JPH0147075B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a single-chip color camera, and more particularly to improving resolution in a single-chip color camera using a solid-state image sensor.

Background technology A single-chip color camera uses one imaging unit to obtain color signals. For example, in a single-chip color camera that uses an image pickup tube for the imaging unit, a color filter is used to obtain high-frequency signals. A luminance signal is obtained by extracting a chrominance signal from a frequency-modulated signal and extracting an output signal from an image pickup tube via a low-pass filter.

However, in the single-chip color camera with the above configuration, since the color signal is obtained from a signal modulated to a high frequency by a color filter, there is a problem that the S/N ratio of the color signal deteriorates. are doing.

On the other hand, a single-chip color camera using a solid-state image sensor directly samples the time-series output color signal using a sampling signal having a frequency four times higher than the subcarrier frequency sc. This extracts the high frequency components of the luminance signal. When such a method is used, it is possible to use up to a band of 4sc/2=2sc according to the sampling theorem, so it is possible to obtain an image with high horizontal resolution.

In this case, the vertical stripe color filter has a repeating RGB array as shown in FIG. 1a, and the repetition frequency of each array is 4/3 times the subcarrier frequency sc. Therefore, by sampling the time-series output signals from the solid-state image sensor at 4/3sc with a phase difference of 120 degrees as shown in FIG. ，
The R signal, G signal, and B signal shown in d are extracted. Note that FIG. 1e shows the luminance signal Y.

However, in a single-chip color camera using the above-mentioned solid-state image sensor, the modulated color signal spatially modulated by the RGB vertical stripe color filter is applied to 2/3 of the Nyquist limit Ws/2 determined by the number of horizontal pixels. have problems that occur. That is, the signal E spatially modulated by _{the vertical stripe} color filter shown in _FIG . E _G , E _B are red, green, and blue electric signals,
Ey is the luminance signal expressed as Ey = 1/2 ( _ER + E _G + E _B ), and Wc is the angular frequency of the modulated color signal expressed as Wc = 2/3 x Ws/2, which is 4/3sc. . Ws is the sampling angular frequency of horizontal pixels, which is 4sc.

In this way, in the single-chip color camera with the above configuration, the vertical stripe color filter
The repetition of RGB is 4/3sc, and the difference in level of the luminance signal for each color stripe appears on the screen as vertical stripes of 4/3sc.

DISCLOSURE OF THE INVENTION Accordingly, an object of the present invention is to provide a single-panel color filter that increases the resolution and prevents the occurrence of vertical stripes on the screen due to the difference in luminance signal level between each stripe of a vertical stripe color filter. The purpose is to provide cameras.

In order to achieve such an object, the single-chip color camera according to the present invention processes signals outputted in time series from a solid-state image sensor having an RGB vertical stripe color filter at a frequency that is 4/3 times the subcarrier frequency sc. Color separation is performed by sampling, and a color difference signal and a low-frequency luminance signal are created using the separated color signals, and a high-frequency component of the luminance signal is extracted from the luminance signal obtained by sampling the output signal of the solid-state image sensor at 4sc. In a single-chip color camera that obtains a luminance signal by combining the high frequency component of this luminance signal and the low frequency component of the luminance signal created from the separated color signal, the high frequency component of the luminance signal is An optical or electrical trap for cutting off 4/3sc is provided in the path for creating the area component.

In a single-chip color camera configured in this way, vertical stripes that occur on the screen can be easily and reliably removed due to the level difference in the brightness signal for each stripe in the vertical stripe color filter. It has excellent effects.

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 3 is a block diagram showing an embodiment of a single-chip color camera using a solid-state image sensor according to the present invention. In the figure, 1 is a lens, and 2 is a solid-state imaging device having a stripe filter on its front surface, on which a subject image supplied through the lens 1 is formed. 3 and 4 are an infrared cut filter and an optical low-pass filter provided between the lens 1 and the solid-state image sensor 2. Reference numeral 5 denotes a backup amplifier that amplifies the signal output from the solid-state image sensor 2 and supplies the amplified signal to each sample-and-hold circuit 6 to 9 for YRGB signals. In this case, the sampling period of the sample and hold circuit 6 is 4sc, and the sampling period of the sample and hold circuits 7 to 9 is 4/3sc. 10-13 are low-pass filters provided on the output side of each sample-and-hold circuit 6-9, and the low-pass filter 10 has a cutoff frequency set to 2sc and a trap frequency set to 4sc. The cutoff frequency is set to 2/3sc and the trap frequency is set to 4/3sc. Amplifiers 14 to 17 amplify and output the output signals of the low-pass filters 10 to 13, respectively. This is a trap circuit that receives the output signal of the amplifier 14 as input, cuts the 4/3sc component, and outputs the high frequency component _YH of the luminance signal.
7 amplification degrees are controlled. 22 is trap circuit 1
A brightness matrix circuit that adds the high-frequency component _YH of the brightness signal supplied from 8 and the low-frequency component _YL of the brightness signal made from the RGB signals supplied from process circuits 19 to 21 and outputs a brightness signal. ,23,
24 is a color difference matrix circuit which inputs the output signals of the process circuits 19 to 21 and outputs color difference signals RY and BY, respectively; 25 is a brightness signal outputted from the brightness matrix circuit 22 and the color difference matrix circuits 23 and 24; 26 is the output of the encoder 25, which is input to the encoder 25 via the band filter 27.
This is a mixing circuit that mixes the signals supplied from the TV and the synchronization signal and outputs a color television signal.

In the single-chip color camera configured in this way, the signal output in time series from the solid-state image sensor 2 via the buffer amplifier 5 is sampled at a cycle of 4sc in the sample-hold circuit 6. As a result, high-frequency components of the luminance signal are extracted. The output signal of the sample and hold circuit 6 is passed through a low pass filter 10 with a cutoff frequency of 2sc and a trap frequency of 4sc, further amplified by an amplifier 14, and then supplied to a trap circuit 18. The trap circuit 18 cuts the 4/3 sc signal component contained in the signal supplied from the amplifier 14. That is, the generation of vertical stripes is prevented by outputting the high frequency component _YH of the luminance signal from which the signal component caused by the luminance signal level difference between each stripe in the vertical stripe color filter is removed.

On the other hand, the sample and hold circuits 7 to 9 are connected to each other.
By sampling the output signal of the buffer amplifier 5 at a cycle of 4/3 sc with a phase difference of 120 degrees, RGB signal components are output. The output signals of the sample and hold circuits 7 to 9 are outputted via low pass filters 11 to 13, amplifiers 15 to 17, and process circuits 19 to 21, respectively. In this case, the amplifiers 15 to 17 are used for high-frequency components of the luminance signal output from the trap circuit 18.
Correction is applied to each color signal component by gain control by _YH . Then, for the output signals of each process circuit 19 to 21, the low frequency component Y _L of the luminance signal is obtained in the luminance matrix circuit 22, and the high frequency component Y _H of the luminance signal output from the drive circuit 18 is added. As a result, the luminance signal Y is output. Further, the color difference matrix circuits 23 and 24 input the output signals of the process circuits 19 to 21 to generate color difference signals R-
Y and BY are output. encoder 25
performs modulation by inputting the luminance signal Y outputted from the luminance matrix circuit 22 and the color difference signals RY and BY outputted from the color difference matrix circuits 23 and 24, respectively.
By mixing this modulated output with a synchronizing signal, it is output as a color television signal.

Note that a trap circuit 18 is provided in the luminance signal system to cut out the 4/3sc signal component, but since the luminance signal has up to around 4.5MHz, the band is sufficient, and along with this, the resolution A high-quality image can be obtained.

Further, in the above embodiment, the case where the 3/4 sc component included in the luminance signal is cut using an electrical trap has been described, but it can also be used with optical means. And in this case,
It is sufficient to provide an optical low-pass filter 4 in front of the solid-state image sensor 2 to cut out the 4/3 sc component.

As explained above, the single-chip color camera according to the present invention effectively utilizes the characteristics of the solid-state image sensor, so the resolution is increased, and the brightness difference between each stripe in the vertical stripe color filter increases the resolution. It has an excellent effect of preventing the occurrence of vertical stripes on the screen.

[Brief explanation of drawings]

1A to 1E are diagrams showing the relationship between the arrangement of vertical stripe color filters and the sampling phase, FIG. 2 is a diagram showing the relationship between each color signal component and the phase, and FIG. FIG. 2 is a block diagram showing one embodiment. 1...Lens, 2...Solid-state image sensor, 3...Infrared cut filter, 4...Optical low-pass filter, 5...Buffer amplifier, 6-9...Sample hold circuit,
10-13...Low pass filter, 14-17...Amplifier, 18...Trap circuit, 19-21...Process circuit, 25...Encoder, 26...Mixing circuit, 2
7... Bandwidth filter.

Claims (1)

[Claims] 1. By sampling signals output in time series from a solid-state image sensor having a vertical stripe color filter at a frequency 4/3 times the subcarrier frequency sc in the NTSC system. Color separation is performed, and a color difference signal and a low-range luminance signal are created using the separated color signals, and a high-range luminance signal is created from a signal obtained by sampling the output signal of the solid-state image sensor at a frequency four times the subcarrier frequency sc. In a single-chip color camera that combines and outputs this high-range luminance signal and the low-range luminance signal, a vertical stripe color filter is applied by cutting the 4/3sc signal component to the high-range luminance signal system. 1. A single-panel color camera characterized by being provided with an electrical or optical trap to prevent the occurrence of vertical stripes on the screen caused by