, upper right, lower right, and lower left of the basic filter array pattern 21A. FIG. 8 shows the state of the filter array when the basic filter array patterns 21C shown in FIG. In addition, the description method of a figure is the same as that of FIG. As shown in FIG. 8, also in the arrangement of the third embodiment, the periodicity of the Bayer arrangement is reduced, and all rows and columns include an R filter, a G filter, and a B filter. Occurrence is suppressed.

  Next, FIGS. 9A to 9C show the arrangement of the basic filter array patterns 21D, 21E, and 21F when the unit filter arrays 20A to 20D are arranged in the remaining three patterns. FIG. 9 is drawn in the same manner as FIG. 3, FIG. 5, and FIG. As illustrated, in the array (21D) of FIG. 9A, each row and each column includes only two colors of RGB. Further, in the array (21E) in FIG. 9B, each row includes only two colors in RGB, and in the array (21F) in FIG. 9C, each column includes only two colors in RGB. Therefore, the arrangements of FIGS. 9A to 9C are inferior from the viewpoint of suppressing false colors as compared with the first to third embodiments.

  10 and 11, six basic patterns based on the unit filter array 20A are the basic patterns when the unit filter array 20B rotated by 90 degrees is used as a reference instead of the unit filter array 20A. An example showing that it corresponds to one of the following.

  FIG. 10 shows a filter arrangement of the basic pattern when the unit filter array 20B is defined as a reference and arranged at the upper left of the basic pattern, and 20A is arranged at the upper right, 20D is arranged at the lower right, and 20C is arranged at the lower left. Further, FIG. 11 shows a filter arrangement when four basic patterns of FIG. Here, referring to the area surrounded by the broken line in FIG. 11, this is determined based on the unit filter array 20A, 20B (90 degree rotation) is upper right, 20C (180 degree rotation) is lower right, and 20D (270 degree rotation). ) Corresponds to the one placed in the lower left. That is, the filter arrangement in FIG. 11 corresponds to the basic pattern 21C in FIG. Thus, patterns other than the six types of patterns based on the unit filter array 20A described with reference to FIGS. 3 to 9 are represented by any of these six types of patterns.

  As described above, according to the present embodiment, it is possible to achieve high resolution through the omission of the optical low-pass filter while preventing moiré and false color in the image sensor with a very simple configuration. Further, in the electronic endoscope apparatus using the on-chip color filter of the present embodiment, due to the improvement in resolution, even if the low-pass filter is omitted, for example, the generation of false color and moire is small, so the low-pass filter is omitted, for example. And the tip can be further reduced in size. In the present embodiment, since the RGB ratio is the same as that of the Bayer array, color reproduction equivalent to that of the Bayer array can also be realized.

  The on-chip color filter of the present embodiment only needs to include the repetition of the basic pattern (basic filter array pattern) of the present embodiment, and only m × n (m and n are integers) of the above basic patterns. Not necessarily configured. For example, the peripheral edge of the color filter may be constituted by a part of the basic pattern.

  In the present embodiment, the electronic endoscope apparatus has been described as an example. However, the on-chip color filter of the present embodiment may be used in other imaging apparatuses, for example, in an imaging element such as a camera or a mobile phone. May also be applied.

DESCRIPTION OF SYMBOLS 10 Electronic endoscope apparatus 11 Electronic scope 12 Processor apparatus 13 Monitor apparatus 14 Image pick-up element 15 On-chip color filter 20A-20D Unit filter array 21A-21F Basic filter array pattern

Claims (4)

  It includes a filter array in which a basic filter array pattern consisting of four rows and four columns of filters is repeatedly arranged vertically and horizontally. The basic filter array pattern includes a G filter in the upper left and lower right, an R filter in the upper right, and a B filter in the lower left. The unit filter array of two rows and two columns is composed of a combination of four unit filter arrays rotated clockwise by 0, 90, 180, and 270 degrees, and the upper left, upper right, and lower right of the basic filter array pattern. In the lower left, the unit filter array is rotated by 0, 90, 270, and 180 degrees, or rotated by 0, 180, 90, and 270 degrees, or is rotated by 0, 90, 180, An on-chip color filter for an image sensor, wherein 270 degree rotated ones are arranged in this order.   In the upper left, upper right, lower right, and lower left of the basic filter array pattern, the unit filter array is rotated by 0, 90, 270, and 180 degrees, or rotated by 0, 180, 90, and 270 degrees. 2. The on-chip color filter according to claim 1, wherein the filters are arranged in this order.   An image sensor on which the on-chip color filter according to claim 1 is mounted. An electronic endoscope equipped with the imaging device according to claim 3.

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