Method and system for detecting sharpness of an object image

• US 4,133,606 A
• Filed: 11/11/1975
• Issued: 01/09/1979
• Est. Priority Date: 11/13/1974
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Yokota, Hideo, Hosoe, Kazuya, Asaeda, Tsuyoshi, Shingu, Tamotsu
• Primary Examiner(s): Adams, Russell E.
• Application Number:
  US05/631,133
• Time in Patent Office: 1,155 Days
• Field of Search: 354/25, 250/201, 250/209, 318/640
• US Class Current: 396/101
• CPC Class Codes: G02B 7/365 by analysis of the spatial frequency components of the image

Abstract

The present invention relates to a method and a system for detecting the sharpness of the object image by detecting the amount of the component of a certain specified frequency, whereby the object image formed by means of an image forming optical system is detected by an image sensitive element consisting of a number of fine photo sensitive elements arranged respectively integrated on one plane, while the outputs of the above mentioned photo sensitive elements are delivered out one after another in accordance with the arrangement order of the above mentioned elements by means of a signal time series means so as to carry out an electrical scanning of the above mentioned object image in such a manner that the then obtained scanning outputs of the object image are successively converted by means of an A - D (analogue-digital) converting means into digital signals which are put in a small computer in which an estimation function for estimating the amount of the component of a certain specified frequency in the spectrum of the spacial frequencies of the object light beam forming the above mentioned object image is programmed in advance.

Claims

1. An automatic focusing system comprising:

(A) an image forming optical system having an optical axis and shiftable along the axis so as to form an object image on a predetermined imaging plane;

(B) driving means operatively coupled with said optical system for shifting the optical system along the optical axis;

(C) image sensing means comprising n photosensitive elements addressed differently from each other one plane, said sensing means being disposed at positions to receive the object image formed by the optical system on said imaging plane, said n-photosensitive elements serving for producing respective output signals corresponding to the light intensity impinging thereon;

(D) scanning means for repeatedly scanning the object image on the imaging plane during the shifting of the optical system by said driving means and for sequentially sending out each analogue output of said n-photosensitive elements of said image sensing means in the order of each address of said n-photosensitive elements, said scanning means being electrically connected to each of said n-photosensitive elements;

(E) A - D converting means to convert each analogue output of the n-photosensitive elements being sent out sequentially by said scanning means into a digital signal, said converting means being electrically connected to said image sensing means;

(F) a processing device for consecutively taking each address signal of the n-photosensitive elements addressed in turn by said scanning means and the digital signals being produced by said A - D converting means and for evaluating the distribution of the specific spatial frequency spectrum in the image light beam forming the object image;

on the basis of a Fourier-function;

wherein said processing means includes;

(F-1) a function value generating means to produce a sine-cosine function value of said specific spatial frequency on each address of the n-photosensitive elements, said generating means being electrically connected to said scanning means for producing the function value in response to each address signal;

(F-2) multiplying means to calculate a product of said sine-cosine function value and the digitally converted value of the output of the photosensitive element at the address corresponding thereto;

said multiplying means being electrically connected to said function value generation means and said A-D converting means;

(F-3) first accumulating means to consecutively add the values calculated by said multiplying means cumulatively for calculating the total sum of said products on all of the n-photosensitive elements, said accumulating means being electrically connected to said multiplying means;

(F-4) second accumulating means to consecutively add the digital signals being produced by said A-D converting means cumulatively for calculating the total sum of said digital signals on all of the n-photosensitive elements, said accumulating means being electrically connected to said A-D converting means;

(F-5) dividing means to divide the value calculated by said first accumulating means by the value calculated by said second accumulating means, said dividing means being electrically connected to said first and second accumulating means;

(F-6) first register means to record the value calculated by said dividing means as an l'"'"'th (l=1, 2, 3, . . .) scan is completed when the scanning of the object image is repeated several times during the shifting of the optical system by the driving means, said register means being electrically connected to said dividing means;

(F-7) second register means to record the calculated value of said dividing means as an (l-1)th scan is completed when the scanning of the object image is repeated several times during the shifting of the optical system by the driving means, said second register means being electrically connected to said first register means and recording the value calculated by said dividing means as the (l-1)th scan on said first register means when l'"'"'th scan is completed; and

(F-8) comparing means to judge which one of the value recorded by said first and second register means is larger than the other when each scan is completed, said comparing means being electrically connected to said first and second register means and producing a predetermined control signal when the values recorded by said registers become at least equal to each other; and

(G) control circuit means to stop said driving means in response to said predetermined control signal produced by said comparing means, said circuit means being electrically connected to said driving means and said comparing means;

so as to achieve automatic focusing of the image forming optical system on the object.

2. An automatic focusing system comprising:

(A) an image forming optical system having an optical axis and shiftable along the axis so as to form an object image on a predetermined imaging plane;

(B) driving means operatively coupled with said optical system for shifting the optical system along the optical axis;

(C) image sensing means comprising n photosensitive elements on one plane and addressed differently, said sensing means being disposed at positions to receive the object image formed by the optical system on said imaging plane, said n-photosensitive elements respectively serving for producing analogue signals corresponding to the light intensity thereon;

(D) scanning means for repeatedly scanning the object image on the imaging plane during the shifting of the optical system by said driving means and for sending out each analogue output of said n-photosensitive elements of said image sensing means in the order of each address of said n-photosensitive elements, said scanning means being electrically connected to each of said n-photosensitive elements;

(E) A-D converting means to convert each analogue output of the n-photosensitive elements being sent out in time series by said scanning means into a digital signal, said converting means being electrically connected to said image sensing means;

(F) a processing device to consecutively taking each address signal of the n-photosensitive elements being addressed in turn by said scanning means and the digital signals being produced by said A-D converting means for evaluating the distribution of the specific spatial frequency spectrum in the image light beam forming the object image on the basis of a Walsh-function;

said processing means including;

(F-1) function value generating means to produce a Walsh-function value of said specific spatial frequency on each address of the n-photosensitive elements, said generation means being electrically connected to said scanning means for producing the function value in response to each address signal;

(F-2) multiplying means to calculate a product of said Walsh function value and the digitally converted value of the output of the photosensitive element at the address corresponding thereto;

said multiplying means being electrically connected to said function value generation means and said A-D converting means;

(F-3) first accumulating means to consecutively add the values calculated by said multiplying means cumulatively for calculating the total sum of said products or all of the n-photosensitive elements, said accumulating means being electrically connected to said multiplying means;

(F-4) second accumulating means to consecutively add the digital signals being produced from said A-D converting means cumulatively for calculating the total sum of said digital signals on all of the n-photosensitive elements, said accumulating means being electrically connected to said A-D converting means;

(F-5) dividing means to divide the value calculated by first accumulating means by the value calculated by said second accumulating means, said dividing means being electrically connected to said first and second accumulating means;

(F-6) first register means to record the calculated value by said dividing means as an l'"'"'th (l=1, 2, 3, . . .) scan is completed when the scanning of the object image is repeated several times during the shifting of the optical system by the driving means, said register means being electrically connected to said dividing means;

(F-7) second register means to record the calculated value of said dividing means as an (l-1)th scanning is completed when the scanning of the object image is repeated several times during the shifting of the optical system by the driving means, said register means being electrically connected to said first register means and recording the value calculated by said dividing means as the (l-1)th scan on said first register means when l'"'"'th scan is completed; and

(F-8) comparing means to judge which one of the values recorded by said first and second register means is larger than the other when each scan is completed, said comparing means being electrically connected to said first and second register means and producing a predetermined control signal when the values recorded by said registers become at least equal to each other; and

(G) a control circuit means to stop said driving means in response to said predetermined control signal from said comparing means, said circuit means being electrically connected to said driving means and said comparing means;

so as to achieve automatic focusing of the image forming optical system to the object.

3. An image sharpness detecting system for detecting the sharpness of an object image formed by an image forming optical system on a predetermined imaging plane, comprising:

(A) image sensing means comprising n-photosensitive elements addressed differently from each other on one plane, said sensing means being disposed at positions able to receive the object image formed by the optical system on said imaging plane, said n-photosensitive elements producing respective analog signals corresponding to light intensity;

(B) scanning means scanning the object image on the imaging plane by transmitting each analogue output of said n-photosensitive elements of said image sensing means in the order of each address of said n-photosensitive elements, said scanning means being electrically connected to each of said n-photosensitive elements;

(C) A-D converting means to convert each analog output of the n-photosensitive elements transmitted in time series by said scanning means into digital signal, said converting means being electrically connected to said image sensing means; and

(D) a processing device for consecutively receiving each address signal of the n-photosensitive elements addressed in turn by said scanning means and the digital signals from said A-D converting means and for evaluating the distribution of the specific spatial frequency spectrum in the image light beam forming the object image on the basis of a Fourier function;

said processing means including;

(D-1) function value generating means to produce a sine-cosine function value of the specific spatial frequency on each address of the n-photosensitive elements, said generating means being electrically connected to said scanning means for producing said function value in response to each of said address signals;

(D-2) multiplying means to calculate a product of said sine-cosine function value and the digitally converted value of the output of the photosensitive element at the address corresponding thereto;

said multiplying means being electrically connected to said function value generation means and said A - D converting means;

(D-3) first accumulating means for consecutively and cumulatively adding the values calculated by said multiplying means to accumulate the total sum of said products on all of the n-photosensitive elements, said accumulating means being electrically connected to said multiplying means;

(D-4) second accumulating means to consecutively and cumulatively add the digital signals from said A-D converting means for calculating the total sum of said digital signals on all of the n-photosensitive elements, said accumulating means being electrically connected to said A-D converting means; and

(D-5) dividing means to divide the value calculated by said first accumulating means by the value calculated by said second accumulating means, said dividing means being electrically connected to said first and second accumulating means and providing an electrical output representative of the sharpness of the object image formed by said image forming optical system on the imaging plane.

4. An image sharpness detecting system for detecting the sharpness of the object image formed by an image forming optical system on a predetermined imaging plane, comprising:

(A) image sensing means comprising n-photosensitive elements at positions and addresses different from each other on one plane, said sensing means being disposed at a position able to receive the object image formed by the optical system on said imaging plane, said n-photosensitive elements respectively, generating analog signals corresponding to light intensity;

(B) scanning means for scanning the object image on the imaging plane and supplying each analog signal from each of said n-photosensitive elements of said image sensing means in the order of each address of said n-photosensitive elements, said scanning means being electrically connected to each of said n-photosensitive elements;

(C) A-D converting means to convert each analog signal of the n-photosensitive elements being supplied sequentially by said scanning means into a digital signal, said converting means being electrically connected to said image sensing means;

(D) a processing device for consecutively processing each signal of the n-photosensitive elements being addressed in turn by said scanning means and converted by said A-D converting means and according to Walsh-function for evaluating the distribution of the specific spatial frequency spectrum in the image light beam forming the object image;

said processing means including;

(D-1) function value generating means to supply a Walsh-function value of the specific spatial frequency on each address of the n-photosensitive elements, said generating means being electrically connected to said scanning means for supplying the function value in response to each address signal;

(D-2) multiplying means to calculate the product of said Walsh-function value and the digitally converted value of the output of the photosensitive element at the address corresponding thereto, said multiplying means being electrically connected to said function value generating means and said A - D converting means;

(D-4) second accumulating means to consecutively and cumulatively add the digital signals from said A-D converting means for calculating the total sum of said digital signals on all of the n-photosensitive elements, said accumulating means being electrically connected to said A-D converting means;

(D-5) dividing means to divide the value calculated by said first accumulating means by the value calculated by said second accumulating means, said dividing means being electrically connected to said first and second accumulating means and providing an electrical output representative of the sharpness of the object image formed by said image forming optical system of the imaging plane.