JP2007072095A - Imaging method and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent wrong focus control from being performed due to high-luminance subject. <P>SOLUTION: An evaluated value SC, which is not processed to remove high luminance, is set as an evaluated value used for AF processing. Whether an entire screen is dark is decided in S11, and whether the entire screen is very bright is decided in S13. When it is decided that the overall screen is dark or very bright and that a high luminance part, such as a bright spot exists in the entire dark screen in S12, whether a difference between the presence of a high-luminance mask and the absence of the high-luminance mask is equal to or larger than a predetermined value is decided in S15. When the difference between the presence of the high-luminance mask and the absence of the high-luminance mask is not equal to or larger than the predetermined value, processing is finished. When the difference is equal to or higher than the predetermined value, processing that the focal position is not taken as a focusing position is performed in S16. Thus, a peak due to the high-luminance subject is decided as being false and is excluded from the candidates for focusing position, and the AF processing is performed based on the evaluated value SC. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging method and an imaging apparatus capable of obtaining a still image, a moving image, and the like.

  In the imaging apparatus, there has been proposed a focus control apparatus that utilizes the fact that the integrated value of the level of the middle and high frequency components in the imaging signal becomes maximum at the in-focus position. As described in Patent Document 1 below, the middle and high frequency components in the imaging signal are extracted by a high-pass filter, the extracted middle and high frequency components are integrated to obtain an evaluation value, and the focus is set to maximize the evaluation value. The position is controlled.

Japanese Patent Laid-Open No. 3-243071

  In such an autofocus device, when a high-luminance part such as a video light, a fluorescent lamp, or a mirror reflecting light is present on the subject, the level of the medium-high luminance component in the imaging signal becomes very large. Accordingly, the evaluation value obtained by integrating the medium and high luminance components includes a high luminance portion, and the evaluation value for autofocus is an incorrect value. The reason for this is that a high luminance portion such as a bright spot has a relatively large evaluation value as a result of integration even in a blurred image in an out-of-focus state.

  In Patent Document 1, in order to solve such a problem, the imaging signal is compared with a threshold of a predetermined level, and an imaging signal equal to or higher than the threshold is masked. The process described in Patent Document 1 will be described with reference to FIG.

  FIG. 7A shows an example of a level change of a captured image signal (luminance signal) in a one-dimensional direction, for example, a horizontal direction, and a threshold value THR1 having a relatively high luminance level is set. In FIG. 7, T1, T2, T3,... Indicate timings defined by the clock signal. This timing corresponds to an interval of one pixel or an interval of several pixels. FIG. 7B shows a signal of a mid-high frequency component obtained by supplying the image signal to the high-pass filter. The mid-high range component has a level corresponding to the level change amount (absolute value of level difference) before and after each interval. Since the level of the mid-high frequency component corresponds to the contrast, the signal of the change of the mid-high frequency component is referred to as a contrast signal.

  One or a plurality of focus control frames are set in the captured image, and an evaluation value is obtained in each frame. A plurality of sampling points are set within the change range of the focus lens position, and an evaluation value is calculated from the contrast signal as shown in FIG. 7B at each sampling point. For example, the peak value of the horizontal contrast signal in the frame is used as an evaluation value, or the evaluation value is obtained by further integrating the horizontal contrast signal in the vertical direction. Since the image is not blurred at the in-focus position, the contrast becomes large. Then, the maximum position of the evaluation value peak of each sampling point in the change range of the focus position is set as the focus position, and the focus lens is controlled at that position.

  In FIG. 7A, the levels before and after T11 in the image signal exceed the threshold value THR1. Therefore, as shown in FIG. 7C, the period of the timing T10-T12 in the contrast signal is removed by the mask width A that masks the two intervals before and after the timing T11. However, depending on the mask width A, the removal width is too small, and there is a problem that a high-luminance portion that cannot be removed remains.

  Next, the level of the threshold value THR1 is further reduced, and a mask width B for masking two intervals before and after the timing T11, that is, a period from the timing T9 to T13 is set. As shown in FIG. 7D, the high-intensity portion can be completely removed by the mask width B.

  Further, the threshold value THR1 is reduced, and a mask width C for masking the interval between the timing T11 and the previous five intervals, that is, the period from the timing T6 to T16, is set. As shown in FIG. 7E, since the mask width C is too wide to be removed, there arises a problem that the contrast signal (T6-T9) other than the high-contrast contrast signal is also removed.

  As described above, the method described in Patent Document 1 cannot remove a contrast signal due to a high-brightness subject if the mask width is too small, whereas if the mask width is too wide, an object having actual contrast can be removed. There was a problem that could not be detected. That is, it is very difficult to set the threshold level appropriately.

  Accordingly, an object of the present invention is to provide an imaging method and an imaging apparatus that eliminate the difficulty of setting a threshold level for removing a contrast signal from a high-luminance subject.

In order to solve the above-described problems, the present invention captures an object through a focus lens and converts the object light into an electrical signal.
A signal extraction step of extracting the first focus control signal based on the middle and high frequency components in the luminance signal obtained in the imaging step;
A signal extraction step of extracting a second focus control signal from which a high-luminance portion of the first focus control signal is removed;
An evaluation signal generating step for generating a first evaluation value according to the position of the focus lens from the first focus control signal;
An evaluation signal generating step for generating a second evaluation value from the second focus control signal according to the position of the focus lens;
A comparison in which the difference between the first evaluation value and the second evaluation value at the positions where the lens positions are substantially the same is detected, and the first evaluation value is excluded from the focus position candidates when the detected difference is large. Steps,
An imaging method comprising the step of controlling the position of the focus lens using both the first evaluation value processed in the comparison step and the first evaluation value not processed in the comparison step.

An imaging means for imaging a subject through a focus lens and converting the subject light into an electrical signal;
Signal extraction means for extracting a first focus control signal based on a middle-high frequency component in the luminance signal obtained by the imaging means;
Signal extraction means for extracting a second focus control signal from which a high-luminance portion of the first focus control signal is removed;
An evaluation signal generating means for generating a first evaluation value from the first focus control signal according to the position of the focus lens;
An evaluation signal generating means for generating a second evaluation value according to the position of the focus lens from the second focus control signal;
A comparison in which the difference between the first evaluation value and the second evaluation value at the positions where the lens positions are substantially the same is detected, and the first evaluation value is excluded from the focus position candidates when the detected difference is large. Means,
An image pickup apparatus including means for controlling the position of the focus lens based on the first evaluation value processed by the comparison means.

  According to the present invention, it is possible to prevent out-of-focus due to a high-luminance subject. In the present invention, the setting range for removing high brightness is reduced, and even if the contrast signal from all high brightness subjects cannot be removed, a false peak due to the high brightness subject can be detected and correctly focused. . In the present invention, the circuit scale can be reduced by reducing the set width.

An imaging apparatus according to an embodiment of the present invention will be described below with reference to the drawings. The overall configuration of one embodiment is shown in FIG. In FIG. 1, reference numeral 1 indicates a focus lens group. Subject light that has passed through the focus lens group 1 is incident on an image sensor 2 using an element such as a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), and an image signal corresponding to the subject light is obtained from the image sensor 2. It is done. An example of the imaging device is a digital camera, but a PDA (Personal Digital Assistants),
It may be a mobile phone or the like, or may be a device that captures moving images.

An imaging signal from the imaging device 2 is supplied to an AGC (Automatic Gain Control) 3, and AGC
3, the image pickup signal whose level is controlled is supplied to the A / D converter 4 and converted from an analog image pickup signal to a digital image pickup signal. A digital image pickup signal from the A / D converter 4 is supplied to the digital image processing unit 5 and the optical detector 8.

The image signal is processed in the digital image processing unit 5. The output signal of the digital image processing unit 5 is recorded on a recording medium 6 such as a memory card and displayed on an image display unit 7 such as an LCD (Liquid Crystal Display). The optical detector 8 generates a contrast signal that is an AF (Auto Focus) signal for autofocus control. In addition to the contrast signal, the optical detector 8 generates an automatic exposure signal and an auto white balance signal.

  The contrast signal generated by the optical detector 8 is supplied to the system controller 9. The system controller 9 is composed of, for example, a microcomputer, controls the entire imaging apparatus, sets a width for removing a high-luminance portion from the contrast signal supplied from the optical detector 8, and forms a contrast signal after removal of the high-luminance portion. Then, the in-focus position is calculated using both the evaluation value obtained from the contrast signal after removal of the high luminance part and the evaluation value obtained from the contrast signal from which the high luminance part is not removed. The system controller 9 generates a motor drive signal so that the in-focus position can be obtained, and outputs the generated motor drive signal to the motor drive circuit 10. The focus lens group 1 is controlled by the motor drive circuit 10 so as to be in the in-focus position.

  FIG. 2 shows a configuration of a contrast signal extraction portion inside the optical detector 8. The digital image signal is supplied to the luminance signal generation circuit 81, and a luminance signal is generated. The generated luminance signal is supplied to a filter arithmetic circuit 82 serving as an extraction unit and a high luminance counter 84 serving as a high luminance determination unit. The filter calculation circuit 82 extracts the middle and high frequency components in the luminance signal, outputs the contrast signal corresponding to the middle and high frequency components as it is, and supplies the contrast signal to the high luminance removal circuit 83. The contrast signal after high luminance removal from which the high luminance peripheral portion is removed from the high luminance removal circuit 83 is obtained. These contrast signals are supplied to the system controller 9 and used to generate an evaluation value for focus control.

  The high-intensity counter 84 compares each pixel level of the image signal with a threshold value, determines, for example, pixels that are equal to or higher than the threshold value as high-intensity, and generates a high-intensity removal signal. A high luminance removal signal is supplied to the high luminance removal circuit 83 and used to remove the high luminance peripheral portion. Further, the count value of the high luminance counter 84 is supplied to the system controller 9.

  Note that a control signal is supplied from the system controller 9 to the luminance signal generation circuit 81, the filter operation circuit 82, the high luminance removal circuit 83, and the high luminance counter 8 which are components of the optical detector 8 shown in FIG. . With this control signal, for example, when an evaluation value is generated by paying attention to a predetermined part of an image, for example, an image of a frame near the center, or an evaluation value is generated by paying attention to images of a plurality of evaluation frames. Frame switching control is possible. The evaluation value is obtained for each set frame.

  Here, the evaluation value SC generated from the contrast signal before high luminance removal and the evaluation value SR generated from the contrast signal after high luminance removal will be described with reference to FIG. Here, the evaluation value is a horizontal peak value of the contrast signal of each frame, a value obtained by integrating the horizontal peak value of each frame in the vertical direction, or the like.

  FIG. 3A shows an example of a level change with respect to a change in the lens position of the focus lens group 1 of the evaluation value SC generated from the contrast signal before high luminance removal. Level peaks occur at, for example, positions A, B, and D of the evaluation value SC. The peak at the position D is a false peak that occurs at a blurred bright spot where a bright subject, for example, a bright spot exists. When focus control is performed using such an evaluation value SC, the focus position of the lens is controlled to D, which causes a problem of focusing on a blurred high-luminance subject.

  FIG. 3B and FIG. 3C show an example SRa and another example SRb generated from the contrast signal from which the high luminance part is removed by the high luminance removal circuit 83, respectively. In the case of the evaluation value SRa, the setting range for removing the high-luminance portion is inappropriate, and thus the high-luminance portion cannot be removed, and a part of the false peak remains. In the case of the evaluation value SRb, since the setting width is appropriate, the high luminance part is removed and the false peak is removed. Here, in the case of the evaluation value SRa, since the high-luminance portion has not been completely removed, new peaks are generated at the position C and the position E. As a result, when the evaluation value SRa is used, the position C or the position E may be erroneously detected as the in-focus position. However, in one embodiment of the present invention, focus control is performed using the evaluation value SC. However, this problem does not occur. In the case of the evaluation value SC, the peaks exist only at the positions A, B, and D.

  In the embodiment of the present invention, even when all the peaks due to high luminance cannot be completely removed because the setting width is inappropriate, the configuration of the optical detector 8 shown in FIG. You can focus. The processes shown in FIGS. 4, 5, and 6 are performed by the system controller 9.

  FIG. 4 shows the entire processing according to the embodiment of the present invention. In the first step S1, an evaluation value SC that has not been subjected to high luminance removal is set as an evaluation value used for AF processing. In the next step S2, a comparison process is performed between the evaluation value SR with high luminance removed and the evaluation value SC without high luminance removal. The comparison process is a comparison between values at each sampling position of the evaluation value.

  In the case of the evaluation values SRa and SRb in FIG. 3, even if the setting range for removal is too narrow, the false peak at the position D is a value significantly smaller than the original level by the high luminance partial removal processing. Has been. Therefore, the result of the comparison is a large value. With this, the peak at the position D in the evaluation value SC is determined to be false and is excluded from the focus position candidates. In step S3, the final AF processing is performed using the comparison result between the evaluation values SR and SC with reference to the evaluation value SC. The AF process in step S3 is a process in which, for example, a peak position obtained by excluding a position where the difference between the evaluation value SRa and the evaluation value SRa is equal to or greater than a certain value from the peak position of the evaluation value SC, in this example, the B lens position is set as the in-focus position. .

  FIG. 5 explains the process of step S2 in more detail. In step S11, it is determined whether or not the entire screen is dark. If the entire screen is not dark, it is determined in step S13 whether or not the entire screen is very bright. If the entire screen is not very bright or dark, the processing of the present invention is unnecessary, and the processing ends. If it is determined that the entire screen is very bright or dark, a high brightness determination process is performed in step S12. As described later, the high brightness determination process is a process for determining whether or not there is a high brightness portion such as a bright spot in the entire very bright screen or the entire dark screen.

In step S12, if it is determined that there is a high luminance part, the high luminance determination flag FL is turned ON ("1"), and if it is determined that there is no high luminance part, the high luminance determination flag FL is turned OFF.
("0"). In step S14, it is determined whether or not it is determined that there is a high luminance portion from the value of the high luminance determination flag FL. If it is determined that there is no high-luminance portion, the processing of the present invention is unnecessary, and the processing ends.

  In step S15, it is determined whether or not the ratio between the presence of the high brightness mask and the absence of the high brightness mask is greater than or equal to a predetermined value. The ratio can be obtained from the difference between the presence of the high brightness mask and the absence of the high brightness mask. If the difference between the presence of the high-intensity mask and the absence of the high-intensity mask is not greater than or equal to the predetermined value, the process is terminated. Made. Above, the process of step S2 is complete | finished.

  FIG. 6 shows an example of the high luminance determination processing S12 for determining whether or not there is a high luminance portion (for example, a bright spot) in the processing shown in FIG. In the determination, threshold values A and B to be compared with the image signal are set. The threshold A is a value set on the brighter side than the threshold B. A value obtained by counting pixels having a value exceeding the threshold A is defined as a high luminance count value KA. A value obtained by counting pixels having a value exceeding the threshold B is set as a high luminance count value KB. The ratio of these count values KA and KB is C. That is, C = KA / KB.

In step S21, the threshold value THR for which the ratio C is set It is determined whether or not it is greater than or equal to KK. C ≧ THR In the case of KK, the high brightness determination flag FL is set to ON (“1”). On the other hand, C <THR In the case of KK, the high luminance determination flag FL is set to OFF (“0”). For example, in the case of a high-luminance subject, since there are many high-luminance pixels, both the count values KA and KB are large, and it is determined that the luminance is high. On the other hand, for a non-bright subject, the count value KA is small and the count value KB is large, so the ratio C is THR. Since it is smaller than KK, it is not determined as a high-luminance subject.

  As described above, in the embodiment of the present invention, the evaluation value SC shown in FIG. 3A and the evaluation value SRa shown in FIG. 3B are used to evaluate two evaluation values at each sampling position within the lens position change range. And the evaluation value at the sampling position D in the evaluation value SC at which this difference is equal to or greater than a predetermined threshold value is excluded from the focus position candidates, and the position of the focus lens is erroneously controlled at this position. Can be prevented.

  Although one embodiment of the present invention has been specifically described above, the present invention is not limited to the above-described embodiment, and various modifications based on the technical idea of the present invention are possible. .

It is a block diagram which shows the whole structure of one embodiment of this invention. It is a block diagram of an example of the optical detector in one embodiment of this invention. It is a basic diagram which shows the example of the evaluation value used for description of one embodiment of this invention. It is a flowchart for demonstrating the whole flow of the process of one Embodiment of this invention. It is a flowchart for demonstrating the process for preventing focusing on a false peak in the process of one Embodiment of this invention. It is a flowchart for demonstrating the process for determining the presence or absence of a high-intensity subject in the process of one Embodiment of this invention. It is a basic diagram for demonstrating the conventional focus control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Focus lens group 2 ... Imaging device 8 ... Optical detector 9 ... System controller 81 ... Luminance signal generation circuit 82 ... Filter arithmetic circuit 83 ... High luminance removal circuit

Claims (3)

An imaging step of imaging a subject through a focus lens and converting the subject light into an electrical signal;
A signal extraction step of extracting a first focus control signal based on the middle and high frequency components in the luminance signal obtained in the imaging step;
A signal extraction step of extracting a second focus control signal from which a high-luminance portion of the first focus control signal is removed;
An evaluation signal generating step for generating a first evaluation value according to the position of the focus lens from the first focus control signal;
An evaluation signal generating step for generating a second evaluation value according to the position of the focus lens from the second focus control signal;
A difference between the first evaluation value and the second evaluation value at a position where the lens positions are substantially the same is detected, and when the detected difference is large, the first evaluation value is determined as a focus position. A comparison step to exclude from the candidate,
An imaging method comprising: controlling the position of the focus lens using both the first evaluation value that has been processed in the comparison step and the first evaluation value that has not been processed in the comparison step .   An imaging method in which the comparison step is performed only when it is determined that the first focus control signal includes a high-luminance subject. Imaging means for imaging a subject through a focus lens and converting the subject light into an electrical signal;
A signal extraction means for extracting a first focus control signal based on a middle-high frequency component in the luminance signal obtained by the imaging means;
Signal extraction means for extracting a second focus control signal from which a high-luminance portion of the first focus control signal is removed;
Evaluation signal generating means for generating a first evaluation value from the first focus control signal according to the position of the focus lens;
Evaluation signal generating means for generating a second evaluation value according to the position of the focus lens from the second focus control signal;
A difference between the first evaluation value and the second evaluation value at a position where the lens positions are substantially the same is detected, and when the detected difference is large, the first evaluation value is determined as a focus position. Comparison means to exclude from the candidate,
An imaging apparatus comprising: means for controlling the position of the focus lens based on the first evaluation value processed by the comparison means.

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