JP2007233222A - Focus detecting device for video camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focus detecting device for a video camera which has the circuit scale substantially equal to that in a method for extracting high-frequency components from luminance signal and which can fully secure focusing accuracy, even for a video having few G signals. <P>SOLUTION: A focusing position is obtained by selecting a signal, having the largest amplitude from among video signals of red, green and blue that are the three primary colors of light by an NAM generation part 104, halfway through signal processing in a video signal processing part 103, and controlling the position of the lens with a lens control part 107 so that the value obtained by integrating the absolute value of the high-frequency components, extracted from the selected video signal by a high-frequency components extraction part 105 in a predetermined area by a focusing discrimination part 106, become maximum. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a focus detection apparatus that uses a high-frequency component of a video signal to detect the focus of a video camera.

  2. Description of the Related Art Conventionally, in a video camera, a focus detection device that determines a focus position where a high-frequency component extracted from a video signal is maximized is often used for focus detection. This utilizes the fact that the image becomes clear when the subject is focused, that is, the high-frequency component of the image signal is increased. A luminance signal is often used as a signal for extracting the high frequency component.

  A video signal obtained by photographing a normal subject contains a large number of G signals among the three primary colors of red, green, and blue, that is, R, G, and B signals. Detection can be performed. However, in the case of an image with few G signals, the luminance signal is small, so the high frequency component obtained from the luminance signal is small. This is because the G signal occupies about 60% of the luminance signal in the NTSC (National Television System Committee) or PAL (Phase Alternation By Line) video system, so the luminance signal is small if the G signal is small. Because.

  Then, the focus is detected from a small high-frequency component. As a result, the influence of quantization noise and random noise increases, and the focus detection accuracy deteriorates. As a specific example, a case where the video signal is an R signal and a G signal are 0 and the B signal is a signal having a waveform shown in FIG. 7A will be described as follows. First, when the signal of FIG. 7A is A / D converted, the signal waveform of FIG. 7B is obtained. In the case of the NTSC or PAL video system, the B signal is included in the luminance signal by about 11%. Therefore, if there are no G and R signals, the luminance signal is the signal shown in FIG. Here, the dotted line in FIG. 7 indicates the quantization interval. Then, the luminance signal is almost indistinguishable from noise, and it becomes extremely difficult to detect the focus. Although there is almost no state of only the B signal in the actual video signal, since the same tendency is observed in a bluish video, the focus detection accuracy is inevitably deteriorated.

  On the other hand, if the configuration disclosed in Patent Document 1 is used, the in-focus position is detected by evaluating the high-frequency component of the G signal and the high-frequency component of the R signal or B signal. Even for a video signal with a small amount of R signal and a large proportion of B signal, the detection accuracy is higher than in the case of detecting focus from a luminance signal.

  This will be described with a specific example as follows. FIG. 8 is a block diagram showing a configuration of a video camera including a circuit for detecting an in-focus state disclosed in Patent Document 1, and FIG. 9 is a block diagram showing a configuration of a NAM (Non Additive Mixing) generator. In FIG. 8, the light that has passed through the lens 801 is converted into an electric signal by the image sensor 802. The signal is subjected to signal processing such as white balance in the video signal processing unit 803. The video signals of the three primary colors red, green, and blue, that is, R, G, and B, are extracted from the middle, and a high frequency component extraction unit R, G, and B high frequency components are extracted at 804 to 806, respectively. Here, a band pass filter is used for extraction of the high frequency component.

  Then, as shown in FIG. 9, the amplitude comparison circuit 901 compares the amplitude of the high frequency component of the B signal and the high frequency component of the R signal in the NAM generation unit 807, and the larger one is selected based on the comparison result. The higher one of the amplitudes of the high frequency components of the R signal and B signal can be obtained, and when there is almost no R signal, the high frequency component of the B signal is obtained. Focusing is determined based on the high-frequency component of the B signal and the high-frequency component of the G signal extracted from the high-frequency component extraction unit 804. When there is almost no G signal, there is almost no high-frequency component of the G signal. , The high frequency component of the G signal is ignored, and the high frequency component of the B signal is used as a signal for determining focus.

  Then, when the lens position is controlled by the lens control unit 809 so that the high-frequency component of the B signal is maximized, the in-focus position is obtained. Therefore, even in the case of an image with few G and R signals and many B signals, the detection accuracy for obtaining the in-focus position does not decrease much compared to the case in which the in-focus position is obtained from the luminance signal.

In addition, although the Example described in patent document 1 described the example using axial chromatic aberration, as above-mentioned, it extracted from B signal also about the image | video in case there are few R signals and G signals. Since the high frequency component is used, there is an effect that the detection accuracy of the in-focus position does not drop much compared to the case where the high frequency component extracted from the luminance signal is used.
JP-A-8-102955 (paragraph numbers 0007 to 0008)

  In the above-described configuration, the focusing accuracy is improved for an image with few G signals, compared to a method of extracting a high frequency component from a luminance signal. However, the number of circuits for extracting high-frequency components is tripled, and further, a circuit for determining the size of high-frequency components is also required, so that the circuit scale becomes larger compared to a method for extracting high-frequency components from luminance signals.

  The present invention provides a focus detection device for a video camera that is substantially the same in circuit scale as a method for extracting a high-frequency component from a luminance signal, and that can ensure sufficient focusing accuracy even for an image with little G signal. For the purpose.

  An in-focus detection device for a video camera according to a first aspect of the present invention includes a lens that collects light of a subject, an imaging unit that converts light imaged through the lens into an electrical signal, and an output from the imaging unit Video signal processing means for performing predetermined signal processing including color adjustment, frequency characteristic adjustment and gradation correction, and light extracted after the predetermined signal processing in the middle of the video signal processing means. A NAM generating means for selecting the largest signal among the three primary colors of red, green and blue video signals; a high frequency component extracting means for extracting a high frequency component of the video signal output from the NAM generating means; It is characterized by comprising focusing determining means for determining whether or not focusing is performed based on the amount of high-frequency component, and lens control means for controlling the lens according to the determination result of the focusing determining means.

  A focus detection device for a video camera according to a second invention of the present application includes a lens that collects light of an object, an imaging unit that converts light imaged through the lens into an electrical signal, and an output from the imaging device. Video signal processing means for performing predetermined signal processing including color adjustment, frequency characteristic adjustment and gradation correction, and light extracted after the predetermined signal processing in the middle of the video signal processing means. A NAM generating means for selecting the largest signal among the three primary colors of red, green and blue video signals; a high frequency component extracting means for extracting a high frequency component of the video signal output from the NAM generating means; It is characterized by comprising focusing determining means for determining whether or not focusing is performed based on the amount of the high frequency component, and display means for displaying the determination result of the focusing determining means.

  According to the present invention as described above, it is possible to provide a focus detection device for a video camera which has substantially the same circuit scale as a method for extracting a high-frequency component from a luminance signal and can improve focusing accuracy even for an image with little green.

  In addition, even when focusing manually, the circuit scale is almost the same as the method of extracting high-frequency components from the luminance signal, and a signal that is a guide for focusing can be obtained even for images with little green color, Displaying the signal on a monitor or the like in a visually recognizable format makes it easier for the camera operator to find the in-focus position, particularly for bluish images with low human eye sensitivity.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block diagram showing the configuration of a focus detection apparatus for a video camera according to Embodiment 1 of the present invention, and FIG. 2 is a block diagram showing the configuration of a NAM (Non Additive Mixing) generator. In FIG. 1, light from a subject is collected by a lens 101 and converted into an electric signal by an image sensor 102. This electric signal is subjected to A / D conversion after the noise specific to the solid-state image sensor is removed by the video signal processing unit 103, color adjustment such as white balance, frequency characteristic adjustment such as contour correction, and gamma correction. The signal processing as the camera including the tone correction is performed, and the video signal as the camera is output.

  From the middle of the video signal processing unit 103, the three primary colors green, blue, and red, that is, G, B, and R video signals are taken out, and the NAM generation unit 104 extracts the N, That is, the signal with the highest signal level is selected. Therefore, when there are few R signals and G signals, the level of the B signal is higher than that of the R signal and the G signal, so the B signal is selected.

  Then, the high frequency component extraction unit 105 extracts the high frequency component of the NAM signal. Here, a band pass filter is used for extraction of the high frequency component. Next, the focus determination unit 106 integrates the absolute value of the high frequency component for one field in each designated area of the screen. Then, when the lens control unit 107 controls the position of the lens so that the integrated value comes to the position of the vertex of the curve shown in FIG. FIG. 4 is a diagram illustrating the relationship between the integral value of the high frequency component of the video signal and the position of the lens. This control is a so-called hill-climbing control method. First, move the lens in one direction, move the lens in the opposite direction when the integral value of the high-frequency component decreases, and move the lens in the same direction as the high-frequency component increases. . If this operation is repeated, the position where the high-frequency component is reduced appears regardless of the movement. The fact that the high-frequency component is reduced by either movement means that the high-frequency component is maximum at that position, and that position becomes the in-focus position. In FIG. 4, the peak of the peak of the curve is the in-focus position.

  Next, the operation of the NAM generation unit 104 will be described with reference to FIG. In FIG. 2, first, the level comparison circuit 201 compares the levels of the B signal and the R signal, and based on the comparison result, the selection circuit 202 selects the signal having the larger level of the B signal and the R signal. The Similarly, the level comparison circuit 203 compares the G signal and the output signal of the selection circuit 202, that is, the larger amplitude of the B signal and the R signal, and the selection circuit 204 selects the larger level. Therefore, the signal having the highest level among the R, G, and B signals is selected.

  With the above operation, even when there is little green light with a small circuit scale, focusing accuracy can be improved with a smaller circuit scale than a circuit that determines the focus position from the luminance signal.

  Note that the G, B, and R signals input to the NAM generating unit 104 may be negative or too large. At this time, as shown in FIG. 3, a circuit for limiting the amplitude is obtained before obtaining the NAM signal, such as the amplitude limiting circuits 301 to 303. For example, a negative signal is set to 0, and an excessively large signal is limited by setting an upper limit based on the number of bits. By doing so, the number of bits of the circuit in the NAM generation unit 104 and the high frequency component extraction unit can be reduced, and the circuit scale can be further reduced.

(Embodiment 2)
FIG. 5 is a block diagram showing a configuration of a focus detection apparatus for a video camera according to Embodiment 2 of the present invention, and FIG. 6 is a view showing a viewfinder screen displaying a focus detection result. In FIG. 5, the same components as those in FIG. The difference from the first embodiment is that the focus determination unit 106 and the lens control unit 107 in FIG. 1 are eliminated, and a display conversion unit 501 and a viewfinder 502 are provided. As shown in FIG. 5, the high frequency component extracted by the high frequency component extraction unit 105 is converted into a bar graph or numerical value by the display conversion unit 501 and displayed on the viewfinder 502 as shown in FIG. When focusing, it can also be used as a guide for the in-focus position.

  Of course, it goes without saying that the focus detection apparatus of the first embodiment and the second embodiment may be combined to switch the focus of the video camera to automatic or manual.

  By using the focus detection circuit of the video camera of the present invention, the focus position can be obtained with high accuracy even with a small circuit scale and a small amount of green images, which is useful for a video camera that automatically focuses.

  In addition, by using the focus detection circuit of the video camera of the present invention, the focus detection result is displayed on the viewfinder even with a small circuit scale and a little green image, which is also useful for a manually focused video camera. It is.

1 is a block diagram showing a configuration of a focus detection circuit of a video camera according to Embodiment 1 of the present invention. The block diagram which shows the structure of the NAM production | generation part in the focus detection circuit of the video camera of Embodiment 1 of this invention. The block diagram which shows the structure of the NAM production | generation part which provided the amplitude limiting circuit in the focus detection circuit of the video camera of Embodiment 1 of this invention. The figure which shows the relationship between the integrated value of the high frequency component of the video signal and the lens position The block diagram which shows the structure of the focus detection apparatus of the video camera of Embodiment 2 of this invention. The figure which shows the screen of the viewfinder which displayed the focus detection result of the focus detection apparatus of the video camera of Embodiment 2 of this invention. The figure which shows the waveform of B signal A block diagram showing a configuration of a video camera including a circuit for detecting a conventional in-focus state A block diagram showing a configuration of a NAM generating unit of a video camera including a circuit for detecting a conventional in-focus state

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Lens 102 Image pick-up element 103 Image | video signal processing part 104 NAM production | generation part 105 High frequency component extraction part 106 Focus determination part 107 Lens control part 201,203 Level comparison circuit 202,204 Selection circuit 301,302,303 Amplitude limiting circuit 501 Display conversion Part 502 Viewfinder

Claims (3)

A lens for condensing the light of the subject, an imaging means for converting the light imaged through the lens into an electrical signal, and a signal output from the imaging means for adjusting the color, adjusting the frequency characteristics, and Video signal processing means for performing predetermined signal processing including tone correction, and red, green and blue video signals which are three primary colors of light extracted after predetermined signal processing in the middle of the video signal processing means NAM generating means for selecting the largest signal, high frequency component extracting means for extracting a high frequency component of the video signal output from the NAM generating means, and whether or not the focus is based on the amount of the high frequency component An in-focus detection device for a video camera, comprising: an in-focus determining means for determining; and a lens control means for controlling the lens in accordance with a determination result of the in-focus determining means. A lens for condensing the light of the subject, an imaging means for converting the light imaged through the lens into an electrical signal, a color adjustment, a frequency characteristic adjustment and a step in the signal output from the imaging device; Video signal processing means for performing predetermined signal processing including tone correction, and red, green and blue video signals which are three primary colors of light extracted after predetermined signal processing in the middle of the video signal processing means NAM generating means for selecting the largest signal, high frequency component extracting means for extracting a high frequency component of the video signal output from the NAM generating means, and whether or not the focus is based on the amount of the high frequency component An in-focus detection device for a video camera, comprising: an in-focus determining means for determining; and a display means for displaying a determination result of the in-focus determining means. 3. The in-focus detection apparatus for a video camera according to claim 1, wherein the NAM generating means includes amplitude limiting means for limiting the amplitude of the input video signal.

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