Method and system for detecting whether an optical system is in focus using an improved interpolation technique

• US 4,883,951 A
• Filed: 03/21/1989
• Issued: 11/28/1989
• Est. Priority Date: 11/10/1986
• Status: Expired due to Term

• Current Assignee: Fuji Electric Company Limited (Fuji Electric Systems Company Limited)
• Original Assignee: Fuji Electric Company Limited (Fuji Electric Systems Company Limited)
• Inventors: Nishinbe, Takashi, Yokoyama, Shotaro
• Primary Examiner(s): Westin, Edward P.
• Application Number:
  US07/326,799
• Time in Patent Office: 252 Days
• Field of Search: 250/201, 250/204, 354/402, 354/406-409, 356/1, 356/4
• US Class Current: 250/201.1
• CPC Class Codes: G02B 7/34 using different areas in a pupil plane

Abstract

In a focus detection system in which light from an object is incident on at least two photosensor arrays via an optical system to form two images on the photosensor arrays, the relative displacement between the two images is determined in order to detect whether the optical system is in focus or not. A correction term which is formed by f(i₀ +2) and f(i₀ +1) or f(i₀ -2) and f(i₀ -1) is added to f(i_0-1)-f(i₀) or f(i₀ +1)-f(i₀), so that the amount of image deviation between the two images is obtained. Here i₀ is the value of i when a function f(i) is minimized, the function f(i) expressing the inconsistency between the two images, corresponding to an amount of relative displacement i×p between the two images obtained discretely. The symbol p represents the pitch of the at least two photosensor arrays.

Claims

1. A focus detection system in which light from a object is incident on first and second photosensor arrays via an optical system to form a first image on the first array and a second image on the second array to obtain a relative displacement amount X between the first image with respect to the first array and the second image with respect to the second array, so as to determine whether said optical system is in focus or not, each array generating a respective pattern of signals in response to light falling on the photosensors of the respective array, said system comprising:

means for storing a function f(i) expressing inconsistency between the pattern of signals from the first array and the pattern of signals from the second array when the patterns are shifted with respect to one another by a shift amount i and compared with each other, the shift amount i being an integer which represents the difference between a photosensor position in the first array and a photosensor position in the second array;

means for obtaining function values f(i₀), f(i₀ -1), f(i₀ -2), f(i₀ +1) and f(i₀ +2) corresponding to i₀, (i₀ -1), (i₀ -2), (i₀ +1) and (i₀ +2), were i₀ is the value of the shift amount i when f(i) is at a minimum;

means for computing an amount I =X/p (p =pitch of the arrayed photosensors in the photosensor arrays) from said function values, said amount I being given by formulas (1) and (2) below;

space="preserve" listing-type="equation">I=i.sub.0 +1/2-{f(i.sub.0 +1)-f(i.sub.0)}/A (1)

where

A=2{B₁ +K₁ (B.sub. -B₂)}

B₁ =f(i₀ -1)-f(i₀)

B₂ =f(i₀ +2)-f(i₀ +1)

k₁ =a constant between 0 and 0.5

space="preserve" listing-type="equation">I=i.sub.0 -1/2+{f(i.sub.0 -1)-f(i.sub.0)}/C (2)

where

C=2{D₁ +K₁ (D₁ -D₂)}

D₁ =f(i₀ +1)-f(i₀)

D₂ =f(i₀ -2)-f(i₀

     1)

K₁ =a constant between 0 and 0.5

means for comparing said function value f(i₀ -1) with said function value f(i₀ +1) to judge whether

(a) f(i₀ -1)>

f(i₀ +1),

(b) f(i₀ -1)=f(i₀ +1), or

(c) f(i₀ -1)<

f(i₀ +1); and

means for obtaining said amount I given by said formula (1) in the case of (a), or given by I=i₀ in the case of (b), or given by said formula (2) in the case of (c).

2. A focus detection method in which light from an object is incident on first and second photosensor arrays via an optical system to form a first image on the first array and a second image on the second array to obtain a relative displacement amount X between the first image with respect to the first array and the second image with respect to th second array, so as to determine whether said optical system is in focus or not, each array generating a respective pattern of signals in response to light falling on the photosensors of the respective array, said method comprising the steps of:

obtaining function values f(i₀), f(i₀ -1), f(i₀ -2), f(i₀ +1) and f(i₀ +2) for a function f(i) expressing inconsistency between the pattern of signals from the first array and the pattern of signals from the second array when the patterns are shifted with respect to one another by a shift amount i and compared with each other, the shift amount i being an integer which represents the difference between a photosensor position in the first array and a photosensor position in the second array, i₀ being the value of i when the value of f(i) is at a minimum;

computing an amount I =X/p (p =pitch of the arrayed photosensors in the photosensor arrays) from said function values, said amount I being given by formulas (1) and (2) below;

space="preserve" listing-type="equation">I=i.sub.0 +1/2-{f(i.sub.0 +1)-f(i.sub.0)}/A (1)

where

A=2{B₁ +K₁ (B₁ -B₂)}

B₁ =f(i₀ -1)-f(i₀)

B₂ =f(i₀ +2)-f(i₀ +1)

k₁ =a constant between 0 and 0.5

space="preserve" listing-type="equation">I=i.sub.0 -1/2+{f(i.sub.0 -1)-f(i.sub.O)}/C (2)

where

C=2{D₁ +K₁ (D₁ -D₂)}

D₁ =f(i₀ +1)-f(i₀)

D₂ =f(i₀ -2)-f(i₀ -1)

K₁ =a constant between 0 and 0.5

comparing said function value f(i₀ -1) with said function value f(i₀ +1) to judge whether

(a) f(i₀ -1)>

f(i₀ +1),

(b) f(i₀ -1)=f(i₀ +1), or

(c) f(i₀ -1)<

f(i₀ +1); and

obtaining said amount I given by said formula (1) in the case of (a), or given by I=i₀ in the case of (b), or given by said formula (2) in the case of (c).

3. A focus detection system in which light from an object is incident on first and second arrays of photosensors via an optical system to provide a first image impinging on the first array and a second image impinging on the second array, wherein the photosensors of the first array generate a pattern of signals F(1), F(2), F(3), . . . and the photosensors of the second array generate a pattern of signals S(1), S(2), S(3), . . . and wherein the photosensors of the arrays are disposed at a predetermined pitch, said system comprising:

means for evaluating a function f(i) expressing inconsistency between the patterns of signals, where ##EQU6## i=an integer representing the difference between a photosensor position in the first array and a photosensor position in the second array

j=an integer representing a photosensor position in both arrays;

means for selecting, from the integers i, a value i₀ at which f(i) is minimized;

means for obtaining function values f(i₀), f(i₀ -1), f(i₀ -2), f(i₀ +1) and f(i₀ +2) corresponding to i₀, (i₀ -1), (i₀ -2), (i₀ +1) and (i₀ +2), respectively;

means for computing an amount I from said function values, said amount I being given by formulas (1) and (2) below;

space="preserve" listing-type="equation">I=i.sub.0 +1/2-{f(i.sub.0 +1)-f(i.sub.0)}/A (1)

where

A=2{B₁ +K₁ (B₁ -B₂)}

B₁ =f(i₀ -1)-f(i₀)

B₂ =f(i₀ +2)-f(i₀ +1)

k₁ =a constant between 0 and 0.5

space="preserve" listing-type="equation">I=i.sub.0 -1/2+{f(i.sub.0 -1)-f(i.sub.O)}/C (2)

where

C=2{D₁ +K₁ (D₁ -D₂)}

D₁ =f(i₀ +1)-f(i₀)

D₂ =f(i₀ -2)-f(i₀ -1)

K₁ =a constant between 0 and 0.5;

means for comparing said function value f(i₀ -1) with said function value f(i₀ +1) to judge whether

(a) f(i₀ -1)>

f(i₀ +1),

(b) f(i₀ -1)=f(i₀ +1), or

(c) f(i₀ -1)<

f(i₀ +1); and

means for generating a defocus signal from said amount I given by said formula (1) in the case of (a), or given by I=i₀ in the case of (b), or given by said formula (2) in the case of (c), the defocus signal being used to control the position of the optical system.