JP2008109278A - IMAGING DEVICE, IMAGING DEVICE CONTROL METHOD, AND COMPUTER PROGRAM - Google Patents

Abstract

A shading correction is performed and an S / N of a video signal is prevented from being deteriorated or an entire screen is prevented from being darkened.
A CCD 104 that performs photoelectric conversion, a zoom operation unit 114 that changes a focal length by moving a zoom lens 102 in an optical axis direction, an aperture operation unit 113 that operates a diaphragm 103, and a signal from the CCD 104 are amplified. And a variable gain amplifier 106 having a variable gain for controlling the change of the maximum aperture diameter of the diaphragm 103 according to the focal length for shading correction of the video signal. When the gain is the upper limit value, the aperture 103 is permitted to open beyond the maximum aperture diameter determined according to the focal length.
[Selection] Figure 1

Description

  The present invention relates to an imaging apparatus that performs shading correction, a control method for the imaging apparatus, and a computer program.

  It has been practiced to provide a zoom mechanism and control the diaphragm as a countermeasure for shading. The basic idea is to make the peripheral light amount drop caused by shading inconspicuous by reducing the aperture. For example, in Patent Document 1, a zoom lens having a main diaphragm that can be narrowed down to a small diaphragm to change FNO and a sub-diaphragm that is located behind the main diaphragm and changes the diaphragm aperture by a zoom operation. Are listed. Further, in Patent Document 2, since the open F value varies depending on the focal length, there may be a sense of incongruity due to the change in peripheral light amount depending on the zoom speed, so the open F value correction changes according to the zoom speed. Measures to make it are listed.

  Here, open F value correction according to a general focal length will be described. When the lens has the focal length on the wide-angle side in the zoom mechanism (hereinafter referred to as the “wide end”), there is almost no phenomenon that the amount of light decreases at the peripheral portion. Therefore, in many cases, the original F value of the lens becomes the open F value as it is. On the other hand, when the lens has the focal length closest to the telephoto side in the zoom mechanism (hereinafter referred to as “tele end”), the difference between the light amount at the center and the light amount at the peripheral part is larger than that at the wide end Therefore, a phenomenon generally called shading occurs. This phenomenon is more likely to occur as the F value is closer to the open end at the telephoto end. For this reason, the aperture is stopped until a value at which shading does not matter, and this value is set as the open F value at the telephoto end. Since the shading occurs in accordance with the focal length even at the focal length between the tele end and the wide end, the open F value is determined based on the same concept.

  Further, correction by image processing is also performed as a measure against shading. There are several algorithms, but basically, the signal at the periphery of the lens where the amount of incident light is lower than the center is amplified to compensate for the lack of light and cancel shading.

JP-A-9-222628 JP 11-183778 A

  In the conventional technique in which the open F value is changed according to the focal length and the shading is made inconspicuous, various problems occur due to the change of the open F value. One of them is as follows. That is, when the zoom is performed from the position where the focal length is on the wide end side to the tele end side, the open F value is further reduced, and thus the absolute light quantity incident on the image sensor is reduced. The decrease in the amount of incident light will be compensated by increasing the gain at the amplifier in the subsequent stage. However, if the gain is increased, the S / N of the video signal will deteriorate, or if the gain cannot be compensated by increasing the gain, the entire screen will become darker. There was a problem that.

  The present invention has been made in view of the above points, and performs shading correction that makes shading inconspicuous, and prevents the S / N of a video signal from deteriorating or the entire screen from becoming dark. With the goal.

The present invention relates to an image sensor that performs photoelectric conversion, a focal length changing unit that changes a focal length by moving a lens in an optical axis direction, a diaphragm operating unit for operating a diaphragm, and an amplifying signal from the image sensor. In addition, the present invention relates to an image pickup apparatus including a variable amplifying unit whose amplification degree is variable, and performs control for changing the maximum aperture diameter of the diaphragm according to a focal length for shading correction of a video signal. At the same time, when the degree of amplification in the variable amplifying means is an upper limit value, control is performed to allow the aperture to open beyond the maximum aperture diameter determined according to the focal length.
Further, the present invention performs shading correction by locally changing the amplification factor of an image pickup device that performs photoelectric conversion, focal length changing means that changes the focal length by moving the lens in the optical axis direction, and the like. The present invention relates to an image pickup apparatus including a shading correction unit that can perform a noise removal and a noise removal unit that can locally change the intensity of noise removal, and the local amplification used during the shading correction by the shading correction unit The control is performed so that the degree of noise and the intensity of noise removal at the same location by the noise removing means have a certain relationship.

  According to the present invention, it is possible to perform shading correction that makes shading inconspicuous, and to prevent the S / N of the video signal from deteriorating and the entire screen from becoming dark.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
(First embodiment)
As an embodiment of the present invention, a method for controlling the open F value based on the focal length of the lens and the gain of the amplifier will be described. In this embodiment, by changing the open F value by looking at the focal length and the gain of the amplifier at the subsequent stage, if the screen becomes dark without being compensated for by increasing the gain, the amount of peripheral light is allowed to be incident on the image sensor. The purpose is to maintain the amount of light.

  FIG. 1 is a block diagram illustrating a configuration of an imaging apparatus according to the present embodiment. The light incident from the lens 101 is incident on the CCD 104 after the focal length is determined by the position of the zoom lens 102 and the amount of light is controlled by the diaphragm 103. Noise is removed from the signal photoelectrically converted by the CCD 104 by correlated double sampling in a CDS (Correlated Double Sampling) circuit 105. The gain is amplified by the variable gain amplifier 106 and amplified to a desired level, and then converted into digital data by the AD converter 107. The digital data converted by the AD converter 107 is processed by a signal processing circuit 108, a signal output unit 109 for outputting a video signal, a display unit 110 for monitoring an image, and a recording for recording video data. It is output to the medium 111.

  Apart from the above signal flow, there is a system for controlling each part. A microcomputer (hereinafter referred to as “microcomputer”) 112 controls processing in the signal processing circuit 108 and controls the gain of the variable gain amplifier 106. Further, the microcomputer 102 controls a diaphragm operation unit 113 for operating the diaphragm 103 and controls a zoom operation unit 114 for operating the zoom lens 102.

In the case of general control, the microcomputer 112 that operates the zoom lens 102 with the zoom operation unit 114 determines the control range on the open side of the diaphragm 103 from the viewpoint of shading correction by looking at the current focal length. For example, assuming that the control aperture is limited to F ₀ at the focal length f, the relationship shown in Table 1 below is assumed.

In this case, the microcomputer 112 calculates the current focal length from the current position of the zoom lens 102. If the focal length exceeds 50 mm, the aperture 103 and the variable gain amplifier 106 are controlled in a state where the control opening aperture value F ₀ is limited according to the values in Table 1 so that appropriate brightness can be obtained. To do.

In order to correct the shading in such a manner that the control open aperture value F ₀ is limited and controlled, the aperture value of the aperture 103 is reduced from the control open aperture value F ₀ after changing the focal length by the zoom lens 102. Sometimes there is no change. On the other hand, when the aperture value of the aperture 103 is opened more than the control opening aperture value F ₀ , the aperture 103 is stopped to the control opening aperture value F _0, and the gain of the variable gain amplifier 106 is increased as the amount of incident light decreases. Maintain proper brightness.

On the other hand, in this embodiment, the microcomputer 112 advances the control according to the flowchart shown in FIG. At this time, the diaphragm 103 is allowed to open beyond the control opening diaphragm value F ₀ only when the gain of the variable gain amplifier 106 is the maximum value.

  First, in step S201, normal exposure control is performed. In step S202, it is determined whether or not the zoom lens 102 has moved according to an operation of a zoom operation key (not shown).

  If it is determined in step S202 that the zoom lens 102 has not moved, the process returns to step S201 to continue normal exposure control.

  When it is determined in step S202 that the zoom lens 102 is moving, the process proceeds to step S203, where it is determined whether the current focal length f is 50 mm or more. This is because the control aperture value correction is performed for shading correction at a focal length of 50 mm or more in Table 1. At the focal length that is less than 50 mm, since the controlled open aperture value correction is not performed, the process returns to step S201 to perform the normal exposure control.

If it is determined in step S203 that the focal length f is 50 mm or longer, the process proceeds to step S204, and exposure control similar to normal is performed within the range of the control opening aperture value F ₀ determined in Table 1.

  In step S205, it is determined whether the zoom lens 102 has moved. If it is determined in step S205 that the zoom lens 102 has not moved, the process proceeds to step S206. If it is determined that the zoom lens 102 has moved, the process proceeds to step S210.

  In step S206, it is determined whether or not the gain of the variable gain amplifier 106 is the maximum value (upper limit value) as a result of the exposure control in step S204. If it is determined in step S206 that the maximum value is not reached, it is determined that normal brightness is secured, and control is continued after returning to step S204.

If it is determined in step S206 that the maximum value has been reached, it is considered that the conventional brightness could not be maintained even by increasing the gain by correcting the control aperture value. In this case, after considering hysteresis for preventing oscillation in step S207, in step S208, the aperture 103 is set within a range of F _K which is the lens's original maximum aperture value and the control maximum aperture value F ₀ at the current focal length f. Control to control exposure. In the exposure control in step S208, the gain of the variable gain amplifier 106 is kept at the maximum value. This is to avoid instability by simultaneously controlling the gain of the variable gain amplifier 106 and the aperture value of the aperture 103.

  In step S209, it is determined whether the zoom lens 102 has moved. If it is determined in step S209 that the zoom lens 102 is moving, the process proceeds to step S210, and it is determined whether the current focal length f is 50 mm or more. If it is determined in step S210 that the focal length f is 50 mm or more, the open aperture value correction value for shading correction has changed, so the process returns to step S204 and normal exposure is performed within the control open aperture range. Take control. If the focal length f is less than 50 mm in step S210, it means that the full aperture value correction for shading is no longer performed. In this case, the process returns to step S201 to perform normal exposure control.

If it is determined in step S209 that the zoom lens 102 has not moved, the process proceeds to step S211. In step S211, control is performed between the lens's original full aperture value F _K and the controlled wide aperture value F ₀ at the current focal length f. At this time, when the information from the signal processing circuit 108 is confirmed and the microcomputer 102 determines that the brightness is higher than the appropriate brightness under the condition that the gain of the variable gain amplifier 106 is the maximum value, the process proceeds to step S212. move on. In step S212, after performing oscillation prevention hysteresis processing, the process returns to step S204, and normal exposure control is performed within the range of the control opening aperture value.

As described above, the aperture is opened to the original open aperture value of the lens only when the gain of the variable gain amplifier 106 is the maximum value at the focal length in which the control open aperture value F ₀ is corrected for shading correction. The exposure control is permitted.

  With this control, it is possible to correct the peripheral light amount drop characteristic of the lens for a subject with sufficient brightness. That is, shading caused by a decrease in the amount of light around the lens can be suppressed for a subject having sufficient brightness.

  On the other hand, in a subject where the gain of the variable gain amplifier 106 is the maximum value, it is possible to avoid the phenomenon that an image with sufficient brightness for shading correction cannot be obtained, and when the lens is used on the tele side. The sensitivity as a camera has increased. That is, only when the gain of the variable gain amplifier 106 is the maximum value, by permitting the control open aperture value of the aperture 103 to be controlled to the original open aperture value of the lens, it is possible to perform exposure control due to insufficient incident light quantity in a dark subject. It is possible to avoid the phenomenon of darkening beyond the range.

(Second Embodiment)
As an embodiment of the present invention, a method of simultaneously using a shading correction unit and a noise removal unit for shading correction by looking at the focal length of a lens will be described. In the present embodiment, shading correction due to a decrease in peripheral light amount that changes depending on the focal length is performed by image processing, and at that time, the S / N on the screen is made constant by setting noise reduction having characteristics opposite to the shading correction coefficient. The purpose is to keep.

  FIG. 3 is a block diagram illustrating a configuration of the imaging apparatus according to the present embodiment. The light incident from the lens 301 has its focal length determined by the position of the zoom lens 302, and the amount of light is controlled by the diaphragm 303, and then enters the CCD 304. Noise is removed from the signal photoelectrically converted by the CCD 304 by correlated double sampling in a CDS circuit inside an AFE (Analog Front End) 305. Then, the gain is amplified by a variable gain amplifier inside the AFE 305 and amplified to a desired level, and then converted into digital data by an AD converter inside the AFE 305.

  Digital data output from the AFE 305 is processed by the signal processing circuit 308. Inside the signal processing circuit 308, the shading correction unit 306 corrects the peripheral light amount drop phenomenon caused by the optical system. The shading correction algorithm will be described later. The digital data output from the shading correction unit 306 is input to the noise removal unit 307, and the noise component is suppressed. A noise suppression algorithm will also be described later. The output of the noise removal unit 307 is output from the signal processing circuit 308, and is output to a signal output unit 309 for outputting a video signal, a display unit 310 for monitoring an image, and a recording medium 311 for recording video data. The

  Apart from the above signal flow, there is a system for controlling each part. The microcomputer 312 controls processing in the shading correction unit 306 and the noise removal unit 307 inside the signal processing circuit 308 and controls the gain of the variable gain amplifier inside the AFE 305. The microcomputer 312 controls a diaphragm operation unit (not shown) for operating the diaphragm 303 and controls a zoom operation unit 313 for operating the zoom lens 302.

  Here, an algorithm for shading correction performed by the shading correction unit 306 will be described. In the present embodiment, it is assumed that the lens does not require shading correction when the focal length of the lens is equal to or less than fa, the lens shading becomes the largest at the focal length fb, and the shading amount of the lens hardly changes at the focal length fb or longer.

The shading amount S _fb (h, v) at the focal length fb at which the lens shading is maximized is adjusted to a known amount by the microcomputer 312. The shading amount is defined as a signal level ratio where 1 is the highest level signal in one screen when a uniform subject is photographed. Note that h and v represent a horizontal position and a vertical position, respectively.

The microcomputer 312 detects the position of the zoom lens 302 via the zoom operation unit 313. Then, the shading correction unit 306 performs shading correction by controlling the shading correction gain G _sh as shown in Table 2 according to this value.

Next, a noise suppression algorithm performed by the noise removing unit 307 will be described. In the noise reduction process in the noise removal unit 307, the strength of noise removal is controlled according to the ratio of increasing the gain with respect to the position where the gain G _sh is increased from 1 by the shading correction unit 306. For this reason, the method used in the noise removal unit 307 is required to change the noise removal level locally, in other words, for each two-dimensional position. Here, the noise filter NF (k ) Is used. Since the correction value at the target pixel position (h, v) is expressed in Table 2, k representing the noise removal strength is expressed in Table 3.

To summarize the above description, the noise removal unit 307 applies a noise filter having an intensity corresponding to the gain G _sh when the shading correction unit 306 causes the S / N ratio to deteriorate if the position of the pixel having the large gain G _sh remains unchanged. As a result, noise can be suppressed and the entire screen can be maintained at a uniform S / N. That is, when performing shading correction, the S / N of the entire screen can be suppressed to the same level by combining the magnitude of the local gain to be corrected and the strength of the noise filter that removes noise.

  An object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the above-described embodiments to a system or apparatus, and the computer (or CPU or MPU) of the system or apparatus stores the storage medium. Needless to say, this can also be achieved by reading and executing the program code stored in.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code itself and the storage medium storing the program code constitute the present invention.

  As a storage medium for supplying the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (basic system or operating system) running on the computer based on the instruction of the program code. Needless to say, a case where the functions of the above-described embodiment are realized by performing part or all of the actual processing and the processing is included.

  Furthermore, after the program code read from the storage medium is written in the memory of the expansion board inserted into the computer or the function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that the CPU or the like provided in the board or function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

It is a block diagram which shows the structure of the imaging device which concerns on 1st Embodiment. 5 is a flowchart for explaining control in the imaging apparatus according to the first embodiment. It is a block diagram which shows the structure of the imaging device which concerns on 2nd Embodiment.

Explanation of symbols

101, 301 Lens 102, 302 Zoom lens 103, 303 Aperture 104, 304 CCD
105 CDS circuit 106 Variable gain amplifier 107 AD converter 108, 308 Signal processing circuit 109, 309 Signal output unit 110, 310 Display unit 111, 311 Recording medium 112, 312 Microcomputer 113 Aperture operation unit 114, 313 Zoom operation unit 305 AFE
306 Shading correction unit 307 Noise removal unit

Claims (6)

An image sensor that performs photoelectric conversion;
Focal length changing means for changing the focal length by moving the lens in the optical axis direction;
An aperture operating means for operating the aperture;
Variable amplification means that amplifies the signal from the image sensor and makes the amplification variable;
In order to correct shading of the video signal, control is performed to change the maximum aperture diameter of the diaphragm according to the focal length, and when the amplification degree in the variable amplifying means is an upper limit value, it is determined according to the focal length. An imaging apparatus comprising: control means for performing control to permit opening of the diaphragm beyond a maximum aperture diameter. An image sensor that performs photoelectric conversion;
Focal length changing means for changing the focal length by moving the lens in the optical axis direction;
A shading correction means capable of performing shading correction by locally changing the amplification degree of the signal;
Noise removing means capable of locally changing the intensity of noise removal;
Control means for performing control in which the local amplification degree used at the time of shading correction by the shading correction means and the intensity of noise removal at the same location by the noise removal means are related so as to have a certain relationship An imaging apparatus characterized by the above. An image sensor that performs photoelectric conversion, a focal length changing unit that changes the focal length by moving the lens in the optical axis direction, an aperture operating unit for operating the aperture, amplifies the signal from the image sensor, and A method for controlling an image pickup apparatus including variable amplification means having a variable amplification degree,
In order to correct shading of the video signal, control is performed to change the maximum aperture diameter of the diaphragm according to the focal length. A method for controlling an imaging apparatus, comprising: a procedure for performing control for permitting opening of the diaphragm beyond a maximum aperture diameter. An image sensor that performs photoelectric conversion, a focal length changing unit that changes the focal length by moving the lens in the optical axis direction, and a shading correcting unit that can perform shading correction by locally changing the signal amplification degree. And a method for controlling an imaging apparatus comprising noise removing means capable of locally changing the intensity of noise removal,
It has a procedure of performing a control in which the local amplification degree used at the time of shading correction by the shading correction unit and the intensity of noise removal at the same location by the noise removal unit are related to each other so as to have a certain relationship. Control method for imaging apparatus. An image sensor that performs photoelectric conversion, a focal length changing unit that changes the focal length by moving the lens in the optical axis direction, an aperture operating unit for operating the aperture, amplifies the signal from the image sensor, and A computer program for controlling an imaging apparatus having variable amplification means with variable amplification,
In order to correct shading of the video signal, control is performed to change the maximum aperture diameter of the diaphragm according to the focal length, and when the amplification degree in the variable amplifying means is an upper limit value, it is determined according to the focal length. A computer program for causing a computer to execute a process of permitting opening of the diaphragm beyond a maximum aperture diameter. An image sensor that performs photoelectric conversion, a focal length changing unit that changes the focal length by moving the lens in the optical axis direction, and a shading correcting unit that can perform shading correction by locally changing the signal amplification degree. And a computer program for controlling an image pickup apparatus including a noise removing unit that can locally change the intensity of noise removal,
Causing the computer to execute a process of performing control in which the local amplification degree used at the time of shading correction by the shading correction means and the intensity of noise removal at the same location by the noise removal means are related to each other. A computer program characterized by the above.

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