US5040228A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method and apparatus for automatically focusing an image-acquisition device
Assignee: Nokia Bell Labs
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Filing: 1989-08-28
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Granted: 1991-08-13
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Expires: 2009-08-28
Abstract
Abstract Autofocusing of a lens (18) on a television camera (12) is achieved by first processing the image captured by the camera to establish a histogram of the intensity gradients for each of a plurality of small areas (pixels) in the captured image. From the histogram of the pixel intensity gradients, a focus index value, indicative of the sharpness of focus of the captured image, is established. The just-computed focus index value is then compared to the previously established value which is initially set to zero. The difference between the just- established and previously established focus index values establishes the direction in which the lens is incrementally stepped to more sharply focus the image. The steps of (a) capturing the image, (b) establishing the intensity gradient histogram, (c) comparing focus index value to the previously established value, and (d) incrementally stepping the lens are repeated as long as the just-established focus index values exceeds the previous value. Once the focus index value no longer exceeds the previously established value, the lens is stepped by an amount dependent on the just-established and previously established focus index values to sharply focus the image.
Inventors
- 👤 Chinmoy B. Bose
- 👤 Ilyoung Kim
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-04 14:09
CPC Classifications
H; H04; H04N; H04N23/00; H04N23/60; H04N23/67; H04N23/673
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
245 words
A method for adjusting the focus of an image-acquisition device so that the image-acquisition device captures the image of an article in sharp focus, comprising the steps of: (a) establishing a current focus index value as having an initial value of zero; (b) capturing the image of at least a portion of an article with an image-acquisition device having adjustable focus; (c) processing the image captured by the image-acquisition device to determine an intensity gradient for all of the small areas within the image; (d) establishing a histogram of the gradient intensities of all the pixels in the image; (e) establishing a new focus index value from the histogram of the pixel intensity gradients; (f) comparing the current focus index value to the new focus index value to determine in which direction the focus of the image-acquisition device should be adjusted so that the captured image is more sharply focused, thereby increasing the focus-index value; (g) substituting the new focus index value for the current focus index value; (h) incrementally stepping the focus of the image-acquisition device in the direction expected to increase the focus index value; (i) repeating the steps of (b)-(h) until the new focus index value no longer exceeds the current focus index value; (j) adjusting the focus of the image-acquisition device in the opposite direction by a step amount established in accordance with the difference between the new and current focus index values so that the captured image is sharply focused.
Claim 2
Independent Claim
245 words
A method for adjusting the focus of an image-acquisition device so that the image-acquisition device captures the image of an article in sharp focus, comprising the steps of: (a) establishing a current focus index value as having an initial value of zero; (b) capturing the image of at least a portion of an article with an image-acquisition device having adjustable focus; (c) processing the image captured by the image-acquisition device to determine an intensity gradient for all of the small areas within the image; (d) establishing a histogram of the gradient intensities of all the pixels in the image; (e) establishing a new focus index value from the histogram of the pixel intensity gradients; (f) comparing the current focus index value to the new focus index value to determine in which direction the focus of the image-acquisition device should be adjusted so that the captured image is more sharply focused, thereby increasing the focus-index value; (g) substituting the new focus index value for the current focus index value; (h) incrementally stepping the focus of the image-acquisition device in the direction expected to increase the focus index value; (i) repeating the steps of (b)-(h) until the new focus index value no longer exceeds the current focus index value; (j) adjusting the focus of the image-acquisition device in the opposite direction by a step amount established in accordance with the difference between the new and current focus index values so that the captured image is sharply focused.
Claim 3
Dependent Claim
74 words
The method according to claim 1 wherein the new focus index value is established in with the relationship ##EQU4## where A is a constant, g i represents a successive one of N (N being an integer ≦35) pixel gradient intensity values, each above a noise threshold n 0 and each lying in the range between g max , the maximum pixel intensity gradient, and g max -h, h being an integer greater than N.
Claim 4
Dependent Claim
75 words
The method according to claim 1 wherein the new focus index value is established in accordance with the relationship: ##EQU5## where B is a constant, g i represents a successive one of N (N being an integer ≦35) pixel gradient intensity values, each above a noise threshold n 0 and each lying in the range between g max , the maximum pixel intensity gradient, and g max -h, h being an integer greater than N.
Claim 5
Dependent Claim
83 words
The method according to claim 1 wherein the step amount by which the focus on the optics system is finally adjusted is given by the term S-ΔS where S is the incremental amount which the focus adjustment is normally stepped, and ΔS is a signed quantity given by ##EQU6## where M new is the most recently computed focus index value, M 0 is the second most recently computed focus index value, and M -1 is the third most recently computed focus index value.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1994-08-12 | 1995-02-11 | 1995-08-13 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1998-08-12 | 1999-02-11 | 1999-08-13 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2002-08-12 | 2003-02-11 | 2003-08-13 | $7700.00 | Window Closed / Lapsed |