Patent Publication Number: US-2012039592-A1

Title: Video camera supplementary white light control method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to video camera control technology and more particularly, to a video camera supplementary white light control method, which controls the operation of the supplementary lighting device subject to luminance of the scene. 
     2. Description of the Related Art 
     For the advantages of image pickup and real-time monitoring characteristics, video cameras are intensively used for crime fighting to protect people&#39;s lives and properties. Following development of technology, advanced digital video cameras can be used for remote surveillance and security control. 
     In the daytime, due to sufficient ambient light, a video camera can catch clear images. However, when at night, due to insufficient ambient light, a video camera cannot catch images. Therefore, an IR camera or IR video camera may be used with a supplementary lighting device at night. Due to the characteristic of being capable to sense white light (visible light) and infrared light (invisible light), an IR camera or IR video camera can be used in daylight as well as at night. However, an IR camera or IR video camera simply can catch black and white images that cannot show picture details. Color shift and overexposure of images captured at night are further problems may be encountered. Further, due to a different focal point between white light (daylight) and infrared light (night), an IR camera or IR video camera must use a lens having a long depth of field, or be equipped with a day/night auto switch for switching to the desired wavelength, thereby increasing the cost. There is known daylight cameras equipped with a supplementary white-light lighting device for use in daylight as well as at night. These daylight cameras eliminate the problems of IR cameras, and save the cost. However, the light emitted by the supplementary white-light lighting device may cause the lighting device control sensor to make an error control, resulting in an image pickup failure. According to conventional techniques, it is to project the supplementary white light onto the field to be photographed, avoiding dispersion of the emitted light to cause a sensor error. However, this method narrows the camera shooting range (due to insufficient light), and increases the dead angle of the camera. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide a video camera supplementary white light control method, which uses a filter to remove the unnecessary wavelengths from the light sensor so that the video camera can accurately control the operation of a supplementary lighting device subject to the luminance data computed by the light sensor, avoiding error. 
     It is another object of the present invention to provide a video camera supplementary white light control method, which allows the video camera and the supplementary lighting device to be separately installed, avoiding fogging to interfere with normal image sensing of the video camera due to a temperature rise. 
     To achieve these and other objects of the present invention, a video camera supplementary white light control method used in a video camera having installed therein a microcontroller, an image pickup device, a light sensor and a filter for controlling the operation of a supplementary lighting device that may be installed in the video camera or disposed outside the video camera. The method is to let the wavelengths beyond the overlapped area of the wavelength range sensed by the image pickup device and the wavelength range of the white light emitted by the supplementary lighting device to be removed by the filter, so that the light sensor can receive a predetermined wavelength of light and computes the luminance of the received light. Thus, the microcontroller can compare the computed luminance data to a reference data, and then controls the operation of the supplementary lighting device subject to the comparison result. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit block diagram of a video camera system in accordance with a first embodiment of the present invention. 
         FIG. 2  is a circuit block diagram of a video camera system in accordance with a second embodiment of the present invention. 
         FIG. 3  is a circuit block diagram of a video camera system in accordance with a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , a video camera system is shown comprising a video camera  1  and a supplementary lighting device  2 . 
     The video camera  1  has installed therein a microcontroller  11  for operation control, an image pickup device  12  and a light sensor  13  respectively and electrically connected to the microcontroller  11  and a filter  14  connected to the light sensor  13 . 
     The supplementary lighting device  2  is mounted in the video camera  1  and electrically connected to the microcontroller  11 , comprising a plurality of white LEDs (light emitting diodes)  21 . 
     When the image pickup device  12  picks up visible light images, the light sensor  13  computes the luminance of the scene sensed by the image pickup device  12 . When the light sensor  13  is receiving the light of the scene, the light of the scene goes through the filter  14  into the light sensor  13 . When the light passes through the filter  14 , the filter  14  removes the unnecessary wavelengths from the light. The wavelengths of light to be removed by the filter  14  are the wavelengths beyond the overlapped area of the wavelength range sensed by the image pickup device  12  and the wavelength range of the light emitted by the white LEDs  21  of the supplementary lighting device  2 , so that the light sensor  13  simply receives the light within a predetermined wavelength range for computing the luminance. For example, the image pickup device  12  can sense the light of wavelength 400˜650 nm and the wavelength of the white LEDs  21  is 400˜750 nm, thus the wavelength of the light passing through the filter  14  is 400˜650 nm. After computation of the luminance of the light received by the light sensor  13 , the data of the luminance value is transmitted to the microcontroller  11 . The microcontroller  11  has a reference luminance range set therein. If the luminance value received from the light sensor  13  is below the reference luminance range, the microcontroller  11  immediately drives the supplementary lighting device  2  to turn on the white LEDs  21 , giving light to the scene that is sensed by the image pickup device  12 . If the luminance value received from the light sensor  13  surpasses the reference luminance range, the microcontroller  11  immediately drives the supplementary lighting device  2  to turn off the white LEDs  21 , stopping the fill light. Thus, the white LEDs  21  of the supplementary lighting device  2  are automatically controlled to emit light or not to emit light subject to the luminance of the scene being sensed by the image pickup device  12 . 
     Therefore, the key technique of the present invention to enhance the function of the video camera  1  is the use of the filter  14  to remove the unnecessary wavelengths from the light of the scene passing to the light sensor  13 , i.e., to remove the wavelengths not receivable by the image pickup device  12  and the wavelengths of the light not emitted by the white LEDs  21 , so that the light sensor  13  simply receives the light within the predetermined wavelength range for computing the luminance, and the microcontroller  11  can control the supplementary lighting device  2  to turn on/off the white LEDs  21  subject to the luminance of the scene accurately. When using the video camera  1  in the night, the filter  14  removes the unnecessary wavelengths of light, and the microcontroller  11  controls the operation of the white LEDs  21  to regulate the illumination accurately subject to the predetermined luminance range. Further, the fill range of the supplementary lighting device  2  is widened and free, avoiding error of the light sensor  13  due to the illumination of the supplementary lighting device  2 . 
       FIG. 2  illustrates an alternate form of the present invention. According to this embodiment, the video camera  1  and the supplementary lighting device  2  are separately provided and electrically connected together by a signal line  3 . Thus, the microcontroller  11  can drive the supplementary lighting device  2  to turn on/off the white LEDs  21  through the signal line  3 . Thus, the waste heat produced during operation of the white LEDs  21  does not affect the operation of the video camera  1 , avoiding fogging due to a rise in temperature. 
       FIG. 3  illustrates another alternate form of the present invention. According to this embodiment, the video camera system comprises a video camera  1  and a supplementary lighting device  2 . 
     The video camera  1  has installed therein a microcontroller  11  for operation control, an image pickup device  12 , a light sensor  13  and a wireless signal transmitter  15  respectively and electrically connected to the microcontroller  11 , and a filter  14  connected to the light sensor  13 . 
     The supplementary lighting device  2  comprises a plurality of white LEDs (light emitting diodes)  21 , a wireless signal receiver  22 , and a microprocessor  23 . The white LEDs  21  and the wireless signal receiver  22  are respectively electrically connected to the microprocessor  23 . 
     When the image pickup device  12  picks up visible light images, the light sensor  13  computes the luminance of the scene sensed by the image pickup device  12 . After computation of the luminance of the light received by the light sensor  13 , the data of the luminance value is transmitted to the microcontroller  11  for comparing to the reference luminance range set in the microcontroller  11 . Thus, the microcontroller  11  outputs a modulated control signal through the wireless signal transmitter  15  to the wireless signal receiver  22  wirelessly, subject to the comparison result. Upon receipt of the wireless control signal by the wireless signal receiver  22 , the modulated control signal is demodulated by the microprocessor  23  for controlling the white LEDs  21 , giving light to the scene that is sensed by the image pickup device  12 . 
     If the luminance value received from the light sensor  13  surpasses the reference luminance range, the microcontroller  11  immediately sends a wireless control signal to the supplementary lighting device  2  wirelessly to turn off the white LEDs  21 , stopping the fill light. By means of wireless signal transmission control, the supplementary lighting device  2  can be installed in any desired place within a certain distance away from the video camera  1 . 
     Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.