JP2003163831A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus having a wide dynamic range and capable of photographing a sharp image with less blurring in the image. <P>SOLUTION: The imaging apparatus uses an imaging device for providing a progressive output to compose a high-speed shutter image subjected to exposure control by an electronic shutter with a low-speed shutter image subjected to exposure control by a mechanical shutter thereby producing a video signal with a wide dynamic range. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup device, and more particularly to an image pickup device suitable for high resolution and wide dynamic range.

[0002]

2. Description of the Related Art In a conventional image pickup apparatus using an image pickup device such as a CCD (Charge Coupled Device), expansion of the dynamic range is an important issue. The dynamic range mentioned here is a range of luminance levels in an input video signal at the time of image pickup, and a wide dynamic range means that it is possible to image from a low luminance part to a high luminance part. In this sense, one of the methods for expanding the dynamic range is to shorten the exposure time and make it difficult for the CCD to saturate with respect to a high-luminance input image signal. However, when the exposure time is shortened in this way, there is a problem that the amount of signal in the low-luminance portion decreases and the S / N becomes worse.

Therefore, a method has been proposed in which a total of two images, a high-speed shutter image and a low-speed shutter image, are taken by changing the shutter speed, and these images are combined. Regarding such an imaging device, for example, Japanese Patent Laid-Open No. 2001-016499
It is described in Japanese Patent Publication No. This image pickup device prevents saturation of a high-luminance portion and combines S / N of a low-luminance portion by synthesizing both images using a high-speed shutter image with a wide dynamic range and a low-speed shutter image with good S / N. The purpose is to prevent the decrease of N.

[0004]

When two images are combined as described in the above publication, the timings at which these images are picked up are generally deviated by a fixed time. Therefore, when the subject moves, there is a problem that blurring occurs in the composite image.

If the exposure interval when capturing these two images is sufficiently short with respect to the movement of the subject on the image capturing screen, there is no practical problem. When imaging at field intervals of television signals (1 / 60th of a second in the case of the NTSC system), for example, when the high-speed shutter has a sufficiently high shutter speed relative to 1/60 second and the low-speed shutter has 1/60 second, the average The exposure interval is 1/120 second. here,
As an example of the shooting condition, it is assumed that a distance of 5 m before the right and left of the screen is shot. In this case, an object moving at a speed of 2 m per second will cross the screen in 5 seconds. At this time, 1/1
The distance traveled in 20 seconds is about 1.7 cm. Therefore, if the object is sufficiently larger than 1.7 cm, such a deviation can be tolerated. Further, depending on the resolution of the CCD, in the case of a VGA size CCD having an image size of 640 × 480, the above movement is about 2 pixels at most. As described above, when shooting a moving object that moves at a low speed to some extent or a walking person, this is not a big problem in many scenes.

On the other hand, as the resolution of CCDs has increased, 100
So-called megapixel CCD with over 10,000 pixels
Has become commonplace. In such a CCD, the time required to read the exposed signal increases in proportion to the number of pixels, assuming that the reading time per pixel is constant. When the wide dynamic range imaging described above is performed using such a CCD, the exposure interval between the high speed image and the low speed image becomes large.

Now, consider a CCD having twice the number of pixels both horizontally and vertically with respect to this CCD. The CCD is assumed to be an interline type CCD. In this case, the time required to read the signal exposed by the CCD as described above is four times as long. In the example described above, the exposure interval is 1/60
It was seconds. Here, it is assumed that the low-speed shutter image is captured at a shutter speed of 1/60 second, and the high-speed shutter image is captured at a sufficiently high shutter speed. At this time, it takes four times 1/60 seconds, that is, 1/15 second, to read the accumulated signal in all the pixels. In this case, the exposure interval is 7/120 seconds, and the shutter interval is significantly increased as compared with the case where the number of pixels is low.

As described above, when a high-resolution CCD is used, for example, it is assumed that an image is taken at a distance of 5 m before the left and right sides of the screen. In this case, the distance moved in 7/120 seconds is about 12 cm. The width of a person is 20-30
If it is about cm, the image is blurred and the resolution of a moving object is significantly reduced. As described above, when a high-resolution CCD is used and the image synthesizing process is applied for widening the dynamic range described above, there is a problem that a blur of the image occurs and a clear image cannot be captured.

Therefore, an object of the present invention is to provide an image pickup apparatus capable of taking a clear image.

[0010]

In order to solve the above-mentioned problems, the present invention combines a high-speed shutter image whose exposure is controlled by an electronic shutter and a low-speed shutter image whose exposure is controlled by a mechanical shutter to synthesize a video signal with a wide dynamic range. To generate.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 is a block diagram showing an image pickup apparatus according to an embodiment of the present invention. Reference numeral 10 is a lens, 11 is a mechanical shutter, and 12 is a CCD. Reference numeral 13 is an A / D conversion circuit, 14 is a YC processing circuit for generating a luminance signal Y and a color difference signal C from a CCD output signal after A / D conversion, and 15 is a memory for storing an image signal. Reference numeral 16 denotes a synthesis processing circuit that synthesizes the image signal stored in the memory 15 and the image signal output by the YC processing circuit 14 to generate a synthetic image. Reference numeral 17 is a control circuit. 18 is a drive circuit, C
A drive pulse is supplied to the CD 12 to drive it, or a drive pulse is supplied to the mechanical shutter 11 to open and close it.

Next, the operation of the image pickup apparatus according to this embodiment will be described. The light incident through the lens 10 is
An image is formed on the light receiving surface of the CCD 12. The CCD 12 is a progressive readout type interline CCD,
The formed optical signal is photoelectrically converted and a video signal is output.

Details of the CCD 12 will be described with reference to FIG. FIG. 2 is a diagram showing the configuration of the CCD 12. Reference numeral 21 denotes a pixel that performs photoelectric conversion, and a plurality of pixels are vertically and horizontally arranged two-dimensionally. Reference numeral 20 denotes a vertical transfer unit that transfers the signal accumulated in each pixel in the vertical direction. A horizontal transfer unit 23 transfers the signal accumulated in each pixel in the horizontal direction. 22 is an output amplifier. The transfer of the signal charge from each pixel to the vertical transfer unit 20 is performed simultaneously for all pixels. The transferred signal charges are transferred to the horizontal transfer unit 23 and then output via the output amplifier 22.

The CCD 12 has a so-called electronic shutter function of resetting the signal charges accumulated in each pixel all at once. With this electronic shutter function, the time for accumulating signal charges in each pixel, that is, the shutter speed can be changed. Also, this CCD 12
Is for progressive reading in which the signals accumulated in all pixels are sequentially read for each horizontal line.

In this embodiment, the exposure time is changed to 2
A single image is taken and then combined to expand the dynamic range. A method of controlling the exposure time of the CCD 12 by the control circuit 16 will be described.

FIG. 3 is a signal waveform diagram showing the photographing timing of a wide dynamic range image. Reference numeral 30 denotes a vertical synchronizing signal, and 31 denotes a signal amount accumulated in the pixels of the CCD 12. Reference numeral 32 is an output signal waveform of the CCD 12.
In the present embodiment, an electronic shutter function, as described below, is provided to prevent the shooting interval between two consecutive images from being opened.
The mechanical shutter 11 is also used.

At time T0, the electronic shutter is closed and the signal 31A accumulated before T0 is reset. This reset operation is performed by setting the electronic shutter pulse 33, which is normally low level at time T0, to high level. By superposing the electronic shutter pulse 33 on the substrate voltage of the CCD 12, the electric charge accumulated in the pixel 21 (FIG. 2) is reset. Therefore, the signal waveform 3 in FIG.
At 1A, the increasing signal with time goes to zero at T0.

Time T1-T0 from the time T0 when the pixel 21 is reset to the time T1 when the accumulated signal 31B is read out.
Corresponds to the shutter speed of a high-speed image. The high-speed shutter image whose signals have been accumulated until time T1 is transferred from the pixel 21 (FIG. 2) to the vertical transfer unit 20 at time T1. Time T
From 1 onward, time T3 which is the next signal read timing
During the scanning period up to, the CCD 12 outputs a high-speed shutter image for each line sequentially from the horizontal transfer unit. In FIG. 3, 32B is an output signal waveform of a high speed image.

After exposing the high speed shutter image, the low speed shutter image is exposed. Reference numeral 31C in FIG. 3 indicates the signal accumulation amount in the CCD of the low-speed shutter image. The shutter speed of the low-speed shutter image is the time from the time T1 when the accumulated signal 31B of the high-speed shutter image is read to the exposure end time T2 of the low-speed shutter image, that is, T.
2-T1. Here, the exposure of the low-speed shutter image,
The process is continued after the exposure end time T1 of the high-speed shutter image. As a result, the shutter interval between the high speed shutter and the low speed shutter does not increase, and an image with less blur can be generated.

However, an electronic shutter cannot be used to expose from T1 to T2. this is,
This is because the electronic shutter resets the charge accumulated in the pixel and cannot retain the charge accumulated until T2.

Therefore, in order to set the end time of the low speed shutter, the mechanical shutter 11 (FIG. 1) is used.
The mechanical shutter 11 is open at time T1 when the exposure of the low speed shutter image is started. Then, at time T2 when the exposure is stopped, the mechanical shutter 11 is closed, thereby stopping the exposure. To open and close such a mechanical shutter 11, as shown in FIG. 3, a mechanical shutter pulse 34 is supplied to the mechanical shutter 11 (FIG. 1) with a drive pulse having a low level before time T2 and a high level after time T2. It is realized in. The mechanical shutter 11 includes a drive mechanism such as a motor (not shown) and instantaneously shields light by a drive pulse indicated by 34 in FIG. The exposure time of the low-speed shutter image is controlled to be T2-T1, and this low-speed shutter image is transferred from the pixel to the vertical transfer unit at T3, and then T3.
It is output from the CCD during the subsequent scanning period. In FIG. 3, 32C is the output signal waveform of the low speed image.

As described above, in this embodiment, the electronic shutter function is used when capturing a high-speed shutter image, and the mechanical shutter 1 is used when capturing a low-speed shutter image.
Control is performed so that 1 is used.

As described above, CC in FIG.
At D12, the high-speed shutter image and the low-speed shutter image are alternately output. After the A / D conversion circuit 13 performs A / D conversion on this, the YC processing circuit 14 generates a luminance signal Y and a color difference signal C for each of the high-speed shutter image and the low-speed shutter image. The high-speed shutter image is input to the memory 15 and combined with the low-speed shutter image output from the YC processing circuit 14 in the combination processing circuit 16.

The series of processes described above is performed by the control circuit 17 controlling the drive circuit 18, the YC processing circuit 14, and the memory 15 at a predetermined timing. The control circuit 17 can be usually realized by a microcomputer and software that describes the control contents thereof.

The combining processing circuit 16 adds the high speed shutter image and the low speed shutter image at a predetermined ratio, or selects either the high speed shutter image or the low speed shutter image to perform the combining process of both images. In this way, the ratio of the low-speed shutter image is increased in the part having a relatively low brightness level in the image, and the ratio of the high-speed shutter image is increased in the part having a high brightness level. By such a combining process, it is possible to generate a reproduced image in which there is no whiteout due to saturation in the high-luminance portion and which has a good S / N in the low-luminance portion.

In the embodiment described above, the mechanical shutter 11 is used to control the exposure time of the low speed shutter image. However, as long as it has a similar light blocking effect, it is not limited to the mechanical shutter, and other light blocking means such as a liquid crystal shutter using liquid crystal may be used. When a liquid crystal shutter is used, it is advantageous in terms of service life because it does not have the mechanical wear of a mechanical shutter.

In the description of the above embodiment, FIG.
In the timing waveform of, the low-speed shutter image, the high-speed shutter image, and the timing for capturing one image each,
It is also possible to perform this continuously and apply it to a high-resolution moving image.

As described above, in the image pickup apparatus according to the embodiment of the present invention, it is possible to shoot a clear image with high resolution, a wide dynamic range, and little image blur.

[0029]

According to the present invention, it is possible to provide an image pickup apparatus capable of taking a clear image.

[Brief description of drawings]

FIG. 1 is a block diagram showing an image pickup apparatus according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a CCD image sensor according to an embodiment of the present invention.

FIG. 3 is a signal waveform diagram showing image pickup timing in one embodiment of the present invention.

[Explanation of symbols]

11 ... Mechanical shutter 12 ... CCD 14 ... YC processing circuit 15 ... Memory 16 ... Synthesis processing circuit 17 ... Control circuit 20 ... Vertical transfer unit 21 ... Pixel 22 ... Output amplifier 33 ... Electronic shutter pulse 34 ... Mechanical shutter pulse

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/19 H04N 5/335 Q 5C051 5/335 1/04 103Z 5C072 (72) Inventor Tsutomu Usui Kanagawa F-term (Reference) 2H002 CC00 CC01 DB02 DB19 FB23 GA35 JA07 JA08 ZA01 2H081 BB15 BB21 5B047 AB04 BA03 BB04 BC05 BC06 CA06 CA17 DB01 DC20 5C022 AC42 AC52 AC52 AC52 292, Yoshida-cho, Totsuka-ku, Yokohama AC74 5C024 CX47 CX52 CX53 CX54 CX56 DX01 GY04 HX23 HX57 5C051 AA01 BA02 DA06 DB01 DB07 DB22 DB26 DC03 DC04 DC07 DE07 DE11 DE26 EA01 5C072 AA01 BA16 DA13 EA05 FA03 FB19 FB23

Claims (4)

[Claims] 1. A photoelectric conversion element that stores a pixel signal, an image pickup element that outputs the pixel signal stored in the photoelectric conversion element, and a pixel signal stored in the photoelectric conversion element are reset.
An electronic shutter means for controlling the exposure time, a light-shielding means for shielding the light incident on the photoelectric conversion element and controlling the exposure time, and a first exposure time controlled by the electronic shutter means,
An image pickup apparatus comprising: a switching unit that switches a second exposure time different from the first exposure time so as to be controlled by the light shielding unit. 2. The image pickup apparatus according to claim 1, wherein the first exposure time is shorter than the second exposure time. 3. A plurality of photoelectric conversion elements arranged horizontally and vertically, a vertical transfer section for vertically transferring pixel signals stored in the plurality of photoelectric conversion elements, and a horizontal transfer section connected to the vertical transfer section. A horizontal transfer unit that transfers and outputs a pixel signal in the direction, an electronic shutter unit that controls the exposure time by resetting the pixel signals accumulated in the plurality of photoelectric conversion elements at arbitrary timing, and the photoelectric conversion element A light-blocking unit for blocking the light incident on the light source and varying the exposure time, an image sensor for progressively outputting the signal accumulated in the photoelectric conversion element, and the image sensor for the first image and the first image having different exposure times. Two
Control means for controlling the electronic shutter means and the light-shielding means so as to alternately output the images, and image synthesizing means for synthesizing the first image and the second image to generate a synthetic image. An imaging device, which is provided. 4. The exposure time of the first image is shorter than the exposure time of the second image, and the exposure time of the first image is controlled by the electronic shutter means to expose the second image. 4. The time is controlled by the light shielding means.
The imaging device according to.