JPS63294077A - Image pickup device - Google Patents

Abstract

PURPOSE:To attain a picture good in an S/N required as the picture without using the A/D converter of a high bit by providing a means for emphasizing the high frequency of the output signal of an image pickup element and an A/D converting means or the like and emphasizing the high frequency before an A/D conversion. CONSTITUTION:In the image pickup element 101, the picture is transformed to an electric signal, before the output signal thereof is converted to a digital signal in the A/D converting circuit 103, it goes to a high frequency emphasized signal by an analog high frequency emphases circuit 102 under the state of an analog signal. Then, the output of the circuit 102 is converted to the digital signal in the circuit 103, the digital signal is further processed through a digital signal processing circuit 104. In this case, if the noise of the element 101 is defined to be N1, the noise of the circuit 103 to be N2 and the gain of the circuit 102 to be alpha, the quantity of the noise at the time of providing the circuit after the circuit 103 goes to be alpha(N1+N2) and the quantity of the noise at the time of providing the circuit 102 before the circuit 103 goes to alphaN1. Thereby, the deterioration of the S/N can be reduced and the picture good in the S/N required as the picture can be attained without using the A/D converter of the high bit.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an aperture correction circuit for an imaging device.

BACKGROUND OF THE INVENTION In conventional imaging devices, an aperture correction circuit is essential in order to improve the sharpness of images. Aperture correction is performed by detecting the contour of the video signal between each pixel in the horizontal direction and adding it to the original video signal. The prior art is disclosed in Japanese Patent Laid-Open No. 58-236607.

FIG. 4 shows a configuration diagram of a conventional horizontal aperture correction circuit when it is digitized. In the figure, 401 is an image sensor, 402 is a MU/D converter, 403 is a digital aperture correction circuit, 404 is a digital signal processing circuit, and 406 is a system control circuit that comprehensively controls the above circuits. Further, 406 to 411 are block diagrams of the digital aperture correction circuit 403, 406 and 407 are digital delay circuits, and 408 to 411 are digital adders/subtractors.

In the conventional imaging device configured as described above, the output signal from the imaging element 401 is converted into a digital signal by the MU/D converter 402, and the digital aperture correction circuit 403 performs contour enhancement to improve the sharpness of the image. After that, the digital signal processing circuit 404 performs other signal processing. Also, in the digital aperture correction circuit, two digital delay circuits 406 and 407 are used.
By adding and subtracting the delayed signals obtained in (Figure 1) and (Figure 2), an aperture correction signal (Figure 2) is obtained, and an aperture-corrected signal (Figure 2) is created.

Problems to be Solved by the Invention However, with the above configuration, only 5 of the resulting images
/N is determined by the noise component N1 of the image sensor 401 and the quantization noise N2 of the MU/D converter 402. In particular, regarding quantization noise, if the number of bits for digitization is n, the S/N ratio is determined as follows.

5p-p/Nrms = 8.0+6nCdB':l
(TV signal) From this, as a mu/D converter, s b
When using the itOm/D circuit, the S of about 56 (dB)
/N. However, in the subsequent digital signal processing section, for example, the digital aperture correction circuit, the noise component will also be amplified by that much, so approximately 12
dB, and also in digital gamma correction, the amplification degree in dark areas of the video signal is very large compared to the amplification degree when no gamma correction is performed, so quantization noise in dark areas becomes noticeable, so it is about 3 to 611B. S/N deteriorates. Therefore, generally the S/N required for NTSG signals is
In order to obtain 4s (:dB) or more, an additional 2 to 3 bits are required as the number of digital pits.
This has the problem of requiring an expensive 10 bit or more MU/D converter.

In view of the above, an object of the present invention is to provide an imaging device that can obtain an image with good S/H required as an image without using an expensive high-bit human/D converter.

Means for Solving the Problems The present invention comprises an image sensor, a means for emphasizing high frequencies of an output signal of the image sensor, and an analog-to-digital conversion means, and is configured such that the high-frequency emphasis is performed before analog-to-digital conversion. It features an imaging device with a

Effect of the Invention With the above-described configuration, the present invention can prevent deterioration of 57H in the digital signal processing section by emphasizing the high frequency range of the output signal of the image sensor as an analog signal and then converting it from analog to digital. A good image with the necessary S/N can be obtained without using a converter.

Embodiment FIG. 1 shows a basic block diagram of an imaging apparatus in a first embodiment of the present invention. In FIG. 1, 101 is an image sensor that converts light into an electrical signal, 102 is an analog high frequency emphasis circuit that emphasizes the high range of an analog signal that is the output signal of the image sensor, 103 is an analog-digital converter,
104 is a digital signal processing circuit, IQ5 is a drive circuit that provides necessary locks to the image sensor 101 and analog emphasis circuit 102, and 106 is a system control circuit that comprehensively controls the entire system.

The operation of the imaging apparatus of this embodiment configured as described above will be described below. The image sensor IQ1 converts the image into an electrical signal, and the output signal is converted into a high-frequency emphasized signal by the analog high-frequency emphasizing circuit 102 ( aperture corrected signal) and then Mu/D circuit 1
03, it is converted into a digital signal. A digital signal processing circuit 104 performs digital signal processing such as digital γ correction, a drive circuit 106 supplies pulses, and a system control circuit 106 comprehensively controls the entire circuit including the above circuits.

Next, FIG. 2 shows an example of an analog high frequency emphasis circuit used in this embodiment. 0 is a block diagram, and ('b) is a signal waveform diagram. In the same figure (&), 201 is an image sensor;
202 to 204 are clock delay circuits composed of sample and hold circuits; 205 is an amplifier for amplifying the output signal of the clock delay circuit (FIG. 2(b) shows x2);
06 is an amplifier that amplifies the sum signal of the clock delay circuit (('b) in the same figure shows the version-4), 207 to 209 are adders, 21o is a drive circuit for the image pickup element and the clock delay circuit, and 211 is an amplifier for amplifying the sum signal of the clock delay circuit. This is the entire analog high frequency enhancement circuit. Also, the same figure (b) shows the position (0') to (to) shown in the same figure (IL))
This figure shows a signal waveform diagram.

The operation of the analog high-frequency emphasis circuit used in the image sensor of this embodiment configured as described above will be described below.

The output signals of the image sensor 201 are sequentially input to a clock delay circuit which delays them by an arbitrary clock period using a clock corresponding to the pixels of the image sensor. Then, as shown in the waveforms of various parts (in the figure), adders 2o7゜208, 209 obtain a sum signal of each delayed signal, amplifiers 205, 206 obtain a signal obtained by weighting each delayed signal, etc. Perform the calculation to obtain a signal with the necessary high-frequency emphasis.

The imaging device of this embodiment configured as described above will be described below. For example, the S/N of an image obtained by an imaging device that performs digital signal processing is determined by the noise N of the imaging device.
1 and quantization noise N2 of the Mu/D circuit.

Therefore, if a high frequency emphasis circuit is provided after the A/D circuit for digital signal processing, the S/H
The noise component related to the deterioration of is (N1+N2),
If the gain of the high-frequency emphasis circuit is α, the amount of noise is α(N1
10N2).

On the other hand, if a high frequency emphasis circuit is provided as analog signal processing before the MU/D circuit, the S/D circuit by the high frequency emphasis circuit is
The noise component related to the deterioration of H is N, and if the gain of the high-frequency emphasis circuit is α, the amount of noise is αN.

From this, it is possible to reduce the deterioration of signal 1 when the high-frequency emphasis circuit is provided as an analog process before the A/D circuit.

Furthermore, as mentioned above, in the analog high-frequency emphasis circuit, it is possible to obtain a signal with the necessary high-frequency emphasis by adding and multiplying the signal delayed by the necessary lock period using the sample-hold circuit. This has the advantage that addition and multiplication can be realized with a smaller circuit scale than in the case of digital signals.

In addition, in the frequency region where high frequency enhancement is applied, for example, in the case of the NTSC system, noise around 3.58 M142 (color signal modulation frequency) in the luminance component is converted to low frequency noise of the color signal, which adversely affects the image. Therefore, the frequency range in which high frequency enhancement is applied is set below the above color signal modulation frequency. Alternatively, for the same purpose, a method may be used in which a 358 MHz trap is added to the high frequency emphasis circuit in order to reduce noise around 3.58 MHz.

As described above, according to this embodiment, the high frequency emphasis circuit is
By providing analog signal processing in front of the circuit,
Compared to the case where a high-frequency emphasis circuit is provided as a digital signal processing device after the Mu/D circuit, the quantization noise caused by digitization that occurs in the Mu/D circuit is emphasized by the high-frequency emphasis circuit, and the S/N of the image is reduced. It will no longer deteriorate. Therefore, N.T.
Even when obtaining the necessary S/N (= approximately 46 dB or more) as an SC signal, the S/N deterioration in the digital signal processing system is γ.
The deterioration due to correction etc. is about 6 dB, and the S/N of the 8-bit MU/D circuit is about 58 dB, so it is high bit.
It is possible to obtain a good image without using an expensive M/D circuit.

FIG. 3 is a basic block diagram of an imaging device showing a second embodiment of the present invention. In the figure, 301 is an image sensor;
2 is an analog high frequency emphasis circuit, 303 is a mu/D circuit, 30
4 is a digital high-frequency emphasis circuit, 306 is a digital signal processing circuit, 306 is a drive circuit that supplies clocks to the image pickup device and the analog high-frequency emphasis circuit, and 307 is a system control circuit.

The difference between this figure and the block diagram of FIG. 1 is that a 3o4 digital high frequency emphasizing circuit is provided after the MU/D circuit.

The operation of the imaging apparatus of the second embodiment configured as described above will be described below.

The output signal of the image sensor 301 is subjected to a predetermined high-frequency emphasis in an analog high-frequency emphasis 302, and then converted into a digital signal in a MU/D circuit 303. After high-frequency emphasis is applied to the signal as a digital signal in a digital high-frequency emphasis circuit 304, a digital signal processing circuit 305 performs signal processing such as digital γ correction. At this time, the system control circuit 307 comprehensively controls the entire system.

Here, the digital high-frequency emphasis circuit will be explained. As explained in the conventional example, the digital high frequency enhancement circuit is configured to calculate a digital signal delayed by an arbitrary pixel period using a digital delay circuit and add the resulting correction signal to the original signal. It is possible to configure the delay circuit and the arithmetic circuit with higher accuracy than in the case of a circuit, and it is also possible to easily adjust the correction amount under system control.

In imaging devices such as single-chip digital cameras, when high-frequency emphasis is applied as analog signal processing, the frequency range is limited to below the color signal modulation frequency, but when high-frequency emphasis is applied as digital signal processing, Frequency range is not limited.

As described above, according to this embodiment, the high frequency emphasis circuit is connected to the A/D
By providing the circuit before and after the circuit, that is, in both the analog signal processing section and the digital signal processing section, the predetermined high-frequency emphasis can be performed in the analog processing section, and the remaining high-frequency emphasis can be performed in the digital processing section. As explained in the example, adding high-frequency emphasis using analog processing prevents S/N deterioration due to quantization noise in the A/D circuit that accompanies digitalization, and limiting it in the frequency domain by adding high-frequency emphasis using digital processing. It is possible to apply high-frequency emphasis without any interference, and it is also possible to obtain greater precision and ease of adjustment. As a result, even if an imaging device requires 12 dB of high frequency enhancement, by applying 9 dB of high frequency enhancement in the analog processing section, the remaining 3 dB of high frequency enhancement and digital
The total S/N deterioration with 6 (iB) in correction is sdB. Therefore, 8 bit (DA/D circuit (7) S/N
Since N is 56 dB in total, it is 47 dB in total, so it is possible to obtain a good S/H image without using a high-bit mu/D circuit. It is possible to perform high frequency adjustment in the frequency band.

Although the first embodiment shows a high-frequency emphasis circuit using analog signal processing, it is clear that the circuit is not limited to this, and the second embodiment shows a digital high-frequency emphasis circuit, but the present invention is not limited to this. It is also clear that this is not the case. Further, in the first and second embodiments, the image signal input is an image sensor, but the present invention is not limited to this, and other image signal input circuits may be used.

Furthermore, in the description of the frequency domain in which high frequency enhancement is applied in the first embodiment, the case of the NTSC system is shown, but it is clear that the system is not limited to this system.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, according to the present invention, it is possible to obtain a good image with high frequency emphasis (aperture correction) without using a high-frequency mu/D circuit, and its practical effects are as follows. big.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an imaging device according to an embodiment of the present invention, FIG. 2 is a circuit diagram of the main parts used in the same embodiment, FIG. 2B is an operating waveform diagram thereof, and FIG. 3 is a diagram of the present invention FIG. 4B is a block diagram of the conventional imaging device, and FIG. 4B is its operating waveform diagram. 1o1...Image sensor, 102...Analog high frequency emphasis circuit, 103...Human/D circuit, 1
04...Digital signal processing circuit, 106...
...Drive circuit, IQ6...System control circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3

Claims (8)

[Claims] (1) An imaging device comprising an image sensor, a means for emphasizing a high frequency range of an output signal of the image sensor, and an analog-to-digital conversion means, the high-frequency emphasizing means being provided before the analog-to-digital conversion means. Device. (2) Claim 1, characterized in that the high frequency enhancement means is configured to add and subtract one or more signals obtained by delaying the pixel signal of the image sensor and the original signal that is not delayed.
The imaging device described in Section 1. (3) The imaging device according to claim 1 or 2, wherein the high frequency enhancement means is configured to weight pixel signals of the imaging device. (4) The imaging device according to any one of claims 1 to 3, wherein the high frequency enhancement means is configured to perform color modulation at a frequency lower than the color modulation frequency of the output signal of the imaging device. . (5) an image sensor, a first means for enhancing the high frequency range of the output signal of the image sensor, and an analog-digital conversion means;
It is characterized by comprising a second means for high-frequency emphasizing the output signal of the analog-to-digital converting means, and the first high-frequency emphasizing means and the second high-frequency emphasizing means are provided before and after the analog-to-digital converting means, respectively. An imaging device that uses (6) The first high frequency enhancement means is configured to add and subtract one or more signals obtained by delaying the pixel signal of the image sensor and the original signal that is not delayed. The imaging device according to item 5. (7) The imaging device according to claim 5 or 6, wherein the first high-frequency emphasis means is configured to weight pixel signals of the imaging device. (8) The first high frequency enhancement means is configured to perform color modulation at a frequency lower than the color modulation frequency of the output signal of the image sensor. imaging device.