JPH10108207A - Image pickup device and method for eliminating longitudinal stripe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the image pickup device employing an image pickup element of full pixel readout without deterioration in an image due to longitudinal stripes and to provide the method for eliminating longitudinal stripes. SOLUTION: A reference numeral 2 denotes an image pickup element that reads out signals of respective pixels non-additively and successively and provides odd numbered and even numbered scanning line signals from two output terminals. Each output from the image pickup element 2 is amplified by amplifier circuits 5, 6 and synchronized by line memories 11-13 to be inputted to a color separation circuit 16. A detection circuit 24 is connected to a G output side of the color separate circuit 16 to detect a frequency component as 1/2 times of a sampling frequency of a G signal, that is, an output level difference of the amplifier circuits 5, 6 and the result is inputted to an MPU 43, which controls the amplifier circuits 5, 6 so that the output level difference is minimized. Thus, longitudinal stripes occurred in an image due to the output level difference are eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus having a progressive scan image pickup element.

[0002]

2. Description of the Related Art In recent years, with the advance of semiconductor technology, a solid-state imaging device capable of reading out signals by sequential scanning (all-pixel reading solid-state imaging device, hereinafter referred to as all-pixel imaging device) has been developed. This all-pixel image pickup device can capture a high-resolution image with less blurring even for a moving subject than a conventional interlace scan (interlaced scan) image pickup device.

That is, in an interlaced scanning image sensor, one frame image is composed of two fields having a time difference of one field period. Therefore, when a moving subject is imaged, the image is jagged due to the time difference between the fields. Occurs. In addition, if an image of one field is extracted so as not to be jagged, the vertical resolution is reduced to half. On the other hand, since the all-pixel image sensor can scan all the scanning lines for one frame in one field period, the above-described problem does not occur.

[0004] Utilizing such features, all-pixel image sensors are expected to be applied to still image capturing cameras, computer input cameras, and the like.

[0005] The signal processing circuit of a single-chip all-pixel imaging device is as follows.
For example, a configuration as shown in FIG. 9 is conceivable. Hereinafter, a conventional example will be described with reference to FIG.

[0006] The incident light from the subject is transmitted to the imaging optical system 101.
Thus, an image is formed on the CCD 102, which is an all-pixel image sensor, and is converted into an electric signal by the CCD 102. CCD1
A color filter array for color imaging is attached on 02. The color filter array is a filter array as shown in FIG.

The converted electric signal is transferred in a vertical register and a horizontal register in accordance with a timing signal from a timing generation circuit (not shown), and signals for two scanning lines are output in parallel from two output terminals of the CCD 102. . That is, signals of odd-numbered scanning lines are output from one of the two output terminals of the CCD 102, and signals of even-numbered scanning lines are simultaneously output from the other. By adopting such an output method, it is possible to output a progressive scanning signal at the same reading speed as that of an interlaced scanning CCD.

[0008] Each signal is supplied to a noise reduction circuit 103,
After being processed by the 104 and the amplification circuits 105 and 106, they are converted into digital signals by the AD conversion circuits 107 and 108 and input to the camera process circuit 130 from the input terminals 128 and 129. The input digital signals are time-axis converted into line-sequential signals by the 1H memories 109 and 110. The read clock for the 1H memories 109 and 110 is twice as fast as the write clock. The timing in this operation is shown in FIG. After that, the signals for three lines are further synchronized by the 1H memories 111 and 112, and the signals are input to the color separation circuit 113 and the outline emphasis circuit 117, respectively.

The three primary colors of RGB demodulated by the color separation circuit 113 are limited to required bands by low-pass filters 114, 115, and 116, and interference components such as moire are removed. After the level of each of the band-limited GBR signals is adjusted by the white balance circuit 118, the contour signal extracted by the contour emphasis circuit 117 is added to the G signal by the adder 119. Furthermore, high-pass filter 1
The high-frequency component of the G signal whose contour has been corrected by 20 is extracted and added to the R and B signals by adders 121 and 122. After that, the γ correction circuits 123, 124, 125
After the correction, the luminance signal Y and the color difference signals RY and BY are converted by the matrix circuit 126.

Further, when a standard video output is required for monitor output or the like, the luminance signal and the color difference signal are input to the scan conversion circuit 127. The scan conversion circuit 127 has a configuration as shown in FIG. 11, for example, and converts a sequential scan signal into an interlace scan signal. The timing is shown in FIG.

The exposure information detected by the exposure detection circuit 131 is taken into the MPU 132, and the aperture value of the imaging optical system 101 and the amplification factors of the amplification circuits 105 and 106 are adjusted so that the exposure becomes an appropriate value. It is controlled from the MPU 131.

Next, the configuration of the color separation circuit 113 is shown in FIG.
FIG. 14 shows the operation. FIG. 14A shows an undelayed signal among signals for three scanning lines input to the color separation circuit 113, and FIG. 14B shows a signal delayed by one horizontal scanning period (hereinafter 1H). The signal delayed by 2H is shown in FIG.
Are shown below.

[0013] Of these three system signals, the signal shown in FIG. 14A and the signal shown in FIG.
0 is added to generate a signal interpolated in the vertical direction. This signal is shown in FIG. When the signal interpolated in the vertical direction and the 1H delay signal are alternately selected for each dot by the selector 141, a G signal is obtained. FIG. 14E shows a selector selection signal, and FIG.
(F).

[0014]

However, the above-mentioned prior art has the following problems a, b and c.

A. The amplification factors of the signals in the amplification circuits 105 and 106 are controlled by the MPU 132. However, since the amplification circuits have individual variations, even if the same amplification factor is set, the amplification factors between the amplification circuits 105 and 106 are different. , The amplification factor becomes a different value, and a difference may occur in the level of the video signal between the odd-numbered scanning line and the even-numbered scanning line.

B. When color separation is performed by the method shown in FIG. 13, if there is a difference between the signal levels of the odd-numbered scanning lines and the even-numbered scanning lines, vertical stripes having a period of 2 dots are mixed into the G signal, which causes the image to be displayed. It significantly deteriorates.

C. Also, if the band of the G signal is limited by a low-pass filter that suppresses the frequency of the vertical stripe to remove the vertical stripe, even the necessary information is suppressed, and as a result, the resolution of the G signal deteriorates. Would.

The present invention has been made under such circumstances, and has as its object to provide an image pickup apparatus using an image pickup element for reading out all pixels and free from image deterioration due to vertical stripes, and a method for removing vertical stripes. Things.

[0019]

In order to achieve the above object, according to the present invention, the image pickup apparatus is configured as in the following (1), and the vertical stripe removing method is configured as in the following (2).

(1) The signals of the respective pixels are sequentially read out without addition, and the odd-numbered and even-numbered scanning line signals are respectively converted into the first and second signals.
An image pickup device that outputs from the signal output means, a first and a second amplifier circuit that amplifies the signals that are output from the first and second signal output means, respectively, and the first and second amplifier circuits. Control means for controlling the amplification factor;
And the signal amplified by the second amplifier circuit,
A color separation circuit for separating primary colors by vertical interpolation; and a detection circuit for detecting a frequency component of a half of a pixel period from an output of the color separation circuit, wherein the control means outputs the output of the detection circuit. An imaging apparatus for controlling an amplification factor of each of the first and second amplifier circuits so as to minimize a level.

(2) The signals of the respective pixels are sequentially read out without addition, and the odd-numbered and even-numbered scanning line signals are respectively converted into the first and second signals.
An imaging device comprising: an imaging element that outputs from the signal output unit; and first and second amplification circuits that amplify the signals from the first and second signal output units, respectively.
A method for removing vertical stripes in an output image of an imaging device, wherein the output levels of the first and second amplifier circuits are controlled to be equal.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to examples of an "imaging device".

[0023]

FIG. 1 is a block diagram showing the configuration of an "imaging device" according to an embodiment.

In FIG. 1, reference numeral 1 denotes an image forming optical system for forming a subject image on an image pickup device, 2 denotes a CCD as a solid-state image pickup device for sequentially reading out signals by scanning, and 3 and 4 denote noises of output signals of the CCD 2. Noise reduction circuit to reduce, 5 and 6 are CCD
Amplifying circuits for amplifying the signal of the CCD 2 to an appropriate level; A / D converter circuits 7 and 8 for converting the signal of the CCD 2 into digital signals; and 9 and 10 input terminals of the process circuit 42.

Reference numerals 11, 12, 13, and 14 denote line memories for delaying the signal of the CCD 2 by one scanning line time, and reference numeral 15 extracts a vertical contour signal from signals of six scanning lines synchronized by the line memories 11 to 14. This is a vertical contour extraction circuit.
Reference numeral 16 denotes a color separation circuit that generates a GBR primary color signal from the signals synchronized by the line memories 11, 12, and 13, reference numeral 17 denotes a base clip circuit that slices a small amplitude portion of the vertical contour signal, and reference numeral 18 denotes a band of the vertical contour signal. , A horizontal contour extraction circuit for extracting a horizontal contour signal from the G signal, a base clip circuit for slicing a small amplitude portion of the horizontal contour signal, and a gain adjustment for adjusting a gain of the horizontal contour signal. A circuit 22, an adder 22 for adding the horizontal contour signal and the vertical contour signal, and a gain adjusting circuit 23 for adjusting the gain of the contour signal.

Reference numeral 24 denotes a detection circuit for detecting a frequency component that is half the pixel sampling frequency from the G signal.

Reference numerals 25, 26, and 27 denote low-pass filters that limit the signal band, reference numeral 28 denotes a white balance circuit that adjusts white balance, reference numeral 29 denotes an adder that adds a contour signal to the G signal, and reference numeral 30 denotes a high band of the G signal. High-pass filters to be extracted, 31 and 32 are adders for adding the high band of the G signal extracted by the high-pass filter 30 to the R and B signals, and 33, 34 and 35 are gamma correction circuits.

Reference numeral 36 denotes a matrix circuit for generating a luminance signal Y and color difference signals RY and BY from the primary color signals.
Is a low-pass filter for limiting the band of the color difference signal, 39 is a scan conversion circuit, 40 and 41 are output terminals of a process circuit 42, and 42 is a process circuit for processing a CCD signal.

Reference numeral 43 denotes an MPU for controlling the amplification factors of the amplifier circuits 5 and 6, and reference numeral 44 denotes an exposure detection circuit for extracting exposure information from Y, RY, and BY signals.

Next, the operation of the above configuration will be described.

The incident light from the subject is imaged by the imaging optical system 1 on the CCD 2 which is an all-pixel image pickup device.
In step 2, it is converted into an electric signal. On the CCD 2, a color filter array for color imaging is attached. The color filter array is, for example, an array as shown in FIG.

The converted electrical signals are output in parallel from two output terminals of the CCD 2 for two scanning lines. That is, the signal of the odd-numbered scanning line is output from one, and the signal of the even-numbered scanning line is output from the other.

After the output signal from the CCD 2 is processed by the noise reduction circuits 3 and 4 and the amplification circuits 5 and 6,
The signals are converted into digital signals by the D conversion circuits 7 and 8. The digitally converted signals for two scanning lines are input to the process circuit 42 from the input terminals 9 and 10, and the signals for six scanning lines are synchronized by the line memories 11, 12, 13 and 14.

The signals for six scanning lines are supplied to a vertical contour extraction circuit 15.
And a vertical contour signal is extracted. The vertical contour signal extraction circuit 15 is constituted by a high-pass filter in the vertical direction, and has a transfer characteristic as shown in FIG. 3, for example, when the number of pixels of the CCD 2 is 640 × 480. The vertical contour signals for two scanning lines extracted by the vertical contour signal extraction circuit 15 are used to reduce the circuit scale at the subsequent stage.
The signal is converted into a dot sequential signal having a frequency twice as high as the frequency read from the CCD 2. That is, as shown in FIG. 4, the signals of the odd-numbered scanning lines and the even-numbered scanning lines are converted into time-division multiplexed dot-sequential signals. The vertical contour signal extracted by the vertical contour signal extraction circuit 15 is obtained by slicing a small-amplitude part in the base clip circuit 17 for noise reduction and then by the low-pass filter 18.
Unwanted bands in the horizontal direction are eliminated.

On the other hand, the line memories 11, 12, 1
The signal synchronized by 3 is separated by a color separation circuit 16 into a GBR primary color signal in accordance with a timing signal from a timing generator (not shown). These signals also have a form in which signals for two scanning lines are time-division multiplexed. Each signal is limited to an appropriate band by low-pass filters 25, 26, 27. For example, in the case of the color filter array as shown in FIG. 2, the sampling point of G exists in each column, so that the horizontal band is に 対 し of the horizontal sampling frequency of the CCD 2. Therefore, the pass band of the low-pass filter 25 is set to about 1/2 of the sampling frequency of the CCD 2. On the other hand, since there is only one sampling point for R and B in two columns, the band is 1/2 of the G signal, and the pass band of the low-pass filters 26 and 27 is about 1/4 of the sampling frequency of the CCD 2. Is set. 5A shows an example of the transfer characteristics of the low-pass filter 25.
An example of the transfer characteristics of No. 27 is shown in FIG.

At the same time, the separated G signal is input to a horizontal contour extraction circuit 19, and a horizontal contour signal is extracted. The extracted horizontal contour signal is processed by the base clip circuit 20 and the gain adjustment circuit 21 and then added by the adder 22 to the above-described vertical contour signal. The added contour signal is adjusted to an appropriate level by the gain adjustment circuit 23 and then added to the G signal by the adder 29.

On the other hand, the level of the frequency component that is half the sampling frequency of the G signal detected by the detection circuit 24 is input to the MPU 43 in order to detect an error in the amplification factor between the amplification circuits 5 and 6. Is done.

Each of the signals band-limited by the LPFs 25, 26, and 27 is changed in the gain of the RB signal by the white balance circuit 28 so that the levels of the white portions match. next,
The high band of the wideband G signal is extracted by the high-pass filter 30 and added to the R and B signals by the adders 31 and 32. The characteristics of the high-pass filter 30 are complementary to the characteristics of the low-pass filters 26 and 27, and aim to make the bands of the G signal and the RB signal uniform.

Thereafter, after the γ correction is performed by the γ correction circuits 33, 34 and 35, the luminance signal Y is
And the color difference signals RY and BY are converted to the color difference signals RY.
Y and BY are band-limited by low-pass filters 37 and 38 to about の of the band of Y. The three signals of Y, RY, and BY are input to an exposure detection circuit 44, and exposure information is detected. The detected exposure information is taken into the MPU 43 and the aperture value of the imaging optical system 1 and the amplification factors of the amplification circuits 5 and 6 are set to M so that the exposure becomes an appropriate value according to the luminance of the subject.
Controlled by the PU 43.

Finally, the Y, RY, and BY signals are input to the scan conversion circuit 39. In the scan conversion circuit 39, the input Y, RY, and BY signals are switched by switching pulses generated by timing generation means (not shown) to generate two video signals for each scanning line. This signal is, for example, in a form in which RY and BY are selected one pixel at a time for each of two pixels of Y, and are time-divided in the order of Y, RY, Y, and BY. At this time, Y, RY,
BY are all signals on the same scanning line.

FIG. 6 is a timing chart. At this time, one clock of the output signal is twice the sampling rate of the Y signal. If one of the two systems is taken out, it is an interlaced scanning signal, and if both are used, it becomes a progressive scanning signal. The two generated video signals are output from output terminals 40 and 41.

FIG. 7 shows the configuration of the color separation circuit 16 in detail. FIG. 8 shows the operation of the color separation circuit 16.

The color separation section color-separates signals for one scanning line based on signals for three scanning lines. Since the G signal is obtained with the sampling phase shifted by π for each scanning line, a cycle equal to the sampling frequency of the CCD signal is obtained by alternately sampling the signal of the center scanning line and the signal obtained by adding the upper and lower scanning lines. Is obtained. 8A shows a signal of the central scanning line, and FIG. 8B shows a signal obtained by adding upper and lower scanning lines. By selecting these signals at the timing shown in FIG. 8C by the switch 73, the G signal shown in FIG. 8D is obtained. Although the 3H signal in FIG. 7 has been described above, the G signal is also separated for the 4H signal by the same processing.

Further, since the RB signal is obtained in a form sampled at every other scanning line at half the sampling frequency of the CCD signal, the signal of the central scanning line and the signal obtained by adding the upper and lower scanning lines are respectively obtained. Are sampled and held at twice the cycle of the sampling of the CCD signal, and are alternately selected at twice the cycle of the horizontal scanning frequency. That is, the signals shown in FIGS. 8A and 8B are sampled and held by the D flip-flops 72 and 74 and the switches 75 and 76 to obtain the signals shown in FIGS. When the center scanning line is a signal represented by 4H, the RB signal is similarly separated.

Thereafter, the signals for two scanning lines obtained as described above are time-division multiplexed at twice the frequency of the sampling by the CCD signal switches 79, 80, and 81 to be combined into one system signal.

In the amplification circuits 5 and 6, the amplification rate is controlled by the MPU 43 to perform amplification so that the level of the video signal becomes appropriate. There is a difference in signal level between the second scan line and the even scan line. When color separation is performed in this state by the above-described method, as shown in FIG. 8D, vertical stripe noise having a period of two dots is mixed into the G signal, and the image is significantly deteriorated. Conversely, if the amplification circuits 5 and 6 are corrected so that the level of the signal of the two-dot period is minimized, the error of the amplification factor is automatically corrected.

That is, a frequency component having a period of 2 dots is detected by the detection circuit 24, and based on the detected frequency component, the MPU 43 corrects the value of the amplification factor given to the amplification circuits 5 and 6, thereby using a special object. Thus, it is possible to automatically calibrate the error of the amplification factor between the two amplification circuits during normal photographing without correcting the amplification factor.

As described above, according to the present embodiment,
A high-resolution image without image degradation due to vertical stripes can be obtained while using an image sensor for reading all pixels.

[0049]

As described above, according to the present invention,
A high-resolution image without image degradation due to vertical stripes can be obtained while using an image sensor for reading all pixels.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment.

FIG. 2 is a diagram showing an example of a color filter array.

FIG. 3 is a diagram showing transfer characteristics of a vertical contour emphasis circuit;

FIG. 4 is an explanatory diagram of dot sequential signal formation.

FIG. 5 is a diagram showing transfer characteristics of LPFs 25, 26, and 27;

FIG. 6 is an explanatory diagram of output signal formation of a process circuit.

FIG. 7 is a diagram illustrating a configuration of a color separation circuit.

FIG. 8 is a timing chart of the circuit of FIG. 7;

FIG. 9 is a block diagram of a conventional example.

FIG. 10 shows 1H memories 109 and 110 in a conventional example.
Peripheral operation explanatory diagram

FIG. 11 is a diagram showing a conventional scan conversion circuit.

FIG. 12 is a timing chart of the circuit of FIG. 11;

FIG. 13 is a diagram showing a configuration of a conventional color separation circuit.

14 is a timing chart of the circuit of FIG.

[Explanation of symbols]

 2 Solid-state imaging device 5, 6 Amplification circuit 16 Color separation circuit 24 Detection circuit 43 MPU

Claims (2)

[Claims] 1. A signal of each pixel is sequentially read out without addition,
An image sensor for outputting odd and even scan line signals from the first and second signal output means, and first and second amplifying signals output from the first and second signal output means, respectively. Amplifying circuit, control means for controlling the amplification factors of the first and second amplifying circuits, and separation into primary colors by vertical interpolation based on the signals amplified by the first and second amplifying circuits. A color separation circuit; and a detection circuit for detecting a frequency component of a half of a pixel period from an output of the color separation circuit, wherein the control unit controls the output level of the detection circuit to be a minimum. An imaging apparatus for controlling the amplification factors of first and second amplifier circuits. 2. The signal of each pixel is sequentially read out without addition,
An image sensor for outputting odd-numbered and even-numbered scanning line signals from first and second signal output means, respectively, and first and second amplifier circuits for amplifying signals from the first and second signal output means, respectively. A vertical stripe removal method for an output image of the imaging device, wherein the output levels of the first and second amplifier circuits are controlled to be the same.