JP2005094432A - Image server - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image server and an image server system which never delay a focusing operation if an exposure time changes, have high controllability and can transmit high-quality and stable images. <P>SOLUTION: This image server is provided with a focusing position control means 8b for determining a focusing position on the basis of the maximum value of a focus evaluation value detected by a video signal level detecting means 5c, and a focus lens driving section 7a for moving the focus lens by a predetermined control amount on the basis of a command from the control means 8b. When an exposure time is changed to a time longer than a predetermined time, the control means 8b determines a large control amount corresponding to the change in exposure time, moves the focus lens by the control amount to detect the maximum value of focus evaluation value, and performs focus control. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention provides an image server that allows a user to take a video while remotely operating a camera unit via a network such as the Internet, and stably transmits image data, and further connects the image server and the client terminal via the network. It relates to the connected image server system.

  Recently, an image server that obtains an image by remotely controlling a camera unit via a network such as the Internet has attracted attention. In such an image server, the exposure time is changed when the subject becomes dark and the normal exposure mode is changed to the long exposure mode, and when the subject becomes bright, the long exposure mode is changed to the normal exposure mode. However, when the normal exposure mode is changed to the long exposure mode, auto gain control (hereinafter AGC control), auto iris (hereinafter AI), auto white balance (hereinafter AWB), auto focus (hereinafter AF), etc. The control information for automatic control cannot properly follow a change caused by an extended exposure cycle. That is, in the normal exposure mode, control information such as AGC, AI, AWB, and AF is obtained for each frame at a predetermined cycle and automatically controlled to transmit image data. In the long exposure mode, evaluation is performed over a long cycle. When the value information is fixed and the normal exposure mode is switched to the long exposure mode, a sense of incongruity remains strong and, for example, a sharp change in brightness cannot be dealt with. Moreover, in such a case, since the client controls after receiving this, the operation of the camera unit is also poor in operability and delayed.

When changing to such a long exposure mode, the response speed of automatic signal amount control is reduced only in the long exposure mode in order to prevent a good output image from being obtained unless the incident light quantity changes for a while. An imaging apparatus provided with means has been proposed (see Patent Document 1).
JP-A-1-305671

  As described above, the conventional image server cannot appropriately follow the change due to the extended exposure period, and the evaluation value information is fixed over a long period in the long exposure mode, for example, the brightness is steep. I couldn't cope with the change. Furthermore, when the focus was deviated, the out-of-focus state continued for a long time and was difficult to see. In addition, the imaging apparatus of (Patent Document 1) copes with exposure mode switching by preventing iris oscillation or the like due to a response speed delay, but there is no specific disclosure regarding autofocus.

  There are several methods for detecting the in-focus position in autofocus, but a method that uses a high-frequency component of a video signal is often used in a network camera or the like. FIG. 4 is an explanatory diagram of the principle of conventional autofocus, FIG. 5A is an explanatory diagram showing the evaluation value level and control value of autofocus in the normal exposure mode in the conventional image server, and FIG. It is explanatory drawing which shows the evaluation value level of autofocus in the long exposure mode in the image server of (a), and its control value. When the focus position is detected by the video signal, as shown in FIG. 4, there is a property that the high frequency component of the video signal shows the maximum value in a focused state. This is because an image with a sharp outline is obtained in a focused state, and naturally high frequency components increase. If this property is used, the in-focus position is when the maximum value is reached after the peak of the high frequency component or when the gradient becomes zero.

The conventional AF control shown in FIGS. 5A and 5B is focused using this property. The focus evaluation value used here is obtained by extracting the high-frequency component of the video signal described above. At the time of out-of-focus, the level of the focus evaluation value is low and rises when the focus is achieved, and reaches the maximum value at the time of focusing. Therefore, conventionally, the focus lens is moved in the direction in which the level of the evaluation value increases, and the position where the maximum value is obtained is obtained as the in-focus position.

  In order to find the focal position, the focusing lens is moved by equal distances according to the control value. Here, the equidistant distance is for ease of explanation, and the actual condition will be described later. When the exposure time is the normal exposure time, the movement instruction is usually once per 1v (vertical synchronization signal timing period), and the movement is performed by equal distances in the direction in which the level of the focus evaluation value increases. As shown in FIG. 5A, the focus evaluation value increases with a change in the control value (movement of the focus lens), reaches a maximum at a certain point, and decreases at time T7. This indicates that the focus evaluation value has decreased again after reaching the maximum value. This means that the control value immediately before the focus evaluation value has decreased (the moving position of the focus lens) can be used as the focus control value. The focus lens is set to this value.

  Next, at the time of long exposure, the period for obtaining the video signal is extended with the extension of the exposure period, and accordingly, the signal level detection period is also extended, and the position setting period of the focus lens is naturally increased, resulting in a response. Becomes slower. In FIG. 5 (b), the exposure time is twice as long as that in the case of normal exposure, but the period until the focus evaluation value reaches the maximum value (time until T7 *) is doubled. With this, the response time until focusing is doubled or more. In the conventional image server and image server system, there is a problem that, when switching to the long exposure mode, the position setting of the focus lens becomes long, it takes time for focus control, and the responsiveness is poor. .

  By the way, the case where the focusing lens is moved by the same distance has been described above. However, since the size of the focus evaluation value varies, the actual amount is controlled in relation to the gradient in order to cope with this. ing. That is, the gradient is detected at the start of control, and when the gradient is larger than a predetermined value, it is considered that the focus shift is large, and therefore the control is performed with a large amount of movement. On the other hand, when the gradient is smaller than the predetermined value, it is considered that the peak is in the vicinity, so the movement amount is reduced. The former is a phase for mountain climbing approaching the peak, and the latter is a phase for confirming the position of the peak. In the phase, the movement amount is also changed according to the gradient.

  For example, when the motor for driving the focus lens is a stepping motor, in the hill-climbing phase with a large gradient, the motor is rotated by 16 steps, 12 steps, and 8 steps according to the gradient. Similarly, in the peak confirmation phase with a small gradient, the phase is rotated by four steps, two steps, or one step according to the gradient. However, even if the amount of movement is changed in the phase, there is no change in that the focus takes time and the responsiveness deteriorates when the mode is changed to the long exposure mode.

  Therefore, an object of the present invention is to provide an image server that does not delay the focusing operation even if the exposure time changes, has high controllability, and can transmit a high-quality and stable image.

In order to solve the above problems, the image server of the present invention includes a focus position control unit that determines a focus position based on the maximum focus evaluation value detected by the signal level detection unit, and a command from the focus position control unit. When a focus lens drive unit that moves the focus lens by a predetermined control amount is provided, and the exposure time is changed to a period longer than the predetermined period, the focus position control means responds to the change of the exposure time. The main feature is that a large control amount is determined, the focus lens is moved by the control amount, the maximum focus evaluation value is detected, and focus control is performed.

  According to the present invention, when the exposure time is changed to set the long exposure mode in which the video signal is output with a period longer than the predetermined period, the focusing operation takes time even when the long exposure mode is set. Easy and comfortable autofocus control. High controllability and high quality and stable images can be transmitted.

  A first embodiment for implementing the present invention includes a signal level detection unit that detects a signal level of a video signal output from an imaging unit, and a video signal level control that adjusts the level of the video signal output from the imaging unit. A focus evaluation value detected by the signal level detection means, the video server processing the video signal output from the video signal level control means, performing the video signal processing and performing compression processing, and outputting the image data to the outside A focus position control means for determining the focus position based on the maximum value of the lens, and a focus lens drive section for moving the focus lens by a predetermined control amount in response to a command from the focus position control means, and a predetermined exposure time. If the period is changed to a period longer than this period, the focus position control means determines a large control amount corresponding to the change in the exposure time, and moves the focus lens by the control amount. The image server is characterized in that the maximum value of the focus evaluation value is detected and the focus is controlled, and the long exposure mode in which the video signal is output with a period longer than a predetermined period by changing the exposure time. In this case, the control amount for the focusing position control means to move the focusing lens according to the exposure mode is preferably determined to be a control amount that is [long exposure period / normal exposure period] times that of normal exposure. This makes it possible to quickly detect the maximum focus evaluation value and determine the in-focus position based on this maximum value. Control is possible. High controllability and high quality and stable images can be transmitted.

  In the second embodiment for implementing the present invention, in addition to the first embodiment, focus evaluation before and after the in-focus position control unit moves the focus lens by a predetermined control amount to change the control amount. A change amount of the value is calculated, a focus evaluation value change rate indicating the change in the change amount is obtained, and the position of the previous focus lens when the focus evaluation value change rate is reversed from positive to negative is the in-focus position. The calculation for determining the in-focus position is simple and can be easily performed.

  In the third embodiment for implementing the present invention, in addition to the first or second invention, when the video signal is output at a cycle longer than a predetermined cycle by changing the exposure time of the imaging means, the focus is increased. When the evaluation value change rate becomes smaller than a predetermined value, the focus position control means is an image server that reduces the control amount, and a precise position can be detected when the maximum value is detected.

  In the fourth embodiment for implementing the present invention, in addition to the third embodiment, when the focus evaluation value change rate becomes smaller than a predetermined value, the control amount when the in-focus position control means has a predetermined cycle is used. Since the image server reduces the focus evaluation value change rate finely by changing the control amount, a precise position can be detected when the maximum value is detected.

  In addition to any one of the first to fourth embodiments, the fifth embodiment for implementing the present invention is an image server in which the focus evaluation value is a high-frequency component of the video signal detected by the signal level detection means, The in-focus position can be easily detected from the video signal obtained by the imaging means.

According to a sixth embodiment of the present invention, an image server according to any one of the first to fifth embodiments, a client terminal that can acquire image data from the image server, and the image server and the client terminal are connected. The image server system is characterized in that the transmission of image data from the image server is not delayed even if the exposure time changes, and even if there is a sharp change in brightness Can obtain stable images.

  Hereinafter, an image server and an image server system according to Embodiment 1 of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an image server and an image server system according to Embodiment 1 of the present invention, and FIG. 2 is a configuration diagram of an image server according to Embodiment 1 of the present invention.

  In FIG. 1, 1 is an image server that captures a subject and transfers image data. 2 is a user that receives and displays an image transferred from the image server 1, and can control the image server 1 with a camera control signal. A client terminal 3 such as a PC is a network such as the Internet, which can transfer images and transmit camera control signals. Reference numeral 4 denotes a DNS server for converting to an IP address when accessed by a domain name. The image server system according to the first embodiment includes an image server 1, a client terminal 2, and a network 3. The client terminal 2 will be described later.

  In FIG. 2, 5 is a camera unit that is provided in the image server 1 and shoots a subject, converts it into an image signal, and outputs the image signal, and 5a includes an image sensor such as a CCD or CMOS that photoelectrically converts the subject image. The image pickup means 5b controls the amount of light input to the image pickup means 5a and is a light amount adjustment means that can be configured by the shutter function of the image pickup means 5a although a mechanical aperture is often used.

  5c controls the level of the video signal output from the image pickup means 5a. When the signal level output from the image pickup means 5a becomes small, AGC (auto gain control) control is performed to increase the gain to optimize the signal level. The video signal level control means 5d for processing the output signal from the video signal level control means 5c, and the video signal processing means 5d1 for generating the luminance signal (Y) and the color signals (Cb, Cr), 5d1 This is a signal level detection means for extracting a high frequency component from the output signal (luminance signal) of the means 5d by a high pass filter or a band pass filter and detecting this as a focus evaluation value.

  Specific processing performed by the video signal processing means 5d includes luminance / color separation, CDS (correlated double sampling circuit), white balance, contour correction, gamma correction, and the like. The generated video signal may have a form in which a luminance signal and a color signal are separated, a synthesized form, a form of a primary color RGB signal, or the like. Although the camera unit 5 is built in the image server 1 in the first embodiment, it may be an external camera as a separate body from the image server 1. Reference numeral 5e denotes a focusing lens that can be moved to a focus position for AF control.

  Reference numeral 6 denotes image signal compression means for capturing the luminance signal and the color signal input from the camera unit 5 at a predetermined timing and compressing / encoding the image signal. The compression executed by the image signal compression means 6 is performed in MPEG or other formats including JPEG, DCT processing, quantization, encoding, etc. are performed, and a predetermined header is added. In this DCT (Discrete Cosine Transform) process, discrete cosine transform is performed in order to express an image signal with DCT coefficients as frequency components. Each DCT coefficient is quantized by dividing by each coefficient that is an element of the quantization table, and encoding is performed by setting the quantized coefficient calculated by this quantization to a data amount that matches the frame rate of the network. .

Next, reference numeral 7 denotes an image pickup means drive section that generates a drive signal for the image pickup means 5a, and 7a denotes a focus lens drive section that includes a motor or the like for moving the focus lens 5e. The focus lens driving unit 7a moves the focus lens 5e to the in-focus position by a predetermined movement amount as a unit. Reference numeral 8 denotes driving of the image pickup means 5a of the camera unit 5, control of the video signal processing means 5d, control of the focus lens driving unit 7a (AF), control of the light amount adjusting means 5b (AI).
A control unit for controlling AGC / AWB and the like. In accordance with an instruction from the browser of the client terminal 2 sent from the network 3, control is performed to change the image compression processing mode processing and generate HTML data, image data, and the like. In accordance with the drive mode instructed by the control unit 8, the drive signal of the image pickup means 5a and the focus lens drive unit 7a are operated to change the focus.

  8a is a control level adjusting means for performing AGC control when the exposure time is changed and the long exposure mode is set. The AGC control performed by the control level adjusting means 8a is basically the same as the operation for normal auto gain control. However, in the long exposure mode, the correction amount of the set value to the video signal level control means 5c is partially controlled differently from that in the normal exposure mode according to the video signal level. If the exposure time is, for example, 2v (twice the timing period of the vertical synchronization signal), the correction amount of the set value to the video signal level control means 5c calculated at that time based on the video signal level is the normal basis. This is twice the correction amount. As a result, even when the exposure mode is switched, the responsiveness of AGC control is equivalent to that during normal exposure.

  8b, when AF control is performed, the high frequency component of the luminance signal detected by the signal level detection means 5d1 is recorded as an evaluation value for each exposure time, the evaluation value change rate described later is calculated, and the evaluation value becomes the maximum value. In-focus position control means for discriminating The in-focus position control means 8b issues a command to move to the focus lens driving unit 7a every time the exposure time changes, moves the focus lens 5e by a predetermined amount of movement, and sets the position when there is focus. Set as the in-focus position. The evaluation value for each exposure time is stored in the evaluation value storage unit 10a of the storage unit described later.

  Reference numeral 9 denotes a network interface between the image server 1 and the network 3. An instruction from the browser is transmitted to the camera unit 5 and HTML data, image data, and the like from the image server 1 are transmitted to the network 3. Reference numeral 10 denotes a storage unit for the CPU or the like constituting the control unit 8 to read out programs and data. Reference numeral 10a denotes an evaluation value storage unit that stores an evaluation value for each exposure time in order to detect the maximum value of the evaluation value when performing AF control. In the evaluation value storage unit 10a, in addition to the evaluation value, the evaluation value change rate is calculated and stored every time the focus lens driving unit 7a moves.

  Subsequently, the image server 1 according to the first embodiment executes AF control when the normal exposure mode is changed to the long exposure mode, and the change in the autofocus evaluation value and the control value when the mode is changed. Will be described. FIG. 3 is an explanatory diagram of the autofocus evaluation value level and its control value in the long exposure mode of the image server according to Embodiment 1 of the present invention. FIG. 5A shows the change in the evaluation value level of the autofocus in the normal exposure mode and the control value in the image server of the first embodiment, and will be referred to here.

As shown in FIG. 5A, in the normal exposure mode during AF control, the focus position control unit 8b moves the focus lens according to the control value in order to find the focus position. The movement is instructed once every 1v of the normal exposure time (timing period of the vertical synchronization signal), and is moved equidistantly in the direction in which the evaluation value level of the focus evaluation value increases. This is because the hill-climbing servo is executed as shown in FIG. The in-focus position control means 8b detects the focus evaluation value for each movement, and calculates the ratio with the evaluation value detected immediately before. This ratio is the evaluation value change rate, which is a change in the gradient of the evaluation value. For example, in FIG. 5A, since the change amounts are A and B from time T1 to time T2 and from time T2 to time T3, respectively, the evaluation value change rate is B / A. Similarly, from time T2 to time T3, from time T3 to time T4, the evaluation value change rate is C / B, from time T4 to time T5, and from time T5 to time T6, the evaluation value change rate is D / C. Similarly, E / D, F / E, and so on. Although the gradient change is a difference of each time, it can be seen that the evaluation value change rate indicates the gradient change because the movement amount is fixed. The in-focus position control means 8b calculates the evaluation value change rate and stores it in the evaluation value storage unit 10a.

  In this way, the focus evaluation value rises with time, that is, with a change in control value (movement of the focus lens), reaches a maximum at time T6, and decreases again at time T7. This can be determined from the evaluation value level and the change in evaluation value from positive to negative. As described above, since the focus evaluation value has reached the maximum value at time T6 and has decreased again, the control value immediately before the focus evaluation value has decreased is the in-focus control value, and the in-focus position control means 8b This is set as the focusing position of the lens.

  Next, when the long exposure mode is set, as shown in FIG. 3, in the 2v period from the time point T1 to the time point T2 (twice the timing period of the vertical synchronization signal), the exposure is twice the normal time. The period during which the focus evaluation value can be obtained is doubled. Therefore, since the period for moving the focusing lens is also doubled, the focusing lens is moved with a control amount twice that of the normal time. That is, a control amount that is [long exposure period / normal exposure period] times as large as in normal exposure is suitable. Thereby, the movement amount per 1v period becomes the same. As in the normal exposure mode, the change amount A between the evaluation value level at time T1 and the evaluation value level at time T2 is stored. Next, in the 2v period from time T2 to time T3, the focusing lens is moved by the same control amount as the control amount from time T1 to time T2, and the evaluation value level at time T2 and the evaluation value level at time T3 are A change amount B is obtained, compared with the change amount A, and a ratio between the change amount A and the change amount B and an evaluation value change rate B / A are calculated.

  Continuing such calculation, for example, when the evaluation value change rate B / A is smaller than a predetermined value such as 0.05, it can be determined that the evaluation value level has approached the maximum value, so the in-focus position control means 8b It is preferable to make the control amount at the next time point smaller than before. For example, in the case of FIG. 3, the control amount may be returned to the control amount between 1v at the normal exposure. In this state, detailed calculation is continued in the same manner as in the normal exposure control, and as shown in FIG. 3, since the evaluation value decreases from time T4 to time T5, the focus position control means 8b sets the control value at time T4. Judged as the in-focus position. At the same time, the focusing position of the focusing lens is set in the 1v period. With this control, it is possible to shorten the time until focusing even in double exposure for a long time. Further, when the evaluation value change rate B / A does not become smaller than a predetermined value such as 0.05 at the time T3 and the evaluation value change rate B / A is reversed to negative, the evaluation value level at the time T2 The maximum value is detected. In this case, since there is an in-focus position in the vicinity of the focus lens position at the time point T2, control is performed to determine the focus lens position at which the evaluation value level is maximized by returning it while approaching the focus lens position at the time point T2. However, the focus position control means 8b performs the control so that the detailed calculation is continued in the same way as the control during the normal exposure, and the control value at the time point T4 at which the decrease in the evaluation value is observed is determined as the focus position.

  As described above, the image server and the image server system according to Embodiment 1 can perform comfortable autofocus control without taking a long time for the focusing operation even in the long exposure mode. The same time AF control can be performed at all times, high controllability, and high quality and stable images can be transmitted. In particular, the image server is effective for an image server including a camera unit including a camera unit that calculates an autofocus evaluation value for each frame.

  The present invention can be applied to an image server and an image server system that take a video while remotely operating a camera unit via a network and stably transmit image data.

1 is a configuration diagram of an image server and an image server system according to Embodiment 1 of the present invention. Configuration diagram of the image server in Embodiment 1 of the present invention Explanatory drawing of the evaluation value level of the autofocus in the long exposure mode of the image server in Embodiment 1 of this invention, and its control value Illustration of the principle of conventional autofocus (A) Explanatory drawing which shows the evaluation value level of the autofocus in the normal exposure mode in the conventional image server and its control value, (b) The evaluation value level of the autofocus in the long exposure mode in the image server of (a) And explanatory diagram showing its control value

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image server 2 Client terminal 3 Network 4 DNS server 5 Camera part 5a Imaging means 5b Light quantity adjustment means 5c Video signal level control means 5c1 Signal level detection means 5d Video signal processing means 6 Image signal compression means 7 Imaging means drive part 8 Control part 8a Control level adjustment means 8b Focus position control means 9 Network interface 10 Storage unit

Claims (6)

A signal level detection means for detecting the signal level of the video signal output from the imaging means; and a video signal level control means for adjusting the level of the video signal output from the imaging means, the output from the video signal level control means An image server that processes the compressed video signal, performs compression processing, and outputs image data to the outside,
Focus position control means for determining the focus position based on the maximum focus evaluation value detected by the signal level detection means, and focus for moving the focus lens by a predetermined control amount in response to a command from the focus position control means A lens drive,
When the exposure time is changed to a cycle longer than a predetermined cycle, the focusing position control means determines a large control amount corresponding to the change of the exposure time, and moves the focus lens by the control amount. An image server that detects a maximum value of the focus evaluation value and performs focus control. The focus position control means moves the focus lens by a predetermined control amount, calculates a change amount of the focus evaluation value before and after changing the control amount, and a focus evaluation value change rate indicating the change of the change amount The image server according to claim 1, wherein the position of the previous focusing lens when the focus evaluation value change rate is reversed from positive to negative is determined as the in-focus position. When the image signal is output with a period longer than a predetermined period by changing the exposure time of the imaging unit, when the focus evaluation value change rate becomes smaller than a predetermined value, the in-focus position control unit 3. The image server according to claim 1, wherein the control amount is decreased. 4. The image server according to claim 3, wherein when the focus evaluation value change rate becomes smaller than a predetermined value, the in-focus position control means decreases the control amount at the predetermined period. The image server according to claim 1, wherein the focus evaluation value is a high-frequency component of a video signal detected by the signal level detection unit. An image server according to claim 1, a client terminal capable of acquiring image data from the image server, and a network to which the image server and the client terminal are connected. An image server system.

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