JPS5919492A - Image pickup device - Google Patents

Abstract

PURPOSE:To suppress a false signal due to an object having a low vertical correlation, by providing a limiter in a chrominance signal forming circuit. CONSTITUTION:An output from an image pickup means where color filters are arranged to each picture element is inputted to a product circuit 7 to form chrominance signals B-R and M by using the vertical correlation of the output of each picture element. The chrominance signals B-R and M are inputted respectively to an adder/subtractor circuit 12 via a B-R separating circuit 8, an M separating circuit 10, limiter circuits 51, 52 and low pass filters 9, 11. The limiter circuits 51, 52 limit the output of the separation circuits 8, 10 within a prescribed range to suppress a false signal due to an object having a low vertical correlation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color solid-state imaging device that obtains color image signals using a solid-state imaging device.

A charge transfer device (hereinafter referred to as CCD) is used as a color solid-state imaging device.
Although single-chip, dual-chip, and triple-chip cameras using one, two, or even three CCI cameras have been considered, the present invention is particularly directed toward improving single-chip imaging devices that use one CCI chip. It is something that is involved.

Conventionally, in a single-chip solid-state imaging device using a solid-state imaging device such as a CCD, a color mosaic filter and each imaging cell of the imaging device are matched in a 1:1 ratio to separate each color signal. .

The color mosaic filter used in this disgusting single-chip solid-state imaging device is a so-called Bayer filter in which red, green, and w filter elements are arranged in a mosaic pattern in order to save the number of imaging elements such as #, i, and CCD. It is known that color filters are used in an array. An example of a color filter arranged in a mosaic pattern is Ltdyv-
If you try to make a single-chip color camera by combining it with a multi-layer CCD, the problem is that due to its structure, there is a considerable amount of signal leakage between adjacent cells, which causes color mixture and makes color separation uncertain. occurs. A method for solving this problem has already been proposed by the present applicant, for example, in Japanese Patent Laid-Open No. 115085/1985, and the problem of color mixing has been solved to a large extent, but in this case, there is a correlation in the vertical direction of the screen. For example, in images with no vertical correlation, such as horizontal striped patterns, false color signals are generated, deteriorating the image quality of the obtained image1. The disadvantages of this will be explained in detail with reference to FIGS. 1, 2, and 3.

FIG. 1 is a schematic diagram of an example of a color mosaic filter suitable for a frame transfer type CCU. This color mosaic filter uR (red), G (green), B (blue),
It is composed of a combination of M (magenta - red → - blue) and It is formed by combining.

FIG. 2 is an example of a signal processing circuit block diagram of a solid-state imaging device that combines the color mosaic filter and CCD. To explain its operation, the output signal 2a of the CD 2 is driven by the control signal generator 1.
The signal 2a and the signal 3a are added by the adder 4 and guided to the low-pass filter 5, where the brightness threshold signal 5a (Y=R-+ 2G+B) is delayed by one horizontal scanning period.
becomes. Also, the signal 2a and the signal 3a are subtracted by the subtracter 6 (B - R), Ml ~ (B - R), -M,...
It becomes a color difference signal like... These color difference signals are aligned in polarity (BR) by an inversion control signal in the product circuit 7, and become repeated signals of B-R and M, such as M, (BR), Ml, . This signal is processed by the (B-R) separation circuit jli!, which is composed of the following sample hold circuits, etc. In i8 and M separation circuit 10 (B −
R) and M continuous signals are separated into the subsequent low-pass filter 9.
Approximately 500 required for the color signal of the NTSC signal at 11
Limited to KHz band. This color signal (B-R
) as 9a and M as lla are subtracted in the adder/subtractor circuit 12 to produce the R' signal 12 a (M-B+R
=2R=R,'), B' signal 12b (B
-R+M=2B=B').

Next, the process circuit 13 outputs 5a as the luminance signal Y.
s 12a as color signal R' 12b as XB' undergoes signal processing such as γ correction and black clipping and is output as luminance signal Y', color difference signal R''-Y', BH-YL. The signal is modulated by a subcarrier 14G from a control signal generator 1 in a balanced modulator 14 to produce a chroma signal 1.
4a, which is added with the luminance signal Y' and the synchronization signal 15G in the adder 15 to become the NTSC signal 15a. Using this screen, color signals are formed by the color signal forming circuits from the subtracter 6 to the process circuit 13.

As shown above, a vehicle that obtains a color image signal by combining the frame transfer type COD and a color mosaic filter can be produced, but the above-described embodiment has the following drawbacks.

That is, in actual shooting, there are situations where the vertical correlation of images, which is the premise of this method, does not hold, so for example, under direct sunlight, a person wearing glasses, a car window or its metal frame, etc. When considering the case of photographing an object with very high COD, the COD will be used at or near saturation in a specific part of the subject. In such a part, since there is no vertical correlation of the subject, the amplitude of the false color signal becomes extremely large. This phenomenon is particularly noticeable when the boundary between light and dark is oblique to the scanning direction or when the width of the subject image is an integral multiple of the width of the image pickup cell.

Color Figure 3 shows the shaded area 170 of the color mosaic filter in Figure 1 in order to simply explain the principle of false signal generation.
It is extracted [-].

In the following, we will discuss L7 as only this part is illuminated with strong light.

By the way, in the explanation of the signal processing block diagram of FIG. 2 mentioned above, the color difference signal which is the output signal of the product circuit 7 is B-RXMX B-R, M on the premise of the vertical correlation of the subject image.
However, in order to treat the color difference signal more strictly, we will use the CCD corresponding to each color filter in Fig. 3.
The output signal levels are Bl, Gl, R2, G2゜G, respectively.
3. M4. Color filter symbol B, like G4.

A number will be added after G, R, and M to indicate the difference.

R2°G2. The shaded part 190 consisting of M4 is the signal 3aK of the (n-1)th line.
Therefore, the output signal of the product circuit 7 in Fig. 2 (
B−R) and M are respectively B−R=(Bl→G 1 ) −(R2+G2)−−(
1) M= (M4 +G4) -G3
=-(2). Here, when white light is irradiated to each color filter, each signal level of R, G, and H is R:G:
The transmittance of the filter is set so that B=1:1'1, and the signal level of M+G is expressed by Vsat. fL
V8aj means the saturation signal level of FiCCD.

Under the above conditions, considering a state in which white light is incident on the shaded area 18o in FIG. 3 and no light is incident on the shaded area 190,
(BR,M) is K(
BR, M)=(÷Vsat, +”-:Vaat,
), so the color signals before B' and red R' are (B',
R') -('-V8aj, l -V8aj,
) --(8). By the way, actually color filter B
Regarding -H, white light is incident only on B1, so the color signals B and R at that time are (B, R) = (:Vsat, , o) - □ (4
). However, when comparing the results of equations 8) and (4), the values of the color signal front B' are the same, but the values of the color signal red R' are different. As in this example, even though there is no incident light on the color filter R, the color signal R' (=
One of the reasons why -Vsat, ) occurs is because the green G signal is mixed in when calculating the color signal.

The present invention provides a color solid-state imaging device having a signal processing circuit that alleviates the above-mentioned drawbacks.

FIG. 4 is a diagram showing an embodiment of the present invention.

In this figure, the same components as in FIG. 2 are given the same numbers.

The feature of this embodiment is that the B-R as part of the color signal forming circuit
This is because limiter circuits 51 and 52 are provided, for example, at the subsequent stage of the separation circuit 8 and the M separation circuit 1o.

Hereinafter, the function of the limiter circuits 51 and 52 will be explained using a part of the color filter shown in FIG.

The signal limiting range by the limiter circuit can be set by the method described below. ,.

That is, in the color filter of FIG. 3, B1°R2,
White light is incident on each of M4 [Matatoki (R-B)
The possible signal levels of and M can be found using equations 〇) and (2). The result is; Vaat, > (B
-R)>-%V3gt,--□(5)7Vsat
, > M > 0-- (6) Therefore, the output of the limiter circuit 51#'1B-R separation circuit 8 is configured to be limited within the signal amplitude range shown by equation (5). Similarly, the limiter circuit 52 outputs the output of the M separation circuit 10 (6)
It is configured to limit the signal amplitude within the signal amplitude range shown by the formula.

Next, let's compare the improvement effect of the limiter (b) circuit with the case without a conventional limiter circuit. The comparison method is performed using the method that pointed out the shortcomings of the generation of false signals earlier. The results are shown in Table 1.

Referring to Table 1, it can be seen that when the conditions for irradiating the white light to the color filter in FIG. 3 are as shown in Table 1, the improvement effect of the limiter circuit is particularly remarkable for the red color signal.

As explained above, it has been found that the embodiment shown in FIG. 4 has an improvement effect in reducing false signals, but the present invention is not limited to the embodiment shown in FIG. It is also possible to limit the amplitude of the output signals R' and B' of the low-pass filters 9 and 101 and the adder/subtractor circuit 12, and it is not impossible to say that there is an improvement effect even if the output signals R' and B' of the low-pass filters 9 and 101 are limited in amplitude.

Next, the signal processing block diagram of the second embodiment of the present invention is shown in Fig. 5.
In all the figures shown, the same parts as in FIG. 4 are given the same numbers. In the embodiment shown in FIG. 5, the limiters 51 and 52 limit the signal amplitudes of B-R and M (2) as in the previous embodiments (can reduce false signals), but in this embodiment, the effect of suppressing false signals is further increased. ) In this embodiment, the output signal of the M separation circuit 10 is transmitted to the limiter 52.
, and the limited signal is passed through a low-pass filter 5.
3 limits the band to the extent of a color signal, and converts the absolute value (or either positive or negative) of the limit signal to the inverting circuit 5.
The chroma signal 14a of the balanced modulator 14 is determined by the gain control circuit 5 according to the determination result.
It is suppressed by 6.

This embodiment also uses the block 1 based on the output of the limiter 52.
In addition to suppressing the chroma signal 14a with 00, the chroma signal 14a may be suppressed based on the output of the limiter 51.

Next, the third example @6 is the same as the example shown in FIG.
An H delay line 57 is added.

In other words, it is not limited to the method of generating color signals from the vertical correlation between OH and IH as shown in Fig. 4, but also the method of generating color signals from the vertical correlation of OH and IH as shown in Fig. 5.
It can also be applied to a method of generating color signals using the vertical correlation of the three horizontal scanning lines of 2H and 2H.

Fig. 7 It is a partially modified version of the embodiment shown in Fig. 6.
Like FIGS. 5 and 6, the same functional elements as in the signal processing circuit block diagram are given the same numbers.

In Figure 6, the color signal is obtained after averaging the signals using three horizontal scanning lines and improving the vertical correlation, so the R-B, M separation circuit as shown in Figure 4 After +
) Merely installing a transmitter will have a small improvement effect. Therefore, in the embodiment shown in FIG. 7, false signals are detected by OH and IH (
This book attempts to suppress false signals using a circuit having the same configuration as block 100 in FIG. 5 by using signals with relatively low correlation on only two lines (I, L, H and 2H).

Similarly, the present invention is an interline transfer type CCD or MO
Needless to say, the present invention is also applicable when used in an 8-inch solid-state imaging device.

As described above, in the present invention, by providing a limiter in the color signal forming circuit, it is possible to suppress false signals caused by a subject having a low vertical correlation by a large 1/F.

Note that the present invention is not limited to the limited range of the IJ mitter in the embodiment, but, for example, the width limited range of the K IJ mitter is narrowed to the extent that the color saturation of a subject with high vertical correlation is sacrificed to some extent. It may be.

In that case, false signals can be suppressed more effectively for subjects with low vertical correlation.

Further, according to the embodiment of the present invention, in order to detect the magnitude of vertical correlation, a color signal exceeding a predetermined positive or negative color saturation level is detected, and the amplitude of the color signal is thereby limited. Because it is configured to do so, it is possible to sufficiently increase the color saturation for subjects with high vertical correlation, and to prevent the generation of false signals for subjects with low vertical correlation. .

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an example of a conventional color mosaic filter, Fig. 2 is a block diagram of a signal processing circuit of a conventional color solid-state imaging device, Fig. 3 is an enlarged view of the main parts of the color mosaic filter, and Fig. 4 is a schematic diagram showing an example of a conventional color mosaic filter. A signal processing circuit block diagram showing a first embodiment of the present invention, and FIGS. 5, 6, and 7 are signal processing circuit block diagrams showing second, third, and fourth embodiments, respectively. 2 is CCD, 3.57 is IH delay line, 6tj subtracter, 8
Reference numerals denote a BR separation circuit, an IOViM separation circuit, a 51/52 limiter, 55 a black clip circuit, and 56 a gain control circuit. 1014 et al Δ

Claims (2)

[Claims] (1) an imaging means consisting of a plurality of picture elements, a color filter arranged for each picture element, and a color signal forming means for forming a color signal using vertical correlation of the output of each picture element; An imaging device comprising: a limiting means for limiting the amplitude of a color signal to be formed by the color signal forming means within a predetermined range. (2) A detection means for detecting that the chrominance signal exceeds a predetermined amplitude level is provided, and the gain of the chroma signal is limited by the output of the means [Recited in Claim 7 (1)] imaging device.