WO2014115144A1

WO2014115144A1 - Enhancing infrared measurement accuracy in a specified area

Info

Publication number: WO2014115144A1
Application number: PCT/IL2014/050080
Authority: WO
Inventors: Ernest Grimberg; Alexander Burd; Yossi Cohen
Original assignee: Opgal Optronics Indudtries Ltd
Current assignee: Opgal Optronics Indudtries Ltd
Priority date: 2013-01-28
Filing date: 2014-01-22
Publication date: 2014-07-31
Anticipated expiration: 2015-07-28

Abstract

Enhancing infrared measurement accuracy and thereby allowing remote diagnostics of various states that are characterized by minute temperature difference, beyond the capabilities of current infrared imaging systems is provided herein. Embodiments of the invention utilize the exact fusing of a visible light image and an infrared image, achieved by setting the system at a known spatial relationship in which they are both focused at the intersection of their optical axes, and identifying a well contrasting infrared region within a focused visible light image, to visually identify an uninfluenced target region that serves as a reference region for infrared temperature difference measurements. Using this reference allows enhancing the resolution of the infrared imaging by an order of magnitude.

Description

ENHANCING INFRARED MEASUREMENT ACCURACY IN A SPECIFIED AREA

TECHNICAL FIELD

The present invention relates to the field of infrared imagery, and more particularly, to enhancing the accuracy of infrared measurements. BACKGROUND OF THE INVENTION

Figure 1 is a schematic illustration of an eye 90, showing the eyelid 91, the sclera 81, the iris 82 and the limbus 92, which is the sclerocorneal junction on the edge of the iris, an area that is characterized by low blood supply.

Various diseases of the eye include local inflammation, dryness or any other disease may potentially be identified by infrared imaging. However, the temperature differences occurring in such inflammation cannot be identified by prior art infrared imaging as they are too slight for focusing of infrared cameras thereupon (see e.g. Tan et al. 2009, "Infrared thermography on ocular surface temperature: A review", Infrared physics and technology 52: 97-108).

Similarly, there are many other medical, industrial and agricultural cases, in which a very slight temperature difference may be of diagnostic value, yet the actual differences are below the focusing power of current infrared cameras.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides an imaging system comprising: (i) a visible light imaging system arranged to capture a specified area and having a pixel size selected to be larger than a blur circle of optics of the visible light imaging system within a specified range, to yield a given depth focusing range with respect to the specified area; (ii) an infrared imaging system arranged to capture the specified area; (iii) a controller arranged to move the visible light imaging system together with the infrared imaging system until a first reference area within the specified area, having an infrared contrast to its surrounding above a first specified threshold, is in focus of the infrared imaging system and/or high contrast features in the first reference area coincide on the images of both systems; (iv) a processor arranged to fuse the captured visible light image with the infrared image using the first reference area as depicted by both imaging systems, to yield a fused image having a visible light component and an infrared component; and (v) an infrared image processor, arranged to compare infrared measurements of at least one target region in the specified area with infrared measurements of a second reference area within the specified area, the second reference area being determined according to the visible light component of the fused image, wherein the infrared image processor is arranged to identify a temperature difference below a second specified threshold.

These, additional, and/or other aspects and/or advantages of the present invention are: set forth in the detailed description which follows; possibly inferable from the detailed description; and/or learnable by practice of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of embodiments of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings in which like numerals designate corresponding elements or sections throughout. In the accompanying drawings:

Figure 1 is a schematic illustration of a human eye;

Figure 2 is a high level schematic block diagram of an imaging system imaging the eye, according to some embodiments of the invention; and

Figure 3 is a high level flowchart illustrating a method of enhancing infrared measurement accuracy in a specified area, according to some embodiments of the invention.

DETAILED DESCRIPTION

With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is applicable to other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

Figure 2 is a high level schematic block diagram of an imaging system 100 imaging eye 90, according to some embodiments of the invention.

Imaging system 100 comprises a visible light imaging system 110 and an infrared imaging system 120, both arranged to capture a specified area such as the eye. For example, visible light imaging system 110 and infrared imaging system 120 may be positioned at an angle to each other and set at spatial relationships that provide focusing of both systems 110, 120 at an intersection of their optical axes. Infrared imaging system 120 may be set perpendicular to the eye's plain (along lines 111 and 121 respectively, with the optical axis of eye 90 similar to the optical axis of infrared imaging system 120), and visible light imaging system 110 may be set at a small angle to infrared imaging system 120 and to the eye's optical axis.

Visible light imaging system 110 is arranged to have large pixels relative to the lens blur circle, in order to yield a wide depth focusing range 111 with respect to the specified area. For example, if system 100 is to be placed 10 cm from the eye, the focusing range of visible light imaging system 110 may be 5 cm to 15 cm from the eye. Depth focusing range 111 is defined by the range within which the blur circle of the optics of visible light imaging system 110 is smaller than the pixel size of the imaging array. The pixel size is selected to yield depth focusing range 111 that is appropriate for the application.

In other words, the pixel size is selected to be larger than a blur circle of optics of visible light imaging system 110 within a specified range, to yield a given depth focusing range 111 with respect to the specified area. For example, in an optical system having a blur circle of Ιμπι in diameter within the required focusing range, the pixel size may be selected to be 10-12μπι, to include the blur circle within the pixel over al least the whole range 111.

Imaging systems 110, 120 are movably controlled by a controller 130, e.g. by means of a controllable mechanical apparatus (not shown). The whole imaging systems 110, 120 are moved (and not just their optics) in order to move the intersection of their optical axes until it falls in the specified area, which is indicated by the congruence of the images from systems 110, 120. Controller 130 is arranged to move visible light imaging system 110 together with infrared imaging system 120 while maintaining the set spatial relationships between them, until a first reference area 91 having high contrast thermal features (e.g. a fold in the eyelid) within the specified area is in focus of infrared imaging system 120 and/or the images of systems 110, 120 coincide on the high contrast features of first reference area 91, indicating that first reference area 91 is at the intersection of the optical axes of systems 110, 120. The coincidence of the images assures that both images are focused at the right distance from the target, e.g. eye 90. First reference area 91 is selected as an area the exhibits an infrared contrast to its surrounding above a first specified threshold (e.g. 0.1 °C) that is well detectable by infrared imaging system 120 and is further approximately in a focal plane 121 of a target region of system 100 (see below). Additional image processing methods may be used to ensure congruence of the infrared and visible light images.

Imaging system 100 may further include a processor 140 arranged to fuse the captured visible light image with the infrared image using first reference area 91 as depicted by both imaging systems 110, 120, to yield a fused image 145 having a visible light component and an infrared component. Both components are well focused, as infrared imaging system 120 is focused on focal plane 121 as described above and visible light imaging system 110 was selected to be focused over a wide range of focal lengths 111 around the specified area. Finally, imaging system 100 comprises an infrared image processor 150, arranged to compare infrared measurements of the target region in the specified area with infrared measurements of a second reference area 92 (e.g. the sclerocorneal limbus) within the specified area. Second reference area 92 is selected as a region having a constant temperature in respect to the state that is to be identified. For example, if inflammation is to be identified, second reference area 92 is selected to have a temperature that is least influenced by the inflammation, such as a region having low blood supply (measurable eye diseases are not limited to inflammation, and may include other cases in which minute temperature differences are diagnostic, such as dryness and other conditions such as mentioned in Tan et al. 2009 cited above).

Infrared measurements may comprise, in addition to temperature and temperature differences, also geometric features of the specified area (e.g. size and dimensions, area such as pupil size in case of the eye, reflectance, etc.).

System 100 does not measure a distance to the specified area, but identifies a position of the specified area at a pre-calibrated distance that is determined by the preset spatial relationship between the cameras (imaging systems 110, 120). System 100 identifies the correct position by a coinciding of visible light and infrared images of the specified area. The position identification is used to ensure focusing of infrared system 120 at second reference area 92.

Second reference area 92 is determined according to the visible light component of fused image 145, and is useful as a reference region for fine measurements by infrared imaging system 120. Using second reference area 92 as an exactly identified region (by identification in the visible light) having an uninfluenced temperature, infrared image processor 150 is arranged to identify a temperature difference below a second specified threshold (e.g. 0.01°C) thus enhancing infrared measurement accuracy in a specified area, and allowing the diagnosis of previously non- measurable conditions. The ability to enhance measurement accuracy in second reference area 92 relies upon the pre-focusing of infrared imaging system 120 on first reference area 91, as described above.

In case of the ophthalmic application described above, first specified threshold may be within the range of 0.1-0.3°C (100-300 m°K) while second specified threshold may be within the range of 0.01-0.03°C (10-30 m°K). That is, selecting and using reference areas 91 and 92 enables an increase of an order of magnitude in the achievable infrared temperature resolution using existing infrared imaging system 120.

Further applications may comprise medical treatment in fields such as gynecology, plastic surgery and cardiac surgery, imaging in the chemical industries such as biochemical and food industrial factories, as well as water related imaging for example for monitoring water stress in plants or detecting water leaks etc.

In each field of application, reference areas 91 and 92 must be carefully selected to be within a single plain and exhibit the corresponding thresholds (namely a first threshold that can be easily detected and a second threshold that can be detected only assuming infrared focus achieved using visible light imaging system 110.

In one example, in the field of reconstruction surgery, first reference area 91 may be cutting edges or structure feature or differences (like nipple location) that can be used for focus adjustment. Damage to blood vessels may be minimized by using the system to thermally detect blood vessels, using a vessel-less area as second reference area 92.

In another example, in the field of agriculture, slight thermal differences may be used to indicate the level of water stress in a plant, and thus detection thereof may be used as an irrigation monitoring device, e.g. in viticulture.

Figure 3 is a high level flowchart illustrating a method 200 of enhancing infrared measurement accuracy in a specified area, according to some embodiments of the invention.

Method 200 enhances infrared measurement accuracy in a specified area (stage 210) by carrying out the following stages: configuring a visible light imaging system to have a pixel size that is larger than a blur circle of optics of the visible light imaging system within a specified range, to yield a given depth focusing range with respect to the specified area (stage 220); setting the visible light imaging system and an infrared imaging system, each having an optical axis, at spatial relationships that provide focusing of both systems at an intersection of their optical axes (stage 222); selecting a first reference area having high contrast thermal features within the specified area, having an infrared contrast to its surrounding above a first specified threshold (stage 225), e.g. 0.1 °C; moving the visible light imaging system together with an infrared imaging system while maintaining the set spatial relationships between them, until the first reference area is at the intersection of the optical axes and the high contrast thermal features of the first reference area coincide on both images generated by the visible and infrared imaging systems (stage 230); capturing a visible light image and an infrared image of the specified area (stage 235); fusing the captured visible light image and infrared image using the first reference area (stage 240); determining a second reference area within the specified area according to the visible light component of the fused image (stage 245); comparing infrared measurements of a target region in the specified area with infrared measurements of the second reference area (stage 250); and identifying temperature differences below a second specified threshold between the target region and the second reference area (stage 255) e.g. 0.01 °C.

In embodiments, method 200 may comprise setting the infrared imaging system with its optical axis perpendicular to the specified area.

In embodiments, method 200 may be configured to detect thermally a water level in a plant.

In embodiments, the specified area may be a skin area, the first reference area may be a cutting edge or a structural feature in the skin area and the second reference area may be a vessel-less area in the skin area.

System 100 and method 200 enhance infrared measurement accuracy and thereby allow remote diagnostics of various states that are characterized by minute temperature difference, beyond the capabilities of current infrared imaging systems. System 100 and method 200 utilize the exact fusing of a visible light image and an infrared image, achieved by identifying a well contrasting infrared region within a focused visible light image, to visually identify an uninfluenced target region that serves as a reference region for infrared temperature difference measurements. Using this reference allows enhancing the resolution of the infrared imaging an order of magnitude.

In the above description, an embodiment is an example or implementation of the invention. The various appearances of "one embodiment", "an embodiment" or "some embodiments" do not necessarily all refer to the same embodiments.

Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the invention may be described herein in the context of separate embodiments for clarity, the invention may also be implemented in a single embodiment.

Embodiments of the invention may include features from different embodiments disclosed above, and embodiments may incorporate elements from other embodiments disclosed above. The disclosure of elements of the invention in the context of a specific embodiment is not to be taken as limiting their used in the specific embodiment alone.

Furthermore, it is to be understood that the invention can be carried out or practiced in various ways and that the invention can be implemented in embodiments other than the ones outlined in the description above.

The invention is not limited to those diagrams or to the corresponding descriptions. For example, flow need not move through each illustrated box or state, or in exactly the same order as illustrated and described.

Meanings of technical and scientific terms used herein are to be commonly understood as by one of ordinary skill in the art to which the invention belongs, unless otherwise defined.

While the invention has been described with respect to a limited number of embodiments, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of some of the preferred embodiments. Other possible variations, modifications, and applications are also within the scope of the invention.

Claims

1. An imaging system comprising:

a visible light imaging system arranged to capture a specified area and having a pixel size selected to be larger than a blur circle of optics of the visible light imaging system within a specified range, to yield a given depth focusing range with respect to the specified area;

an infrared imaging system arranged to capture the specified area, and set at spatial relationships that provide focusing of both systems at an intersection of their optical axes;

a controller arranged to move the visible light imaging system together with the infrared imaging system while maintaining the set spatial relationships between them, until a first reference area within the specified area, having an infrared contrast to its surrounding above a first specified threshold, is at the intersection of the optical axes to coincide on images taken by both systems;

a processor arranged to fuse the captured visible light image with the infrared image using the first reference area as depicted by both imaging systems, to yield a fused image having a visible light component and an infrared component; and

an infrared image processor, arranged to compare infrared measurements of at least one target region in the specified area with infrared measurements of a second reference area within the specified area, the second reference area being determined according to the visible light component of the fused image, wherein the infrared image processor is arranged to identify a temperature difference below a second specified threshold.

2. The imaging system of claim 1, wherein the controller is arranged to move the visible light imaging system together with the infrared imaging system until high contrast features in the first reference area coincide on images of both systems.

3. The imaging system of claim 1, wherein the infrared imaging system is set with its optical axis perpendicular to the specified area.

4. The imaging system of claim 1, wherein the specified area is an eye, the first reference area is an eyelid or an eyelash of the eye, the second reference area is a limbus of the eye, the first specified threshold is between 0.1-0.3 °C and the second specified threshold is between 0.01- 0.03 °C.

5. The imaging system of claim 1, wherein the specified area is a skin area, the first reference area is a cutting edge or a structural feature in the skin area and the second reference area is a vessel-less area in the skin area.

6. The imaging system of claim 1, configured to detect thermally a water level in a plant.

7. A method of enhancing infrared measurement accuracy in a specified area, the method comprising:

configuring a visible light imaging system to have a pixel size that is larger than a blur circle of optics of the visible light imaging system within a specified range, to yield a given depth focusing range with respect to the specified area;

setting the visible light imaging system and an infrared imaging system, each having an optical axis, at spatial relationships that provide focusing of both systems at an intersection of their optical axes;

moving the visible light imaging system together with the infrared imaging system while maintaining the set spatial relationships between them, until a first reference area within the specified area, having an infrared contrast to its surrounding above a first specified threshold, is at the intersection of the optical axes to coincide on images taken by both systems;

fusing a captured visible light image of the specified area with a captured infrared image of the specified area, using the first reference area as depicted by both imaging systems, to yield a fused image having a visible light component and an infrared component; and

comparing infrared measurements of at least one target region in the specified area with infrared measurements of a second reference area within the specified area, the second reference area being determined according to the visible light component of the fused image, to identify a temperature difference below a second specified threshold,

wherein the first and second reference areas are distinct and the second specified threshold is smaller than the first specified threshold.

8. The method of claim 7, wherein the moving comprises moving the systems together until high contrast features in the first reference area coincide on images of the systems.

9. The method of claim 7, further comprising setting the infrared imaging system with its optical axis perpendicular to the specified area.

10. The method of claim 7, wherein the specified area is an eye, the first reference area is an eyelid or an eyelash of the eye, the second reference area is a limbus of the eye, the first specified threshold is between 0.1-0.3 °C and the second specified threshold is between 0.01- 0.03 °C.

11. The method of claim 7, wherein the specified area is a skin area, the first reference area is a cutting edge or a structural feature in the skin area and the second reference area is a vessel- less area in the skin area.

12. The method of claim 7, configured to detect thermally a water level in a plant.