JP2005070450A - Video camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To adjust a focus in a short time when a subject field abruptly changes. <P>SOLUTION: An image sensor 16 photographs a subject field through a focusing lens 12 and a passive sensor 42 and a CPU 44 measures the distance to a subject belonging to a focus area. The focus is adjusted by the CPU 44 based upon a live image signal outputted from the image sensor 16 and the measurement result of the distance to the subject. Here, the CPU 44 decides whether the movement quantity of the focus area per unit time exceeds a threshold and makes the passive sensor 42 effective when the decision result is affirmative, and ineffective when inaffirmative. The focus is adjusted based upon at least the output of the passive sensor 42 when the passive sensor 42 is made effective and based upon the live image signal from the image sensor 16 when the passive sensor 42 is made ineffective. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a video camera, and more particularly to a video camera having a continuous AF function that keeps focusing on a subject, for example.

An example of a conventional device of this type is disclosed in Patent Document 1. This prior art determines whether or not the current state is an in-focus state, and attempts to change conditions for restarting the continuous AF function in accordance with the determination result. As a result, the response characteristics of the shooting operation can be improved and the power consumption can be suppressed.
JP 2003-5024 A [G02B 7/28]

    However, since the conventional technology uses a so-called contrast detection method, the entire object scene changes suddenly due to high-speed panning or tilting, or a new subject suddenly appears in the object field. In this case, there is a problem that it takes time to adjust the focus.

    Therefore, a main object of the present invention is to provide a video camera capable of adjusting the focus in a short time when the change of the object scene is severe.

  The video camera according to the first aspect of the present invention is a photographing means for photographing a subject field through an optical lens, a measuring means for measuring a distance to an arbitrary subject belonging to the subject field, and an interval between the optical lens and a light receiving surface of the photographing means. Adjusting means for adjusting the image based on the image signal output from the photographing means and the measurement result of the measuring means, and determining whether or not the amount of motion per unit time of any area belonging to the object scene exceeds the first threshold And a control unit that validates the measurement unit when the discrimination result of the discrimination unit is affirmative and invalidates the measurement unit when the discrimination result of the discrimination unit is negative.

  According to the first aspect of the present invention, the photographing means photographs the scene through the optical lens, and the measuring means measures the distance to an arbitrary subject belonging to the scene. The distance between the optical lens and the light receiving surface of the photographing unit is adjusted by the adjusting unit based on the image signal output from the photographing unit and the measurement result of the measuring unit.

  However, it is determined by the determining means whether or not the amount of motion per unit time of an arbitrary area belonging to the object scene exceeds the first threshold value. The control means validates the measurement means when the discrimination result of the discrimination means is affirmative, and invalidates the measurement means when the discrimination result of the discrimination means is negative. Accordingly, the interval is adjusted based on at least the measurement result when the measuring means is validated, and the interval is adjusted based on the image signal when the measuring means is invalidated.

  In adjusting the distance between the optical lens and the light receiving surface of the photographing means, the adjustment speed based on the measurement result of the measurement means is faster than the adjustment speed based on the image signal. Therefore, by enabling the measuring means when the amount of motion per unit time of an arbitrary area belonging to the scene exceeds the first threshold, the focus can be quickly adjusted when the scene changes rapidly. Can be adjusted.

  Further, in adjusting the distance between the optical lens and the light receiving surface of the photographing unit, the adjustment accuracy based on the measurement result of the measurement unit is lower than the adjustment accuracy based on the image signal. For this reason, by invalidating the measurement means when the amount of motion is equal to or less than the first threshold, erroneous focus adjustment can be avoided and adjustment accuracy can be improved.

  The video camera according to the invention of claim 2 is dependent on the video camera of claim 1, and the adjusting means determines at least a direction for changing the interval based on the measurement result, and the direction determined by the determining means. First interval changing means for changing the interval is included.

  One possible cause of delaying focus adjustment in the prior art when the object scene changes suddenly is that the direction in which the interval is changed is unknown. Therefore, in the invention of claim 2, at least the direction in which the interval is changed is determined based on the measurement result. As a result, the time required for focus adjustment can be shortened.

  The video camera according to the invention of claim 3 is dependent on the video camera of claim 2, wherein the determining means further determines the amount of change of the interval, and the first interval changing means changes the interval according to the amount of change determined by the determining means. To do.

  Another possible cause of delay in focus adjustment in the prior art when the field of view changes suddenly is considered to be a limit in the frame rate of the image signal. Therefore, in the invention of claim 3, the change amount is further determined based on the measurement result. As a result, the time required for focus adjustment can be shortened.

  The video camera according to the invention of claim 4 is dependent on the video camera of claim 3, and the change amount of the interval by the first interval changing means is smaller than the change amount determined by the determining means. As described above, the adjustment accuracy based on the measurement result of the measurement unit is lower than the adjustment accuracy based on the image signal. Therefore, in the invention of claim 4, the actual change amount of the interval is made smaller than the determined change amount. Thereby, after the change by the first interval changing means is completed, the interval can be adjusted with high accuracy based on the image signal.

  The video camera according to the invention of claim 5 is dependent on the video camera of claims 2 to 4, and the adjusting means changes the interval in a direction in which the high-frequency component of the partial image signal corresponding to an arbitrary subject among the image signals increases. The second interval changing means further includes Focus adjustment is realized by changing the interval in the direction in which the high-frequency component increases.

  According to a sixth aspect of the present invention, there is provided a video camera according to any one of the first to fifth aspects, comprising: an extracting means for extracting a high frequency component of an arbitrary region from an image signal of each screen output from the photographing means; and an extracting means. The image processing apparatus further includes a calculation unit that calculates the inter-screen difference of the extracted high-frequency component as a motion amount. As a result, the amount of movement can be accurately obtained.

  The video camera according to the invention of claim 7 is dependent on any one of claims 1 to 6, and further includes an activation unit that activates the adjustment unit when the amount of motion in an arbitrary area with respect to the specific screen exceeds the second threshold. Prepare. As a result, continuous AF can be realized while reducing power consumption.

  The video camera according to the invention of claim 8 is dependent on claim 7, and the specific screen is a screen when the interval is set to the optimum value by the previous adjustment by the adjustment means.

  A video camera according to a ninth aspect of the present invention is dependent on any one of the first to eighth aspects, and the measurement means performs measurement by a phase difference detection method. Thereby, the distance to the subject can be measured in a short time.

  According to the present invention, when the amount of motion per unit time of an arbitrary region belonging to the scene exceeds the first threshold, the measurement unit is enabled to focus when the scene changes rapidly. It can be adjusted in a short time. Further, by invalidating the measuring means when the amount of motion is equal to or less than the first threshold value, it is possible to avoid an erroneous focus adjustment and improve the adjustment accuracy.

  The above object, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

  Referring to FIG. 1, a digital video camera 10 of this embodiment includes a focus lens 12 and an aperture unit 14. The optical image of the object scene is irradiated onto the light receiving surface, that is, the imaging surface of the image sensor 16 through these members. On the imaging surface, a charge corresponding to the optical image of the subject, that is, a raw image signal is generated by photoelectric conversion.

  When displaying a real-time moving image of a subject, that is, a through image, on the LCD monitor 34, the CPU 44 instructs the driver 20 to open the aperture and instructs the driver 22 to repeat pre-exposure and thinning-out reading. The driver 20 releases the aperture amount of the aperture unit 14, and the driver 22 repeatedly executes pre-exposure of the image sensor 16 and thinning-out reading of the raw image signal generated thereby. Pre-exposure and thinning readout are executed in response to a vertical synchronization signal generated every 1/30 seconds. As a result, a raw image signal corresponding to the optical image of the subject is output from the image sensor 16 at a frame rate of 30 fps.

  The output raw image signal of each frame is subjected to a series of processes of noise removal, level adjustment and A / D conversion by the CDS / AGC / AD circuit 24, thereby obtaining raw image data as a digital signal. The signal processing circuit 26 performs processing such as white balance adjustment, color separation, and YUV conversion on the raw image data output from the CDS / AGC / AD circuit 24 to generate image data in YUV format. The generated image data is written into the SDRAM 30 by the memory control circuit 28 and then read out by the same memory control circuit 28. The video encoder 32 converts the image data read out by the memory control circuit 28 into a composite video signal conforming to the NTSC format, and supplies the converted composite video signal to the LCD monitor 34. As a result, a through image of the subject is displayed on the monitor screen.

  When the shutter button 40 is operated, the CPU 44 issues an image compression command at a rate of once every 1/30 seconds in response to the vertical synchronization signal. The JPEG codec 46 executes JPEG compression every time an image compression command is issued. Specifically, the JPEG codec 46 reads one frame of image data from the SDRAM 30 through the memory control circuit 28, performs JPEG compression on the read image data, and passes the compressed image data, that is, JPEG data through the memory control circuit 28. Write to SDRAM 30. In this way, multiple frames of JPEG data are accumulated in the SDRAM 30. The CPU 44 also sequentially reads JPEG data from the SDRAM 30 through the memory control circuit 28 and records the read JPEG data on the recording medium 50 through the I / F circuit 48. When the shutter button 40 is operated again, the CPU 40 interrupts the output of the image compression command, and interrupts the recording process after all the JPEG data stored in the SDRAM 30 has been recorded.

  Of the image data generated by the signal processing circuit 26, Y data is provided to the luminance evaluation circuit 36 for exposure control. Referring to FIG. 2, the luminance evaluation circuit 36 assigns a photometric area E0 to the center of the object scene, assigns a photometric area E1 to the periphery of the object field, and belongs to the Y data belonging to the photometry area E0 and the photometry area E1. Each piece of Y data is integrated every frame. The CPU 44 fetches the luminance evaluation value Iy [0] obtained for the photometric area E0 and the luminance evaluation value Iy [1] obtained for the photometric area E1 in response to the vertical synchronization signal, and pre-exposure set in the driver 22 The time is adjusted based on the luminance evaluation values Iy [0] and Iy [1].

  The Y data generated by the signal processing circuit 26 is also given to the AF evaluation circuit 38 for focus control according to the contrast detection method. Referring to FIG. 3, the AF evaluation circuit 38 assigns a focus area F0 to the center of the object scene, and integrates high frequency components of Y data belonging to the focus area F0 for each frame. The CPU 44 takes in the AF evaluation value Iyh obtained by the integration process in response to the vertical synchronization signal, and drives the driver 18 based on the AF evaluation value Iyh. As a result, the focus lens 12 is placed at the focal point. The AF evaluation value Iyh obtained when the focus lens 12 is placed at the in-focus point is particularly defined as “optimal AF evaluation value Iyhs”.

  The CPU 44 also compares a variable ΔIyh1 indicating the absolute difference between the AF evaluation value Iyh and the optimum AF evaluation value Iyhs sequentially fetched from the AF evaluation circuit 38 with a threshold value TH1 (= Iyhs * 0.05), and the variable ΔIyh1 is a threshold value. Focus adjustment is performed again when TH1 is exceeded. This realizes continuous AF that keeps the focus on the object scene.

  However, when a sudden movement occurs in the subject belonging to the focus area F0, it takes time to adjust the focus in the contrast detection method. In addition to the fact that the AF evaluation value Iyh can be obtained only once per frame, it is unclear whether the movement start direction of the focus lens 12 is the closest end side or the infinity side. This is due to that.

  Therefore, in this embodiment, a variable ΔIyh2 indicating a difference absolute value between two AF evaluation values Iyh obtained in succession is compared with a threshold value TH2 (= fixed value), and when the variable ΔIyh2 exceeds the threshold value TH2, a passive state is obtained. The focus adjustment according to the phase difference detection method is executed using the sensor 42.

  More specifically, in the passive sensor 42, the optical image of the object scene is irradiated to the image sensor 42c through the optical lens 42a and to the image sensor 42d through the optical lens 42b. The image signals output from the image sensors 42c and 42b are given to the CPU 44. Since there is a shift (phase difference) between the object scene captured by the image sensor 42c and the object scene captured by the image sensor 42b, the CPU 44 selects the focus area F0 shown in FIG. The phase difference of the image signal belonging to the focus area F0 ′ that is substantially the same as that of the focus area F0 ′ is detected, and the distance to the subject belonging to the focus area F0 ′ is measured based on this phase difference.

  Further, the CPU 44 calculates the movement direction Ds and the movement amount Ls to the focal point based on the measured distance, and moves the focus lens 12 by the movement amount Ls−ΔL according to the movement direction Ds. Referring to FIG. 4, focus lens 12 moves to the vicinity of the focal point. When the movement according to the movement amount Ls−ΔL is completed, the CPU 44 executes focus adjustment according to the contrast detection method. As a result, the focus lens 12 reaches the focal point.

  As described above, by using the phase difference detection method and the contrast detection method in combination, high-speed and high-precision focus adjustment is realized when the object scene changes instantaneously.

  Note that the CPU 44 is a multitask CPU equipped with a multitask OS such as μITRON, and the above-described exposure control and focus control are realized by an AE task and an AF task, respectively. Also, JPEG data recording is realized by a recording task.

  Specifically, the CPU 44 executes processing according to the flowcharts shown in FIGS. 5 to 8 according to the control program stored in the flash memory 52.

  First, the AE task and the AF task are activated in steps S1 and S3 in FIG. 5, respectively, and the through image processing system is activated in step S5. As a result, a through image corresponding to the optical image of the object scene input to the image sensor 16 is displayed on the LCD 34. When the shutter button 40 is operated, YES is determined in step S7, and the recording task is activated in step S9.

  In step S11, image compression processing is executed. Specifically, an image compression command is given to the JPEG codec 46 in response to the vertical synchronization signal. As a result, one frame of image data is provided from the SDRAM 30 to the JPEG codec 46, and one frame of JPEG data output from the JPEG codec 46 is written into the SDRAM 30. When such image compression processing is completed, it is determined in step S13 whether or not the shutter button 40 has been operated. If NO, the process returns to step S11. Therefore, unless the shutter button 40 is operated again, the image compression process is repeated, and JPEG data of successive frames is accumulated in the SDRAM 30. If the shutter button 40 is operated, “YES” is determined in the step S13, and the process returns to the step S7.

  The AF task activated in step S1 follows the flowcharts shown in FIGS. First, in step S21, the flag PSV_AFflg is set to “1”. The flag PSV_AFflg is a flag for determining whether or not focus adjustment using the passive sensor 42 is necessary, and indicates that “1” is necessary and “0” is not necessary. The focus adjustment using the passive sensor 42 is first requested by the process of step S21.

  In step S23, the state of the flag PSV_AFflg is determined. If PSV_AFflg = 1, the process proceeds to step S25, and if PSV_AFflg = 0, the process proceeds to step S33. In step S25, the distance to the subject belonging to the focus area F0 ′ is measured. Specifically, the image signal is taken from each of the image sensors 42c and 42d provided in the passive sensor 42, and the distance to the subject is measured based on the shift of the image signal in the focus area F0 ′. When the distance is obtained, the process proceeds to step S27, and the movement direction (= Ds) of the focus lens 12 and the movement amount (= Ls) of the focus lens 12 to the focal point are calculated.

  In step S29, it is determined whether or not the calculated lens movement amount Ls is an error. If it is determined that an error has occurred, a step width, which will be described later, is set to a standard width in step S35, and the process proceeds to step S37. On the other hand, if it is determined that there is no error, the process proceeds to step S31, and the focus lens 12 is moved by the movement amount Ls−ΔL in the movement direction Ds. When the process of step S21 is completed, the step width is set to a very small width in step S33, and the focus adjustment according to the CCD_AF process, that is, the contrast detection method is executed in step S37. As a result, the focus lens 12 reaches the focal point shown in FIG.

  In step S39, the AF evaluation value Iyh obtained when the focus lens 12 is brought into focus, that is, the optimum AF evaluation value Iyhs is set in the register 44a. In step S41, the process waits for a predetermined time. In step S43, the AF evaluation value Iyh is fetched from the AF evaluation circuit 38. In step S45, the absolute difference value ΔIyh1 is obtained according to the equation (1).

  In step S47, the obtained difference absolute value ΔIyh1 is compared with a threshold value TH1. Then, as long as the absolute difference value ΔIyh1 is equal to or less than the threshold value TH1, the processes in steps S41 to S47 are repeated. When the absolute difference value ΔIyh1 exceeds the threshold value TH1, the process proceeds from step S47 to step S49 in order to perform focus adjustment again. In step S49, the absolute difference value ΔIyh2 is obtained according to Equation 2.

  By the calculation according to Equation 2, the difference absolute value ΔIyh2 indicates the amount of movement (change amount) of the subject belonging to the focus area F0 in one frame period. In step S51, the difference absolute value ΔIyh1 is compared with a threshold value TH1. When the difference absolute value ΔIyh1 exceeds the threshold value TH1, the flag PSV_AFflg is set to “1” in step S53, and when the difference absolute value ΔIyh1 is equal to or less than the threshold value TH1, the flag PSV_AFflg is set to “0” in step S55. When the process of step S53 or S55 is completed, the process returns to step S23. Therefore, if the amount of movement of the subject belonging to the focus area F0 is small, the focus is adjusted only according to the contrast detection method. If the amount of movement of the subject belonging to the focus area F0 is large, the focus is adjusted according to the phase difference detection method and the contrast detection method. Adjusted.

  If the entire scene changes suddenly due to high-speed panning or tilting, or if a new subject suddenly appears in the scene, YES is determined in step S51, and the subject or camera Is determined to be NO in step S51.

  The CCD_AF process in step S37 shown in FIG. 6 follows a subroutine shown in FIG. First, in step S61, the focus lens 12 is moved by one step. This movement width is equal to the minute width determined in step S33 (or S73) or the standard width determined in S35. In step S63, the AF evaluation value Iyh is fetched from the AF evaluation circuit 38 in response to the vertical synchronization signal, and in the subsequent step S65, whether or not the focus lens 12 has exceeded the in-focus point is determined based on the AF evaluation value Iyh that has been taken so far. To do.

  If NO is determined in step S65, the difference absolute value ΔIyh2 is obtained in accordance with the above-described equation 2 in step S69, and the difference absolute value ΔIyh2 is compared with the threshold value TH3 in step S71. When the difference absolute value ΔIyh2 is lower than the threshold value TH3, the process directly returns to step S51. However, if the difference absolute value ΔIyh2 is equal to or less than the threshold value TH3, the step width is set to a very small width at step S73, and the process returns to step S61. When YES is determined in the step S65, the process proceeds to a step S67, and the focus lens 12 is returned to the in-focus point. When the focus lens 12 reaches the in-focus point, the routine returns to the upper-level routine.

  As can be seen from the above description, the image sensor 16 captures the object scene through the focus lens 12, and the CPU 44 measures the distance to the subject belonging to the focus area F0 ′ based on the output of the passive sensor 42 (S25). The focus is adjusted by the CPU 44 based on the raw image signal output from the image sensor 16 and the measurement result of the distance to the subject (S31, S37).

  However, the CPU 44 determines whether or not the absolute difference value ΔIyh2 indicating the amount of movement per unit time of the focus area F0 exceeds the threshold value TH2 (S51), and activates the passive sensor 42 when the determination result is affirmative. On the other hand (S53), when the determination result is negative, the passive sensor 42 is invalidated (S55). Therefore, when the passive sensor 42 is activated, the focus is adjusted based on at least the output of the passive sensor 42 (S31), and when the passive sensor 42 is deactivated, based on the raw image signal from the image sensor 16. The focus is adjusted (S37).

  The focus adjustment speed based on the output of the passive sensor 42 is faster than the focus adjustment speed based on the raw image signal from the image sensor 16. For this reason, by enabling the passive sensor 42 when the difference absolute value ΔIyh2 exceeds the threshold value TH2, the focus can be adjusted in a short time when the object scene changes rapidly.

  The focus adjustment accuracy based on the output of the passive sensor 42 is lower than the focus adjustment accuracy based on the image signal from the image sensor 16. For this reason, by invalidating the passive sensor 42 when the difference absolute value ΔIyh2 is equal to or less than the threshold value TH2, erroneous focus adjustment can be avoided and adjustment accuracy can be improved.

  In this embodiment, only the focus lens is moved in the optical axis direction for focus adjustment. However, the image sensor may be moved in the optical axis direction instead of or together with the focus lens. .

  In this embodiment, ranging is performed using a phase difference detection type passive sensor. Alternatively, ranging may be performed using an active sensor that emits infrared rays. .

  Furthermore, in this embodiment, focus adjustment is executed with a single focus area as a reference, but a plurality of focus areas are allocated on the screen, and focus adjustment is executed with reference to the plurality of focus areas. It may be.

  Furthermore, in this embodiment, the focus adjustment according to the contrast detection method is always executed after the focus adjustment according to the phase difference detection method. However, if the focus lens is moved over the movement amount Ls, the contrast detection method is performed. No focus adjustment is required.

It is a block diagram which shows one Example of this invention. It is an illustration figure which shows an example of the several photometry area allocated to the object scene. It is an illustration figure which shows an example of the some focus area allocated to the object scene. It is a graph which shows the relationship between a focus lens position and AF evaluation value. It is a flowchart which shows a part of operation | movement of FIG. 1 Example. It is a flowchart which shows a part of other operation | movement of FIG. 1 Example. It is a flowchart which shows a part of other operation | movement of FIG. 1 Example. It is a flowchart which shows a part of operation | movement of FIG. 1 Example further.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Digital camera 12 ... Focus lens 16 ... Image sensor 36 ... Luminance evaluation circuit 38 ... AF evaluation circuit 44 ... CPU
42 ... Passive sensor

Claims (9)

Photographing means for photographing the object scene through an optical lens;
Measuring means for measuring a distance to an arbitrary subject belonging to the scene;
An adjusting means for adjusting an interval between the optical lens and a light receiving surface of the photographing means based on an image signal output from the photographing means and a measurement result of the measuring means;
A discriminating means for discriminating whether or not the amount of motion per unit time of an arbitrary area belonging to the scene exceeds a first threshold; and when the discrimination result of the discriminating means is affirmative, A video camera comprising control means for invalidating the measurement means when the discrimination result of the discrimination means is negative.   2. The adjustment unit includes a determination unit that determines at least a direction in which the interval is changed based on the measurement result, and a first interval change unit that changes the interval in a direction determined by the determination unit. The listed video camera. The determining means further determines a change amount of the interval;
The video camera according to claim 2, wherein the first interval changing unit changes the interval according to a change amount determined by the determining unit.   The video camera according to claim 3, wherein a change amount of the interval by the first interval change unit is smaller than a change amount determined by the determination unit.   5. The adjustment unit according to claim 2, further comprising a second interval changing unit that changes the interval in a direction in which a high-frequency component of a partial image signal corresponding to the arbitrary subject in the image signal increases. The video camera described in. Extraction means for extracting a high-frequency component of the arbitrary region from the image signal of each screen output from the photographing means; and calculation means for calculating the inter-screen difference of the high-frequency component extracted by the extraction means as the amount of movement. The video camera according to claim 1, further comprising:   The video camera according to claim 1, further comprising an activation unit that activates the adjustment unit when the amount of movement of the arbitrary region with respect to the specific screen exceeds a second threshold value.   The video camera according to claim 7, wherein the specific screen is a screen when the interval is set to an optimum value by a previous adjustment by the adjustment unit.   The video camera according to claim 1, wherein the measurement unit performs measurement by a phase difference detection method.

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