JP2007104222A - Imaging apparatus and imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of suppressing occurrence of vertical shading even if dark horizontal shading is large or dark current is large. <P>SOLUTION: In the imaging apparatus, signals VOB0-VOB8 outputted over a vertical OB clamp period among sensor output signals corresponding to a vertical OB region are clamped so that their levels come to be OB clamp level L1 according to vertical OB clamp pulses. A signal VOB9 is outputted without being clamped across a period S105 represented by VOB clamp level sampling pulses. Here, the period S105 is identical with a horizontal OB period (HOB period) S103. A clamp voltage generating circuit 107 makes the level of signals outputted without clamped by a clamping circuit 103 to be an OB clamp level L2 of the horizontal OB period (HOB period) S103 in a horizontal OB clamp period. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging apparatus and an imaging method.

  In an imaging device such as a digital camera, in order to faithfully reproduce the gradation of a subject, an optical black region (hereinafter referred to as a light-shielding film) provided with a light-shielding film on an imaging surface among imaging signals output from an imaging device. The imaging signal output from the OB area) is clamped to a predetermined level. As a method for performing such a clamping operation, for example, there is a digital feedback clamping method for shortening the response time of the clamping operation (see, for example, Patent Document 1). In addition, there is a method of feeding back the A / D output to the analog part before the A / D (see Patent Document 2).

  Next, an imaging apparatus using a digital feed clamp method will be described with reference to FIGS. FIG. 4 is a block diagram showing a main part configuration of an imaging apparatus using a conventional digital feedback system. FIG. 5 is a diagram schematically showing the configuration of the imaging surface in the imaging device of FIG. FIG. 6 is a timing chart showing output timings of various signals in the imaging apparatus. FIG. 7 is a timing chart showing the clamping operation when the dark current is large. FIG. 8 is a diagram schematically showing dark horizontal shading. FIG. 9 is a timing chart showing the clamping operation when there is dark horizontal shading. FIG. 10 is a diagram schematically showing an image obtained when there is dark horizontal shading.

  As shown in FIG. 4, the imaging apparatus using the digital feed clamp method includes an imaging element 101 such as a CCD that photoelectrically converts an image and outputs an imaging signal. As shown in FIG. 5, the imaging element 101 is provided with an effective pixel region 1, a vertical OB region 2, and a horizontal OB region 3. An imaging signal output from the imaging element 101 is input to the PGA circuit 102. The PGA circuit 102 includes a double correlation sampling circuit that reduces noise of accumulated charges of the image sensor 101 and a circuit that adjusts the gain of the image signal. The imaging signal output from the PGA circuit 102 is coupled in an alternating manner by passing through the capacitor C and input to the clamp circuit 103.

  The clamp 103 sets the voltage level of the imaging signal output from the PGA circuit 102 to the voltage level generated by the clamp voltage generation circuit 107 with the OB clamp pulse generated by the clamp pulse generation circuit 206 (hereinafter referred to as clamp). Called). The imaging signal output from the clamp circuit 103 is converted into, for example, a 12-bit digital signal by an A / D converter (ADC) 104, and this digital signal is input to the signal processing circuit 105 and the clamp voltage generation circuit 107. The The signal processing circuit 105 performs predetermined signal processing on the digital signal.

  The clamp pulse generation circuit 206 generates an OB clamp pulse indicating the timing when clamping with the voltage output from the clamp voltage generation circuit 107. The digital signal output from the A / D converter 104 is input to the clamp voltage generation circuit 107.

  The clamp voltage generation circuit 107 takes in the input digital signal in accordance with the OB clamp pulse from the clamp pulse generation circuit 206. Here, the captured digital signal is a signal corresponding to the imaging signal (OB level of the Y signal) corresponding to the vertical and horizontal OB regions 2 and 3 from the imaging device 101. Then, the clamp voltage generation circuit 107 integrates the captured signal for each horizontal line or integrates at predetermined intervals, and generates a clamp voltage such that the integration value becomes a constant value. The generated clamp voltage is input to the clamp circuit 103. In this manner, a closed loop is formed among the clamp circuit 103, the A / D converter 104, and the clamp voltage generation circuit 107. As a result, the clamp voltage output from the clamp voltage generation circuit 107 is the signal processing circuit. 5 is fed back so as to keep the OB level of the signal inputted to 5 constant.

  In the imaging apparatus having such a configuration, as shown in FIG. 6, a horizontal synchronization signal, a sensor output signal, and an OB clamp pulse are output during one frame period S7 indicated by the vertical synchronization signal. Here, the sensor output signal is an image pickup signal from the image pickup device 101, a sensor output signal S 1 corresponding to the vertical OB region 2, a sensor output signal S 2 corresponding to the horizontal OB region 3, and a sensor corresponding to the effective pixel region 1. Includes output signal S3.

  The sensor output signal S1 is output in synchronization with one horizontal period S6 indicated by the horizontal synchronization signal over the vertical OB clamp period S9. The sensor output signals S2 and S3 are output every horizontal period S6 over the horizontal OB clamp period S10 following the vertical OB clamp period S9. During the vertical OB clamp period S9, the vertical OB clamp pulse S4 is output. Further, the horizontal OB clamp pulse S5 is output during the horizontal OB clamp period S10.

Here, when the dark current is large, as shown in FIG. 7, with respect to the sensor output signals in the vertical and horizontal OB regions, the dark current component becomes level L5 with respect to level L4 when the dark current is zero. The sensor output signals corresponding to the vertical and horizontal OB regions are brought close to the level VOB by the above-described clamping operation. As a result, the dark current component is suppressed.
Japanese Patent Laid-Open No. 08-195894 Japanese Patent Laid-Open No. 09-083836

  However, in the case of an imaging device having both a vertical OB region and a horizontal OB region, there may be dark horizontal shading in which the dark output changes in the horizontal direction due to its characteristics. For example, as shown in FIG. 8, when the left side of the screen is set to “0”, the dark output change (Vsh) increases as the screen moves to the right side.

  As described above, signals corresponding to the vertical OB region and the horizontal OB region are brought close to the level VOB by clamping. With respect to the vertical OB region, it is necessary to suppress a large dark current component, so that a signal over almost the entire area of one horizontal line is used for clamping. Therefore, if there is a dark output change that increases as it moves to the right side of the screen as shown in FIG. 8, the increased dark output is clamped so as to approach the level VOB. Thereafter, when clamping is performed on a signal corresponding to the horizontal OB region close to the left side of the screen in FIG. 8, the clamp circuit operates to eliminate the dark output difference. As a result, vertical shading corresponding to the dark output difference 6 appears in the output after clamping as shown in FIG. As a result, as shown in FIG. 10, the upper left part of the screen is blackened.

  An object of the present invention is to provide an imaging device and an imaging method capable of suppressing the appearance of vertical shading even when horizontal dark shading is large or dark current is large.

  In order to achieve the above object, the present invention provides an image pickup device having a vertical optical black region and a horizontal optical black region and an image pickup signal output from the image pickup device according to a period indicated by the clamp period signal. In the imaging apparatus, comprising: a clamp circuit that clamps in response to a signal; a clamp period signal generation circuit that generates the clamp period signal; and a clamp voltage generation circuit that generates the clamp voltage based on an output of the clamp circuit The period signal generation circuit corresponds to the vertical optical black area between a vertical clamp period of the imaging signal corresponding to the vertical optical black area and a horizontal clamp period of the imaging signal corresponding to the horizontal optical black area. Generating a sampling period signal that indicates a period for sampling without clamping the imaging signal to be Ramp voltage generating circuit, on the basis of the clamp circuit of the image pickup signal output without being clamped in accordance with the sampling period signal, it provides an image pickup apparatus and generates a clamp voltage in the horizontal clamp period.

  In order to achieve the above object, the present invention provides an image pickup device having a vertical optical black region and a horizontal optical black region and an image pickup signal output from the image pickup device according to a period indicated by the clamp period signal. In the imaging apparatus, comprising: a clamp circuit that clamps in response to a signal; a clamp period signal generation circuit that generates the clamp period signal; and a clamp voltage generation circuit that generates the clamp voltage based on an output of the clamp circuit The period signal generation circuit corresponds to the horizontal optical black area between a vertical clamp period of the imaging signal corresponding to the vertical optical black area and a horizontal clamp period of the imaging signal corresponding to the horizontal optical black area. Generating a sampling period signal that indicates a period for sampling without clamping the imaging signal to be Ramp voltage generating circuit, on the basis of the clamp circuit of the image pickup signal output without being clamped in accordance with the sampling period signal, it provides an image pickup apparatus and generates a clamp voltage in the horizontal clamp period.

  In order to achieve the above object, the present invention provides an image pickup device having a vertical optical black region and a horizontal optical black region and an image pickup signal output from the image pickup device according to a period indicated by the clamp period signal. In an imaging method of an imaging apparatus, comprising: a clamp circuit that clamps in response to a signal; a clamp period signal generation circuit that generates the clamp period signal; and a clamp voltage generation circuit that generates the clamp voltage based on an output of the clamp circuit The clamp period signal generation circuit causes the vertical optical black between the vertical clamp period of the imaging signal corresponding to the vertical optical black area and the horizontal clamp period of the imaging signal corresponding to the horizontal optical black area. Sampling period signal indicating the period for sampling the image signal corresponding to the area without clamping it And generating a clamp voltage in the horizontal clamp period based on an image signal output from the clamp circuit without being clamped according to the sampling period signal by the clamp voltage generation circuit. provide.

  In order to achieve the above object, the present invention provides an image pickup device having a vertical optical black region and a horizontal optical black region and an image pickup signal output from the image pickup device according to a period indicated by the clamp period signal. In an imaging method of an imaging apparatus, comprising: a clamp circuit that clamps in response to a signal; a clamp period signal generation circuit that generates the clamp period signal; and a clamp voltage generation circuit that generates the clamp voltage based on an output of the clamp circuit The horizontal optical black between the vertical clamp period of the imaging signal corresponding to the vertical optical black area and the horizontal clamp period of the imaging signal corresponding to the horizontal optical black area by the clamp period signal generation circuit. Sampling period signal indicating the period for sampling the image signal corresponding to the area without clamping it And generating a clamp voltage in the horizontal clamp period based on an image signal output from the clamp circuit without being clamped according to the sampling period signal by the clamp voltage generation circuit. provide.

  According to the present invention, it is possible to suppress the appearance of vertical shading even when dark horizontal shading is large or dark current is large.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a main part configuration of an imaging apparatus according to an embodiment of the present invention. FIG. 2 is a timing chart showing a clamping operation when there is dark horizontal shading in the imaging apparatus of FIG. FIG. 3 is a timing chart of the OB clamp pulse by the clamp pulse generation circuit 106 of FIG.

  As shown in FIG. 1, the image pickup apparatus of the present embodiment has a circuit configuration similar to that of the conventional image pickup apparatus shown in FIG. Here, the same blocks are denoted by the same reference numerals, and description thereof is omitted. And a different part from the conventional imaging device is demonstrated.

  In the present embodiment, the clamp pulse generation circuit 106 generates a VOB clamp level sampling pulse for instructing to sample an imaging signal corresponding to the vertical OB region without clamping. The VOB clamp level sampling pulse is input to the clamp circuit 103 during a period between the vertical clamp period of the imaging signal corresponding to the vertical OB area and the horizontal clamp period of the imaging signal corresponding to the horizontal OB area. The clamp circuit 103 outputs the imaging signal of the vertical OB region in the corresponding period without being clamped according to the VOB clamp level sampling pulse. The imaging signal output without being clamped is converted into a digital signal by the A / D converter 104 and then input to the clamp voltage generation circuit 107. The clamp voltage generation circuit 107 generates a clamp voltage in the horizontal clamp period based on the input digital signal.

  Specifically, as shown in FIG. 3, 10 rows of signals VOB <b> 0 to VOB <b> 9 are sequentially output from the imaging device 101 as imaging signals corresponding to the vertical OB area of the imaging device 101 in the vertical OB portion period S <b> 101. The Here, among the signals VOB0 to VOB9 in the vertical OB section period S101, an OB clamp pulse for clamping each of the signals VOB0 to VOB8 is output from the clamp pulse generation circuit 106. As a result, the signals VOB0 to VOB8 are clamped in the clamp circuit 103 during the period of the OB clamp pulse (that is, a period corresponding to one horizontal line). The VOB clamp level sampling pulse (S105 in FIG. 2) is output to the signal VOB9, and this signal VOB9 is output without being clamped. The period indicated by the VOB clamp level sampling pulse is the same period as a horizontal OB part period (HOB part period) S103 described later.

  In the effective pixel portion period S102 following the vertical OB portion period S101, a signal including an imaging signal corresponding to the horizontal OB area and an imaging signal corresponding to the effective pixel area is sequentially output. The effective pixel part period S102 includes a horizontal OB part period (HOB part period) S103, which is a horizontal scanning period of an imaging signal corresponding to the horizontal OB area, and an effective pixel, which is a horizontal scanning period of the imaging signal corresponding to the effective pixel area. Part horizontal scanning period S104. Here, in the horizontal OB portion period (HOB portion period) S103, an OB clamp pulse for clamping an imaging signal corresponding to the horizontal OB region is output. As a result, the imaging signal corresponding to the horizontal OB region is clamped.

  In the imaging apparatus having such a configuration, as shown in FIG. 2, a horizontal synchronization signal, a sensor output signal, and an OB clamp pulse are output during one frame period indicated by the vertical synchronization signal. Here, the sensor output signal is an image pickup signal from the image pickup element 101, and includes a sensor output signal corresponding to the vertical OB region, a sensor output signal corresponding to the horizontal OB region, and a sensor output signal corresponding to the effective pixel region 1. .

  Of the sensor output signals corresponding to the vertical OB region, the signals VOB0 to VOB8 output over the vertical OB clamp period are clamped according to the vertical OB clamp pulse so that the level thereof becomes the OB clamp level L1. . A VOB clamp level sampling pulse is output to the signal VOB9, and the signal VOB9 is output without being clamped over a period S105 indicated by the VOB clamp level sampling pulse. Here, the period S105 indicated by the VOB clamp level sampling pulse is the same period as the horizontal OB part period (HOB part period) S103.

  Thus, the signal output without being clamped by the clamp circuit 103 is input to the clamp voltage generation circuit 107. As a result, the level of the signal output without being clamped by the clamp circuit 103 is set to the OB clamp level L2 in the horizontal OB section period (HOB section period) S103 (see FIG. 3) of the horizontal OB clamp period. Become. Therefore, even when the image sensor 101 having both the vertical OB area and the horizontal OB area is used, it is possible to suppress level fluctuation due to the influence of dark shading as in the prior art. As a result, even when dark current is large, the appearance of vertical shading can be suppressed, and the OB level of the imaging signal input to the signal processing circuit 108 can be held constant.

  In the present embodiment, the signal VOB9 is not clamped over the period S105 indicated by this VOB clamp level sampling pulse. Instead, it is also possible to use a configuration in which a HOB clamp level sampling pulse is output and a signal corresponding to the horizontal OB area is sampled in the first period of the horizontal OB section period (HOB section period) of the horizontal OB clamp period. It is.

1 is a block diagram illustrating a configuration of main parts of an imaging apparatus according to an embodiment of the present invention. 3 is a timing chart showing a clamping operation when there is dark horizontal shading in the imaging apparatus of FIG. 1. 3 is a timing chart of an OB clamp pulse by the clamp pulse generation circuit 106 of FIG. It is a block diagram which shows the principal part structure of the imaging device using the conventional digital feedback system. It is a figure which shows typically the structure of the imaging surface in the image pick-up element of FIG. It is a timing chart which shows the output timing of various signals in an imaging device. It is a timing chart which shows a clamp operation when dark current is large. It is a figure which shows dark horizontal shading typically. It is a timing chart which shows a clamp operation in case there is dark horizontal shading. It is a figure which shows typically the image obtained when there exists darkness horizontal shading.

Explanation of symbols

101 Image sensor 103 Clamp circuit 106 Clamp pulse generation circuit 107 Clamp voltage generation circuit

Claims (4)

An image pickup device having a vertical optical black region and a horizontal optical black region, a clamp circuit for clamping an image pickup signal output from the image pickup device according to a clamp voltage according to a period designated by a clamp period signal, and the clamp In an imaging apparatus comprising: a clamp period signal generation circuit that generates a period signal; and a clamp voltage generation circuit that generates the clamp voltage based on an output of the clamp circuit;
The clamp period signal generation circuit includes the vertical optical black area between a vertical clamp period of an imaging signal corresponding to the vertical optical black area and a horizontal clamp period of an imaging signal corresponding to the horizontal optical black area. Generate a sampling period signal that indicates a period for sampling without clamping the imaging signal corresponding to
The image pickup apparatus, wherein the clamp voltage generation circuit generates a clamp voltage in the horizontal clamp period based on an image pickup signal output without being clamped according to the sampling period signal from the clamp circuit. An image pickup device having a vertical optical black region and a horizontal optical black region, a clamp circuit for clamping an image pickup signal output from the image pickup device according to a clamp voltage according to a period designated by a clamp period signal, and the clamp In an imaging apparatus comprising: a clamp period signal generation circuit that generates a period signal; and a clamp voltage generation circuit that generates the clamp voltage based on an output of the clamp circuit;
The clamp period signal generation circuit includes the horizontal optical black area between a vertical clamp period of an imaging signal corresponding to the vertical optical black area and a horizontal clamp period of an imaging signal corresponding to the horizontal optical black area. Generate a sampling period signal that indicates a period for sampling without clamping the imaging signal corresponding to
The image pickup apparatus, wherein the clamp voltage generation circuit generates a clamp voltage in the horizontal clamp period based on an image pickup signal output without being clamped according to the sampling period signal from the clamp circuit. An image pickup device having a vertical optical black region and a horizontal optical black region, a clamp circuit for clamping an image pickup signal output from the image pickup device according to a clamp voltage according to a period designated by a clamp period signal, and the clamp In an imaging method of an imaging apparatus, comprising: a clamp period signal generation circuit that generates a period signal; and a clamp voltage generation circuit that generates the clamp voltage based on an output of the clamp circuit.
The vertical optical black region between the vertical clamp period of the imaging signal corresponding to the vertical optical black region and the horizontal clamp period of the imaging signal corresponding to the horizontal optical black region by the clamp period signal generation circuit. Generate a sampling period signal that indicates a period for sampling without clamping the imaging signal corresponding to
An image pickup method, wherein the clamp voltage generation circuit generates a clamp voltage in the horizontal clamp period based on an image pickup signal output from the clamp circuit without being clamped according to the sampling period signal. An image pickup device having a vertical optical black region and a horizontal optical black region, a clamp circuit for clamping an image pickup signal output from the image pickup device according to a clamp voltage according to a period designated by a clamp period signal, and the clamp In an imaging method of an imaging apparatus, comprising: a clamp period signal generation circuit that generates a period signal; and a clamp voltage generation circuit that generates the clamp voltage based on an output of the clamp circuit.
The horizontal optical black region between the vertical clamp period of the imaging signal corresponding to the vertical optical black region and the horizontal clamp period of the imaging signal corresponding to the horizontal optical black region by the clamp period signal generation circuit. Generate a sampling period signal that indicates a period for sampling without clamping the imaging signal corresponding to
An image pickup method, wherein the clamp voltage generation circuit generates a clamp voltage in the horizontal clamp period based on an image pickup signal output from the clamp circuit without being clamped according to the sampling period signal.

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