Abstract:
An image capture device to eliminate flicker includes an image detection unit forming consecutive preview images at a predetermined rate, each formed with a group of parameters, and a flicker elimination unit acquiring the exposure count of the preview images, plotting the exposure count to form a waveform, determining whether the exposure count is fluctuating, analyzing the information of the waveform to allow determination of modulation of one of the group of parameters if the exposure count is fluctuating, and modulating one of the group of parameters according to the analysis result.

Description:
BACKGROUND 
     1. Technical Field 
     The invention relates to image capture and, particularly, to an image capture device providing image previews with uniform brightness and a method thereof. 
     2. Description of the Related Art 
     In general, charge-coupled device (CCD) systems such as video cameras or digital still cameras include a CCD image sensor and a lens module. The CCD image sensor repeats readout of an image signal generated thereby as consecutive preview images at a predetermined rate, such as 30 frames per second (FPS), the system being National Television System Committee (NTSC)-compliant. Problems may result in a CCD system when capture is performed under fluorescent lighting conditions operated at a commercial frequency of 50 Hertz (Hz). As shown in  FIG. 5 , a graph illustrating autofocus of a common image capture device, horizontal axis represents preview time in milliseconds (ms) and the vertical axis brightness in lux (lx) of such a fluorescent lighting condition. During preview, the CCD image sensor is exposed at a uniform exposure of Yms to acquire consecutive preview images corresponding to different focus conditions of the lens module, such as a focus lens thereof positioned at different focus positions P 1 ˜P k  (in  FIG. 5 , k being a natural number). As shown, brightness values L 1 ˜L k  of the consecutive preview images are not equal, since the sampling rate of the CCD image sensor (30 Hz) is not compatible with the illuminative frequency of 50 Hz, and flicker results. This can decrease autofocus accuracy if a contrast measurement method is used. 
     Therefore, it is desirable to provide an image capture device and method thereof, which can overcome the limitations described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present image capture device and method should be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present image capture device and method. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a functional block diagram of an image capture device including a value integration module, according to an exemplary embodiment. 
         FIG. 2  is a waveform graph output by the value integration module of  FIG. 1 , illustrating the relationship between exposure of the preview images and preview time. 
         FIG. 3  is another waveform graph output by the value integration module of  FIG. 1 , also illustrating the relationship between exposure of the preview images and preview time. 
         FIG. 4  is a flowchart of an image capture method, according to another exemplary embodiment. 
         FIG. 5  is a graph illustrating autofocus of a related-art image capture device. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present image capture device and method will now be described in detail with reference to the drawings. 
     Referring to  FIG. 1 , an image capture device  100 , according to an exemplary embodiment, includes an image detection unit  110  and a flicker elimination unit  120 . In this embodiment, the image capture device  100  is a digital still camera, although any other image capture device such as a cellular phone having a camera module is equally applicable while remaining well within the scope of the disclosure. 
     The image detection unit  110  is NTSC-compliant. When the image detection unit  110  is used with a 50 Hz power supply, and the exposure time of the image detection unit  110  is not equal to integer times of the cycle of ambient light brightness by a light source, flicker occurs in consecutive preview images generated by the image detection unit  110  (see  FIG. 2 ). 
     The flicker elimination unit  120  includes an acquisition module  121 , a value integration module  122 , an identification module  123 , an analysis module  124 , and a modulation module  125 . 
     The acquisition module  121  is configured for acquiring the exposure count of the preview images generated by the image detection unit  110 . The exposure count conforms to the formula EV=AV+TV=BV+SV, wherein EV represents the exposure count, AV an aperture value, TV exposure time, BV brightness, and SV an automatic gain control (Agc) value. The AV, the TV, the BV and the SV can be regarded as parameters and changed with the EV. 
     The value integration module  122  is configured for receiving the exposure count and plotting the exposure count to form at least one waveform. 
     If the image detection unit  110  functions precisely with a cycle period substantially equal to 33.33 ms, the exposure count will be plotted as a first waveform  101  shown in  FIG. 2 . However, if not, the cycle period may accordingly deviate from 33.33 ms. The exposure count is plotted as a second waveform  105  as shown in  FIG. 3 . In theory, the second waveform  105  can be discriminated into three sub-waveforms  102 ,  103 ,  104 , all of which can be identified by the identification module  123  and analyzed by the analysis module  124 . 
     Referring back to  FIG. 1 , the identification module  123  is configured for determining whether the exposure count is fluctuating, or in other words, whether a waveform is detected. If so, the preview images flicker and further analysis and modulation of the TV or the SV are required. 
     The analysis module  124  is configured for analyzing waveform components such as peak values, trough values, and amplitude values combining the two, to determine modulation of the TV or the SV. In this embodiment, half of the amplitude of the waveform is set as a standard value and the amplitude value represents the exposure count. 
     The modulation module  125  is configured for modulating parameters such as the SV or the TV to form a reverse waveform  101 ′, in broken line, shown in  FIG. 2 , or reverse sub-waveforms  102 ′,  103 ′,  104 ′ shown in  FIG. 3 , so as to smooth the original waveform  101  shown in  FIG. 2 , or the original waveforms  102 ,  103 ,  104  into straight lines  111  and  112 , respectively. 
     Referring to  FIG. 4 , an image capture method of the image capture device  100  is applicable when each cycle period of an image detection unit  110  is not an integer. 
     In step  410 , exposure count of preview images is acquired. In this embodiment, the exposure count of the image detection unit  110  can be plotted by an acquisition module  121  and represented by the formula EV=AV+TV=BV+SV, wherein EV represents the exposure count, AV the aperture value, TV exposure time, BV brightness, and SV the Automatic gain control (Agc) value. Furthermore, the AV, the TV, the BV and the SV can be regarded as parameters and changed with the EV change. 
     In step  420 , a first waveform  101  or a second waveform  105  (see  FIGS. 2 and 3 ) is respectively plotted according to the exposure count. In general, the second waveform  105  can be discriminated into three sub-waveforms  102 ,  103 ,  104 . In this embodiment, the horizontal axis and the vertical axis represent preview time (ms) and brightness (lx), respectively. 
     In step  430 , it is determined whether flicker occurs in the preview images according to the first waveform  101  or the second waveform  105 , in this embodiment, based on amplitude thereof. If the amplitude does not present as zero, flicker is determined to be present and step  440  is implemented. If the amplitude presents as zero, no flicker is present and step  450  is implemented. 
     In step  440 , first waveform  101  or second waveform  105  is analyzed according to peak values, trough values, and amplitude values composed of the two. In this embodiment, half the amplitude is set as a standard value and the amplitude values represent the exposure count. 
     In step  450 , original values of the waveform are retained without modulating. 
     In step  460 , the parameter such as the SV or the TV value relative to the EV is modulated according to the analysis to form a first reverse waveform  101 ′ and a second reverse waveform  105 ′ composed of the sub-waveforms  102 ′,  103 ′,  104 ′ to smooth the amplitude of the original waveform tending to straight lines  111 ,  112 , respectively. 
     The image capture method of the image capture device  100  can modulate parameters such as SV or TV value according to the EV to produce the reverse waveform and thereby eliminate original waveform tending to the straight line, normalizing brightness of the preview images and eliminate flicker. 
     It will be understood that the above particular embodiments and methods are shown and described by way of illustration only. The principles and the features of the present invention may be employed in various and numerous embodiment thereof without departing from the scope of the invention as claimed. The above-described embodiments illustrate the scope of the invention but do not restrict the scope of the invention.