JP3796421B2 - Imaging apparatus and imaging method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to correction of noise component data included in an image signal captured by an imaging apparatus.
[0002]
[Prior art]
In a solid-state imaging device, it is known that noise is generated due to various factors in the process of signal processing. Among them, there are two known fixed pattern noises in solid-state image sensors: random uneven noise that produces an image that looks like frosted glass, and streak noise that is aligned vertically or horizontally. It has been.
[0003]
As a method for correcting these noises, a method using a circuit as shown in FIG. 9 has been conventionally used. That is, noise component data of the image sensor for one screen is stored in the frame memory 52 in advance. Then, when the image signal generated by the image sensor 51 is output to the process circuit 7, the noise component stored in the frame memory 52 is subtracted from the image signal by the subtracter 6 and output.
[0004]
[Problems to be solved by the invention]
However, in the above conventional example, the noise component data of the image sensor stored in the frame memory is fixed, and thus, for example, dark current uneven noise that changes according to a change in temperature is effectively removed. There was a problem that I could not.
Furthermore, in the above conventional example, even when it is not necessary to correct the image pickup signal, the correction is performed uniformly. In this case, the image quality is not improved but the image quality is deteriorated. was there.
[0006]
The present invention has been made to solve the above-described problems, and an object of the present invention is to enable appropriate noise correction according to the noise state at the time of shooting.
[0007]
[Means for Solving the Problems]
The imaging apparatus according to the present invention includes an imaging region that generates an image signal by photoelectric conversion, a light shielding unit that shields light from a subject to the imaging region, and the imaging region that is not shielded by the light shielding unit. A drive unit that performs a first operation of reading out the generated image signal, a second operation of reading out noise component data generated in the imaging region in a state where the image signal is shielded by the light shielding unit, and the second operation of the drive unit. The correction means for reading out the noise component data and correcting the image signal read out by the first operation, and when the subject brightness is low, the correction is performed by the correction means and the subject brightness is high. In this case, it has control means that does not perform the correction by the correction means.
In addition, the imaging apparatus of the present invention includes an imaging region that generates an image signal by photoelectric conversion, a light shielding unit that shields light from a subject to the imaging region, and the imaging in a state where the light shielding unit does not shield the light. A driving unit that performs a first operation of reading an image signal generated in the area, and a second operation of reading out noise component data generated in the imaging region in a state where the image signal is blocked by the light blocking unit; and the second of the driving unit. The correction means for reading the noise component data by the operation and correcting the image signal read by the first operation, and the control for performing the correction by the correction means in response to increasing the gain of the image signal Means.
The imaging method of the imaging device according to the present invention is an imaging method of an imaging device having an imaging region that generates an image signal by photoelectric conversion, the light shielding step of shielding light from a subject to the imaging region, and the light shielding step. Driving to perform a first operation for reading an image signal generated in the imaging region without being shielded by light and a second operation for reading out noise component data generated in the imaging region while being shielded by the light shielding step. A correction step of reading noise component data by the second operation of the driving step and correcting the image signal read out by the first operation, and the correction step when the luminance of the subject is low And a control step that does not perform the correction in the correction step when the luminance of the subject is high.
The imaging method of the imaging device of the present invention is an imaging method of an imaging device having an imaging region that generates an image signal by photoelectric conversion, the light shielding step of shielding light from a subject to the imaging region, A first operation for reading an image signal generated in the imaging region in a state where light is not shielded by the light shielding step, and a second operation for reading out noise component data generated in the imaging region while being shielded by the light shielding step. A driving step to perform, a correction step of reading out the noise component data by the second operation of the driving step, correcting the image signal read out by the first operation, and increasing the gain of the image signal And a control step for performing the correction in the correction step.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a solid-state imaging device of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram of a solid-state imaging device showing a first embodiment of the present invention. In FIG. 1, the parts denoted by the same reference numerals as those of the conventional solid-state imaging device shown in FIG. 9 indicate the same functional parts as those of the conventional one.
In the first embodiment, a signal line to which no photosensitive pixel is connected is provided in a part of the image sensor, and a signal obtained from this signal line is used as noise component data of the image sensor, thereby being influenced by the photosensitive pixel. The noise component in the image sensor can be surely removed without increasing the size of the entire apparatus.
[0014]
The image sensor 1 is driven by a driver 8. The driver 8 is driven by the drive pulse PDR generated from the synchronization signal generation circuit 9. When the output signal from the image pickup device 1 is switched by the switch 2 and the movable terminal 2a is switched to the fixed terminal A side, it is applied from the terminal A to the one end of the subtractor 6 as the image pickup output Y _S. When the movable terminal 2a is switched to the fixed terminal B side, the output signal from the image sensor 1 is input from the terminal B to the A / D converter 3 and stored in the line buffer 4 as digital noise component data. .
[0015]
This noise component data is D / A converted by the D / A converter 5 and input to the other end of the subtractor 6 as analog noise component data Y _N. Then, the noise component data Y _N is subtracted from the above-described imaging output Y _S to obtain a correction signal Y. The correction signal Y generated in this way is input to the process circuit 7, subjected to processing such as white clip and aperture correction, and output as a video signal Sv.
[0016]
FIG. 2 is a diagram showing a detailed configuration of the image sensor 1, and here, a MOS type image sensor is taken as an example. That is, one pixel is composed of a MOS-FET (MOS type field effect transistor) 11 and a photodiode 12. A predetermined number of pixels are regularly arranged in the horizontal direction and the vertical direction to form a photosensitive portion. The charges generated in the photosensitive portion are read out through the horizontal signal line 13 and the vertical signal line 14 connected to each pixel.
[0017]
This charge read operation will be described in more detail. First, in the vertical direction, an address signal ADR for designating a read line is input to the decoder 15, and the designated read line is transmitted to the vertical register 16. The horizontal lines 13 designated in this way are sequentially scanned according to the address signal ADR. Next, in the horizontal direction, signals of pixels connected to one horizontal line designated by the address signal ADR are sequentially output by the action of the horizontal register 17 through the vertical signal line 14.
[0018]
The present embodiment is characterized in that a dummy line 18 to which no photosensitive pixel is connected is provided at the uppermost portion of the horizontal line. The dummy line 18 is designated when capturing the fixed pattern noise in the vertical direction, which will be described later.
[0019]
Next, the overall operation of the solid-state imaging device of the present embodiment shown in FIG. 1 will be described in detail with reference to the timing chart of FIG.
[0020]
3A shows the vertical synchronization signal VD, and FIG. 3B shows the vertical blanking signal VB. First, when the timing enters a vertical blanking period as shown in FIG. 3B, the address signal ADR designates the dummy line 18 shown in FIG. 2 as shown in FIG. 3C. As described above, since no photosensitive pixel is connected to the dummy line 18, the signal output from the dummy line 18 is only a noise component and is used as fixed pattern noise of the image sensor 1.
[0021]
In the vertical blanking period, as shown in FIG. 3D, the switch signal PSW is given to the switch 2 so that the movable terminal 2a selects the fixed terminal B side. Thereby, the noise component data output from the image sensor 1 is input to the A / D converter 3. Further, the A / D converter pulse PCNT1 is turned on as shown in FIG. 3E, and the A / D converter 3 starts to operate. Thus, the noise component data for one horizontal line is A / D converted and stored in the line buffer 4 as a digital signal.
[0022]
Next, when the vertical blanking period ends and the effective period starts, the switch signal PSW is given to the switch 2 so that the movable terminal 2a selects the fixed terminal A side as shown in FIG. As a result, the imaging output Y _{S on} the effective line designated by the address signal ADR during this effective period is input to one end of the subtractor 6.
[0023]
Further, within this effective period, the D / A converter pulse PCNT2 for driving the D / A converter 5 is turned on as shown in FIG. 3 (f), and is stored in the line buffer 4 during the aforementioned vertical blanking period. The noise component data is converted into analog noise component data Y _N and input to the other end of the subtractor 6. In the subtractor 6, an operation of Y = Y _S −Y _N is performed, thereby obtaining a correction signal Y from which the fixed pattern noise component has been removed. Then, the correction signal Y is input to the process circuit 7, where a synchronization signal or the like is added and output as a video signal Sv.
[0024]
In the first embodiment described above, the case where the subtraction process in the subtractor 6 is performed using an analog signal has been described. However, it may be performed using a digital signal. FIG. 4 is a diagram showing a solid-state imaging apparatus as a second embodiment in which the subtraction process is digitally performed in this way. In FIG. 4, the same functional parts as those of the solid-state imaging device shown in FIG.
[0025]
In FIG. 4, the output signal from the image sensor 1 is A / D converted by the A / D converter 3 to be a digital signal. The output signal from the imaging device 1 is the imaging output or noise component data of the imaging device 1 that is switched and output at the operation timing as shown in FIGS. 3A to 3D, as in the above-described embodiment. .
[0026]
A / if D digital signal output from the converter 3 is that the imaging output of the image pickup device 1 and A / D conversion, the image pickup output Y _SD to one end of the subtracter 20 by the switching of the digital signal switch 19 As entered directly. Further, when the digital signal output from the A / D converter 3 is an A / D converted noise component data of the image sensor 1, this digital signal is input to the line buffer 4 by switching the switch 19 and temporarily. After being stored, it is input to the other end of the subtracter 20 as noise component data _YND .
[0027]
Then, the subtracter 20 and the noise component data Y _ND is subtracted from the above-described image pickup output Y _SD correction signal Y _D obtained. The correction signal Y _D is added with a synchronization signal or the like by the process circuit 7, then input to the D / A converter 5, converted into an analog signal, and output as a video signal Sv.
[0028]
In the first and second embodiments described above, the number of times of noise component data fetched from the dummy line 18 has not been described in detail, but this is not limited to one. For example, more accurate noise component data can be obtained by increasing the number of captures and taking the average value.
[0029]
As described above, according to the first and second embodiments, a signal obtained in units of one line from the dummy line 18 to which no photosensitive pixel is connected is transferred to the line buffer 4 having a smaller memory amount than the frame memory, as a noise component. Since it is stored as data and noise correction is performed based on this, noise correction that is not affected by photosensitive pixels is possible without unnecessarily enlarging the device, and noise components in the image sensor are surely obtained. Therefore, it is possible to obtain a good image quality that has been removed.
[0030]
Next, a third embodiment of the present invention will be described.
In the third embodiment, optimum noise correction can be performed according to the state of noise during shooting.
FIG. 5 is a block diagram illustrating the solid-state imaging device of the present embodiment. First, the overall operation of this embodiment will be briefly described with reference to FIG.
[0031]
In FIG. 5, when a shutter button (not shown) is turned on, the light shielding plate 31 is opened, and a subject image is formed on the imaging surface of the CCD 32 by an optical system (not shown) provided in front of the light shielding plate 31. Photoelectric conversion is performed by the CCD 32. The image pickup signal thus obtained is A / D converted by the A / D converter 33 and then stored in the frame memory 34 as an image signal.
[0032]
Next, the light shielding plate 31 is closed and photoelectric conversion is performed by the CCD 32 in the dark state. Image signal obtained thereby, since is obtained by photoelectric conversion performed by blocking all light from the outside of the CCD 32, it is used as the noise component data S _N of the fixed pattern noise of the CCD 32.
[0033]
The noise component data S _N obtained in this way is directly input to one end of the subtractor 36 without undergoing processing such as A / D conversion by the A / D converter 33. The reading of the noise component data S _N is not performed when it is determined that it is unnecessary by a determination operation described later.
[0034]
In synchronism with the input of the noise component data S _N to the subtractor 36, the subject image signal stored in the frame memory 34 is D / A converted by the D / A converter 35 to be an analog image signal. S _D is input to the other end of the subtractor 36. Then, a subtraction process of S = S _D −S _N is performed in the subtractor 36, and the correction signal S from which the noise component of the CCD 32 is removed is obtained.
[0035]
The correction signal S is input to the terminal B of the switch 37. Further, the uncorrected image signal _SD is input to the terminal A of the switch 37, and either the correction signal S or the uncorrected signal _SD is selected by the determination of the system controller 42. This determination method will be described later. The selected signal is given to the recording device 39 after being subjected to predetermined processing by the process circuit 38 and recorded.
[0036]
Next, a method for determining terminal selection of the switch 37 by the system controller 42 described above will be described with reference to the flowchart of FIG.
First, when the shutter is turned on in Step S1, the light shielding plate 31 is opened in Step S2, and the photoelectric conversion of the subject is performed in Step S3, and the imaging signal (subject data) is taken into the frame memory 34.
[0037]
In step S4, the histogram processing of the luminance distribution of the captured subject data is performed, and the highlight point HP and dark point DP of the image are determined from the processing result. FIG. 7 is a diagram showing an example of the result of this histogram processing. This processing result is obtained by classifying pixels into 256 steps based on the captured subject data and arranging them in the order of brightness. A value of 99% of the whole is a highlight point HP, and a value of 1% is a dark point DP.
[0038]
Further, an index (INDEX) is determined from the combination of the highlight point HP and the dark point DP obtained in this way, for example, based on a chart as shown in FIG. Here, when the index is ON, the noise component is read, and when the index is OFF, the noise component is not read.
[0039]
Next, in step S5, it is determined whether the index is ON or OFF. If it is determined that the index is ON, the process proceeds to close the light-shielding plate 31 in step S6, reads the noise component data S _N in step S7 CCD 32 is inputted to one end of the subtractor 36. Next, the correction signal S generated by the subtractor 36 is selected by switching the movable terminal 37a of the switch 37 to the terminal B side in step S8, and this correction signal S is recorded in the recording device 39 in step S10.
[0040]
If it is determined in step S5 that the index is OFF, the process proceeds to step S9 without reading out the noise component data S _N in steps S6 and S7, and the movable terminal 37a is switched to the terminal A side to thereby change the uncorrected signal. _SD is selected, and the uncorrected signal _SD is recorded in the recording device 39 in step S10.
[0042]
In addition, the selection of whether or not to read out the noise component data S _N has been described based on the result of the histogram processing. However, when increasing the gain of the image signal, the noise component data S _N is always read out. Noise correction may be performed without fail.
Further, the subtraction operation in the subtractor 36 may be performed digitally as in the case of the second embodiment described above.
[0043]
As described above, according to the third embodiment, the imaging signal in the dark state generated by closing the light shielding plate is used as the noise component data of the imaging device, and the fixed pattern noise of the imaging device is corrected based on this. Therefore, it is possible to obtain noise component data corresponding to the shooting state for each shooting of one screen, and it is possible to perform optimum noise correction according to the noise state at the time of shooting.
In addition, it is determined whether or not to perform noise correction according to the state of the image signal stored in the frame memory, and noise correction is not performed when correction is not necessary. Optimum noise correction can be performed, and the photographing time for one sheet can be shortened.
[0044]
【The invention's effect】
As described above, according to the present invention, noise component data is generated every time one screen is captured, and noise correction is performed based on the generated noise component data, so that optimal noise correction can be performed. Can always obtain good image quality. In addition, in an imaging apparatus that can not perform noise correction depending on conditions, the imaging time can be shortened when noise correction is not performed.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a solid-state imaging device according to a first embodiment.
FIG. 2 is a diagram illustrating a detailed configuration of an image sensor.
FIG. 3 is a timing chart showing the overall operation timing of the solid-state imaging device.
FIG. 4 is a block diagram illustrating a solid-state imaging apparatus according to a second embodiment.
FIG. 5 is a block diagram illustrating a solid-state imaging apparatus according to a third embodiment.
FIG. 6 is a flowchart for explaining the operation of the third embodiment;
FIG. 7 is a diagram illustrating an example of a result of histogram processing.
FIG. 8 is a diagram illustrating an index determined from a result of histogram processing.
FIG. 9 is a block diagram illustrating a configuration of a conventional solid-state imaging device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Image pick-up element 2 Switch 2a Movable terminal 3 A / D converter 4 Line buffer 5 D / A converter 6 Subtractor 7 Process circuit 9 Synchronous signal generation circuit 13 Horizontal signal line 14 Vertical signal line 18 Dummy line 19 Switch 20 Subtractor 31 Light shielding Plate 32 CCD
33 A / D converter 34 Frame memory 35 D / A converter 36 Subtractor 37 Switch 37a Movable terminal 38 Process circuit 39 Recording device 42 System controller

Claims (5)

An imaging region for generating an image signal by photoelectric conversion;
Light shielding means for shielding light from the subject to the imaging region;
A first operation for reading an image signal generated in the imaging region in a state where the light shielding unit is not shielded from light, and a second operation for reading out noise component data generated in the imaging region while being shielded by the light shielding unit. Driving means for performing
Correction means for reading out noise component data by the second operation of the driving means and correcting the image signal read by the first operation;
A control unit that performs the correction by the correction unit when the luminance of the subject is low, and that does not perform the correction by the correction unit when the luminance of the subject is high;
An imaging device comprising: An imaging region for generating an image signal by photoelectric conversion;
Light shielding means for shielding light from the subject to the imaging region;
A first operation for reading an image signal generated in the imaging region in a state where the light shielding unit is not shielded from light, and a second operation for reading out noise component data generated in the imaging region while being shielded by the light shielding unit. Driving means for performing
Correction means for reading out noise component data by the second operation of the driving means and correcting the image signal read by the first operation;
Control means for performing the correction by the correction means in response to increasing the gain of the image signal;
An imaging device comprising: An image sensor that receives light from an optical system that forms a subject image and obtains an image signal; and
An A / D converter for A / D converting the image signal obtained from the image sensor,
The imaging apparatus according to claim 1, wherein the imaging area is an imaging area in the imaging element. An imaging method of an imaging apparatus having an imaging region that generates an image signal by photoelectric conversion,
A light shielding step for shielding light from the subject to the imaging region;
A first operation for reading an image signal generated in the imaging region in a state where light is not shielded by the light shielding step, and a second operation for reading out noise component data generated in the imaging region while being shielded by the light shielding step A driving process for performing
A correction step of reading out noise component data by the second operation of the driving step and correcting the image signal read by the first operation;
When the subject brightness is low, the correction step performs the correction, and when the subject brightness is high, the control step does not perform the correction in the correction step;
An imaging method for an imaging apparatus, comprising: An imaging method of an imaging apparatus having an imaging region that generates an image signal by photoelectric conversion,
A light shielding step for shielding light from the subject to the imaging region;
A first operation for reading an image signal generated in the imaging region in a state where light is not shielded by the light shielding step, and a second operation for reading out noise component data generated in the imaging region while being shielded by the light shielding step A driving process for performing
A correction step of reading out noise component data by the second operation of the driving step and correcting the image signal read by the first operation;
A control step of performing the correction in the correction step in response to increasing the gain of the image signal;
An imaging method for an imaging apparatus, comprising:

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