JPS5931917B2 - Bandwidth control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a band control circuit suitable for application to a color imaging device employing a phase separation method using a solid-state imaging body such as a CCD (charge-coupled device) as an imaging element.

When two information signals having different information contents are multiplexed and a phase separation method is adopted as a separation method, vertical correlation becomes a problem.

That is, although this separation method requires a strong vertical correlation, in some cases the vertical correlation may be weak or not present at all. Therefore, in such cases where the correlation is weak, it is not possible to completely separate the two information signals, and the other signal multiplexed into one signal component remains, and this residual component is the content of the other signal. may have a negative impact on. A suitable example of this is a color imaging signal obtained by an imaging device.

In other words, when a solid-state image sensor such as a CCD is used as an image sensor, a color image signal in which a color component exists in a luminance component in a multiplexed state is obtained, as will be described later.
When separating the luminance component and color component, the same phenomenon as described above may occur. This will be explained using drawings, but as a solid-state image sensor, CC
D. Among them, especially CC that uses the frame shift method.
Let's explain using D as an example.

FIG. 1 is a schematic diagram of a CCD that uses this frame shift method, where IA is an imaging section on which a desired subject is projected, and a desired number of picture elements 2 are projected in the horizontal and vertical directions. Array formed and configured.

IB is an accumulation section for accumulating carriers for each frame (or field) according to the input light information of the subject obtained by the imaging section IA, and is configured similarly to the imaging section IA. IC is a read register, and carriers for IH (H is one horizontal scanning period) are read out in series.

Note that 3 is a channel stopper. Further, 4 indicates an output terminal. FIG. 2 shows an example of the color filter 5 arranged in front of this CCDI.

This color filter 5 has a transmission area divided into a plurality of parts corresponding to the area of the picture element 2, and every other transmission area is blocked from light in the horizontal scanning direction a so that the transmission area forms a checkered pattern. Ru. The array pitch is γ between adjacent horizontal scanning lines. The light-shielding regions are formed with a shift of the same amount. For example, as shown in the figure, each of the primary color lights of R, G, and B is selected as the light transmitted through the transmission areas arranged in a checkerboard pattern, and these primary color lights are obtained with opposite phases in adjacent horizontal scanning sections. It will be selected by

When a subject is projected and imaged using the color filter 5 formed in such a checkered pattern, the output terminal 4
A color image signal SO as shown in FIG. 3 is obtained.

That is, input information corresponding to the image of the subject to be imaged is sampled for each pixel and converted into an electrical signal, so that a color image signal S is obtained as shown in FIG. 3A. as,
In addition to the modulation component (DC component) SOO that becomes the luminance signal,
A sideband component (AC component) SM is obtained. In this case, the modulation component SDO and the sampling frequency Fc (=1/3.2
Depending on how H) is selected, the sideband component SM
is the modulation component S.

Although it is possible to prevent the modulation component S from being mixed in S. On the other hand, the bandwidth of the modulation component S must be narrowed. If the bandwidth of O is selected to be about 3.5 MHz, for example, as usual,
Accordingly, since the sampling frequency f'c is set high, it is necessary to increase the number of picture elements N in the horizontal scanning direction, which is not practical. Therefore, generally both components S.

O. Signal S with SM overlapped. obtained as. here,
The phase of each color component of R-B constituting the sideband component SM is
Forces obtained with a phase difference of 120° from each other (because the color filter 5 is configured so that the phases are opposite in adjacent horizontal scanning sections, the phase relationship of each color component is shown in Fig. 3A). and B.

Therefore, vertical correlation may be used to separate the modulation component, that is, the luminance component, and the sideband component, that is, the color component.

According to the example in the figure, the signal S obtained in adjacent horizontal scanning periods
. ．． By adding :5S'o, only the luminance component SDO (hereinafter referred to as SY) is obtained, and by subtraction, only the color component SM (hereinafter referred to as S.) is extracted. . However, this operation only holds true when the vertical correlation is strong; in other cases, incomplete separation will always occur, and the color component S will be included in the luminance component SY.

remains. The influence of residual components on images will be explained with reference to FIG. 4 and subsequent figures. For convenience of explanation, as shown in FIG. 4, as the subject 7, we will consider a subject 7R with only red color and a subject 7B with only blue color.

Now, if a horizontal scanning line is imagined to include the boundary line 8 between the subjects 7R and 7B as shown by the dashed line, (N
By scanning each horizontal scanning position from -1) to (N+2), signals SO, -SO4 shown in FIGS. 5A to 5D are obtained. A luminance component SY and a color component S are obtained from these signals SO1 to SO4.

When the above-mentioned signal processing is applied to separate N-1
Since there is a vertical correlation in the signal processing for the line and N line and for the lines N+1 and N+2, complete separation is performed, but between the N(5N+1 lines including the boundary line 8), the color component S is not separated. As shown in FIG. 6, the color component S remains within the band of the luminance component SY. Therefore, when the image is reproduced, the remaining component becomes a bright spot and forms a boundary line as shown in FIG. Therefore, when an image of a strip-shaped subject extending horizontally as shown in Figure 8A is reproduced, the boundary portion in the horizontal direction will be reproduced in a rough manner.As a result, the image quality will deteriorate. to degrade.

This drawback is particularly noticeable when the frequency f'c is low. In addition, in Fig. 7, N, n+1,...
For convenience, . . . indicates horizontal scanning results after vertical correlation.

In consideration of these points, the present invention proposes a circuit that can effectively remove even if one signal component remains in the other signal component. The present invention will be described below with reference to the drawings, but in this example, it is applied to a color imaging device as described above. FIG. 9 is a system diagram showing an example of a color imaging device to which a band-limiting circuit according to the present invention is applied, in which a subject 7 is projected onto a CCD 1 via an optical lens system 9 and a color filter 5, respectively.
The color image signal S obtained in step 1 is supplied to an addition circuit 12 and a subtraction circuit 13 together with the output through a 1H delay circuit 11 in order to separate the multiplexed signals.

Therefore, the brightness component SY is obtained from the addition circuit 12, and the color component S is obtained from the subtraction circuit 13. is obtained. Depending on the content of the subject 7, the separated luminance component SY may contain residual components due to incomplete separation as shown in FIG.

Whether a residual component exists or not can be determined by considering the luminance component after vertical correlation processing. In other words, if the image quality is degraded by the residual components, only the low-frequency components are obtained from the n line and the n+1 line after the correlation process.
Only when the relationship is such that high-frequency components can be obtained from one line, bright spots appear and the image quality deteriorates. Here, in the n(5n+1 line signal after correlation of signals obtained from mutually adjacent horizontal scanning periods, that is, the combined output SY of the adder circuit 12, the combination of the outputs of the n line and the n+1 line is shown in FIG. There are four sets shown from A to D.

First, the output SY obtained from lines n and n+1, respectively.
This is the case where both are only in the low range (A in the same figure). Similarly below,
A case where both include a high frequency range (B in the same figure) or a case where only one of them includes a high frequency range (C and D in the same figure) can be considered. Among these types, image quality deterioration occurs only in the case shown in C of the same figure, so at least if one of the signal components is only in the low frequency range, if processing is performed to remove the high frequency component, Bright spots due to residual components do not occur, and deterioration of resolution (image quality) can be prevented. Also, if both include high frequencies (first
In the case of FIG. 0B), these high-frequency components are not based on residual components due to incomplete separation, but are high-frequency components in the horizontal direction that the subject originally has, so these components are output.

It is clear that a faithful image cannot be reproduced unless this high frequency component is output. 20 shows a band-limiting circuit according to the invention for achieving this purpose.

The band limiting circuit 20 includes a filter circuit 21 that limits the pass band of the luminance component SY, and a control circuit 22 thereof.The control circuit 22 is configured as follows. Control circuit 22
has a 1H delay circuit 23, and the delayed output is supplied to a bandpass filter 24 and then to a detector 25 to extract only high frequency components including at least the color component band. Level detected.

Since the level becomes high only when a high frequency component is present, the detection output is supplied to the trigger circuit 26 to obtain the control output St, which is supplied to the filter circuit 21. The filter circuit 21 includes a low-pass filter 27 that extracts the low-frequency component SOL in the luminance signal SY, a first gate circuit 28A connected to the signal transmission path of the low-frequency component, and a first gate circuit 28A connected in parallel to these. 2 gate circuits 28B.

Note that 29 is a delay circuit for compensating for a time delay caused by the intervention of the low-pass filter 27. The first and second gate circuits 28A and 28B are invertedly controlled.

Reference numeral 31 designates a phase inversion circuit for this purpose, and when there is a control output S1, the first gate circuit 28A is turned on (transmission line closed state).

Next, the operation of this band limiting circuit 20 will be explained.
As shown in Figures B and D, there is a high frequency component S in the luminance component SY of the n line. If H is included, the control output S1 is obtained, so the first gate circuit 28A is turned on.
At this time, since the luminance component SY of the n+1 line is supplied to the filter circuit 21, in this case, the luminance component SY itself shown in ◎ in FIG. 10B and D is obtained as an output. On the contrary, if the high frequency component SDH does not exist (4 in A and C in FIG. 10), the low-pass filter 27 is interposed on the transmission path of the luminance signal SY, so the low-pass filter 27 in FIG. The luminance component SY of the n+1 line shown in is a low frequency component S with the high frequency cut.

Only L will be output. Here, bright spots appear on the screen and the image quality deteriorates when the signal shown in FIG. can be reliably removed.

In this manner, in the present invention, if a residual component exists, the luminance component from which the high frequency portion has been removed is used as the luminance component S' in subsequent signal processing. Therefore, if this luminance component is supplied to the matrix circuit 32 together with the demodulated output of the color component, the output terminals 32a to 32
It is possible to obtain a desired color video signal, for example, a luminance signal Y and color difference signals (R-Y) and (B-Y) of the NTSC system from the video signal c.

Note that the color component S.

A delay circuit 34 interposed in the transmission path is used to correct the time delay caused by the intervention of the band limiting circuit. Further, 35A and 35B are demodulating crystal tubes having different demodulation axes, from which color components such as (B-G) and (R-?) are demodulated. As explained above, in the present invention, the high frequency component of the input video signal one horizontal scanning period before is detected to control the filter circuit 21 for removing the residual component.

Therefore, it is extremely suitable for application to the signal processing circuit of the color imaging device mentioned at the beginning. In other words, by applying the circuit of the present invention, even when capturing an image of an object that includes a boundary part (pattern, etc.) extending in the horizontal direction, residual components can be reliably removed, so there is no deterioration in image quality, and a high-quality image is always obtained. It has the great feature of being able to reproduce

The example explained so far is a consideration of the model-like object 7 as shown in Figure 4, but instead of such a simplified pattern, it is also possible to take a vertical stripe-like object or a diagonal stripe-like object. Even when an image is captured, residual components can be effectively removed in the present invention, and deterioration in image quality can be prevented. Note that in the above example, the case where the circuit of the present invention is applied to an imaging device using a solid-state image pickup body was explained, but the present invention is applicable to a case where two information signals having different information contents are multiplexed, and these information It goes without saying that it is suitable for application to a band limiting circuit in which signals are separated based on a phase separation method.

The configuration of the color filter 5 shown in FIG. 2 is only an example, and the selection of transmitted light etc. is arbitrary.

Since an imaging apparatus can be configured using not only one CCDl but more than one CCDl, it can of course be used in this case as well. 11 and 12 respectively show other examples of the circuit of the present invention, and the embodiment shown in FIG. 11 is a high frequency component S of the luminance component SY.

When detecting the signal, the high-frequency component S including the residual component is compared to the luminance component SY. This is a case where after extracting ll, its presence or absence is detected. Therefore, a subtraction circuit 36 is provided after the delay circuit 23, and by supplying the luminance component SY itself to this subtraction circuit 36, the target high frequency component S is obtained. I
f) The details are extracted. The other circuit configurations are the same and will therefore be omitted. In the example shown in FIG. 12, the filter circuit 21 is configured with a trap circuit, and only when the control output St cannot be obtained, the residual component is removed by trapping the high frequency side of the luminance component SY. This is how it was done.

Although such a trap configuration can of course produce the same effects as described above, this example also has the feature that the configuration of the filter circuit 21 can be further simplified.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of a solid-state image sensor used as an image sensor, Fig. 2 is a partially enlarged plan view of a color filter, and Fig. 3 is an example of a color image signal including the phase relationship of color components. The frequency spectrum diagram shown in Figure 4 is a diagram of a model object.
Figure 5 is a frequency spectrum diagram of a color image signal obtained by imaging the subject in Figure 4, Figure 6 is a frequency spectrum diagram of a part of the signal after signal processing, and Figure 7 is a reproduced image of Figure 4. , FIG. 8 is a diagram for explaining general signal processing, FIG. 9 is a system diagram of main parts showing an example of applying the circuit of the present invention to a color imaging device, and FIG. 10 is a diagram showing vertical correlation. The frequency spectrum diagram after processing, FIG. 11, and FIG. 12 are connection diagrams showing other embodiments of the present invention. 1 is a solid-state image sensor, 5 is a color filter, 20 is a signal processing device, 21 is a filter circuit, 22 is a control circuit, 25 is a detection circuit, 27 is a low-pass filter, 28A, 28B are gate circuits, 32 is a matrix circuit, 35A , 35B is a color demodulation circuit.

Claims (1)

[Claims] 1 Consists of a filter circuit provided on the transmission path of the luminance signal from which the color signal has been removed by taking the correlation between two adjacent lines, and a control circuit that controls the pass band,
This control circuit includes a delay circuit which receives the luminance signal and delays the luminance signal by one horizontal scanning period, and a detection circuit which is provided on the output side of the delay circuit and detects high-frequency components in the luminance signal. and the output of the detection circuit is supplied to the filter circuit, and when the high frequency component is not detected, the filter circuit is controlled so that only the low frequency component of the luminance signal passes through. A band control circuit characterized by: