Abstract:
There is provided an image processing apparatus comprising: a sensor including a plurality of pixels each including a light receiving element, and a scanning circuit for reading out signals in time sequence from the plurality of pixels; and a drive circuit which supplies pulses for driving the scanning circuit, wherein the drive circuit is so arranged to output at least a first pulse and a second pulse smaller than the first pulse, the drive circuit supplying the first pulse to the scanning circuit when a first resolution is selected, and supplying the first pulse and the second pulse to the scanning circuit when a second resolution lower than the first resolution is selected.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sensor having a plurality of light receiving elements and a scanning circuit which reads out signals in time sequence from the plurality of light receiving elements. 
     2. Related Background Art 
     In recent years, in the field of information processing systems, as to one-dimentional image reading apparatus, a development of contact type of equal magnification image sensors in which a plurality of semiconductor optical sensor chips are mounted has been positively pursued in contrast with that of conventional reduction-system line sensors using an optical system. 
     For example, Japanese Laid-open Patent Application No. 05-227362 discloses a contact-type image sensor which has a newly-added control terminal for resolution control, and the resolution of which can be changed by a user according to a use condition. 
       FIG. 1  is a circuit diagram of an integrated circuit of the contact-type image sensor disclosed in the above-described Japanese Laid-open Patent Application. In this conventional art, a control terminal  125  is provided on an image sensor chip. To change the resolution of the image sensor chip, a user inputs through the terminal  125  a high-level or low-level signal for selection between a high resolution mode and a low resolution mode. 
     The circuit shown in  FIG. 1  will be outlined below. A start pulse S 1  and clock pulses CLK are supplied to shift registers  104 . When a shift register  104   a  is started up by the start pulse S 1 , an output from the shift register  104   a  is input to a channel selection switch  103   a  through a NOR gate  121   a  and an AND gate  120   a . The channel selection switch  103   a  is thereby turned on to extract a signal from a photocell  101   a  to a signal line  107   a . Other shift registers  104   b  to  104   f  are successively started up to output a signal from each of photocells  101   b  to  101   l  to the signal line  107   a  or  107   b.    
     When a control signal “H” is input to the control signal input terminal  125 , analog switches  110   a ,  110   b ,  122   a , and  122   b  are switched over to obtain at an image output terminal  111  an image signal of a reading density of 16 dots/mm. When a control signal “L” is input to the control signal input terminal  125 , the analog switch  110   a  is always set in an on state and an image signal of a reading density half the density of the entire photocells  101   a  to  101   l , i.e., 8 dots/mm is obtained at the image output thermal  111 . That is, while all the photocells  101   a  to  101   l  on the sensor IC are always operating, the image signal can be read out from the photocells with being thinned out a part of the signals according to the control signal. Thus, the voltage level of the image signal is always constant and an image processing circuit of a conventional configuration can be used to process the output image signal read out from the photocells. 
     In the above-described readout, however, it is necessary to read signals from all the light receiving elements irrespective of the selection between high resolution reading and low resolution reading and to uniformly set a readout time required for reading from all the light receiving elements. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an image processing apparatus capable of obtaining a reading speed corresponding to the resolution. 
     In order to achieve the above-mentioned object, according to a scope of the present invention, there is provided an image processing apparatus comprising: a sensor including a plurality of pixels each including a light receiving element, and a scanning circuit for reading out signals in time sequence from the plurality of pixels; and a drive circuit which supplies pulses, for driving the scanning circuit, wherein the drive circuit is so arranged to output at least a first pulse and a second pulse smaller than the first pulse, and the drive circuit supplies the first pulse to the scanning circuit when a first resolution is selected, and supplies the first pulse and the second pulse to the scanning circuit when a second resolution lower than the first resolution is selected. 
     Another object and features of the present invention will be apparent by the following embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram of a conventional integrated circuit for a contact-type image sensor; 
         FIG. 2  is a circuit diagram showing a configuration of a sensor chip used in a multichip-type sensor according to an embodiment; 
         FIG. 3  is a circuit diagram showing an example of a configuration of one pixel; 
         FIG. 4  is a timing chart for explaining operation when a low resolution is selected; 
         FIG. 5  is a timing chart for explaining operation when a high resolution is selected; 
         FIG. 6  is a diagram showing a configuration of a circuit for generating normal clock pulses and clock pulses having different pulse widths alternately; 
         FIG. 7  is a timing chart of the circuit shown in  FIG. 4 ; 
         FIG. 8  is a timing chart of block reading; 
         FIG. 9  is a block diagram of a contact-type image sensor unit; 
         FIG. 10  is a block diagram of an image input system using the contact-type image sensor unit shown in  FIG. 9 ; and 
         FIG. 11  is a diagram showing details of the system shown in  FIG. 10 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 2  is a circuit diagram showing an embodiment of a configuration of a sensor chip used in a multichip-type sensor described below. This image sensor chip is formed on the same substrate by a complementary metal-oxide-semiconductor (CMOS) process or the like so as to be integrally combined with other circuit components. In  FIG. 2 , broken-line regions S 1 , S 2 , S 3 , S 4 , . . . , Sn respectively represent pixels. Output signals from the respective pixels S 1  to Sn are output via a common output line L and the amplifier M. The common output line L is reset by a reset transistor RES. The respective pixels S 1 , S 2 , S 3 , S 4 , . . . , Sn are successively selected by D flip-flops F 1 , F 2 , F 3 , F 4 , . . . , Fn constituting a shift register (scanning circuit). 
       FIG. 3  is a circuit diagram showing an example of a configuration of one pixel. The pixel shown in  FIG. 3  represents an example of a photosensor called a CMOS sensor. 
     As shown in  FIG. 3 , the pixel has a photodiode PD (light receiving element), a reset transistor MR, an amplifier transistor MSF forming a pixel amplifier, and a selecting transistor MSEL for selecting a pixel. The selecting transistor MSEL is controlled by the corresponding one of output signals G 1  to Gn from the D flip-flops F 1  to Fn. A photoelectrically converted signal from the photodiode PD is transferred to the gate of the amplifier transistor MSF forming a pixel amplifier and produces a signal which is output through the pixel amplifier MSF and the selecting transistor MSEL. The reset transistor MR is turned on to reset the pixel portion. 
     Referring to  FIG. 2 , when a start signal SIN is input to the D flip-flop F 1  through the D terminal, and when a clock signal (synchronization pulse) CLK is input to the T terminal, the signal G 1  from the D flip-flop F 1  becomes an H level and then is input to the gate of the selecting transistor MSEL of the first pixel S 1 . A signal corresponding to the charge accumulated in the photodiode PD of the first pixel S 1  is thereby output to the common output line L. When the next clock signal CLK is input through the T terminal, the level of the signal G 1  becomes an L level. 
     When at the same time, the signal G 1  is input to the next-stage flip-flop F 2  through the D terminal, and when the clock signal CLK is input to the T terminal, the level of the signal G 2  from the D flip-flop F 2  becomes the H level and then is input to the gate of the selecting transistor MSEL of the second pixel S 2 . A signal corresponding to the charge accumulated in the photodiode PD of the second pixel S 2  is thereby output to the common output line L (signal reading from this pixel is virtually stopped at the time of low-resolution reading described below). Note that the common output line L is reset by the reset transistor RES before the signal is output from each pixel. 
     Reading of a signal is performed in the same manner up to the nth pixel Sn. Signal Gn is output as a signal for starting the next sensor chip, and signal reading of the next sensor chip is also performed in the same manner. 
     In this embodiment, a signal can be selectively read from any pixels by setting as desired the pulse width of the clock signal (synchronization pulse) input to the sensor chip. 
     A case of performing switching between low resolution reading and high resolution reading will be described.  FIG. 4  is a timing chart for explaining the operation in case of low resolution reading, and  FIG. 5  is a timing chart for explaining the operation in case of high resolution reading. 
     A so-called skip reading (thinning-out reading) is performed in case of low resolution reading. As shown in  FIG. 4 , two pulses having different widths T 1  and T 2  are alternately input as the clock pulses CLK to form signals G 1  to Gn so that signals G 1 , G 3 , G 5 , . . . have a pulse width T 11  necessary for normal signal reading of the pixels and signals G 2  , G 4 , . . . have a pulse width T 12  smaller than the pulse width T 11 . Then, normal reading of signals from the pixels S 1 , S 3 , S 5 , . . . is performed to output V 1 , V 3 , V 5 , . . . as output Vout. Signal reading of the pixels S 2 , S 4 , . . . is virtually stopped since the reading period is short. In this case, since there is no need for signal reading of the pixels S 2 , S 4 , . . . , it is desirable to set the level of signals G 2 , G 4 , . . . to the lower limit of the range in which the flip-flop can operate. If it is necessary to perform reading with a further lower resolution, the shift register may be supplied with a train of the clock pulses CLK in which two or three pulses having the width T 2  are interposed between pulses having the pulse width T 1 . 
     All-pixel reading is performed in case of high resolution reading. That is, normal signal reading of all the pixels S 1 , S 2 , S 3 , S 4 , S 5 , . . . is performed. As shown in  FIG. 5 , clock pulses CLK having the pulse width T 1  are input to set the pulse width of signals G 1 , G 2 , G 3 , . . . to the normal pulse width T 11 . 
       FIG. 6  shows a configuration of a sensor drive circuit which generates a normal clock pulse, and which alternately generates clock pulses having different pulse widths.  FIG. 7  is a timing chart of the sensor drive circuit. A normal clock pulse clk 1  and a clock pulse clk 2  where pulse width changes between different widths alternately, are formed from reference clock refclk, and the clock pulse clk 1  or the clock pulse clk 2  is input as the clock pulse CLK to the sensor chip shown in  FIG. 2  as required, thus enabling switching between high resolution reading and low resolution reading. 
     While in this embodiment a circuit capable of alternately generating clock pulses having different pulse widths is used as a hardware to generate a clock pulse, a clock pulse having different pulse widths may alternatively be generated with software, i.e., by using a program. 
     A case of performing block reading, i.e., reading out signals from pixel forming regions selected as desired, will next be described. Needless to say, switching between block reading and all-pixel reading can be performed as well as switching between low resolution reading and high resolution reading. A case of reading out signals from the pixels S 6  to S 8  will be described by way of an example. 
     A train of clock pulses CLK is set in such a manner that, as shown in  FIG. 8 , signals G 6  to G 8  have the normal pulse width required for the signal reading while signals G 1  to G 5  and G 9  to G 11  have a smaller pulse width, thus enabling selective block reading of signals from the pixels S 6  to S 8 . 
     An example of a contact-type image sensor unit constructed by using the above-described multichip-style sensor and an application of the contact-type image sensor unit to an image reading system will be described. 
       FIG. 9  is a block diagram of a contact-type image sensor unit  50 .  FIG. 10  is a block diagram of an image input system using the contact-type image sensor unit  50 . 
     Referring to  FIG. 9 , the contact-type image sensor unit  50  is constituted by a sensor module board  51  and a light source  52 . Each of portions denoted by reference numeral  1  corresponds to the sensor chip described above with reference to  FIG. 2 . Light emitting diodes (LEDs) and light guide members for irradiating an original surface with light from the LEDs are used to form the light source  52 . A different light source, e.g., one constituted by a light source having a plurality of LED chips mounted one-dimensionally, or one formed of a cold-cathode tube, or the like may alternatively be used. On the sensor module board  51 , a plurality of the above-described sensor chips  1  are mounted one-dimensionally on a ceramic board and a signal output (Vout) terminal and a clock signal CLK terminal are connected in common to all the sensor chips in the sensor module. 
     Further, a light source drive terminal  53  for driving/controlling the light source is provided on the contact-type image sensor unit  50 . 
       FIG. 10  shows an example of an image input system  100  using the contact-type image sensor unit  50  shown in  FIG. 9 . The image input system  100  is constituted mainly of a drive circuit  101  for electrically driving the sensor and the light source of the contact-type image sensor unit, and a signal processing circuit  102  for processing signals (such as shading correction) output from the contact-type image sensor unit. The operation of the image input system is controlled by a central processing unit (CPU)  110 . When switching between a high resolution and a low resolution is performed, a resolution control signal (MODE_M) provided as a command to perform switching from a high or low resolution to a low or high resolution is input from the CPU to the image input system. In the image input system, the resolution control signal is supplied to the sensor drive circuit  101 , which includes a drive circuit, such as that shown in  FIG. 6 , for supplying synchronization pulses, and which changes synchronization pulses on the basis of the resolution control signal. Needless to say, switching between all-pixel reading and block reading can be performed by using the same arrangement. 
     Through the resolution control signal output from the external CPU, a high resolution mode (600 dpi) is set, for example, when the resolution control signal is high level, and a low resolution mode (300 dpi) is set when the resolution control signal is low level. Note that, in a case where clock pulses having different pulse widths are alternately generated with software, a synchronization pulse signal is directly generated from the CPU to be supplied to the sensor drive circuit  101 . In such a case, to change the resolution, pixels which will be skipped (thinned out) can be selected as desired by changing a program for producing synchronization pulses. Also, pixels which will be read out by block reading can be selected as desired. 
     According to this embodiment, as described above, there is no need to form a circuit for switching between high resolution reading and low resolution reading (or between block reading and all-pixel reading) in each sensor chip, and thus the size of each sensor chip can be reduced. Among multichip-style image sensors used as contact-type image sensors, smaller ones are particularly in high demand because, in each of applications of the multichip-type image sensors to the contact-type image sensors, the multichip-type image sensor is mounted together with a light source for irradiating the original with light, etc., with being close to each other. Therefore the multichip-type image sensor of the present invention can be preferably used as a contact-type image sensor. 
       FIG. 11  shows details of the system shown in  FIG. 10 . In  FIG. 11 , components identical to those shown in  FIGS. 9 and 10  are denoted by the same reference numerals. 
     The contact-type image sensor unit (hereinafter referred to as “CIS”)  50  is constituted by the sensor module board  51 , a Selfoc lens  201 , an LED array  52 , and a contact glass  202 . 
     Transport rollers  203  are disposed in the front and at the rear of the CIS  50  and are used to place an original. A contact sheet  204  is used to maintain an original in contact with the CIS  50 . The CPU  110  performs overall control of the image reading system including resolution switching. An original detection lever  205  is a lever for detecting insertion of an original. When insertion of an original is detected, that is, when the original detection lever  205  is inclined by insertion of the original to change an output from an original detection sensor  206 , the CPU  110  is informed of this condition, determines that the original has been inserted, starts transport of the original by operating a motor for driving the original transport rollers (not shown), and conducts the reading operation. Here, the CPU may be included in the image reading system. The signal processing circuit  102  may be provided outside the image reading system, e.g., in a computer. The arrangement may alternatively be such that not the original but the CIS  50  is moved. 
     Many widely different embodiments of the present invention may be constructed without departing from scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.