Abstract:
Apparatus for reducing exposing time of an image processing system is disclosed herein. The image processing system including a shift register coupled to a photo-sensing means, the photo-sensing device is used to convert an optical image from a lens to a plurality groups of charge to form an electrical signal. The apparatus includes control device (counter) and a reset gate. The control device generates the first reset signal and the second reset signal depending on whether the image processing system is in a first resolution mode or a second resolution mode. A first number of cells of the photo-sensing device are exposed to the light of the optical image during the first resolution mode, and a second number of cells of the photo-sensing device being exposed to the optical image during the second resolution mode. The first number of cells is greater than the second number of cells. The reset device is used to eliminate the residual charges in the shift register responding to the first reset signal and the second reset signal. The reset device is coupled to the shift register, and throwaway charges generated by the cells of the photo-sensing device, which are not exposed to the light of the optical image.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to apparatus for reducing minimum exposing time of an image-acquiring device of an image processing system, and particularly relates to apparatus for reducing minimum scanning time necessary for a high-resolution-image-acquiring device to scan an object in a low resolution. 
     2. Description of the Prior Art 
     An image processing system makes use of focusing a reflected light beam from an object through a photodetector to generate an electrical signal representing the image of the object for further processing, storing and displaying. Among various applications such as image scanners, camera recorders or facsimile machines everywhere in the modern world, in spite of somewhat differences between these machines, there is one necessary primary step. In other words, it is necessary for an image system to acquire an image signal by converting an image of the object to an electrical signal. 
     Taking an image scanner as example, the block diagram in the prior art is shown in FIG.  1 . It is composed of an exposing timing signal source  8 , a shift control signal source  9 , a light source  10 , a glass surface  11 , a mirror  12 , a lens  13 , a photo-sensing device  14 , a charge coupled device (CCD) shift register  15 , a pre-processing device  16  and a post-processing device  17 . The pre-processing device  16  is implemented by electrically coupling a dc-gain voltage amplifier  16   a , an analogue-to-digital converter (ADC)  16   b . The waveform of the output signal  20 , shown in FIG. 2, of an exposing timing signal source  8  is fed to photo-sensing device  14 . 
     This system mentioned above operates in the way that photo-sensing device  14  converts the light emitted by light source  10 , a text or a picture firstly reflected by the glass surface  11  and secondly reflected by the mirror  12  to an image signal. 
     Note that when the front edge of pulse  21  (FIG. 2) is fed to the photo-sensing device  14 , the photo-sensing device  14  pour out all the charges to the CCD shift register  15 . After the photo-sensing device  14  has poured out all the stored charges, it cumulate the charges produced in the time interval between the back edge of the pulse  21  and front edge of the pulse  23 . Subsequently, the photo-sensing device begins to produce and accumulate charge until next front edge arrives. Thus an optical image is transformed into an electrical signal. The electrical signal parallel output to the CCD shift register  15 , and is serially fed to the pre-processing device  16 . 
     To precisely describe the operation of photo-sensing device  14  responding to the exposing timing signal source  8 , and that of the CCD shift register  15  responding to the shift control signal source  9 . The operation of the system is described below. A line of scanned object is exposed to the light source  10 , and the photo-sensing device  14  transfers the light from the line on the scanned object into a plurality of groups of charges responding to the pulse  19  and pulse  21  of the output signal  20  of the exposing timing signal source  8 . Each cell of the photo-sensing device  14  is exposed to the light from the lens  13  during the exposing time interval between pulse  21  and  23  of the output signal  20  of the exposing timing signal source  8 . After the pulse  21  has arrived at the photo-sensing device  14 , the plurality groups of charges is fed to the CCD shift register  15  at the same time. In addition, each of the plurality groups of charges generated by each cell of the photo-sensing device  14  is fed to the corresponding potential-energy wells of the CCD shift register  15 . 
     Subsequently, each of the plurality groups of charges stored in each potential-energy wells in the CCD shift register  15  is transmitted to the pre-processing device  16  one after another responding to the output clock pulse  30  of the shift control signal source  9 . The plurality groups of charge is stored in each potential-energy well of the CCD shift register  15  before the pulse  23  next to the pulse  21  arrive at the photo-sensing device  14 . In addition, each group of charge stored in each potential-energy well of the CCD shift register  15  is subsequently transmitted to the pre-processing device  16 . In other words, the group of charge stored in the first potential-energy well al of the CCD shift register  15  is transmitted to the pre-processing device  16  responding to the first pulse  31 A 1  of the clock pulse  30  (shown in FIG.  3 ). 
     Then the group of charge stored in the second potential-energy well a 2  of the CCD shift register  15  is transmitted to the pre-processing device  16  responding to the second pulse  31 A 2  of the clock pulse  30  (shown in FIG.  3 ). Finally the group of charge stored in the n&#39;th potential-energy well an of the CCD shift register  15  is transmitted to the pre-processing device  16  responding to the n&#39;th pulse  31 An of the clock pulse  30  (shown in FIG.  3 ). For the operation mentioned above, it is designed that after the n&#39;th pulse  31 An of the clock pulse  30  has been arrived at the CCD shift register  15 , the pulse  23  of the pulse  20  arrives at the photo-sensing device  14 . So the exposing time of the photo-sensing device  14  is a fixed value, i.e., time interval between pulse  21  and pulse  23 , which is a multiplication of pixel rate and pixel number, in spite of the variation of operational mode. 
     The pixel rate mentioned above is the number of group of charge stored in the potential-energy well of the CCD shift register  15  in a unit time interval. The pixel number mentioned above is the number of the potential-energy well of the CCD shift register  15 . In a high resolution mode, more cells of the photo-sensing device  14  are utilized to be exposed to the light source  10 . Whereas, in a low resolution mode, less cells of the photo-sensing device  14  are utilized to expose to the light source  10 . In addition, the lens seat  18  is moved to a position to fit the scope of projection to the photo-sensing device  14 . The position of the lens  13  and the lens seat  18  in the low resolution mode which employing less cells of photo-sensing device  14  is not illustrated in FIG.  1 . However the necessary exposing time interval employed in the high resolution mode is the same as that of the low resolution mode. So the user has to wait for a while even the low resolution mode of the image processing system is employed. This is an origin of waste of time for the user. 
     After the electrical signal has been fed to the pre-processing device  16 , the dc-gain voltage amplifier  16   a  adjusts the dc-gain of the electrical signal and then feed it to the ADC  16   b . Contrast adjustment by a Gamma characteristic is performed by the post-processing means  17 , and then obtained the output signal which can be further processed or displayed. 
     In a traditional image-acquiring device of a modern image processing system, it is necessary to provide the user with the high resolution mode and the low resolution mode for various applications. Fewer cells of photo-sensing device  14  are exposed to the light source  10  in the low resolution mode than the high resolution mode. However, the charges in each cell of the photo-sensing device  14  are transmitted through the CCD shift register  15  to the pre-processing device  16  in both high resolution mode and low resolution mode. So the necessary exposing timing interval for the high resolution mode and the low resolution mode is all the same, which is the multiplication of the pixel rate and the pixel number of the photo-sensing device  14 . And this is the waste of time for the user when a lower resolution mode of the image processing system is employed. In the traditional image-acquiring device of a modern image processing system, when the frequency of the output signal of the shift control signal source is increased to lower the exposing timing interval. It tends to result the residual charges generated in the previous exposing timing interval in the CCD shift register  15 , which affects the charges in the cells of the photo-sensing device  14  in the next exposing timing interval. So the quality of the output image is damaged in the prior art image processing system. 
     SUMMARY OF THE INVENTION 
     To reduce the necessary exposing time of the image-acquiring device of the image processing system, the present invention proposes apparatus for converting an optical image through a lens to an electrical signal. The apparatus mention above includes the following devices. The photo-sensing device is used to expose to the light of the optical image responding to an exposing timing signal from an exposing timing signal source. Thus the optical image is converted to a plurality groups of charge. 
     The shift register is used to parallel receive the plurality groups of charge and serially transmit the plurality groups of charge responding to a shift control signal from a shift control signal source. The serially transmitted plurality groups of charge form the electrical signal. The control device is used to respectively generate a first reset signal and a second reset signal during a first resolution mode and a second resolution mode of the apparatus. The first number of cells of the photo-sensing device is exposed to the light of the optical image during the first resolution mode, and the second number of cells of the photo-sensing device is exposed to light of the optical image during the second resolution mode. The first number of cells of the photo-sensing device is greater than the second number of cells of the photo-sensing device. The period of the first reset signal is proportional to the first number of cells of the photo-sensing device, and the period of the second reset signal is proportional to the second number of cells of the photo-sensing device. In addition, the period of the first reset signal being greater than the second reset signal. 
     The reset device is used to lead the charges in the shift register to ground responding to the first reset signal and the second reset signal. The reset device coupled to the shift register is used to generate the potential-energy well at the end of each period of the first reset signal and the second reset signal. The potential-energy well accommodates and throwaway residual charges in the CCD shift register. The photo-sensing device converts the optical image to the plurality groups of charge responding to the exposing timing signal. The period of the exposing timing signal is no less than the period of the first reset signal when the image processing system is in the first resolution mode. The period of the exposing timing signal is no less than period of the second reset signal when the image processing system is in the second resolution mode. 
     Selection device is used to determine whether the apparatus operates in the first resolution mode or in the second resolution mode according to user&#39;s selection. The user click on a first position of surface of the selection device to generate a first selection signal, and the user click on a second position of surface of the selection device to generate a second selection signal. The apparatus is operated in the first resolution mode according to the first selection signal, the apparatus being operated in the second resolution mode according to the second selection signal. 
     Positioning device is used to drive the lens to a first image-capturing position responding to the first selection signal to project the optical image on the first number of cells of the photo-sensing device during the first resolution mode. The positioning device d is used to drive the lens to a first image-capturing position responding to the second selection signal to focus the optical image on the second number of cells of the photo-sensing device during the second resolution mode. 
     The pre-processing device is used to adjust the dc (direct current) voltage of the electrical signal from the shift register as well as convert the electrical signal from the analog format to the digital format. The post processing device is used to adjust the contrast of the digital electrical signal. The selection device mentioned above can be soft ware or user interface. The positioning device mentioned above can be driving motor, and the pre-processing device can be included in a CCD (Charged Coupled Device). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above features of the present invention will be more clearly understood from consideration of the following descriptions in connection with accompanying drawings in which: 
     FIG. 1 illustrates the schematic diagram of the image processing system in the prior art, which has high resolution mode and low resolution mode; 
     FIG. 2 illustrates the wave form of the exposing timing signal utilized in both high resolution mode and low resolution mode of the prior art image processing system; 
     FIG. 3 illustrates the wave form of the shift control signal utilized to drive the charges in the CCD shift register in both high resolution mode and low resolution mode of the prior art image processing system; 
     FIG. 4 illustrates the schematic diagram of the image processing system in the preferred embodiment of the present invention, which has high resolution mode and low resolution mode; 
     FIG. 5 illustrates the wave form of the exposing timing signal utilized in high resolution mode of the image-acquiring device of the image processing system according to the preferred embodiment of the present invention; 
     FIG. 6 illustrates the wave form of the exposing timing signal utilized in low resolution mode of the image-acquiring device of the image processing system according to the preferred embodiment of the present invention; 
     FIG. 7 illustrates the wave form of the shift control signal utilized to drive the charges in the CCD shift register in both high resolution mode and low resolution mode of the of the image-acquiring device of the image processing system according to the preferred embodiment of the present invention; 
     FIG. 8 illustrates the wave form of the high resolution reset signal utilized in high resolution mode of the image-acquiring device of the image processing system according to the preferred embodiment of the present invention; 
     FIG. 9 illustrates the wave form of the low resolution reset signal utilized in low resolution mode of the image-acquiring device of the image processing system according to the preferred embodiment of the present invention; 
     FIG. 10A illustrates the schematic cross-sectional view of a preferred embodiment of the reset gate in the image-acquiring device of the image processing system according to the preferred embodiment of the present invention; 
     FIG. 10B illustrates the position of the charges and the potential-energy wells induced by individual electrodes of the reset gate in a normal conduction, at this time, the charges are conducted to the CCD shift register; and 
     FIG. 10C illustrates the position of the charges and the potential-energy wells induced by individual electrodes of the reset gate, at this time, the charges in the CCD shift register are conducted to ground. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     To eliminate the extra scanning time in the low resolution operation mode, the image-acquiring device of the image processing system according to the present invention proposes apparatus for reducing minimum exposing timing interval. In the present invention, fewer cells of photo-sensing device are exposed, and the corresponding number of pulses of the shift control signal are utilized to drive the charges in the potential-energy wells within the CCD shift register in the low resolution operational mode. So the exposing timing interval of the image-acquiring device of the image processing system is reduced according to the present invention. 
     The image processing system according to the present invention makes use of focusing light beam from an object through a photodetector to generate an electrical signal representing the image of the object for further processing, storing and displaying. Among various applications such as image scanners, camera recorders or facsimile machines everywhere in the modern world, in spite of somewhat differences between these machines, one primary step is necessary. In other words, it is necessary for an image processing system to acquire an image signal by converting an image of the object to an electrical signal, which performed by an image-acquiring device. 
     Taking an image scanner as an example of the image processing system in the preferred embodiment of the present invention, the block diagram is shown in FIG.  4 . It is composed of an exposing timing signal source  58 , a shift control signal source  59 , a light source  60 , a glass surface  61 , a mirror  62 , a lens  63 , a photo-sensing device  64 , a charge coupled device (CCD) shift register  65 , a reset gate  66 , a counter  67 , a pre-processing device  69  and a post-processing device  70 . The pre-processing device  69  is implemented by electrically coupling a dc-gain voltage amplifier  69   a , an analogue-to-digital converter (ADC)  69   b . The waveform of the first exposing timing signal  80   h  or the second exposing timing signal  80   l , shown in FIG. 5, of an exposing timing signal source  58  is fed to photo-sensing device  64 . 
     In the image-acquiring device of a modern image processing system, for example, the high resolution mode and the low resolution mode are provided to the user for various applications. The user can use the software interface  71  to select the high resolution mode or the low resolution mode as the operation mode of the image processing system. For example, when the user click on the L bottom of the software interface  71 , a selection signal is sent to the positioning means  73 , and positioning means  73  drives the lens  63  from position Ph to position Pl. It is designed that the fewer cells of photo-sensing device  64  are exposed to the light source  60  when the lens  63  locates at the position Pl. So fewer cells of photo-sensing device  64  are exposed to the light source  60  in the low resolution mode than the high resolution mode. 
     When starting acquiring an image in a low resolution mode as described above. The image-acquiring device mentioned above operates in the way that photo-sensing device  64  converts the light emitted by light source  60 , a text or a picture firstly reflected by the glass surface  61  and secondly reflected by the mirror  62  to a plurality groups of charges. A portion of the photo-sensing device  64  is exposed to the light refracted by the lens  63  at the position Pl. 
     Assume a first number of the cell of the photo-sensing device  64  are exposed to the light source  60  in the high resolution mode, and the second number of the cell of the photo-sensing device  64  are exposed to the light source  60  in the low resolution mode. As illustrated in FIG. 4, the second number of the cell of the photo-sensing device  64  exposed to the light source  60  in the low resolution mode is less then the first number of the photo-sensing device  64  in the high resolution mode. Accordingly, the present invention provide the exposing timing signal source  58  that can output the first exposing timing signal  80   h  (FIG. 5) or the second exposing timing signal  80   i  (FIG. 6) responding to the selection of the high or low resolution mode in the software interface  71 . After the plurality groups of charges has been generated by the photo-sensing device  64 , then is transmitted to the corresponding potential-energy wells of the CCD shift register  65  in accordance with the first exposing timing signal  80   h  or the second exposing timing signal  80   i  from the exposing timing signal source  58 . 
     Subsequently, responding to the clock pulse  90  from the shift control signal source  59 , the plurality groups of charge in the potential-energy wells of the CCD shift register  65  are driven one after another to the pre-processing device  69 . Thus the plurality groups of charge form the electrical signal representing one scan line of the scanned image. In other words, one line on the scanned object (text, or picture) is converted to the electrical signal. After the electrical signal has been fed to the pre-processing device  69 , the dc-gain voltage amplifier  69   a  adjusts the dc-gain of the electrical signal and then feed it to the ADC  69   b . Contrast adjustment by a Gamma characteristic is performed by the post-processing means  70 , and then obtained the output signal representing the image, which can be used to further processed or displayed. 
     It is noted that, the image-acquiring device of the image processing system according to the present invention can reduce scanning time in the low resolution scanning mode, and the principle is described below. As illustrated in FIG. 4, when the user utilizes the software interface  71  to select the high resolution mode. The plurality groups of charge generated during the high resolution mode exposing timing interval (i.e., the time between the first pulse  79  and the second pulse  81 ) by the photo-sensing device  64  are driven to the CCD shift register  65  responding to the first pulse  81  (FIG.  5 ). Then, each of the plurality groups of charge stored in the corresponding potential-energy wells in the CCD shift register  65  are driven to the pre-processing device  69  by each pulse ( 91 A 1 ,  91 A 2 , . . . ,  91 An) of the clock pulse  90  (FIG.  7 ). Also, the clock pulse  90  is fed to the counter  67 , and the high resolution reset signal  95   hs  has the period the same as that of the high resolution mode exposing timing interval due to the value transmitted to the counter  67  resulted from the set-up in the software interface  71 . For example, assume the photo-sensing device  64  has 10600 cells, thus the number of pulse between the pulse  91 A 1  and  91 An is 10600. So the high resolution mode exposing timing interval is not less than the multiplicity of 10600 and the pixel rate which stands for how much time does it take for the transmission of each group of charge from the CCD shift register  65  to the pre-processing device  69 . 
     It is also noted that the duration between the first reset pulse  96   hs   1  and the second reset pulse  96   hs   2  is approximately equal to the high resolution mode exposing timing interval between the first pulse  81  and the second pulse  83  in FIG.  5 . Because the second reset pulse  96   hs   2  of the high resolution reset signal  95   hs  from the counter  67  arrive at the reset gate  66 . All the charges stored in the CCD shift register  65  are transmitted to ground by way of the reset gate  66  which is turned on by the second reset pulse  96   hs   2  of the high resolution reset signal  95   hs . The next line on the scanned object (text, or picture) is subsequently driven by the second pulse  83  to the CCD shift register  65 , and is converted to generate the other plurality groups of charge in the next exposing timing interval. 
     In the other respect, as illustrated in FIG. 4, when the user utilizes the software interface  71  to select the low resolution (operation) mode. The plurality groups of charge generated during the low resolution mode exposing timing interval (i.e., the time between the third pulse  98  and the fourth pulse  99 ) by the photo-sensing device  64  are driven to the CCD shift register  65  responding to the fourth pulse  98  (FIG.  6 ). Then, each of the plurality groups of charge stored in the corresponding potential-energy wells in the CCD shift register  65  are driven to the pre-processing device  69  by each pulse ( 91 A 1 ,  91 A 2 , . . . ,  91 Ak) of the clock pulse  90  (FIG.  7 ). Also, the clock pulse  90  is fed to the counter  67 , and the low resolution reset signal  105   s  (FIG. 9) has the period about half of that of the high resolution mode exposing timing interval due to the value transmitted to the counter  67  resulted from the set-up relating to the “L” bottom on the software interface  71 . 
     For example, assume the photo-sensing device  64  has 10600 cells, and the low resolution mode be employed to scan the image. Thus the number of pulse between the pulse  90 A 1  and  90 An is 5300. So the low resolution mode exposing timing interval is not less than the multiplicity of 5300 and the pixel rate which stands for how much time does it take for the transmission of each group of charge from the CCD shift register  65  to the pre-processing device  69 . It is also noted that the duration between the third reset pulse  105   s   2  and the fourth reset pulse  105   s   3  is approximately equal to the low resolution mode exposing timing interval between the third pulse  98  and the third pulse  99  in FIG.  6 . Because the fourth reset pulse  105   s   3  of the low resolution reset signal  105   s  from the counter  67  arrive at the reset gate  66 . All the charges stored in the CCD shift register  65  are transmitted to ground by way of the reset gate  66  which is turned on by the fourth reset pulse  105   s   3  of the low resolution reset signal  105   s.    
     Because the reset gate  66  in the preferred embodiment of the present invention can be implemented by many devices, such as a charge coupled device (CCD). The structure of the reset gate  66  is briefly described in FIG.  10 A. In FIG. 10A, the electrode Ereset of the reset gate  66  is coupled to the counter  67  (FIG.  4 ). At the time when the charges are generated by the photo-sensing device  64  (FIG.  4 ), and has not been transmitted to the CCD shift register  65 , the cross-section of the potential-energy well is illustrated as line PW 1 , and the charges are still in the photo-sensing device  64 . Next, referring to FIG. 10B, the transfer gate and the CCD phase are applied with voltages such that the resulted potential-energy well is as line PW 2 , and the charges in the photo-sensing device  64  flow to the potential-energy well under the CCD phase electrode. 
     When the charges in the CCD shift register  65  is to be eliminated, the CCD phase and the reset gate are applied with voltages such that the charges in the potential-energy well under the CCD phase electrode are conducted to the potential-energy well under the CCD reset drain. Then the charges in the potential-energy well under the CCD reset drain are eliminated (such as conducted to ground). 
     Referring to FIG.  5  and FIG. 6, it is obvious that the necessary exposing time for the low resolution mode is half of that of the high resolution mode. So the image-acquiring device of the image processing system according to the preferred embodiment of the present invention can save the scanning time when operate in low resolution mode. The reset gate and the reset signal utilized to control the reset gate are the elements to reduce the necessary exposing time in low resolution mode, so the scanning time can be reduced in the preferred embodiment of the present invention. In conclusion, there can be many kinds of circuits or structure of the image-acquiring device can perform the function as the present invention. For example, if properly designed, the counter can be spared, or there can be two lens in the image-acquiring device. The two lens are respectively employed in low resolution mode and high resolution mode. In addition, the position means can be driving motor, and the software interface can be implemented not only in a computer as a application interface, but also can be implemented in the image processing system in the preferred embodiment of the present invention. 
     In a low resolution mode, fewer cells of photo-sensing device are used to expose to a scan line of the scanned object, so only a number of potential-energy wells of the CCD shift register are used to store the plurality groups of charge during an exposing timing interval. And the present invention is to lead the residual charges in the potential-energy wells of the CCD shift register to ground whenever the plurality groups of charges generated by the fewer cells of the photo-sensing device had been sent to the pre-processing device. So the waste of time in a lower resolution mode is averted in the present invention. 
     The low resolution mode and high resolution mode in the present invention is just preferred embodiments, there can be several resolution mode can be employed in the present invention, even the user can input the desired resolution. Because the resolution mode is the feature of the present invention, it is only the operational conduction of the present invention, the different resolution modes are not detailed in this specification. 
     As will be understood by persons skilled in the art, the foregoing preferred embodiment of the present invention is illustrative of the present invention rather than limiting the present invention. Having described the invention in connection with a preferred embodiment, the modification will now suggest itself to those skilled in the art. While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.