Patent Publication Number: US-4547864-A

Title: Correlation detecting device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention: 
     The present invention relates to a correlation detecting device to detect a correlation of two images. 
     2. Description of the Prior Art: 
     Heretofore, as an automatic focus detection device, there has been a device to have images of an object introduced through two different optical paths for detecting an in-focus position out of an amount of deviation in two images thereof. In this case, a correlation detecting device to detect correlation between the two images will become necessary. However, since image signals thereof are analog signals, they are very susceptible to a damage by a transfer, etc., therefore, a number of registers to retain said analog signals need to be provided, which constitute shortcomings of complicating circuits and making sizes thereof larger. Thus, this type of correlation detecting device has A/D converted such analog signals and then processed the same. 
     However, such device needs to have circuits to make a high speed A/D conversion and a high speed digital operations, resulting in such shortcomings as an increased cost of circuits and increased technical difficulties. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a correlation detecting device, which has a pair of analog shift registers forming a closed loop, shift means to have a correspondence between each bit in said analog shift registers shifted every time said analog shift registers make one cycle of circulation, and operation means to add differences between signals of corresponding bits of said analog shift registers for every 1 loop of the analog shift registers thus making correlation signals of images, so that image signals can be processed in their form of analog signals themselves and correlation can be detected therefrom by a very simple circuit arrangement. 
     Other objects of the present invention shall be made clear by a concrete example of the invention shown below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The drawing is a circuit diagram of a correlation detecting device to show an example of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Now, an example of the present invention shall be explained based on the drawing. The drawing is to show a circuit arrangement of a correlation detecting device as it is used in an automatic focus detection device which has images of an object introduced through two different optical paths and detects an in-focus position out of deviation of these two images, that is a correlation of the two images. 
     In this drawing, 1 is a light receiving part having a pair of line sensors 1a, 1b, wherein the line sensors 1a, 1b receive light beams reflected from an object 2 separately through different optical paths 3, 4. That is, since a correlation of positions of images received by the line sensors 1a, 1b varies depending on a perspective of the object 2, a detection of a distance to the object 2 or a detection of an in-focus position of a lens can be made based on the same. What is shown as 5 is an analog shift register with 1-bit, and 6 is an analog shift register with 5-bits, while 7 is the same with 4-bits, and CCD, etc. are used therefor, wherein these analog shift registers 5, 6, 7 form a closed loop analog shift register with 10 bits through a change-over switch 8 such as an electronic switch, etc. That is, when the switch 8 is at &#34;a&#34; side, the analog shift register 5 receives image signals, time sequential image signals of 10 bits for example, from the line sensor 1a introduced thereinto and transfers the same in turn to the analog shift registers 6, 7, and when the switch 8 is changed over to &#34;b&#34; side, the input of the image signals from the line sensor 1a is discontinued, and an output terminal of the analog shift register 7 and an input terminal of the analog shift register 5 are connected together, thus the analog shift registers 5, 6, 7 form a closed loop, then input image signals circulate one bit by one bit in synchronism with clock signals from a driving circuit 15 to be described later. What is shown as 9 is an analog shift register with 5 bits and 10 is an analog shift register with 6-bits, and CCD, etc. are used in such registers, forming analog shift registers of a closed loop with 11-bits through a change-over switch 11 such as an electronic switch, etc. And when the switch 11 is at &#34;c&#34; side, image signals, time sequential image signals of 10 bits for example, from the line sensor 1b are introduced into the analog shift register 9 and are transferred in turn, but when the switch 11 is changed over to &#34;d&#34; side, the analog shift registers 9, 10 form a closed loop, and input image signals are circulated in synchronism with clock signals from the driving circuit 15. What is shown as 12 is a differential circuit to detect a difference between an output 5a of the analog shift register 5 and an output 9a of the analog shift register 9, wherein said outputs 5a, 9a are received respectively by field effect transistors 12a, 12b, and differential voltages will be generated at resistors 12d, 12e by a constant current circuit 12c. These differential voltages have current converted by field effect transistors 12f, 12g, thereby producing differential signals at a terminal 12h. This differential circuit 12 may be any circuit such as a known type of an absolute differential amplifier, etc., as long as absolute value signals can be obtained. What is shown as 13 is an analog shift register with 11-bits which shifts one bit by one bit every time the shift registers 5, 6, 7 make one cycle of circulation while adding an output of the differential circuit 12. 
     That is, since the shift registers 5, 6, 7 form a closed loop with 10-bits and the shift registers 9, 10 form a closed loop with 11-bits, corresponding bits being introduced into the differential circuit 12 of the shift registers 5, 6, 7 and those of the shift registers 9, 10 will be shifted by one bit by one bit every time the shift registers 5, 6, 7 make one cycle of circulation. Therefore, the signals input into one bit of the shift register 13 represents the difference in the total image signals received by the line sensors 1a, 1b, thus corresponding image signals take values of difference of shifted images one by one. What is shown as 14 is a minimum value detecting circuit consisting of an inversion amplifier 14a and a peak value detecting circuit 14b, to detect the minimum value out of each bit of the shift register 13. What is shown as 15 is the driving circuit which generates clock signals by a closing of a switch 17 to control the light receiving part 1, the shift registers 5, 6, 7 and the shift registers 9, 10 in synchronism with said clock signals. 
     What is shown as 16 is a decimal frequency divider which receives signals from the driving circuit 15 as an input thereinto, and a resetting thereof is released by a closing of the switch 17. What is shown as 18 is an RS-flip-flop, which has its resetting released by a closing of the switch 17 and has its Q-output changed to a high level when signals at high level are introduced from the decimal frequency divider 16 into a terminal S, then the switch 8 is changed over to &#34;b&#34; side and the shift registers 5, 6, 7 are formed into a closed loop and at the same time the switch 11 is changed over to &#34;d&#34; side, and the shift registers 9, 10 are made to form a closed loop. Also at the same time Q output of the RS-flip-flop is changed to a low level to release a resetting of the shift register 13. What is shown as 19 is an AND gate to produce the clock signals of the driving circuit 15 as its output when Q output of the RS-flip-flop is introduced as an input with a high level. What is shown as 20 is a decimal frequency divider, which has its resetting released when the switch 17 is closed to have signals of the AND gate 19 introduced thereinto. What is shown as 21 is a counter, which has its resetting released when the Q output of the RS-flip-flop is changed to a high level to count the clock signals having a frequency thereof divided into 10 from the decimal frequency divider 20. What is shown as 22 is an AND gate, and when the minimum value detecting circuit detects the minimum value of the shift resistor 13 under a state in which the Q output of the RS-flip-flop is at a high level, a latch circuit 23 is actuated by signals thereof and signals of the counter 21 at that time is latched, for detecting a position of the maximum correlation. What is shown as 24 is processing circuit which detects a distance to an object and an in-focus position of a lens from a display of a correlation based on signals from the latch circuit 23 and from the fact that a perspective of the object corresponds to the position of the maximum correlation. 
     Next, operations of the above-mentioned arrangement shall be explained. 
     When the switch 17 is at an open state as shown in the drawing, each part of the circuit is in a reset state, and clock signals are not generated from the driving circuit 15. Therefore Q outputs of the RS-flip-flop are at a low level, and the changeover switches 8, 11 are connected to respectively &#34;a&#34; side and &#34;c&#34; side, while the analog shift registers 5, 6, 7 as well as the analog shift registers 9, 10 are in a state being connected to the light receiving part 1. 
     When the switch 17 is closed from said state, the reset state of each part in the circuit except the shift register 13 and the counter 21 is released and at the same time the driving circuit 15 starts an operation, then clock signals are given to the light receiving part 1, and the shift registers 5, 6, 7 as well as to the shift registers 9, 10. Therefore, in synchronism with said clock signals the image signals received by the line sensor 1a are transferred in turn from the shift register 5 to the shift registers 6, 7 and at the same time image signals, time sequential image signals of 10 bits for example, received by the line sensor 1b are transferred in turn from the shift register 9 to the shift register 10. 
     When 10 clock signals are generated from the driving circuit 15, signals with a high level from the decimal frequency divider 16 are introduced into &#34;S&#34; input terminal of the flip-flop 18, and the Q output of the RS-flip-flop 18 which has been in a low level up to this moment is changed to a high level. By this, the change-over switches 8, 11 are changed over to &#34;b&#34; side and &#34;d&#34; side respectively and the input of the image signals from the light receiving part 1 into the shift registers 5, 9 is cut off, and at the same time the shift registers 5, 6, 7 as well as the shift registers 9, 10 form closed loops, respectively. At the same time the Q output of the RS-flip-flop 18 becomes to have a low level, therefore a resetting of the shift register 13 is released. Therefore, the difference between corresponding bits of the shift registers 5, 6, 7 and of the shift registers 9, 10 which respectively form closed loops, that is starting with a value of the shift register 5 at a time when 10  clocks much of the clock signals from the driving circuit 15 are generated (a tenth image signal from the line sensor 1a) and a value of an output bit of the shift register 9 (6th image signal from the line sensor 1b) are operated by the differential circuit 12, then results thereof will be added to the first bit of the shift register 13. On the other hand, the Q outputs of the RS-flip-flop give signals of high level to an input terminal at one side of the AND gate 19, therefore the clock signals of the driving circuit 15 will be given also to the decimal frequency divider 20 through the AND gate 19. Therefore, signals of ten clocks are sent from the driving circuit 15, then as the operated outputs of the difference between each bit of the shift registers 5, 6, 7 as well as of the shift registers 9, 10 forming a closed loop respectively make one cycle of circulation around said closed loops, high level signals are produced out of the decimal frequency divider 20 and the shift register 13 is shifted by one bit. Since a number of corresponding bits of the shift registers 5, 6, 7 and that of the shift registers 9, 10 are different by one, when one cycle of circulation is made as mentioned above, the corresponding bits of the shift registers 5, 6, 7 and that of the shift registers 9, 10 will be deviated by one bit each because of a closed loop. Since the clock signals from the driving circuit 15 having the frequency thereof divided by ten are introduced into the shift register 13 as an input, a sum of the absolute values of difference between the corresponding bits, being deviated by one bit each, of the shift registers 5, 6, 7 and of the shift registers 9, 10 for every one cycle will be retained in turn at each bit of the shift register 13. That is, while the shift registers 5, 6, 7 and the shift registers 9, 10 are minor loop shift registers, the shift register 13 is a major shift register, and while the shift registers 5, 6, 7 and the shift registers 9, 10 make one cycle of circulation with 10 clocks of the clock signals of the driving circuit 15, the shift register 13 is shifted by one bit with 11 clocks of the clock signals. Thus, when the shift register 13 makes shiftings by 11 bits, the absolute value of difference between image signals of the shift registers 5, 6, 7 being shifted by 10 bits and those of the shift registers 9, 10 also being shifted by 10 bits can be obtained. That is, the signal Qi at a number i bit from the input terminal of the shift register 13 will be equivalent to ##EQU1## if the signals at a number j from the input terminals of the shift registers 5, 6, 7 and the shift registers 9, 10 are represented by Bj, Aj, respectively. 
     The Q output of the RS-flip-flop releases a resetting of the counter 21, and the counter 21 counts the clock signals having been produced from the decimal frequency divider 20 and having their frequency divided by ten. Since the operation of the shift register 13 also synchronizes with said signals having their frequency divided by ten as mentioned above, when signals of each bit of the shift register 13 are introduced into the minimum value detecting circuit 14 and the minimum value is detected, the latch circuit 23 is actuated through the AND gate 22 which is at an actuated state by the Q output of the RS-flip-flop 18, and the counted value of the counter 21 at that time will be latched. That is, the minimum value of the absolute difference of the image signals shows the maximum correlation, therefore a bit position of the shift register 13 holding said value, that is an amount of shifting until the maximum correlation will be obtained from a number of counting by the counter 21 and will be latched in the latch circuit 23. The signals being latched by the latch circuit 23 are sent to the processing circuit 24, and such operations as a display, a range finding, an in-focus detection, etc. will be done. 
     If CCD and the like are of MOS process type used as the light receiving member in the above example, the light receiving portion can also serve as an analog shift register. Also the switches 4, 8, 11 can be actuated by the opening and closing operation of the transfer gate in CCD, and the summation input can be performed by giving charges to CCD so that it is possible to design a very small correlation detection circuit free from waste. 
     Also, similar effect can be obtained even if, the major shift registers, etc. are replaced with such bipolar as BBD, etc. as an example, or even if the major shift register is made to have the minimum value memory (including an address). 
     As has been explained above, by making minor loops of analog shift registers in the manner mentioned above, a correlation detecting device with a simple analog circuit arrangement not requiring almost any external circuits can be realized, especially since an analog processing of image signals can be made mainly with one chip by including such circuit as mentioned above within a sensor, the circuit arrangement can be made small and a cost therefor can be reduced, so that it will be very useful as a correlation detecting device in an image correlation or in a pattern matching, etc. 
     Also a device of the present invention can naturally be used in all cases in which a detection of correlation is needed.