US6061091A
Expired / Lapsed
US
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Detection of and correction for specular reflections in digital image acquisition
Assignee: Agfa Gevaert NV
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Filing: 1997-05-22
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Granted: 2000-05-09
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Expires: 2017-05-22
Abstract
Abstract Image processing parameters for gradation correction of a digital image from a scene, which includes specular reflections may be seriously influenced by the presence of those specular reflections. Therefore, a method is developed to detect the presence of specular reflections in a scene, to modify the exposure time of the photo-sensitive means, which converts a luminous image to electronic image signals and to apply a gradation correction to the image data thus acquired. In one embodiment a digital camera is used to capture the image data, a cumulative histogram is built and two characteristic cumulative frequencies are used to determine via the histogram specular densities and highlight densities. The relative position of these density values indicates whether specular reflections are present, and give suitable parameters for setting an optimal exposure time and for computing a gradation correction curve.
Inventors
- 👤 Koen Van de Poel
- 👤 Earle Stokes
- 👤 Nick Geybels
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 23:10
CPC Classifications
G; G06; G06T; G06T5/00; G06T5/40; G06T5/90; G06T5/92
Claims Analysis
Total Claims: 20
Claim 1
Independent Claim
183 words
A method for detecting and processing a specular image density level X 1 and a highlight image density level X 2 in an illuminated scene comprising the following steps: exposing a photo-sensitive means by a luminous image from said scene, thereby generating a plurality of digital image signals, each said digital image signal representing a density of a portion of said luminous image; establishing a cumulative histogram for the image density levels of said digital image signals; providing a reference specular cumulative frequency Y 1 ; providing a reference highlight cumulative frequency Y 2 ; converting said specular cumulative frequency Y 1 via said cumulative histogram, to obtain said specular image density level X 1 ; converting said highlight cumulative frequency Y 2 via said cumulative histogram, to obtain said highlight image density level X 2 ; and indicating a presence of specular reflections when a ratio α=∥X MAX -X 2 ∥/∥X MAX -X 1 ∥ is smaller than a predetermined value, wherein X MAX is an image density level greater than or equal to a highest density level within said luminous image.
Claim 2
Independent Claim
183 words
A method for detecting and processing a specular image density level X 1 and a highlight image density level X 2 in an illuminated scene comprising the following steps: exposing a photo-sensitive means by a luminous image from said scene, thereby generating a plurality of digital image signals, each said digital image signal representing a density of a portion of said luminous image; establishing a cumulative histogram for the image density levels of said digital image signals; providing a reference specular cumulative frequency Y 1 ; providing a reference highlight cumulative frequency Y 2 ; converting said specular cumulative frequency Y 1 via said cumulative histogram, to obtain said specular image density level X 1 ; converting said highlight cumulative frequency Y 2 via said cumulative histogram, to obtain said highlight image density level X 2 ; and indicating a presence of specular reflections when a ratio α=∥X MAX -X 2 ∥/∥X MAX -X 1 ∥ is smaller than a predetermined value, wherein X MAX is an image density level greater than or equal to a highest density level within said luminous image.
Claim 3
Dependent Claim
12 words
The method according to claim 1, wherein said predetermined value is 0.875.
Claim 4
Dependent Claim
82 words
The method according to claim 1, wherein: the specular cumulative frequency Y 1 and the highlight cumulative frequency Y 2 are selected such that: the value D 1 =∥Y 1 -Y MIN ∥; and the value D 2 =∥Y 2 -Y MIN ∥; wherein Y MIN is the cumulative frequency of the image level X MIN corresponding to the lowest density level in the luminous image, and wherein 10 -5 ≦D 1 , D 1 ≦(D 2 /2), and D 2 ≦0.1.
Claim 5
Dependent Claim
14 words
The method according to claim 4, wherein: D 1 ≦0.2%; and, D 2 ≦1.0%.
Claim 6
Dependent Claim
33 words
The method according to claim 1, further comprising optimizing an exposure time for exposing said photo-sensitive means based on the image density level of X 1 , X 2 or a combination thereof.
Claim 7
Dependent Claim
26 words
The method according to claim 6, wherein said exposure time is selected to move either X 2 or X 1 to an extreme image density level.
Claim 8
Dependent Claim
18 words
The method according to claim 1, wherein said image signals are further transformed by a gradation correction curve.
Claim 9
Dependent Claim
36 words
The method according to claim 7, wherein said gradation correction curve comprises linear segments, having a start point at X 1 , a break point at X 2 and an end point at X MAX .
Claim 10
Dependent Claim
20 words
The method according to claim 8, wherein said gradation correction curve comprises the break point is smoothed by an arc.
Claim 11
Dependent Claim
82 words
The device according to claim 1, wherein: the specular cumulative frequency Y 1 and the highlight cumulative frequency Y 2 are selected such that: the value D 1 =∥Y 1 -Y MIN ∥; and the value D 2 =∥Y 2 -Y MIN ∥; wherein Y MIN is the cumulative frequency of the image level X MIN corresponding to the lowest density level in the luminous image, and wherein 10 -5 ≦D 1 , D 1 ≦(D 2 /2), and D 2 ≦0.1.
Claim 12
Dependent Claim
14 words
The device according to claim 10, wherein: D 1 ≦0.2%; and, D 2 ≦1.0%.
Claim 13
Independent Claim
197 words
A device for detecting and processing a specular image density level X 1 and a highlight image density level X 2 in a reproduction of an illuminated scene comprising: means for exposing a photo-sensitive means by a luminous image from said scene, thereby generating a plurality of digital image signals, each said digital image signal representing a density of a portion of said luminous image; means for establishing a cumulative histogram for the image density levels of said digital image signals; means for providing a reference specular cumulative frequency Y 1 ; means for providing a reference highlight cumulative frequency Y 2 ; means for converting said specular cumulative frequency Y 1 via said cumulative histogram, to obtain said specular image density level X 1 ; means for converting said highlight cumulative frequency Y 2 via said cumulative histogram, to obtain said highlight image density level X 2 ; and means for indicating a presence of specular reflections when a ratio α=∥X MAX -X 2 ∥/∥X MAX -X 1 ∥ is smaller than a predetermined value, wherein X MAX is an image density level greater than or equal to a highest density level within said luminous image.
Claim 14
Independent Claim
197 words
A device for detecting and processing a specular image density level X 1 and a highlight image density level X 2 in a reproduction of an illuminated scene comprising: means for exposing a photo-sensitive means by a luminous image from said scene, thereby generating a plurality of digital image signals, each said digital image signal representing a density of a portion of said luminous image; means for establishing a cumulative histogram for the image density levels of said digital image signals; means for providing a reference specular cumulative frequency Y 1 ; means for providing a reference highlight cumulative frequency Y 2 ; means for converting said specular cumulative frequency Y 1 via said cumulative histogram, to obtain said specular image density level X 1 ; means for converting said highlight cumulative frequency Y 2 via said cumulative histogram, to obtain said highlight image density level X 2 ; and means for indicating a presence of specular reflections when a ratio α=∥X MAX -X 2 ∥/∥X MAX -X 1 ∥ is smaller than a predetermined value, wherein X MAX is an image density level greater than or equal to a highest density level within said luminous image.
Claim 15
Dependent Claim
12 words
The device according to claim 12, wherein said predetermined value is 0.875.
Claim 16
Dependent Claim
35 words
The device according to claim 12, further comprising means for optimizing an exposure time for exposing said photo-sensitive means based on the image density level of X 1 , X 2 or a combination thereof.
Claim 17
Dependent Claim
25 words
The device according to claim 14, wherein said exposure time is selected to move either X 2 or X 1 to an extreme image level.
Claim 18
Dependent Claim
18 words
The device according to claim 12, wherein said image signals are further transformed by a gradation correction curve.
Claim 19
Dependent Claim
36 words
The device according to claim 16, wherein said gradation correction curve comprises linear segments, having a start point at X 1 , a break point at X 2 and an end point at X MAX .
Claim 20
Dependent Claim
20 words
The method according to claim 17, wherein said gradation correction curve comprises the break point is smoothed by an arc.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 2003-05-09 | 2003-11-08 | 2004-05-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2007-05-09 | 2007-11-08 | 2008-05-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2011-05-09 | 2011-11-08 | 2012-05-09 | $7700.00 | Window Closed / Lapsed |