JPH0149077B2 - - Google Patents

Description

TECHNICAL FIELD The present invention relates to an imaging apparatus for driving an imaging device having a plurality of horizontal shift registers in an improved manner.

[Prior art]

Conventionally, this type of color imaging apparatus uses an imaging device (such as a CCD) that includes a plurality of color separation filters having different spectral characteristics in, for example, a stripe pattern.

For example, as shown in the first diagram, a red light (R) transmission filter, a green light (G) transmission filter, a blue light (B) transmission filter (hereinafter simply R filter, G filter,
Let us consider a case where filters (referred to as B filters) are sequentially arranged on the surface of an imaging device. The light that enters the imaging device through such a filter and optical system is spatially sampled by the color stripe filter and imaging device described above, but in this case, the number of pixels of the imaging device or the pitch of the color stripe filter is sampled spatially. Spatial frequency components of the incident light that correspond to 1/2 or more of the determined spatial sampling frequency cause aliasing distortion. This will be explained using FIG. In each of the diagrams A, B, and C, the horizontal axis represents frequency and the vertical axis represents signal level.

The incident light sampled on the imaging device is read out from the imaging device as an imaging signal by photoelectric conversion, etc., but if we focus on only R (or only G, or only B) of this imaging signal, its repetition frequency is 1/3 of the read frequency. If this repetition frequency fc is used, the baseband component and band wave component of the incident light due to sampling will be as shown in figure A, and the shaded part in the figure is called the aliasing distortion component. When this signal is passed through a low-pass filter having characteristics as shown in the figure B, this aliasing component remains mixed with the baseband component, and this component causes a significant deterioration of the image quality on the display. A method for reducing such aliasing distortion is described in Japanese Patent Application Laid-open No. 120281/1981. In other words, when an achromatic object image is photographed as shown in C in the same figure, if the color separation filter is designed so that the level of the point sequential signal output from the imaging device is 1:1:1, the sideband components will be reduced. By canceling each other out, aliasing distortion can be reduced.

According to this method, aliasing distortion can be reduced at least for achromatic screens.

Of course, such an effect cannot be obtained on a screen with high color saturation, but human visibility is low in the high frequency range when it comes to colors, so it can be ignored.

However, in the case described above, if the color temperature of the photographing light source differs depending on the purpose or location of photographing, the point-sequential signal level becomes unbalanced, eventually resulting in aliasing distortion. Figure 3 shows, for example, the color temperature.
Showing the spectral energy at 3200〓 and 6000〓,
FIG. 4 is a diagram illustrating the drawbacks when a color separation filter is designed so that the output signal level in point sequence becomes constant at 3200, for example. Color temperature level is 3200
If the filter is set so that R, G, and B are 1:1:1 at 〓, as shown in Figure 4, at 6000〓, the long wavelength side, that is, the R side will be weak, and the B side will be strong, so the side The band vector is biased toward the cyan (Cy) side as shown in the fourth diagram, and aliasing distortion occurs.

Furthermore, imaging devices are highly sensitive to infrared light, which may deviate from the visual sensitivity.
In order to prevent this, an infrared cut filter is installed in the optical path of light incidence to the imaging device, but due to unevenness in the thickness that occurs during the manufacturing process of this infrared cut filter, the spectral sensitivity characteristics of this filter vary.
As a result, fluctuations in the R signal level may occur.

The following method is known as a method for eliminating such defects.

That is, this method uses a mechanical color temperature correction filter. In this method, color temperature correction filters are generally prepared, for example, one for daylight, one for fluorescent light, and one for tungsten, and the above correction filters are switched depending on the shooting location. The disadvantages of this method are that several types of correction filters are required, and that the generation of aliasing distortion cannot be completely prevented because the level adjustment of the point-sequential signals is rough.

Furthermore, conventional imaging devices have the drawback of large noise and poor image S/N. For example, Tokkosho
In the television camera using a three-electrode image pickup tube described in Publication No. 55-51395, R, G,
A high-frequency luminance signal is obtained by adding the B signal. That is, the output signals R, G, and B of the three electrodes become as shown in FIG. 5 by scanning with an electron beam, and a luminance signal Y is obtained by combining the respective color signals. In this case, the noise generated in the image pickup tube is generated uniformly in both the signal component region and the invalid component region, so the noise in the combined luminance signal becomes approximately √3 times, and the S/N decreases by that amount. There were some drawbacks.

Furthermore, there are methods such as Japanese Patent Application Laid-Open No. 51-38826 that read out the output of a CCD through a plurality of shift registers and obtain a luminance signal by simply adding the narrow band outputs obtained from each shift register. , In this case, there is a drawback that only a narrowband luminance signal can be formed.

In addition, as disclosed in Japanese Patent Application Laid-Open No. 57-26977, it is known that a broadband luminance signal is formed by dot-sequential level adjustment of the CCD's color point-sequential signal, but with this configuration, the horizontal direction of the CCD is As the number of pixels increases, the driving frequency of the circuit for level adjustment increases, and it is also difficult to match the phase of the point-sequential output from the CCD with the level adjustment signal, making it impractical. .

Furthermore, an imaging apparatus using a solid-state device as shown in FIG. 6, which will be described later, also has the following noise problem. For example, Figure 5B shows the output signals of each horizontal shift register when three horizontal shift registers are driven with pulses in phase with the spatial sampling of the color separation filter. It is necessary to hold the sample.
However, the signals S1, S2, and S3 have arrows A,
Noise of each drive pulse is generated in the portions indicated by B and C due to capacitive coupling between each horizontal shift register output amplifier and the drive electrode, and if this noise portion is sampled and held, modulation noise may occur. Therefore, the timing of sample and hold must avoid the above-mentioned noise, and for this purpose, very highly accurate timing is required. However, this is difficult to realize in practice, considering the operating temperature of the imaging device and changes over time.

〔the purpose〕

The present invention eliminates the above-mentioned drawbacks, provides an imaging device that is suitable for high integration of imaging means, can stably obtain a wideband luminance signal, and can drive an imaging device with less superimposition of noise. The purpose is to do.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an imaging means combined with three types of color separation filters having mutually different color spectral characteristics, and an operation of the imaging means. three signal readout horizontal shift registers for distributing and outputting direction signals for each color signal corresponding to each of the color separation filters, and two horizontal shift registers among the three signal readout horizontal shift registers; drive means for driving the remaining horizontal shift register with in-phase pulses and driving the remaining one horizontal shift register with pulses of opposite phase, and the level of each color signal outputted through the three horizontal shift registers for signal readout is determined by the color temperature. a level control means for controlling white balance according to the level control means; and a point sequentialization means for converting each color signal whose level is controlled by the level control means into a dot sequence by sequentially extracting each color signal at a constant cycle at a constant period to form a wide band luminance signal. , has.

(Function) With this configuration, first of all, even if the number of horizontal pixels increases due to the high integration of the imaging means, the signals in the row direction are distributed to a plurality of signal readout paths before being read out, so each signal can be read out. The drive frequency of the read path can be kept low.

Secondly, since the signal read out in this way has a narrow band, the luminance signal formed from this signal also has a narrow band. However, according to the configuration of the present invention, the signals can be sequentially extracted by the switch means. Since it is point-sequential, it is possible to obtain a wide band luminance signal with little noise.

Thirdly, in the above-mentioned device, white balance control is applied to the signals obtained from multiple signal readout paths before point-sequentialization according to the color temperature, so that a brightness signal with a wide band can always be obtained stably. I can do it.

Fourthly, since noise leakage due to capacitive coupling of drive pulses between horizontal shift register output signals is reduced, modulation noise due to this noise is reduced. Furthermore, it has many features such as the fact that the structure of the point sequentialization means does not need to be special.

〔Example〕

An embodiment of the present invention will be described by taking as an example an imaging device using a CCD type imaging device shown in FIG.

The image sensor shown in Figure 6 is a frame transfer type.
It is a CCD. Information charges photoelectrically converted by the imaging section 1 corresponding to each color filter of the stripe filter are transferred at high speed to the memory section 2 during the vertical retrace period of TV synchronization by driving pulses φ _PI and φ _PS .
Further, the information charges accumulated in the memory section 2 are stored in the seventh
As shown in the figure, the color information corresponding to each stripe filter is distributed and transferred to horizontal shift registers SR1, SR2, and SR3 for each vertical transfer of one horizontal line. Therefore register SR
1, SR2, and SR3 constitute separation means for separating color signals.

FIG. 8 is a block diagram of a signal processing circuit for signals read out from the CCD of the device. clock IC30
A color filter shown in FIG. 1 is pasted on the surface of the imaging device 10 driven by a driver 20 that forms pulses based on the clock pulse of 1, and its output signal corresponds to the color separation filter. Each R, G, and B color signal is obtained separately.

In this case, since the driving pulse φ _S1 of the horizontal shift register SR1 and the driving pulses φ S2 and φ _S3 of the horizontal shift registers SR2 and _SR3 have a pulse phase different by 180°, the color signals are the same as those shown in FIG. S
2. It will look like S3. In the figure, the shaded area indicates the effective signal component. These color signals are converted into a signal waveform in the next-stage sample-and-hold circuit 40 with a cycle width close to about 100% of the drive pulse cycle. Since the signal S1 is controlled by the sample-and-hold pulse P1, and the signals S2 and S3 are controlled by the sample-and-hold pulse P2, the phase difference between the output signals S1', S2', and S3' of the sample-and-hold circuit 40 remains 180 degrees. Retained. From these signals, the switch circuit 50 generates control pulses PW1,
A dot sequential signal S ₀ is formed by PW2 and PW3, and the phases of the color signals R, G, and B included in this signal S ₀ must match the spatial sampling phase of the color separation filter. So switching pulse
PW1, PW2, and PW3 are as shown in the figure, that is, pulse PW1 is a pulse that cuts approximately the middle period of signal S1'.
The timing of PW2 and PW3 is determined so that they are located within the signal period of signals S2' and S3'. By controlling the sample hold timing and switching timing in this way, the output _S0 of the switch circuit 50, which becomes a luminance signal, is sequentially converted into a point where each color signal has sufficient spatial frequency components, as shown in Figure 9. Therefore, high resolution can be obtained.

Also, since only the necessary part of the luminance signal is extracted and switched, the S/N ratio is lower than that of the conventional example.
There is no deterioration.

Moreover, in this way, a plurality of register output signals S1',
Since the duty of S2' and S3' is 50% and the phases are in a positive or negative phase relationship, noise does not enter the signal component.

Furthermore, since at least two of the plurality of register output signals are in opposite phases to each other, when a luminance signal is generated by dot-sequentializing these register outputs, a broadband luminance signal that follows the spatial sampling phase can be easily formed. Can be done.

That is, if the outputs of the plurality of registers were all in phase, it would be impossible to form a luminance signal having the spatial sampling phase as described above without a delay means, but according to the present invention, there is no need to use such a delay means. , switching pulse PW1 to PW3
It is possible to obtain a wideband signal.

Of course, such a method requires three horizontal shift registers.
Not only when one is provided, but also when only two or four
Needless to say, it can also be applied to systems with more than one. The output signal S1' of the sample hold circuit 40,
S2' and S3' are limited by a low-pass filter 60 in the next stage to components in a signal band of approximately 1 MHz necessary as a color signal.

Incidentally, the spatial sampling phases (centroids of sensitivity) of the signals S1', S2', and S3' are as shown in FIG. In the figure, the solid arrows indicate the phase relationships at the time of output from the sample and hold circuit 40, and the broken arrows correspond to the spatial sampling of the color separation filter. It shows the ideal phase (position). Therefore, the signals S1' and S3' are respectively as shown in the figure.
It is necessary to adjust the delay time of T _DL1 and T _DL2 . The delay circuit 70 shown in FIG. 8 is for this purpose.
The luminance signal Y and color signals R, G, and B thus obtained are guided to a process encoder circuit 90 consisting of gamma correction, white clip, black level adjustment circuit, chroma modulator, etc., and become an NTSC signal.

In the above embodiment, the output signal of the sample and hold circuit 40 is directly led to the switch circuit 50, but if a level matching circuit for adjusting each signal level is inserted before the switch circuit, the aliasing distortion of the luminance signal can be considerably reduced. .

Incidentally, if the drive frequency of the horizontal shift register is high, the delay circuit 70 can be omitted. That is, the spatial sampling of the color separation filter is, for example,
If it is about 14MHz, sampling of each color signal corresponds to about 4.8MHz, and in the case of the above example, T _DL1
= 35 ns, T _DL2 = 70 ns, which can be almost ignored with respect to the color resolution of the color signal of approximately 500 KHz to 1 MHz.
Furthermore, instead of providing the delay circuit 70, equivalent delay characteristics may be obtained by slightly changing the cut-off characteristics of the low-pass filter 60.

It goes without saying that the delay circuit 70 may be provided in the signal path before the low-pass filter 60.

〔effect〕

As explained above, the following effects can be obtained by driving two of the three signal readout horizontal shift registers with in-phase pulses and driving the remaining one horizontal shift register with opposite phase pulses. . First, since the noise introduced between the horizontal shift register output signals due to capacitive coupling of drive pulses is reduced, there is no modulation noise caused by this noise.

Second, by sequentially switching and outputting the outputs of each register, point-sequentialization according to spatial sampling can be performed without using a delay circuit when forming a dot-sequential luminance signal, thereby simplifying the configuration.

Thirdly, the timing accuracy of the sample-and-hold pulse may be the same as that of an ordinary pulse.

Also, since the color signal can be generated from a duty cycle of approximately 100% of the drive pulse period, low-frequency noise can be reduced. Furthermore, if the luminance signal is generated by switching the effective components of each color signal, the S/N ratio can be improved.

In this embodiment, a pure color type color separation filter has been described, but a complementary color type color separation filter may be used, or a solid-state device of another type may be used.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a color separation filter, Figure 2 is an illustration of aliasing distortion, Figure 3 is a spectral energy diagram due to differences in imaging light sources, and Figure 4 is an explanation of aliasing distortion due to unbalance of point-sequential signal levels. Figure, 5th
Figure A is an explanatory diagram of conventional luminance signal synthesis, Figure 5B
6 is a schematic diagram of a CCD applicable to the embodiment of the present invention, FIG. 7 is a diagram illustrating transfer of each color signal to a horizontal shift register, and FIG. 9 is an explanatory diagram of the luminance signal synthesis method in FIG. 8, and FIG. 10 is an explanatory diagram of the sampling phase of the color signal in the embodiment of FIG. 8. DESCRIPTION OF SYMBOLS 10... Imaging device, 40... Sample hold circuit, 50... Switch circuit, 60... Low pass filter, 70... Delay circuit.

Claims (1)

[Scope of Claims] 1. An imaging means combined with three types of color separation filters having mutually different color spectral characteristics, and a signal in the row direction of the imaging means that is divided into color signals corresponding to each of the color separation filters. 3 horizontal shift registers for reading signals, and 2 horizontal shift registers among the 3 horizontal shift registers for signal reading are driven with pulses of the same phase, and the remaining 1 horizontal shift register is driven by pulses of the same phase. a drive means for driving with pulses of opposite phase; a level control means for white balance controlling the level of each color signal outputted via the three horizontal shift registers for signal readout according to color temperature; and the level control means. An imaging device comprising: point sequentializing means for sequentially extracting each color signal whose level is controlled by a switch means at a constant period to form a broadband luminance signal.