Patent Publication Number: US-2005134706-A1

Title: Mobile communication terminal equipped with camera and method of controlling the same

Description:
BACKGROUND OF THE INVENTION  
      This application claims the priority of Korean Patent Application No. 2003-94310, filed on Dec. 20, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
      1. Field of the Invention  
      The present invention relates to a mobile communication terminal and, more particularly, to a mobile communication terminal equipped with a camera in which a flash is triggered according to ambient luminance and a method of controlling the mobile communication terminal equipped with a camera.  
      2. Description of Related Art  
      In general, when a camera module incorporated in a mobile communication terminal is operated, a preview mode is triggered to display a picked-up image, which is projected through a lens system, on a liquid crystal display (LCD). The displayed image is captured when a picture-taking button is pressed. The captured image is compressed and stored in an internal memory of the mobile communication terminal.  
      A conventional flash, which is equipped into the mobile communication terminal to take a picture in poor lighting areas, is typically triggered by an optical sensor integrated circuit (IC) which detects the intensity of light. That is, the optical sensor detects the light intensity and compares the detected light intensity with a threshold value which is set in a hardware manner. Subsequently, the optical sensor outputs a digital signal indicating a ‘high’ or ‘low’ level to a general-purpose input/output (GPIO) terminal in a mobile station modem (MSM). The MSM determines whether or not to activate the flash in response to the digital signal.  
      A conventional flash trigger system has the following three drawbacks.  
      Firstly, there is a problem in that the optical sensor IC for detecting the light intensity is expensive. As a result, the total manufacturing cost for the mobile communication terminal increases significantly.  
      Secondly, since some of the GPIO terminals, which are provided in the MSM to be used for application operations in the mobile communication terminal, are used to trigger the flash, it may occur that there are no GPIO terminals available for other application operations in the mobile communication terminal. Furthermore, there is a problem in that since a threshold value, which is used in determining whether the light intensity detected by the optical IC is high or low, is set in a hardware manner, the threshold value cannot be readjusted once the mobile communication terminal has been assembled.  
     SUMMARY OF THE INVENTION  
      The present invention provides a mobile communication terminal equipped with a camera and a method capable of taking a high-quality picture by activating a flash according to ambient luminance when the camera takes a picture.  
      The present invention also provides a mobile communication terminal with a camera and a method capable of easily varying in a software manner a luminance threshold value used in activating the flash.  
      In accordance with an aspect of the present invention, there is provided a mobile communication terminal with a camera, comprising: a luminance sensor unit for outputting an analog electrical signal proportional to ambient luminance; a control unit for generating a preview light enable signal according to the analog electrical signal; and a preview light for emitting light in a preview mode in response to the preview light enable signal.  
      The mobile communication terminal equipped with a camera may further comprise a flash for emitting light in response to a flash enable signal when a camera shutter is triggered.  
      The mobile communication terminal equipped with a camera may further comprise an input unit for allowing a user to set a threshold value arbitrarily.  
      The control unit may compare a light intensity value obtained from the electrical signal with the arbitrarily set threshold value to determine whether or not to generate the preview light enable signal.  
      In accordance with another aspect of the present invention, there is provided a mobile communication terminal equipped with a camera, comprising: a luminance sensor unit for outputting an analog electrical signal proportional to ambient luminance; a light unit for emitting light onto an area to be picture-taken by the camera; and a control unit for comparing a light intensity value obtained from the analog electrical signal with a pre-programmed threshold value to control the operation of the light unit.  
      The control unit may comprise an A/D converter for converting the analog electrical signal inputted from the luminance sensor unit into a digital signal.  
      The luminance sensor unit may comprise a photodiode which is driven by a camera mode selection signal outputted from the control unit to output the analog electrical signal proportional to the ambient luminance.  
      The luminance sensor unit may further comprise a transimpedance amplifier for converting a current signal outputted from the photodiode into a voltage signal.  
      The light unit may comprise a preview light and a flash.  
      Each of the preview light and the flash may comprise: a switch for operating in response to a lighting control signal from the control unit so that electric power can be supplied; a light emitting device for emitting light by being turned on or off; and a resistor for limiting current flow supplied to the light emitting device via the switch.  
      The preview light may be turned on in the preview mode when the light intensity value detected through the luminance sensor unit is less than the threshold value, and the flash may be fired when a camera shutter is triggered.  
      The control unit may comprise an MSM for receiving the analog electrical signal through an HKADC (House Keeping Analog to Digital Converter) terminal to generate the preview light enable signal and outputting the preview light enable signal through a GPIO terminal.  
      In accordance with another aspect of the present invention, there is provided a method of controlling a mobile communication terminal equipped with a camera unit and a light unit, the method comprising the steps of: enabling a luminance sensor unit to detect ambient luminance according to a camera mode selection command; comparing a light intensity value obtained from a signal outputted from the luminance sensor unit with a pre-programmed threshold value; and controlling the operation of the light unit according to the comparison result.  
      The step of controlling the operation of the light unit may further comprise the steps of: lowpass-filtering an analog signal representing the light intensity value outputted from the luminance sensor unit; and converting the lowpass-filtered analog signal into a digital signal.  
      The step of controlling the operation of the light unit may further comprise the step of turning on a preview light provided in the light unit when the light intensity value obtained from the signal outputted from the luminance sensor unit is less than the threshold value.  
      The step of controlling the operation of the light unit may further comprise the step of firing a flash provided in the light unit when the light intensity value obtained from the signal outputted from the luminance sensor unit is equal to or greater than the threshold value and a picture-taking command is input through an input unit  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
       FIG. 1  is a block diagram showing the configuration of a mobile communication terminal in accordance with the present invention;  
       FIG. 2  is a circuit diagram showing the configuration of a luminance sensor unit shown in  FIG. 1 ;  
       FIG. 3  is a circuit diagram showing the configuration of a light unit shown in  FIG. 1 ; and  
       FIG. 4  is a flowchart showing a method of controlling a mobile communication terminal in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Exemplary embodiments in accordance with the present invention will now be described in detail with reference to the accompanying drawings.  
       FIG. 1  is a block diagram showing the configuration of a mobile communication terminal in accordance with the present invention. The mobile communication terminal comprises an input unit  700 , a display unit  400 , a luminance sensor unit  100 , a camera unit  200 , a signal processing unit  300 , a light unit  500  and a control unit  600 .  
      The input unit  700  receives a user command and transfers the user command to the control unit  600  so that the camera unit  200  can take a picture and output the picture in response to the user command. The display unit  400  displays a picked-up image inputted through a lens system under the control of the control unit  600 . The input unit  700  and the display unit  400  can employ well-known configurations.  
      The control unit  600  compares a value indicating light intensity based on an electrical signal, which is output from the luminance sensor unit  100 , with a threshold value which is preset by a program. The control unit  600  controls an ON or OFF state of the light unit  500  according to the comparison result. A mobile station modem integrated circuit (MSM IC) is employed as the control unit  600 , which comprises a device dedicated for communications, a digital signal processor, and other general-purpose microprocessors.  
      The luminance sensor unit  100  outputs an electrical signal proportional to ambient luminance as a picture-taking mode, i.e., a camera mode, is set through the input unit  700 . The electrical signal is input into a House Keeping Analog to Digital Converter (HKADC) terminal of the MSM, which will be described below.  
      As shown in  FIG. 2 , the luminance sensor unit  100  comprises: a low dropout (LDO) regulator U 1  activated in response to a camera selection signal outputted from the control unit  600 ; a photodiode D 1  which is driven by the LDO regulator U 1  and disposed to face a picture-taking area at an opening formed in the mobile communication terminal; and a transimpedance amplifier U 2  which is driven by the regulator U 1  and converts a current signal outputted from the photodiode D 1  into a voltage signal.  
      In accordance with the present invention, since the photodiode D 1  is used for detecting light and the transimpedance amplifier U 2  is used for converting a current signal outputted from the photodiode D 1  into a voltage signal, the mobile communication terminal can be inexpensively manufactured as compared to the conventional mobile communication terminal in which an expensive optical sensor is used to detect light intensity. In addition, there is an advantage in that the light intensity is accurate since it is obtained from an analog signal rather than a digital signal, such as ‘high’ or ‘low’.  
      On the other hand, the camera unit  200  converts a picked-up image signal projected through a lens system into an electrical signal. The camera unit  200  comprises: a lens system; an image pickup unit for converting the image signal outputted from the lens system into an analog signal; and a converter for converting the analog signal outputted from the image pickup unit into a digital signal and converting the digital signal into a signal suitable for an input to the signal processing unit  300 .  
      Here, the lens system comprises one or more small-sized lenses. The image pickup unit is typically constituted by a complementary metal oxide semiconductor (CMOS) or a charge-coupled device (CCD) image pickup element. The converter converts a current or voltage signal outputted from the image pickup unit into a digital signal, which is in turn converted into YUV format. The converter may further comprise a codec for compressing a picked-up image into Joint Photographic Experts Group (JPEG) format.  
      On the other hand, the signal processing unit  300  processes the electrical signal outputted from the camera unit  200  and outputs the processed electrical signal to the display unit  400  or stores the processed electrical signal in its own internal memory. The signal processing unit  300  receives 8-bit YUV-format image data outputted from the camera unit  200  and buffers the received 8-bit YUV-format image data into the internal memory. The signal processing unit  300  may comprise a codec for storing image data in the internal memory and decompressing the stored data. The codec may comprise a JPEG encoder/decoder for compressing a captured image frame into a still image, storing and reading the still image. The signal processing unit  300  may comprise a definition enhancement circuit for improving image quality. Further, the signal processing unit  300  may have a contrast adjustment function and a filtering function for graphic effects.  
      The signal processing unit  300  outputs the image data in 16-bit RGB format to the display unit  400 . In the present embodiment, an image picked up by the camera unit  200  is frame-captured and compressed into the JPEG format in the signal processing unit  300 . The compressed image is stored in a flash memory provided in the signal processing unit  300 . The signal processing unit  300  decompresses the still image stored in the flash memory and the display unit  400  displays the decompressed image.  
      The light unit  500 , which illuminates light onto an area to be picture-taken by the camera unit  200 , includes at least two lights: a preview light  510  for emitting light according to ambient luminance in a preview mode and a flash  520  for emitting light when a camera shutter is triggered. As shown in  FIG. 3 , the lights comprise switches Q 1  and Q 2  for carrying out a switching operation in response to a lighting control signal from the control unit  600 , light emitting devices D 2  and D 3  for emitting light by electric power supplied through the switches Q 1  and Q 2 , and resistors R 5  and R 6  for limiting a current flow to be supplied to the light emitting devices D 2  and D 3  through the switches Q 1  and Q 2 .  
      When a light intensity value inputted from the luminance sensor unit  100  in the preview mode is less than a preset threshold value, the control unit  600  outputs a control signal for turning on the preview light  510 . When the camera shutter is triggered, the control unit  600  outputs a control signal for turning on the flash  520 .  
      As described above, the mobile communication terminal in accordance with the present invention automatically activates the preview light  510  according to the ambient luminance so that an object can be clearly recognized. Moreover, the mobile communication terminal activates the flash  520  so that a sufficient amount of light can be supplied through the lens system when the camera shutter is triggered, whereby a high-quality picture can be taken in poor lighting areas.  
      On the other hand, the control unit  600  comprises an analog-to-digital (A/D) converter  610  for converting an analog signal inputted from the luminance sensor unit  100  into a digital signal; and a light controller  620  for comparing a light intensity value outputted from the A/D converter  610  with a preset threshold value and outputting a lighting control signal to the light unit  500  if the light intensity value is less than the preset threshold value.  
      In accordance with the present invention, a signal indicating the light intensity value outputted from the luminance sensor unit  100  is input into an HKADC terminal rather than into a GPIO terminal of the MSM. Accordingly, the GPIO terminal can be used for other application operations in the mobile communication terminal.  
      The control unit  600  operates to lowpass-filter a signal indicating the light intensity value on a software basis, which is inputted to the HKADC terminal from the luminance sensor unit  100 , and compares the light intensity value with the preset threshold value. When the light intensity value is less than the preset threshold value, the control unit  600  outputs a lighting control signal to the light unit  500  through the GPIO terminal. Here, the preset threshold value is one acquired through repeated experimentation. Alternatively, a user may directly set the threshold value through a setup menu displayed on the mobile communication terminal.  
      In accordance with the present invention, since the luminance threshold value, determining the operation of the light unit  500 , is set in a software manner, the threshold value can be easily changed after the mobile communication terminal is assembled. Moreover, a threshold value setup function may be added to the setup menu in the mobile communication terminal so that a user can directly set the threshold value.  
      A method of controlling a flash function in the mobile communication terminal in accordance with the present invention will now be described with reference to  FIGS. 2, 3  and  4 .  
      As shown in  FIG. 4 , the mobile communication terminal is set to be in an idle mode at ordinary times (S 11 ). When a camera mode is selected through the input unit  700  (S 12 ), the mobile communication terminal in the idle mode is switched into a camera mode in response to a control command from the control unit  600 .  
      When the mobile communication terminal is switched into the camera mode, the control unit  600  drives the luminance sensor unit  100  to detect the luminance of an area to be picture-taken (S 13 ). That is, when a camera enable signal is output from a GPIO terminal in the MSM U 3  to the LDO regulator U 1  in the luminance sensor unit  100 , the LDO regulator U 1  operates in response to the camera enable signal to activate the photodiode D 1  and an operational amplifier (OP-AMP) U 2 .  
      The photodiode D 1  outputs a current in proportion to light intensity. As shown in  FIG. 2 , the current outputted from the photodiode D 1  is applied to a negative (−) input terminal in the OP-AMP U 2 . A voltage on the LDO regulator U 1  is divided by resistors R 1  and R 2 , and the divided voltage across the resistor R 2  is applied, as a reference voltage, to a positive (+) input terminal in the OP-AMP U 2 . A capacitor C 1  connected parallel to the resistor R 2  acts to prevent the reference voltage from being affected by noise.  
      An output signal of the OP-AMP U 2  is fed back to the negative input terminal through a resistor R 4 . The OP-AMP U 2  acts as a transimpedance amplifier for outputting a voltage proportional to an inputted current. Here, capacitors C 2 , C 3  and C 4  are used for reducing the effects caused by noise.  
      As described above, the luminance sensor unit  100  converts a signal indicating the light intensity value proportional to an amount of incident light into a voltage signal, which is in turn inputted into the HKADC terminal of the MSM U 3 .  
      The voltage signal, which is an analog signal, is subjected to a software-based lowpass filtering operation (S 14 ). The A/D converter  610  in the control unit  600  converts the analog signal representing the light intensity value outputted from the luminance sensor unit  100  into digital data (S 15 ).  
      The digital data indicating the light intensity value is compared with the threshold value preset by the light controller  620  (S 16 ). If the detected light intensity value is less than the preset threshold value, the MSM U 3 , the control unit  600 , outputs a preview light enable signal through the GPIO terminal to turn on the preview light  510  provided in the light unit  500 .  
      If the detected light intensity value is equal to or greater than the threshold value, the MSM U 3  does not output the preview light enable signal since the detected ambient luminance is no less than a currently set luminance level.  
      As shown in  FIG. 3 , the preview light enable signal is applied to a base terminal of a transistor Q 1  constituting the preview light  510  to turn on the preview light  510  provided in the light unit  500 , thereby turning on the transistor Q 1  (S 17 ). That is, the electric power is supplied to the light emitting diode D 2  of the preview light  510  through the turned-on transistor Q 1 , so that the light emitting diode D 2  emits light. Accordingly, an object can be clearly recognized through the display unit  400  in the preview mode when a picture is taken in poor lighting areas (S 18 ).  
      When a picture-taking command is input through the input unit  700  in the preview mode (S 19 ), i.e., when a camera shutter is triggered, the light controller  620  outputs a flash enable signal to fire the flash  520 . That is, the MSM U 3  outputs the flash enable signal through another GPIO terminal. The flash enable signal is input into a base terminal of a transistor Q 2 , thereby turning on the transistor Q 2 . Accordingly, the electric power is supplied to the light emitting diode D 3  constituting the flash  520  through the turned-on transistor Q 2 , so that the light emitting diode D 3  emits light (S 20 ).  
      The signal processing unit  300  captures and compresses the taken image, and then stores the compressed image in its own internal memory (S 21 ). Unless an additional picture-taking command or mode switching command is input, the mobile communication terminal remains in preview mode.  
      In accordance with the present invention, it is possible to provide a mobile communication terminal and a method capable of taking a high-quality picture in poor lighting areas by activating first and second light sources, where the first light source enables a user to clearly recognize an object through an LCD in poor lighting areas when a camera mode is activated, and the second light source transfers a sufficient amount of light through a lens when a camera shutter is triggered.  
      In addition, it is possible to easily change a threshold value determining whether or not to turn on the light source, since the threshold value is set in a software manner in the present invention.  
      Further, since the present invention employs a photodiode as an element for detecting light intensity and a transimpedance amplifier as an element for outputting a voltage signal proportional to a current signal outputted from the photodiode, the mobile communication terminal can be manufactured inexpensively as compared to the conventional one employing an optical sensor as an element for detecting the light intensity.  
      Moreover, the present invention uses an HKADC terminal rather than a GPIO terminal in an MSM in triggering a flash, so that the GPIO terminal can be used for other application operations in the mobile communication terminal.  
      While the present invention has been described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the present invention as defined by the following claims.