JP2005303519A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of recording low-noise image data taken at a high sensitivity. <P>SOLUTION: The apparatus records still image data obtained by photographing still images in a pixel addition output mode for outputting image signals composed of added pixel values of a plurality of adjacent pixels. Regardless of a still image or a moving picture, the apparatus records image data obtained by photographing, after setting the pixel addition output mode for outputting image signals composed of added pixel values of a plurality of adjacent pixels when being set to a low luminance. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an imaging apparatus.

In an imaging apparatus using a CCD image sensor as a photoelectric conversion element, such as a digital camera, when photographing a subject in a dark environment, each pixel value of the CCD image sensor is amplified by an auto gain control circuit or the like. . However, if the gain value applied there is set to an unlimited large value, even the noise component is amplified thereby, and the resulting image is an image with significantly deteriorated image quality.
This situation is shown in FIG. A noise component generated in the output image signal of one pixel of the CCD image pickup device 1 is defined as noise 1. A noise component generated in the transfer from the CCD image pickup device 1 to the signal processing circuit 2 is defined as noise 2. As a result of gain increase by the auto gain control circuit (AGC) of the signal processing circuit 2, even noise 1 and noise 2 are amplified and image quality deteriorates.

On the other hand, in order to suppress image quality degradation due to noise, it is considered to add pixel values of adjacent pixels (see paragraph 0003 of Patent Document 1, claim 1 of Patent Document 2, etc.). In Patent Document 1, the configuration described above is called an individual output mode, and this is called an addition output mode. In the addition output mode, it is possible to obtain a large signal component without amplifying the noise component by adding the pixel values of adjacent pixels.
This situation is shown in FIG. The noise component generated in the output image signal of one pixel of the CCD image pickup device 1 is assumed to be noise 1 (not shown in FIG. 2) as described above. For example, when the CCD image pickup device 1 adds pixel values of four adjacent pixels, noise 1 is also added for four pixels. As shown in FIG. 2, the noise component after the addition is defined as noise 1 ′. The noise component generated in the transfer from the CCD image pickup device 1 to the signal processing circuit 2 is referred to as noise 2 as described above. A sufficient signal level is obtained by the addition output of the CCD image pickup device 1. Therefore, even if the signal level is not amplified by the auto gain control circuit (AGC) of the signal processing circuit 2, it is possible to obtain the same signal level as that of the individual output mode described in FIG. 3 (that is, to obtain the same sensitivity). Yes, noise can be suppressed.

In the invention described in Patent Document 1, the image data generated in the addition output mode is used for white balance adjustment, exposure control, and autofocus control when the luminance is low (see Patent Document Paragraph 0120, etc.) The individual output mode was applied during the main photographing for generating photographed image data to be recorded (see paragraph 0121 of the same document).
In the invention described in Patent Document 2, the addition output mode (“addition readout mode” in Patent Document 2) is applied during pre-shooting (preliminary measurement) for a dark subject in moving image shooting to shorten the pre-measurement. (See paragraph 0092 etc. in the same document).
Conventionally, some digital cameras that apply the individual output mode to still image shooting use a technique that applies the addition output mode to movie shooting to record as a frame and keep the frame rate as high as possible. There is something.
JP 2003-319407 A JP 2003-189183 A

In the invention described in Patent Document 1, the individual output mode is applied at the time of main photographing for generating photographed image data to be recorded on the memory card, and the image data generated by the addition output mode is recorded on the memory card and used. There was nothing to do (see paragraph 0121 of the same document).
Further, even in the invention described in Patent Document 2, it is only possible to shorten the preliminary measurement, and Patent Document 2 does not propose applying the individual output mode at the time of actual photographing.
However, as described above with reference to FIGS. 2 and 3, the problem that the image quality deteriorates due to the gain increase at the time of low luminance is also the same in the main photographing that captures an image for recording. There is no change in what happens.
On the other hand, it is possible to obtain a sufficient signal level by increasing the exposure time without increasing the gain, but in this case, there is a problem that deterioration of the image quality cannot be avoided if the limit that causes the influence of camera shake is exceeded. This is also the limit of the longest exposure time.
Also, the use of the conventional additive output mode in movie shooting is only used to maintain and improve the frame rate, and the image data is recorded through the additive output mode of the same number of output pixels regardless of the luminance of the subject. Therefore, the relative image degradation at the time of low luminance is still exposed unless there is any solution.

The present invention has been made in view of the above problems in the prior art, and provides an imaging apparatus capable of recording low-noise image data captured with high sensitivity without causing a cause of camera shake due to a prolonged exposure time. This is the issue.

The invention according to claim 1 for solving the above-described problem is an image sensor having an addition output mode for outputting a pixel signal obtained by adding pixel values of a plurality of adjacent pixels;
An image pickup apparatus comprising recording means for recording still image data obtained by taking a still image with the image pickup device in the addition output mode.

Therefore, according to the first aspect of the present invention, since pixel values of a plurality of adjacent pixels are added to obtain a large pixel value, an increase in noise due to gain increase is avoided, and a low noise still image image is obtained. Data can be recorded. Also, since the pixel values of a plurality of adjacent pixels are added to obtain a large pixel value, a sufficient pixel value can be obtained while avoiding long-term exposure that causes camera shake.
Here, the recording means should not be interpreted in a broad sense including a primary buffer used for signal processing. The recording means in the present invention is for use later by the user. The later arbitrary use of the user corresponds to image display / reproduction based on the instruction of the user at any time, output to an external device, arbitrary use on the external device, and the like. For example, image processing, image display, transmission to other terminals, printing, etc. are applicable to arbitrary use with external devices. Secondary use on printed materials and secondary use with other terminals are also possible. This corresponds to the user's arbitrary use later. The output to the external device includes not only communication but also output via a removable recording medium such as a memory card.

The invention according to claim 2 has, as output modes, an image pickup device having an addition output mode for outputting a pixel signal formed by adding pixel values of a plurality of adjacent pixels and an all-pixel output mode for outputting a pixel signal for each pixel. When,
It is determined whether or not the luminance of the image signal output by the image sensor is equal to or lower than a predetermined reference luminance. When the luminance is determined to be equal to or lower than the reference luminance, the image sensor is set to the addition output mode and is determined not to be lower than the reference luminance. Mode setting means for setting the image sensor to the all-pixel output mode;
An image pickup apparatus comprising: recording means for recording image data obtained by photographing with the image sensor in the output mode set by the mode setting means.

Therefore, according to the invention described in claim 2, since a large pixel value is obtained by adding pixel values of a plurality of adjacent pixels at low luminance, an increase in noise due to gain increase at low luminance is avoided, Low noise image data can be recorded. In addition, the pixel values of a plurality of adjacent pixels are added at low luminance to obtain a large pixel value, so that sufficient pixel values can be obtained while avoiding long-term exposure that causes camera shake even at low luminance. It is done.
Note that the all-pixel output mode is not necessarily required to output the pixel signal of each pixel for all the pixels of the image sensor, as long as it outputs the pixel signal of each pixel for the area necessary for imaging. It is sufficient to output a pixel signal of each pixel for a part of the area.

  According to a third aspect of the present invention, in the image pickup apparatus according to the second aspect, the image data is image data for still images obtained by taking a still image.

Therefore, according to the third aspect of the invention, it is possible to record still image data with high sensitivity and low noise at low luminance.

  According to a fourth aspect of the invention, there is provided the imaging apparatus according to any one of the first to third aspects, wherein the recording means records on a detachable recording medium.

Therefore, according to the fourth aspect of the present invention, it is possible to transfer the low-noise image data to an external device via a detachable recording medium without using a communication means, and the user can use it for distribution to others. .

  A fifth aspect of the present invention is the imaging apparatus according to any one of the first to fourth aspects, further comprising an interface for externally outputting the data recorded in the recording unit.

Therefore, according to the fifth aspect of the present invention, it is possible to output low-noise image data to an external device and further transfer data without requiring the recording medium to be attached or detached.

  According to a sixth aspect of the present invention, the image data obtained by photographing with the image sensor in the addition output mode is complemented by resizing, and the imaging device according to any one of the first to fifth aspects It is.

Therefore, according to the sixth aspect of the present invention, the image size can be supplemented by the amount corresponding to the decrease in the number of pixels in the addition output mode.

  The invention according to claim 7 is characterized in that a code for identifying that the image is captured in the addition output mode is attached to the image data obtained by capturing with the imaging element in the addition output mode. The imaging apparatus according to any one of Items 6.

Therefore, according to the seventh aspect of the present invention, appropriate processing (for example, resize and reversible resize inverse transform) based on the fact that the image was taken in the addition output mode (particularly, the reduction in the number of pixels) in any later use by the user. Can do.
For example, the image obtained in the addition output mode is recorded on the recording unit of the apparatus without resize complementation, and the user can use the apparatus or the external device to supplement the resizing for later use by the user. While suppressing the memory consumption, it is possible to prevent inconveniences such as deterioration of the feeling of use due to the ununiformity of the image size.

  As described above, according to the present invention, low noise image data picked up with high sensitivity can be recorded without causing the cause of camera shake due to a long exposure time, and the low noise image data can be used later for any use by the user. There is an effect that it can be provided.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The following is one embodiment of the present invention and does not limit the present invention.

  As shown in FIG. 2 (a), the imaging apparatus of this embodiment includes a CCD imaging device 1, an analog signal processing circuit 2, an A / D converter 3, a CPU 4, a timing generator 5, and digital signal processing. A circuit 6, a buffer 7, a compression circuit 8, a memory card reader / writer 9, a resizing circuit 10, an external interface 11, and an operation unit 12 are provided.

The CCD image pickup device 1 has a pixel array in which a plurality of pixels are arranged. For the sake of explanation, a pixel array of horizontal 1600 pixels × vertical 1200 pixels is assumed.
The CCD imaging device 1 reads out a pixel signal from the pixel array and outputs a pixel signal obtained by adding pixel values of a plurality of adjacent pixels (here, 2 × 2 pixels), and a pixel addition output mode. The driving is performed in two modes of an all-pixel output mode in which a pixel signal for each pixel is output for all the pixels.
Therefore, the CCD imaging device 1 outputs image data composed of pixel signals of horizontal 1600 pixels × vertical 1200 pixels in the all-pixel output mode. In the pixel addition output mode, the CCD image sensor 1 outputs image data composed of pixel signals of horizontal 800 pixels × vertical 600 pixels. In this pixel addition output mode, high sensitivity and low noise are obtained even with the same exposure time.
Switching between the two modes is performed by the CPU 4 switching the clock signal of the timing generator 5 that generates a drive signal to be given to the CCD image pickup device 1.
The analog signal processing circuit 2 includes a correlated double sampling circuit (CDS) and an auto gain control circuit (AGC).
The CPU 4 takes in the image data output from the CCD image pickup device 1 and subjected to signal processing and A / D conversion by the analog signal processing circuit 2, and performs determination and control described below.

FIG. 1 shows an example of a flowchart of a program executed on the CPU 4.
First, as a premise, this apparatus is set to the still image shooting mode.
Thereafter, when a release button (not shown) included in the operation unit 12 is half-pressed, the first switch S1 is turned on (step T1), and automatic focusing control is performed based on the image signal obtained from the CCD image sensor 1. (AF), exposure calculation (AE), and white balance calculation (WB) are executed (step T2).
Next, when a release button (not shown) is fully pressed, the second switch S2 is turned ON (step T3), and based on the image signal obtained from the CCD image sensor 1, a predetermined area (for example, the center) ) Is less than or equal to a predetermined reference luminance (step T4).

If NO in step T4, the clock signal of the timing generator 5 is switched to set the CCD image pickup device 1 to the all-pixel output mode (step T8).
Subsequently, the image signal output from the CCD imaging device 1 is subjected to noise reduction processing by the CDS circuit of the analog signal processing circuit 2, gain adjusted by the AGC circuit, and further converted to, for example, an 8-bit digital image signal by the A / D converter 3. This is captured (step T9) and a still image is taken. Image data obtained by photographing is subjected to predetermined image processing such as white balance and γ correction by the digital signal processing circuit 6, and then temporarily stored in the buffer 7.
The image data stored in the buffer 7 is read out to the compression circuit 8 and compressed and converted into a predetermined file size by a standardized compression method such as JPEG (step T10), and the obtained image file is converted into a memory card reader / writer. 9 is recorded in the memory card 13.
The above is the control content of the all-pixel output mode in the still image shooting mode.

If YES in step T4, the clock signal of the timing generator 5 is switched to set the CCD image pickup device 1 to the pixel addition output mode (step T5).
Subsequently, the image signal of horizontal 800 pixels × vertical 600 pixels output from the CCD image pickup device 1 is subjected to noise reduction processing by the CDS circuit of the analog signal processing circuit 2, gain adjusted by the AGC circuit, and further by the A / D converter 3. For example, it is converted into an 8-bit digital image signal, captured (step T9), and a still image is taken. Image data obtained by photographing is subjected to predetermined image processing such as white balance and γ correction by the digital signal processing circuit 6, and then temporarily stored in the buffer 7.
The image data of horizontal 800 pixels × vertical 600 pixels stored in the buffer 7 is read out to the resizing circuit 10, and is expanded to the same multiple as the number of pixels 4 added by the CCD image sensor 1, that is, expanded to 4 times to output all pixels. It is converted to the same image size of horizontal 1600 pixels x vertical 1200 pixels as the mode. In this resizing complementation, in order to improve image quality, an existing or future usable image processing technique that generates insufficient pixels in consideration of luminance values and color values of peripheral pixels may be applied. Resizing completion may not be performed. When resizing is not performed, the image data of horizontal 800 pixels × vertical 600 pixels stored in the buffer 7 is sent to the next processing by the compression circuit 8 without changing the processing by the resizing circuit 10. .

Next, the resized image data (image data not resized when not resized) is compressed and converted into a predetermined file size by a compression circuit 8 using a standardized compression method such as JPEG. (Step T10), and the obtained image file is recorded on the memory card 13 by controlling the memory card reader / writer 9. At this time, a code for identifying that the image is captured in the pixel addition output mode is written in the image file. At this time, information on the image size designated by the user may be added and written in the imaging apparatus capable of selecting the image size.
Note that when the present invention is applied to moving image shooting, a file format such as AVI or MPEG can be applied in the same manner.

  As the memory card reader / writer 9, a memory card reader / writer 9 that can detach the memory card 13 is used. Therefore, the user can use the image file recorded by taking out the memory card 13 from the apparatus.

  The external interface 11 is a connection port such as a USB, a communication modem, or a mounting portion thereof. Thus, the image file recorded by wired or wireless communication is output to the external device. The output of the image file to the external device is performed according to a command from the connected partner device or a command input via the operation unit 12. The command includes an identification code of an image file to be output among a plurality of recorded image files. Therefore, it is possible to select and output an arbitrary image file among the plurality of recorded image files.

By performing the resizing as described above, it is possible to prevent a problem that recording is performed with an image size (horizontal 800 pixels × vertical 600 pixels) different from the image size intended by the user (horizontal 1600 pixels × vertical 1200 pixels). . Further, in the later use, it is possible to prevent inconveniences such as deterioration of the feeling of use due to the ununiformity of the image size.
On the other hand, if the image data is recorded in the memory card 13 without complementing the resizing, there is an advantage that a storage capacity can be saved and a large number of images can be taken. In this case, a code (hereinafter referred to as “pixel addition code”) for identifying that the image was captured in the pixel addition output mode written in the image file can be used as follows.
That is, the image data of horizontal 1600 pixels × vertical 1200 pixels obtained in the all-pixel output mode and the image data of horizontal 800 pixels × vertical 600 pixels obtained in the pixel addition output mode are recorded in the memory card 13, and this apparatus Alternatively, when an image is reproduced by an external device such as a personal computer, it is effective to resize and reproduce the image that has been identified and added by the pixel addition code to 1600 horizontal pixels × 1200 vertical pixels. As a result, an image having a uniform size of 1600 horizontal pixels × 1200 vertical pixels can be displayed. The pixel addition code is information that can also indicate the contents of the image addition processing such as the number of pixels added and the adjacent direction.
In addition, when image data is read from the memory card 13 and transmitted from the apparatus to an external device such as a personal computer, the image added with the pixels identified by the pixel addition code is resized to 1600 horizontal pixels x 1200 vertical pixels. It is effective to send. As a result, it is possible to transmit image data of a uniform size of horizontal 1600 pixels × vertical 1200 pixels. In this case, even if the playback software of the external device is not provided with a function for complementing resizing, if the playback is performed as it is, an image can be displayed with a unified size of horizontal 1600 pixels × vertical 1200 pixels.
As described above, when image data is recorded on the memory card 13 without complementing the resizing, by using the pixel addition code, the memory consumption of the apparatus is suppressed and the feeling of use is deteriorated due to the ununiformity of the image size. Inconvenience can be prevented.

When the user can specify the image size, the image size that can be specified by the user may match the image size in the all-pixel output mode, but the image size that can be specified by the user matches the image size in the all-pixel output mode. You don't have to. For example, in an imaging device that has a maximum size of horizontal 1600 pixels × vertical 1200 pixels and can select the maximum size or horizontal 1200 pixels × vertical 960 pixels, if the user specifies horizontal 1200 pixels × vertical 960 pixels, all pixel output In the mode, image data of horizontal 1600 pixels × vertical 1200 pixels is generated and recorded in the memory card 13, while in the pixel addition output mode, the image data of horizontal 800 pixels × vertical 600 pixels stored in the buffer 7 as described above is stored. The resizing circuit 10 may supplement the resizing to horizontal 1200 pixels × vertical 960 pixels and record the result on the memory card 13. Of course, image data of horizontal 1200 pixels × vertical 960 pixels specified by the user may be generated and recorded in the memory card 13 even in the all-pixel output mode.
Further, it may be possible to select whether the memory card 13 is detachable or the external interface 11 is provided. Both may be provided as described above.

Now, in this embodiment, as shown in FIG. 2B, the noise component generated in the output image signal of one pixel of the CCD image pickup device 1 is referred to as noise 1 (not shown in FIG. 2, but shown in FIG. 3). . For example, when the CCD image pickup device 1 adds pixel values of four adjacent pixels, noise 1 is also added for four pixels. Further, as shown in FIG. 2, the noise component after the addition is defined as noise 1 ′. A noise component generated in the transfer from the CCD image pickup device 1 to the analog signal processing circuit 2 is defined as noise 2.
According to this embodiment, a sufficient signal level is obtained by the pixel addition output of the CCD image pickup device 1. Therefore, even if the pixel value is not amplified by the auto gain control circuit (AGC) of the analog signal processing circuit 2, it is possible to obtain the same signal level as that of the individual output mode described in FIG. 3 (that is, the same sensitivity). Noise) can be suppressed. Even in the pixel addition output mode, the pixel value may be amplified by the auto gain control circuit (AGC) according to the input value, but large amplification is not required and noise can be suppressed.

In the above embodiment, a case where a horizontal 1600 pixel × vertical 1200 pixel CCD is used, and in the pixel addition output mode, 2 × 2 4 pixels are added to output horizontal 800 pixel × vertical 600 pixel image data. Although described as an example, these numerical values are arbitrary, and the adjacent direction of the pixel to be added may be only in the horizontal direction or only in the vertical direction.
Further, although step T4 for determining the luminance is provided, this may not be provided for still image shooting, and all processing may be performed in the pixel addition output mode. In that case, high-sensitivity images can be captured without being separated by a predetermined reference luminance, and low-noise still image data can be recorded. Although the number of pixels of image data for still images decreases with respect to the number of pixels of CCD, a still image pickup device with high sensitivity and low noise can be provided.
The image file may be compressed as necessary.

While the present invention is applied to still image shooting, the present invention may not be applied to moving image shooting, for example, a conventional moving image shooting technique may be applied. For example, in the moving image shooting, an image signal output in the pixel addition output mode is always recorded by a standardized recording method such as AVI or MPEG regardless of luminance. In this case, the frame rate can be increased in order to reproduce a moving image with a more natural motion as the number of recording pixels decreases in the pixel addition output mode.

It is a flowchart in one Embodiment of this invention. FIG. 2 is a block diagram of a main part of an imaging apparatus according to an embodiment of the present invention (a) and an image diagram (b) showing a transition of a noise component in a pixel addition output mode. It is a block diagram (a) of an imaging device and an image diagram (b) showing a transition of noise components in the all-pixel output mode.

Claims (7)

An imaging device having an addition output mode for outputting a pixel signal obtained by adding pixel values of a plurality of adjacent pixels;
An image pickup apparatus comprising recording means for recording still image data obtained by taking a still image with the image pickup device in the addition output mode. As an output mode, an imaging device having an addition output mode for outputting a pixel signal obtained by adding pixel values of a plurality of adjacent pixels and an all-pixel output mode for outputting a pixel signal for each pixel;
It is determined whether or not the luminance of the image signal output by the image sensor is equal to or lower than a predetermined reference luminance. When the luminance is determined to be equal to or lower than the reference luminance, the image sensor is set to the addition output mode and is determined not to be lower than the reference luminance. Mode setting means for setting the image sensor to the all-pixel output mode;
An image pickup apparatus comprising: recording means for recording image data obtained by photographing with the image sensor in the output mode set by the mode setting means.   The imaging apparatus according to claim 2, wherein the image data is image data for a still image obtained by capturing a still image.   The imaging apparatus according to any one of claims 1 to 3, wherein the recording unit records on a detachable recording medium.   5. The imaging apparatus according to claim 1, further comprising an interface for outputting data recorded in the recording unit to the outside. 6.   The image pickup apparatus according to any one of claims 1 to 5, wherein image data obtained by shooting with the image pickup device in the addition output mode is complemented for resizing.   7. The code according to claim 1, wherein a code for identifying that the image is captured in the addition output mode is attached to the image data acquired by the imaging element in the addition output mode. 8. The imaging device described.

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