JP2017055260A - On-chip color filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an on-chip color filter capable of capturing a subject image with high image quality even under low illuminance.SOLUTION: Four unit filter arrays are obtained by rotating unit filter arrays arranged in 2 by 2, including C filters, as clear filters, arranged at upper left and lower right, an R filter arranged at an upper right, and a B filter arranged at a lower left, at 0°, 90°, 180° and 270°, respectively. A basic filter array pattern formed of 16 RGB filters is formed by arranging the unit filter arrays in 2 by 2. At the upper left, upper right, lower right, and lower left of the basic filter array pattern, the unit filter arrays rotated e.g., at 0°, 90°, 270° and 180° are disposed in this order, to form the basic filter array pattern. The basic filter array pattern is arranged repeatedly in rows and columns, to form an on-chip color filter for an imaging element.SELECTED DRAWING: Figure 3

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. In the Bayer array, a grid-like 2 × 2 pixel filter array is used as a unit, and the unit 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. Also, a filter array has been proposed in which the Bayer array G filter is replaced with a transparent filter and the light receiving sensitivity of the image sensor is improved, assuming imaging under low illumination conditions (Patent Document 1). On the other hand, in a Bayer array filter array, problems such as moiré or false color occur due to the characteristics of the array. In order to solve these problems, a technique for suppressing moire and false colors by repeatedly arranging a basic filter array pattern composed of 4 × 4 filters vertically and horizontally is proposed (Patent Document 2).

US Patent Application Publication No. 2014/0125838 JP 2013-201723 A

  An object of the present invention is to provide an on-chip color filter that can capture a bright subject image with high image quality even under low illumination.

  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 repeatedly arranged vertically and horizontally, and the basic filter array pattern has at least a predetermined cut at the upper left and lower right. A unit filter array of 2 rows and 2 columns in which a first filter that transmits light having a wavelength longer than the off wavelength, an R filter on the upper right, and a B filter on the lower left is arranged at 0 degrees, 90 degrees, 180 degrees, and 270 degrees clockwise. The unit filter array is composed of a combination of four rotated unit filter arrays, and the unit filter array is rotated by 0, 90, 270, and 180 degrees on the upper left, upper right, lower right, and lower left of the basic filter array pattern, or 0 Rotated in degrees, 180 degrees, 90 degrees, 270 degrees, or 0 degrees, 90 degrees, 180 degrees, 270 degrees It is characterized in that.

  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. Arrange in this order. The first filter is, for example, a clear filter. The first filter may be an ND filter, and the transmittance of the ND filter is preferably 30% to 50%, for example.

  The imaging device of the present invention is characterized by mounting the above-described on-chip color filter.

  An electronic endoscope according to the present invention is characterized by mounting the above-described imaging device.

  According to the present invention, it is possible to provide an on-chip color filter that can capture a bright subject image with high image quality even under low illumination.

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 rotating the R filter, C filter, and B filter of a unit filter array 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 graph which shows the transmittance | permeability characteristic of each filter. It is a top view which shows arrangement | positioning of the unit filter array of a modification.

  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 is obtained by replacing two G filters of two rows and two columns in a Bayer array and a total of four RGB filters with transparent filters C. Correspond. That is, two C filters are arranged in one diagonal direction, and one R (red) filter and one B (blue) filter are arranged in the other diagonal direction. In the example of FIG. 2A, the C 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)} ) The other patterns ( ₄ P ₄ −6 = 18 types) are represented by any of these 6 types of patterns, as will be described later, and the description thereof will be 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).

  In the first embodiment, the light receiving sensitivity of the image sensor 14 is enhanced by replacing two G filters in a Bayer array with, for example, two transparent clear fill filters (C filters). In the first embodiment, as shown in FIG. 4, the periodicity in the Bayer array is reduced, and all rows, columns, and R filters, C filters, and B filters are all included, so moire and false colors are included. Occurrence is suppressed. Further, the C filters are also arranged relatively evenly.

  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.

  Also in the second embodiment, the two G filters in the Bayer array are replaced with two C filters, and the light receiving sensitivity of the image sensor 14 is increased. Also in the filter array, as shown in FIG. 6, the periodicity of the Bayer array is reduced, and all rows and columns include an R filter, a C filter, and a B filter to suppress the generation of moire and false colors. It is done. Further, the C filters are also arranged relatively evenly.

  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.

  Also in the third embodiment, the two G filters in the Bayer array are replaced with two C filters, and the light receiving sensitivity of the image sensor 14 is increased. Also in the filter array, as shown in FIG. 8, the periodicity of the Bayer array is reduced, and all rows and columns include an R filter, a C filter, and a B filter to suppress the generation of moire and false colors. It is done.

  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 shown, in the array (21D) of FIG. 9A, each row and each column includes only two colors in the RCB. In the array (21E) in FIG. 9B, each row includes only two colors in the RCB, and in the array (21F) in FIG. 9C, each column includes only two colors in the RCB. 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.

  Next, the transmittance characteristics of the R filter, C filter, and B filter will be described with reference to FIG. The horizontal axis in FIG. 12 is the wavelength (nm), and the vertical axis is the transmittance (%) of each filter. In the figure, the broken line indicates the transmittance characteristic of the B filter, and the alternate long and short dash line indicates the transmittance characteristic of the R filter. The two-dot chain line is the transmittance characteristic of the C filter.

  As shown in FIG. 12, the C filter has a transmittance of approximately 100% over the entire visible region. In this case, the light receiving sensitivity of the image sensor 14 is significantly increased, but there is a large difference between the amount of light received through the R filter and the B filter, and the color reproducibility may be deteriorated. Therefore, as a modification of the first to third embodiments, the C filter may be replaced with a transmittance characteristic indicated by a solid line in FIG. 12, for example, an ND filter having a transmittance of about 30% to 50%. In such a configuration, the difference between the amount of light transmitted through the B filter and the R filter is reduced, so that the overall light reception sensitivity is somewhat reduced, but the color reproducibility is improved.

  In general, when photographing inside the body using an electronic endoscope, the subject is generally reddish. Therefore, as yet another modification, a long-pass filter having a cutoff wavelength of, for example, about 450 nm to 600 nm can be used instead of the C filter. At this time, the maximum transmittance of the long pass filter is set to about 70% to 100%, for example.

  In the first to third embodiments, the two G filters in the Bayer array are replaced with two C filters. As another modification of the first to third embodiments, for example, FIG. As shown, only one of the two G filters can be replaced with the C filter, and this can be replaced with the C filter and replaced with the ND filter or the long pass filter. In FIG. 13, the C filter is arranged at the upper right and the G filter is arranged at the lower left, but this arrangement may be reversed.

  As described above, in the configurations of the first to third embodiments, the modified examples, and the combination thereof, the light receiving sensitivity of the image sensor is increased by increasing the light transmittance of the on-chip color filter, and the light is bright even under low illuminance. A subject image can be captured. In addition, since the occurrence of moire and false colors can be prevented by using the on-chip color filter that employs the filter arrangement of the first to third embodiments, a high-resolution subject image can be taken even if the optical low-pass filter is omitted.

  In addition, when an imaging device equipped with an on-chip color filter having a configuration of the first to third embodiments, the modified examples, and the combination thereof is applied to an electronic endoscope apparatus, the imaging device has high sensitivity. A bright subject image can be captured even when the distal end of the endoscope inserted into the camera is separated from the subject and the illuminance decreases. Since the optical low-pass filter can be omitted, it is advantageous for further downsizing the distal end of the insertion portion.

  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 (7)

  A filter array in which a basic filter array pattern made up of four rows and four columns of filters is repeatedly arranged vertically and horizontally. The basic filter array pattern transmits light having a wavelength of at least a predetermined cutoff wavelength at the upper left and the lower right. A unit filter array of 2 rows and 2 columns in which one filter, an R filter in the upper right, and a B filter in the lower left are arranged, is a combination of four unit filter arrays rotated clockwise by 0, 90, 180, and 270 degrees. The unit filter array is rotated by 0 degrees, 90 degrees, 270 degrees, 180 degrees, or 0 degrees, 180 degrees, 90 degrees, 270 at the upper left, upper right, lower right, lower left of the basic filter array pattern. The image sensor is characterized in that the one rotated by 0 degrees, or rotated by 0 degrees, 90 degrees, 180 degrees, and 270 degrees are arranged in this order. Chip color filter.   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.   The on-chip color filter according to claim 1, wherein the first filter is a clear filter.   The on-chip color filter according to claim 1, wherein the first filter is an ND filter.   The on-chip color filter according to claim 4, wherein the transmittance of the ND filter is 30% to 50%.   The image pick-up element which mounts the on-chip color filter as described in any one of Claims 1-5.   An electronic endoscope equipped with the image pickup device according to claim 6.

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