JPS6080382A - Color separation filter - Google Patents

Abstract

PURPOSE:To obtain a sharp reproducing picture with a simple circuit by providing a color separation filter which obtains green light from all picture elements and obtains red light and blue light components at a period of one or three picture elements in horizontal direction. CONSTITUTION:A low frequency component of an output signal of an interline transfer (IL)-CCD image pickup element 12 is superposed on a different frequency modulation component, and the modulated red signal is separated at first by passing the output signal through a BPF13 taking a frequency corresponding to the repetitive period of two picture elements as a center frequency. This signal is demodulated by a detector 14 and becomes a red video signal via an LPF15. In passing the output signal of the image pickup element 12 through a BPF16 taking a frequency corresponding to the repetitive period of three picture elements as a center frequency, the modulated blue signal is separated and a blue video signal is obtained similarly via a detector 17 and an LPF18. Moreover, a high frequency component and a low frequency component of the luminance signal are obtained from the LPF, a trap 19 and an LPF11, and a color television signal is obtained by adding them to a process encoder 20 together with a chrominance signal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color separation filter used in a solid-state imaging device for color imaging.

Conventionally, so-called single-chip color cameras using one solid-state 1114 image element use a frequency interleaving method or a color difference line sequential method using an IH delay line that delays a signal for one horizontal scanning period, or an IH delay line, sample holder, and calculation matrix. There was a method using Furthermore, there is a method that uses only a sample holder and a calculation matrix without using an xHa wire. However, both methods have the disadvantage that the circuit becomes complicated due to the use of IH:M[a and a sample holder.

An object of the present invention is to provide a color separation filter that can significantly alleviate the above-mentioned drawbacks and provide a clear reproduced image with a simple circuit.

According to this invention, a video signal corresponding to a green light component can be obtained from all the picture elements, and one of the video signal corresponding to a red light component and the video signal corresponding to a blue light component is divided into two pictures in the horizontal direction. A color separation filter formed on a solid-state image sensor is obtained, which is characterized in that the color separation filter is modulated with a period of 1 pixel, and the other is modulated with a period of 3 pixels in the horizontal direction.

Embodiments of the present invention will be described below with reference to the drawings.

An interline transfer CCD image sensor (hereinafter abbreviated as an IL-CCD image sensor), which is a type of solid-state image sensor, is regularly arranged in the horizontal and vertical directions, as shown in a schematic plan view in FIG. A vertical COD register 2 vertically transfers the signal charge accumulated by photoelectric conversion in the picture element 1, a horizontal COD register 3 horizontally transfers the signal charge, and an output section 4. The arrow in the figure indicates the direction of signal charge transfer.

The IL-CCD image sensor can perform two types of readout operations: a frame accumulation operation in which signal charges accumulated in picture elements are read out in a frame period, and a field accumulation operation in which signal charges are read out in a field period. FIG. 2 schematically shows the field storage operation. Lines in order in the horizontal direction') 71
+ t2 + 'R+..., t8°... are named. In the odd field, first 't + '4 *
The signal charge is transferred from the picture element corresponding to t6 r '8 r... to the vertical CCD register 2, and then the vertical COD
The signal charge for one picture element is transferred by the transfer operation of register 2, and further tl, z, lz, pl? +...
A signal charge is transferred from the picture element corresponding to the vertical COD register 2 to the vertical COD register 2. This result '2 # '4 e La *
J! The signal charge of each picture element corresponding to -s r... is t-111m +llI+ l? The signal charge of the picture element corresponding to y... and the vertical CCI) are added in the register 2. Added AI +111, 13+14
The signal charges of −, As +16.11 +t4, and − are each taken as a signal for one horizontal period. In the even field, the combination of rows of picture elements in the horizontal direction to be added in the vertical CCD register 2 is 1, +13.14+1.
, 1. +1? , change to... In this way, the interlacing operation is performed by changing the combination of two vertically adjacent rows for each field. FIG. 3 schematically shows the frame accumulation operation. Rows in order in the horizontal direction J) '+ + 72 r t
l r..., t8. ... Name it. In the odd field, signal charges are transferred from picture elements corresponding to tI r 13+ tll e . . . to the vertical COD register 2, and then transferred to the output section 4. '2 for even fields
The multi-signal charge of the picture element corresponding to rZ4*t6#... is transferred to the vertical CCD register 2, and then transferred to the output section 4. The following explanation will mainly be made regarding the field storage 8I operation.

FIG. 4 is a schematic partial plan view showing the color arrangement of the color separation filter and the mutual relationship between the color separation filter and the light receiving element according to an embodiment of the present invention. In the figure, multiple V, element 10
are arranged regularly both horizontally and vertically. A color separation filter is formed on each picture element 10. w,G
, Cy, and Ye indicate transparent, green, cyan, and yellow color separation filters, respectively. The color separation filters are arranged at a period of 6 pixels in the horizontal direction and at a period of 2 pixels in the vertical direction.

Only repeating units of 6 pixels in the horizontal direction and 2 pixels in the vertical direction are shown. w, y, c, and a indicate transparent, yellow, cyan, and green color filters, respectively. The transparent color filter, evening, passes through red, green, and blue. Yellow color filters transmit red and green light. A cyan color filter transmits edge and blue light. For example, if you use a yellow color filter, it is not necessary for red and edge light to pass through by 10% (1%), and the source of the red light does not need to be completely cut off.For simplicity, the transmitted light is 1%.
It is assumed that the light that passes through 00 and is cut off is completely cut off. Horizontally from left to right, in horizontal row t1 W
, C, Y, C, W, G, horizontal row t.

In this case, they are arranged in the order of W, G, Y, C, Y, and G. FIG. 5 is a diagram schematically showing the magnitude of the output of each color signal from each picture element in which the above color filter is formed in the case of field accumulation operation, and corresponds to FIG. 4. Note that %R, Q, and B indicate red, green, and blue lights, respectively. As shown in the figure, when the output signal is averaged, B
+200R is obtained. This is used as a luminance signal.

The red signal is a modulation component Rco with a period of 2 pixels in the horizontal direction.
are superimposed as sω and t. However, ω is an angular frequency corresponding to a period of two picture elements. Green light is 3 horizontally
It is superimposed as a modulation component B cosω,t whose period is a picture element. However, ω is an angular frequency corresponding to a period of three picture elements. That is, 1. +1. output signal S(Z,
+Z, ) is expressed by the following formula.

8(tllt2)=B10002G+R+Bcosω3t+R
The output of cosω2 in the other field is exactly the same.

When the output signal expressed by the above equation is passed through a low-pass filter, a low-frequency component R+20+B is obtained, which corresponds to the luminance signal. When the output signal is passed through a bandpass filter whose center frequency is a frequency corresponding to the period of two picture elements, the red modulation component can be separated. When the output signal is passed through a bandpass filter whose center frequency is a frequency corresponding to the period of three picture elements, the blue modulation component can be separated. If the separated red and blue modulation components are detected respectively, the red signal and the blue signal can be demodulated, respectively.

FIG. 6 is a block diagram of a color imaging device using a color separation filter according to an embodiment of the present invention.

In the figure, the color separation filter described using FIG. 4 is combined with the IL-CCD image sensor 12.

In the output signal of the IL-CCD image sensor 12, modulation components of different frequencies are superimposed on low frequency components. When the output signal of the IL-CCD image sensor 12 is passed through a bandpass filter 13 whose center frequency is a frequency corresponding to the repetition period of two picture elements, the modulated red signal is separated. This modulated red signal is demodulated by a detector (demodulator) 14, and then 0
, 5 MHz, a red video signal can be obtained. A bandpass filter 16 whose center frequency is a frequency corresponding to the repetition period of three picture elements.
When the output signal of the IL-CCD image sensor 12 is passed through, the modulated blue signal is separated.

If this modulated blue signal is demodulated by a detector (demodulator) 17 and then passed through a 0.5 MHz low-pass filter 18, a blue video signal can be obtained. The output of the IL-CCD image sensor 12 is passed through a circuit 19 consisting of a low-pass filter and a trap with a frequency corresponding to the repetition period of three picture elements in the horizontal direction, and the modulation component is removed and only the low-frequency component is taken out. A luminance signal of the area component is obtained. The output of the IL-CCD image sensor 12 is filtered through a 0.5 MHz low-pass filter 1.
1, a luminance signal with low frequency components is obtained. The obtained high-frequency component and low-frequency component luminance signals, red video signal, and blue video signal are processed by a process encoder 20 to produce a color television signal K1.

A color imaging device using a color separation filter according to an embodiment of the present invention does not use an IH delay line or a sample holder, and has a simple circuit. Furthermore, since the band of the brightness signal of the high frequency component has a frequency corresponding to a period of three picture elements in the horizontal direction, a much clearer image quality can be obtained compared to the conventional period of four picture elements.

9 to 99 are schematic diagrams showing the color arrangement of color separation filters according to other embodiments of the present invention.

The color separation filters shown in FIGS. 7 and 8 have a repetition period of 6 picture elements in the horizontal direction and 1 picture element in the vertical direction. The color separation filters shown in FIGS. 9 to 71 have an edge reversal period of 6 pixels in the horizontal direction and 2 pixels in the vertical direction. The color separation filters shown in FIGS. 72 to 99 have a repetition period of 12 pixels in the horizontal direction and 2 pixels in the vertical direction.

In the above embodiment, the repetition period of picture elements in the vertical direction is one picture element or two picture elements. Therefore, the phases of the modulation components of the red signal and the blue signal are the same in any horizontal scanning period. For this reason, false signals may occur when capturing an image of a subject with fine vertical stripes of red or blue. False signals are particularly likely to occur in blue, where the repetition period is as large as 3 pixels.

Next, a description will be given of a color separation filter that improves the above-mentioned drawbacks and provides faithful reproduced images even for fine patterns. In other words, the video signal corresponding to the green light component is obtained from all picture elements, and one of the video signal corresponding to the red light component and the video signal corresponding to the blue light component has a period of two pixels in the horizontal direction. The other is modulated with a period of 3 pixels in the horizontal direction, and the modulation components of the period of 3 pixels have a phase difference of 120 degrees in adjacent horizontal scanning periods. be done.

Hereinafter, further improved embodiments of the present invention will be described with reference to the drawings. FIG. 100 is a schematic diagram showing the color arrangement of a color separation filter according to a further improved embodiment of the present invention and the mutual relationship between the color separation filter and the light receiving element. The color separation filters are arranged at a period of 6 pixels in the horizontal direction and at a period of 6 pixels in the vertical direction. Only repeating units of 6 pixels in the horizontal direction and 6 pixels in the vertical direction are shown. The horizontal rows are named 4+ z, l...e Z6 in order. Horizontally from left to right, in horizontal row t1, W;
G, Y.

C, Y, G, in the next row t2 w, c, y, c,
W, G.

In the next rows t and l, Y, C, Y, G, W, in the next row t4, Y, C, W, G, W, C, in the next row tll, Y, G, W.

G, Y, C, in the next row t6, W, G, W, C
, Y, and C are arranged repeatedly. B+20+R is obtained by averaging the output signals in any horizontal scanning period. This is used as a luminance signal. 101st, 1
Figure 02 is a diagram schematically showing the magnitude of the output of each color signal from each picture element in which the color separation filter of Figure 100 is formed in the case of field accumulation operation, and corresponds to Figure 1L ioo. They are from different fields. As shown in the figure, when the output signal is averaged, B + 20 + R
is obtained. This is used as a luminance signal. The output signal for each horizontal scanning period is expressed by the following equation.

5(11+z2)=B+2G+R+Bcosω3t
10 R cos ω2 tS (t3+44)=B+20+R
+Bcos((c+3t-r)+Raosω2t8
(t6+t6 ]=B+20R+Bcos (ω3t
--x )+R cos ω2 tS In the other field:

S (16+11)==B+2()+R+Bcos
(i) 3t+Rcosω2tS(t2+73 t;B
+2()+R+Bcos(ωst-7,w)+Rc
osω2 tS (4+15)=B+2()I-R+B
co! 1(ω3t −−K ) +Rcos ω2 t
The modulation component of the S red signal is modulated with the same phase in each horizontal scanning period. The modulation components of the green signal are adjacent.

The modulation is performed with a phase shift of 120 degrees in matching horizontal scanning periods.

IL-CCD in which the color separation filter shown in Fig. 100 is formed
As in the case of the color separation filter shown in Fig. 4, the output signal from the image sensor is processed by the color imaging device shown in Fig. 6 to obtain the brightness of the high frequency component, the brightness of the low frequency component, a blue signal, and a red signal. You can get a television signal.

In the color separation filter shown in Fig. 100, the repetition period is 3 pixels in the horizontal direction, and the phase of the modulation component of the blue signal is shifted by 120 degrees in the horizontal scanning period. Even when capturing images, faithful reproduction images can be obtained.

103 to 135 are schematic diagrams showing the color arrangement of a color separation filter according to another further improved embodiment of the present invention.

The color separation filters shown in FIGS. 103 to 127 have a repetition period of 6 pixels in the horizontal direction and 6 pixels in the vertical direction. 128th
The color separation filter shown in Figures 1 to 135 has a repetition period of 12 pixels in the horizontal direction and 6 pixels in the vertical direction.

The color separation filter shown in FIG. 136 is a mirror image of the filter shown in FIG. 100, and the same effect as that shown in FIG. 100 can be obtained. If image conversion is also performed on the color separation filters shown in FIGS. 103 to 135, color separation filters having similar effects can be obtained.

The case where the red signal is modulated in two picture element periods and the blue signal is modulated in three picture element periods has been described above.

Conversely, the effects of the present invention can also be obtained when the blue signal is modulated with a two-pixel period and the red signal is modulated with a three-pixel period. In this case, in the above explanation and drawings, Y-+C
, c-ey, R→B, B→几. For example, the color separation filters in Figures 4, IOo, and 136 are converted to those in Figures 137, 138, and 139, respectively.

The color separation filter in Figure 7.8 has a vertical stripe shape,
It can also be applied to frame accumulation operations.

Although the explanation has been made using an interline transfer CCD image sensor as a solid-state image sensor, this invention uses a frame transfer CCD image sensor.
It can also be realized using a CD image sensor. Figure 140 (at
100 is a schematic partial cross-sectional view in the vertical direction of a four-phase drive frame transfer CCD image sensor equipped with the color filter shown in FIG. 100. Figure 140(b).

(C) is a schematic diagram showing the potential distribution under the transfer electrode.

The transfer electrodes of the frame transfer CCD image sensor are arranged sequentially from the output side to ψ4. ψ8. ψ2. ψ, is connected to the driving pulse head by repeating υ. Two electrodes are made to correspond to one row in the horizontal direction. That is, ψ4. 21 lines for the pair ψ3, ψ2, ψ1
42 lines for the pair 63 lines for the next pair ψ4 and ψ3
row, next ψ7. For the pair of ψ1, the correspondence is made as t4°... When interlacing is performed, in odd-numbered fields, ψ and ψ3 are turned on during the accumulation period, resulting in a potential distribution as shown in FIG. 140(b). As a result, %71 +Lz * t3+t4+ 16+t6 +・
A signal is obtained by adding the pairs of... In the even field, ψ and ψ4 remain on during the accumulation period, and the 14th-
The potential distribution becomes as shown in Figure 0 (C). As a result, t
Signals summed in pairs of 2 + 13, t4 + 15 +... are obtained. This signal is exactly the same as in the case of the IL-CCD image sensor.

[Brief explanation of the drawing]

Fig. 1 is a schematic plan view of an interline transfer CCD image sensor, and Figs. 2 and 3 schematically show signal charge readout when all interline transfer CCD image sensors are operated by field accumulation and frame accumulation, respectively. 4 is a schematic diagram showing the color arrangement of a color separation filter according to an embodiment of the present invention, and FIG. 5 is a schematic diagram showing the color arrangement of a color separation filter according to an embodiment of the present invention, and FIG. FIG. 6 is a diagram schematically showing the output, and FIG. 6 is a schematic configuration diagram of a single-chip color imaging device. FIGS. 101 and 102 are diagrams schematically showing the output of each color signal from the interline transfer CCD image sensor in which the color separation filter of FIG. 100 is formed, and 103 to 139
The figures are a schematic cross-sectional view and a potential distribution diagram of the present invention, respectively. 1...Picture element, 2...Vertical CCD register, 3...
Mizuko〇CD register, 4...Output g, 1o...Color filter, 11.15.18...Low pass filter, 1
2...Interline transfer CCD image sensor, 13.1
6...Band pass filter, 14.17...Mensor, 19...Low pass filter todrap, 20...
・Process encoder% Zl * 11 r~t6
...Row numbers assigned sequentially to rows of picture elements in the horizontal direction, ψ1
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Claims (1)

[Claims] A video signal corresponding to the green light component is obtained from all picture elements,
One of the video signals corresponding to the red light component and the video signal corresponding to the blue light component is modulated in the horizontal direction with a period of 2 pixels, and the other is modulated in the horizontal direction with a period of 3 pixels. A color separation filter formed on a solid-state image sensor, characterized by: