JPS60254978A - Color solid-state image pickup device - Google Patents

Abstract

PURPOSE:To eliminate the occurrence of a vertical color error at the sharp vertical contour part of an achromatic picture plane by employing such a color filter array that color difference signals obtained from respective horizontal lines to achromatic color light of reference lighting color temperature are nearly zero. CONSTITUTION:The 1st and the 3rd horizontal picture elements l1, l3, l5, and l7 have color filters Mg' and G' with transmission characteristics shown in a graph (a), and the 1st color difference signal C1 modulated by Mg' and G' is C1=R+B-G; and the spectral transmission characteristics of the color filters Mg'and G' are so determined that C1 is zero when white irradiated at reference lighting color temperature is picked up. Further, the 1st horizontal picture element arrays l1 and l5 and the 3rd horizontal picture element arrays l3 and l7 are so formed that color filters C are 180 deg. out of phase. The 2nd and the 4th horizontal picture element arrays l2, l4, l6, and l8 have color filters Cy' and Ye' with transmission characteristics shown in a graph (b) corresponding to respective picture elements. The 2nd color difference signal modulated by the color filters Cy' and Ye' is C2=B-R. Then, the spectral transmission characteristics of the color filters Cy' and Ye' are so determined as well as the color filters Mg' and G' that the C2 is zero to white irradiated at reference lighting color temperature.

Description

Detailed Description of the Invention (Industrial Field of Application) This relates to a solid-state imaging device for color imaging using the solid-state imaging device according to the present invention (Prior Art and its Problems) A type of solid-state imaging device As shown in the schematic plan view of FIG. 1, the inter-twin transfer CCD image sensor (hereinafter abbreviated as XL-CCD image sensor) is arranged regularly in the horizontal and vertical directions, and has a picture element 1 and a picture element 1. Vertical COD that vertically transfers signal charges photoelectrically converted and accumulated in element 1
It consists of a register 2, a horizontal COD register 3 that transfers in the horizontal direction, and an output section 4.The arrow in the figure indicates the direction of signal charge transfer.0The IL-CCD image sensor has a signal charge accumulated in the picture element. Two types of read operations can be performed: a frame accumulation operation in which signal charges are read out in a frame period, and a field accumulation operation in which signal charges are read out in a field period. Compared to frame storage operation, field accumulation operation takes half the accumulation time 1 + has a small afterimage feeling 0 For this reason, the development of single-chip color imaging devices using field accumulation operation is progressing. Both the imaging device and the force 2-imaging device according to the invention are field storage operated. Figure 2 schematically shows the field accumulation operation.
, It, ls-..., le,..., first, 2. , 2.
,1.,18. The signal charge corresponding to the picture element is transferred to the vertical COD register 2, and then the vertical CCD
The signal charges for one picture element are transferred by the transfer operation of register 2, and further 1. .

1m s z, tl! 7 The signal charge of the picture element corresponding to e... is transferred to the vertical COD register 2.

As a result, the signal charges of the picture elements corresponding to 6゜t4e t6e zs v... are II a 1m e
The signal charge of the picture element corresponding to le e 11 e... and the 0 added in the vertical COD register 2 le + le g 13 + 14 , 15 +
In the 0-even field, where each signal charge of Is g jt +lee is a signal for one horizontal line, the combination of picture elements in the horizontal picture element row to be added in the vertical COD register 2 is l*+ 1m -1a +1m
, le +lr s... ◎In this way, interlace operation is performed by changing the combination of two vertically adjacent horizontal pixel columns for each field.0 IL-CCD imaging as described above. To perform color imaging using a color filter, a color-separated image of a subject is formed by a color filter, this color-separated image is captured by an IL-CCD image sensor, and the output signal of the IL-CCD image sensor is subjected to signal processing. A method of realizing a single-chip color image pickup device using field storage operation such as 0 that obtains color and luminance signals is described in the March 1983 Technical Report of the Methods and Circuits Study Group of the Television Television Society, Tl1lBS87-3, TE.
B887-6 proposes a color arrangement of color filters as shown in FIG. In the figure, Ye, Cy
, Mg, and G indicate yellow, cyan, magenta, and green color filters, respectively. A yellow color filter transmits red and green light, a cyan color filter transmits blue and green light, and magenta transmits red light. and transmits blue light.

With such a color filter arrangement, the signal of each horizontal line in the field accumulation operation described above is zlt z, # 4 from the horizontal picture element columns in order, as shown in FIG.
e・・・・・・18. If you name it as ..., in the numeric field it becomes l+ + It t Im + 4 m・
In the even field, 4 + 4 e /a + Is
It is composed of signal charges of e..., and R indicates a blue signal, a green signal, and a red signal, respectively, and the ratio ti: 1:1. The luminance signal component has a modulation component of the color difference signal with a period of two pixels in the horizontal direction (:a(G) cosvt and (B'iG)
cos wt are alternately superimposed on each horizontal line. However, W is the angular frequency corresponding to the period of two picture elements, that is, 2m+2. output signal 8(11+1m) and/
The output signal 8 (js+ja) of s+4 is expressed by the following formula: 08(1t+1z)=(B+2G+R-B cosw
t+Rcoswt)/2+(BtokanoR-1-Bcoa
wt+Rcos wt-Gcoswt)/2-(1) 841m+14)+=(B+2G+R-Bcosw
t+Rcoswt)/20(B+G+R-Bcosw
t-Rcoswt+Gcomwt)/2-(2) When formulas (1) and (2) are rearranged, the following formula is obtained.

8(4+44)=B4G+R-(B-+G)coswt
(4) Equation (s)t If B00G0R in (4) is used as a luminance signal and the modulation components R+G and B-+o are used as two orthogonal color difference signals as shown in FIG.
A T80 color television signal is constructed. Also, in the case of an even field, S(4+/sl is 8(/.

+l,) and s(4+js) are the same as S(Z, +Z,), and the signal is constructed in the same way as the numeric field. FIG. 6 is a schematic configuration diagram of an enlarged single-plate color imaging device IL-CC provided with the color filter 5 obtained as described above
The output signal of the D image sensor 6 is passed through a low-pass filter 7 to obtain a luminance signal Y in order to remove modulation components, and is also filtered by a bandpass whose center frequency is a frequency corresponding to the repetition period of two picture elements in the horizontal direction. The modulated components are separated by the filter 11 and detected by the detector 12 to obtain color difference signals of RJrG, B=+G.0 These color difference signals are also processed by the narrow band low-pass filter 9.
Using the narrowband luminance signal obtained through the gain switching circuit 10, the white balance circuit 13 corrects each color difference signal and the luminance component of the same horizontal line, and the IH delay line 14 and I
The color difference signals are sequentially and simultaneously converted by the H switching circuit 15, quadrature two-phase modulated by the balanced modulation circuit 16, and then mixed with the luminance signal Y by the mixing circuit 8 to obtain NT8 (J CTV TV 1 signal tube).

By the way, in a color camera system in which a color difference signal is formed on each single horizontal line, a vertical color error occurs almost every time tl. However, with the nine-color filter array shown in Figure ll . This means that the signal on each horizontal line is the sum of signal charges obtained by spatially sampling independently from two adjacent pixels in the vertical direction, and each horizontal line is composed of the signal of one horizontal pixel row. Due to not having done so.

In other words, when the signal of each horizontal line is composed of horizontal pixel columns from each year, as in the case of frame accumulation, the sampling point for the signal of each horizontal line is a single pixel, and the number of repetitions in the vertical direction is The signal composition of each horizontal line does not change at all even if an object with a repeating frequency is incident. Therefore, even if the color difference signal generated under achromatic light is compensated for by the luminance signal of each horizontal line using a white balance correction circuit. However, the compensation does not change at all depending on the pattern of the object, and no vertical color error occurs.

On the other hand, in the field accumulation operation using the color filter array shown in FIG. When one of the two horizontal pixel rows is black, the color difference signal and luminance signal obtained from each horizontal line become the signal composed of the single horizontal pixel row on which light is incident. Not only does the color difference signal itself cause a large error, but also white balance correction, which uses a luminance signal to correct the color difference signal generated under achromatic light, also causes a large error, resulting in an unacceptable vertical color error. In this way, in the conventional method of obtaining color difference signals from each horizontal line using field accumulation, sharp vertical contours or vertical lines are created for each pixel in the vertical direction so that there is no vertical correlation between two adjacent horizontal pixel columns. Large vertical color errors are unavoidable in repeating patterns where there is a difference in brightness.

Such vertical color errors occur regardless of whether the subject is chromatic or achromatic, but while a change in hue in one horizontal line on a chromatic screen is visually unnoticeable, Coloring on an otherwise achromatic screen is recognized as a visually unacceptable defect, and its improvement is desired.

(Objective of the present invention) The present invention provides a solid-state imaging device which greatly reduces the above-mentioned drawbacks of the conventional technology and eliminates the occurrence of vertical color errors at least in the sharp vertical ring area of an achromatic screen. Particularly (Structure of the Invention) In a color solid-state imaging device including at least the present solid-state imaging device and a plurality of color filters arranged in the horizontal and vertical directions corresponding to each picture element of the solid-state imaging device. , 1st. The first color difference signal is obtained from the third horizontal picture element column as a signal modulated with a constant picture element number period, and the second... A second color difference signal is obtained from the fourth horizontal pixel column at the same period of the number of picture elements as the first color difference signal, and the third . The first .obtained from the fourth horizontal pixel column. One of the second color difference signals is one of the second color difference signals. The first .obtained from the second horizontal pixel array. The first color filter array tube is arranged vertically so that the second color difference signal has a phase difference of 1800 degrees.
Second. Third. The 4th and 4th picture elements are arranged sequentially at a repeating period, and each color filter is arranged at a predetermined standard illumination color temperature.
00% brightness level When photographing an achromatic uniform subject, the first.
Each second color difference signal, a third color difference signal obtained by adding each color difference signal of the first and second horizontal picture element columns, and each color difference signal of the third and fourth horizontal picture element columns. The fourth value obtained by adding
A solid-state imaging device is obtained, which has a transmittance characteristic such that the carrier color signal amplitude due to each residual color difference signal component of the color difference signal is 25 − or less of the maximum carrier color signal amplitude. (Summary of the Invention) The present invention solves the drawbacks of the prior art by adopting the above configuration. In the present invention, each horizontal It is a perfect color difference signal format in which the line color difference signal becomes zero when imaging an achromatic object at the standard illumination color temperature, and at the same time, the color signal modulation component in each horizontal pixel row remains zero even when achromatic light is used. By using a color filter array that provides a complete color difference signal format, −
Adjacent vertical direction 2 added as horizontal line signal
This prevents the occurrence of false color difference signals and white balance correction errors on horizontal lines where the signal on one side of the horizontal pixel row has a sharp vertical contour that may be lost, and prevents the occurrence of false color difference signals and white balance correction errors on achromatic screens where visual overlay can also be a hindrance. This prevents vertical color errors.

(Example) Examples of the present invention will be described below with reference to the drawings. FIG. 7 is a schematic partial plan view showing the mutual relationship between the color arrangement of color filters and picture elements in a solid-state imaging device according to an embodiment of the present invention. A plurality of picture elements l are regularly arranged in the horizontal and vertical directions. A color filter is formed on each picture element l. In order of the rows in the horizontal picture element row/1#l! 2#
Name it 4..., E8゜... The first and third horizontal picture element rows 2, , 23 and 1. ．． 1.
is Mg' with transmission characteristics as shown in Fig. 8(a),
C3, which is the first color difference signal component modulated by G', is the ninth color difference signal component.
In particular, as shown in FIG. 3A, the color difference signal is 01=R+B-G, where B is positive and G is negative.

(R, G, and B simply indicate color components.) Mg', G'
The spectral transmission characteristics of the color filter are based on the reference illumination color temperature of 3200
It is necessary to consider the spectral characteristics of silkworms in all optical systems such as the imaging lens and infrared cut filter imaging device when designing the CI so that the CI becomes zero when capturing a white image illuminated at In the example, the O/a filter is designed to increase the transmittance of the G component as much as possible, and the white balance is designed to match the transmittance of the G component of the MgZ color filter. 〇 Figure 9 (a) shows the white of the illumination at 3200°. C when imaged
This is the response characteristic to the wavelength of the first color difference signal, and this integral value is 0, which indicates that the first color difference signal C8 is zero in the achromatic light of illumination at 13.3200°. The phase of the first color difference signal CI is 1 between the horizontal picture element column 11p16 and the third horizontal picture element column tset'r.
As shown in Fig. 7, the color filter arrangement is changed by 1-180 degrees so that the color filters differ by 80 degrees.

On the other hand, the second and fourth horizontal pixel columns 11g1+ and 2. ．． 2. Cy' and Ye' color filters having transmission characteristics as shown in FIG. 8(b) are formed for each pixel. C1, which is the second color difference signal component modulated by this CY's Ye', is expressed as <CY' as shown in FIG. 9(b).
The difference signal between B and B, which is a signal component excluding the G component commonly included in ey, /, becomes a color difference signal of Ct=B-4.
(B and R simply indicate color components) The spectral transmission characteristics of the color filters for Cy' and Ye' are 320 as well as for Mg' and G'.
It is necessary to design so that C3 is zero for white under 0° illumination. Since the number of Ye' filters increases, the Ye' filter is
Figure 9 (b) is 3200.
When the mouth canal image is taken with illumination at 3200°, C, which is the characteristic for the wavelength of the color difference signal, is the same as the 01 color difference signal. C
2 also indicates that this second color difference signal C! are the second and fourth horizontal pixel columns that are modulated.
! #Z4y/, , /, have the same color filter arrangement as shown in Fig. 7, so the color difference signal C3 is in phase in each horizontal pixel column. Field accumulation is performed by the color image sensor with the above color filter arrangement. As mentioned above, for example, in the numeric field, lr+lt +l! 3+2. ．．・
. . . Two adjacent horizontal picture element columns are added together to obtain one horizontal line signal, and I! , +/, the first and second color difference signals themselves and 02 are added together to form the third color difference signal C5, and ts+t+ is I! ,
A fourth color difference signal C1 is obtained by adding the first color difference signal C8 and the second color difference signal C2, which have a phase difference of 180 degrees. That is, Cs = C+ + Cz = (R+ B G ) + (
B R) ... (5) Ca=Cs+Cz=-(R+B
G)+(BR)...(6) A color difference signal is obtained. These C3, C, color difference signals are added to the respective first . Second color difference signal CI,c! is zero in achromatic light, so naturally the result of addition is also zero.The color difference signals C1 and C4 of each horizontal line are also zero in achromatic light.
5) R, G, and B in t (6) are as follows to simplify the explanation:
Only the color components of the signal are shown.

In this way, if the color difference signal of each horizontal line is zero in achromatic light and the color difference signal of each horizontal pixel column is also zero, the adjacent vertical two
There is no error in the color difference signal of each horizontal line for uncorrelated achromatic subjects in the horizontal pixel array, and since the white balance correction is also zero, there is no white balance correction error, and the visual orientation is also impaired. Vertical color errors on achromatic screens can be prevented. These CIt CIt
When the color difference signal of Caw C4 is schematically shown on a vector diagram, as shown in Fig. 10, C8 is approximately B Yt C4
A color difference signal approximately equivalent to a color difference signal of RY can be obtained.

We have described the case of a numeric field above, but in the case of an even field, 6+l, to C4, la +
A color difference signal of C1 can be obtained from is, and vertical color errors can be similarly prevented.

In the above explanation, an ideal case has been described in which each color difference signal C1tC3 of each horizontal pixel column becomes zero under achromatic light.
In reality, due to variations in the spectral characteristics of color filters and image sensors, it is not always possible to reach the ideal zero. From the results of evaluation of the carrier color signal amplitude and vertical color error due to each residual color difference signal when an achromatic, uniform object at 100% luminance level is imaged using standard color temperature lighting, for example, with the NT8C standard method. 100% brightness color bar Cy (cyan) or R (5
) The vertical color error is hardly noticeable if it is less than 15% of the maximum carrier color signal amplitude given by the signal #I;
It has been found that C1tC and C1tC, respectively, are acceptable in practice if they are less than C1tC! If the residual component of each color difference signal of ICm5CI during free color light is within this range, the effects of the present invention can be obtained.

Note that the white balance evaluation of the color difference signal in each single horizontal pixel column can be most accurately evaluated by performing a frame accumulation operation in which the signal of each single horizontal pixel column is used as the signal of each horizontal line. It is also possible to evaluate based on a subject where one of the two horizontal pixel columns added in the field accumulation operation is black, or on the image sensor.

A device similar to the single-chip color imaging device whose schematic configuration diagram is shown in FIG.
SC power 2 - TV signal can be obtained.By the way, as is clear from the above explanation, the effect of the present invention is only effective for achromatic colors of the standard illumination color temperature of the cuff camera.
For white at other illumination color temperatures, the color difference signal does not have white balance, resulting in a vertical color error, but this is because even in conventional methods, the vertical color error does not increase or decrease with respect to the illumination color temperature. Similarly, in the present invention, the occurrence of vertical color errors can be suppressed sufficiently low at least for illumination color temperatures around the reference illumination color temperature. (Effects of the Invention) As described in detail above, according to the present invention, the color difference signals obtained from each horizontal line for achromatic light at the reference illumination color temperature can be prevented from occurring with respect to the illumination of However, the white balance correction is zero or very small, and the color signal modulation components of each horizontal line element array that make up the color difference signal of the Mamaru Can Horizontal Twin are also completely color difference signals, so there is no white balance correction. In colored light, it is almost zero.Even for subjects with no correlation between two adjacent vertical and horizontal pixel columns, color difference signal errors and white balance correction errors almost never occur), which are visually unacceptable. A color solid-state imaging device without vertical color errors in sharp vertical contours of an achromatic screen is realized.

[Brief explanation of drawings]

Figure 1 is a schematic plan view of an interline transfer CCD image sensor, and Figure 2 is a signal charge reading when the interline transfer COD is operated in field accumulation. Figure 3 shows the color filter arrangement during field accumulation operation. FIG. 5 is a diagram schematically showing the output signal of each horizontal line, FIG. 5 is a diagram showing color difference signal vectors, and FIG. 6 is a schematic configuration diagram of a single-chip color imaging device.
7 is a schematic partial plan view showing a color filter array according to an embodiment of the present invention, FIG. 8(8)9(b) is a diagram showing spectral transmission characteristics of each color filter, FIG. )
is a diagram showing the spectral response characteristics of color difference signals in two horizontal lines under achromatic light, and Figure 10 is a diagram showing the vectors of each color difference signal. ...Vertical CCD register, 3...Horizontal CCD register, 4...Output section, 5
...Color filter, 6-...Intertwin transfer CCD
Image sensor, 7...Low pass filter, 8...Mixing circuit, 9...Narrow band low pass filter, 10...Gain switching circuit, 11...Band pass filter, 12...
・Detector, 13... White balance circuit, 14...
・IH delay line, 15...IH switching circuit, 16...Balanced modulation circuit, right, 6° tap...1. , ... Column numbers assigned to horizontal picture element rows in order. Kororo Kuniguchi Day! , Figure 4 ((1) (b) Figure 5 Scale-G Figure 7 Rorororo Hita 11 Days Rororo 1, Rororo Figure Mouth Map No. 3 Days Exit Hita Exit No. 4 Ward Rororo F Exit No. 5 [4 NQ Mouth [〒;] ■ -Noro day Rorororo E ノ. One Rorororo day ノ. Fig. 6 400 500 600 7θO う(t + (tyyn) (a) 400 500 600 TOO 5nL length (1?#) (b) No. Fig. 9 Skin ← and i (labor?1) (I2) Shi skin surface (ηmn (b,) Fig. 10〉-岨

Claims (1)

[Claims] A nine-color solid-state imaging device comprising at least a solid-state imaging device and a plurality of color filters arranged in the horizontal and vertical directions corresponding to each picture frame of the solid-state imaging device; Third
A first color difference signal is obtained as a signal modulated at a constant pixel number period from the horizontal pixel row, and a second color difference signal is obtained as a signal modulated with a constant pixel number period. A second color difference signal is obtained from the fourth horizontal picture element row with the same two picture element periods as the first color difference signal, and the third... The first .obtained from the fourth horizontal pixel column. One of the second color difference signals is one of the second color difference signals. The first .obtained from the second horizontal pixel array. A row of color filters arranged so as to have a phase difference of 180° from the second color difference signal is vertically connected to the first color difference signal. Second. Third. The 4th and 4th picture elements are arranged sequentially at a repeating period,
Furthermore, each color filter has 10
〇-The above-mentioned 1. Each second color difference signal, a third color difference signal obtained by adding each color difference signal of the first and second horizontal picture element columns, and each color difference signal of the third and fourth horizontal picture element columns. It is characterized by having a transmittance characteristic such that the carrier color signal amplitude due to each residual color difference signal component of the fourth color difference signal obtained by addition is 025% or less of the maximum carrier color signal amplitude. Solid-state imaging device.