Patent Description:
This section illustrates useful background information without admission of any technique described herein being representative of the state of the art.

Hyperspectral, or multispectral imaging, is increasingly used in numerous applications and accordingly, cost effective and simple arrangements are needed.

Previously hyperspectral imaging has been performed for example by using pixelized multispectral filters, by using a filter wheel and by using multiplexed LED illumination. Such arrangements often require complex manufacturing processes and are not easily adaptable to different spectral wavelength ranges. In these arrangements it is not possible to adjust wavelength continuously because the pixelized multispectral filters are permanently on top of pixels and the filter wheel can only have a fixed number of filters, typically from <NUM> to <NUM>. Additionally, pixelized multispectral filters are not compatible with the use of compact-sized image sensors because the size of the pixelized filter limits the minimum pixel size.

Furthermore, the use of Fabry-Perot interferometers is known from previous publications <CIT> and <CIT>, as well as <CIT> and the article "<NPL>. Further, the tuning of spectral filters by tilting is known from <CIT> and <CIT>.

The present invention aims to mitigate the problems of the previous solutions by providing a hyperspectral imaging arrangement that can be used to build a cost effective high performance hyperspectral imaging arrangement that is also compatible with small pixel image sensors enabling the construction of very low cost hyperspectral imaging arrangements based on mobile device cameras.

According to a first aspect of the present invention, there is provided an arrangement for hyperspectral imaging according to claim <NUM>.

The arrangement may further comprise an array of light emitting diodes configured to illuminate the target to be imaged; each light emitting diode having a wavelength different from the other light emitting diodes.

The band-pass filter element may comprise a short-pass filter and a long-pass filter.

The band-pass filter element may be configured to pass a predetermined wavelength range of <NUM> to <NUM> or <NUM> to <NUM>.

The imaging sensor may comprise a monochromatic or RGB image sensor.

The imaging sensor may be comprised in a portable electronic device.

According to a second aspect of the present invention, there is provided a method for hyperspectral imaging according to claim <NUM>.

For a more complete understanding of examples not part of the invention and embodiments of the present invention, reference is now made to the following descriptions taken in connection with the accompanying drawings in which:.

The present invention and its potential advantages are understood by referring to <FIG> of the drawings. In this document, like reference signs denote like parts or steps.

<FIG> and <FIG> show schematic principle views of a hyperspectral imaging arrangement <NUM>. <FIG> and <FIG> show a target <NUM> to be imaged with hyperspectral imaging. The target <NUM> is for example a medical target, such as a healing wound, a target the color of which a consumer wishes to measure, an agricultural target, an anti-counterfeit marking target or a target in food processing. The target <NUM> is in an embodiment illuminated with an array 110a,110b of Light Emitting Diodes, LEDs, each LED in the array 110a,110b having a wavelength different from the other LEDs of the array 110a,110b. In an embodiment, the number of LEDs in the array 110a,110b is from <NUM> to <NUM>. In a further example embodiment, the array 110a,110b is comprised in a single element or multiple elements although two elements have been depicted in <FIG> and <FIG>. In an embodiment, the LEDs of the array 110a,110b are configured to be turned on and off separately and independently. In an embodiment, the LEDs of the array 110a,110b cover a wavelength range of a typical low-cost Complementary Metal Oxide Semiconductor, CMOS, image sensor, for example a range of <NUM> to <NUM>. In a further embodiment, the LEDs of the array 110a,110b cover a wavelength range of <NUM> to <NUM>. It is to be noted, that the hyperspectral imaging arrangement <NUM> will function without the LED illumination as well.

<FIG> and <FIG> further show a first optical element <NUM>, i.e. imaging optics element, configured to form a collimated beam through the following elements. The hyperspectral imaging arrangement <NUM> further comprises a first band-pass filter element <NUM>. In an embodiment, the first band-pass filter element comprises a long-pass filter and a short pass filter configured to pass a predetermined wavelength range, such as <NUM> to <NUM> or <NUM> to <NUM>. In an embodiment, the hyperspectral imaging arrangement <NUM> further comprises a second optical element <NUM> configured to guide the beam towards following elements.

The hyperspectral imaging arrangement <NUM> comprises a first adjustable multi passband filter, for example a Fabry-Perot Interferometer, FPI, 150a and, in an embodiment, a second adjustable multi passband filter, for example a Fabry-Perot Interferometer, FPI, 150b. The first adjustable multi passband filter (150a) comprises in an embodiment a multi passband filter configured to be adjusted by tilting. In the invention, the first 150a and the second 150b FPI comprise tiltable, or rotatable, fixed gap FPIs which are configured to be tilted to the same angle in opposite directions as shown in <FIG>, in order to adjust the transmission properties. By tilting the multi passband filters 150a,150b in opposite directions with the same angle, the image is kept at a fixed position enabling the use of small sized image sensors as well. In an embodiment, the multi passband filters comprise FPIs 150a,150b comprising five layer Bragg mirrors on opposite sides of a fused silica wafer.

The hyperspectral imaging arrangement <NUM> further comprises a second optical element, or imaging optics element, <NUM> configured to form an image on the imaging sensor <NUM>. In an embodiment, the imaging sensor comprises a RGB or monochromatic imaging sensor. The use of an RGB image sensor enables to register signal at three spectral bands simultaneously as for example explained in <CIT>. In an embodiment, the imaging sensor <NUM> is comprised in a further device, for example a portable electronic device, such as a digital camera, a smartphone or a tablet computer.

In a further embodiment, in addition to or instead of the first band-pass filter element <NUM>, the hyperspectral imaging arrangement <NUM> comprises a second band-pass filter element (not shown) between the second optical element <NUM> and the imaging sensor <NUM>. In an embodiment, the properties of the second band-pass filter element are similar to those of the first band-pass filter element <NUM>.

<FIG> and <FIG> show schematic principle views of a hyperspectral imaging arrangement <NUM> according to a further example not part of the invention. <FIG> and <FIG> show a target <NUM> to be imaged with hyperspectral imaging. The target <NUM> is for example a medical target, such as a healing wound, or a target the color of which a consumer wishes to measure.

The hyperspectral imaging arrangement <NUM> comprises a first adjustable multi passband filter, for example a Fabry-Perot Interferometer, FPI, <NUM> and, in an embodiment, a second adjustable multi passband filer, for example a Fabry-Perot Interferometer, FPI, <NUM>. The first adjustable multi passband filter (<NUM>) comprises in an embodiment a multi passband filter configured to be adjusted by tilting. In an embodiment, the first adjustable FPI <NUM> comprises a piezo-actuated adjustable gap FPI and the second adjustable FPI <NUM> comprises a tiltable fixed gap FPI. The combination of the first <NUM> and the second <NUM> multi passband filter is in an embodiment configured to be adjusted in such a way that substantially only a single spectral band is transmitted through in turn allowing for the use of a monochromatic imaging sensor.

The hyperspectral imaging arrangement <NUM> further comprises a second optical element, or imaging optics element, <NUM> configured to form an image on the imaging sensor <NUM>. In an embodiment, the imaging sensor comprises a RGB or monochromatic imaging sensor. In an embodiment, the imaging sensor <NUM> is comprised in a further device, for example a portable electronic device, such as a digital camera, a smartphone or a tablet computer.

In a further embodiment, in addition to or instead of the first band-pass filter element <NUM>, the hyperspectral imaging arrangement <NUM> comprises a second band-pass filter element (not shown) between the second optical element <NUM> and the imaging sensor <NUM>. In an embodiment, the properties of the second band-pass filter element are similar to those of the first band-pass filter element <NUM>. Furthermore, in a still further embodiment, the hyperspectral imaging arrangement <NUM> comprises an array of Light Emitting Diodes, LEDs, for illuminating the target <NUM> similar to the array described with reference to <FIG> and <FIG>.

<FIG> show examples of transmission properties of the adjustable multi passband filter of the hyperspectral imaging arrangement according to an embodiment of the invention. In the example, the multi passband filter comprises tiltable Fabry Perot interferometer comprising five layer TiO<NUM>-SiO<NUM> dielectric Bragg mirrors optimized for <NUM>. <FIG> shows a graph 300a of the transmission properties with a tilt angle of <NUM> degrees as a function of wavelength in nanometers and <FIG> shows a graph 300b of the transmission properties with a tilt angle of <NUM> degrees as a function of wavelength in nanometers.

<FIG> shows a flowchart of a method for hyperspectral imaging according to an example. At step <NUM> the target <NUM> to be imaged is illuminated. In an embodiment, the illumination is provided by an array 110a,110b of Light Emitting Diodes as hereinbefore described with reference to <FIG> and <FIG>. In a further embodiment, the ambient light is sufficient to illuminate the target.

At <NUM>, the multi passband filters 150a,150b,<NUM>,<NUM>, for example the FPIs, are adjusted to provide the required transmission properties in order to receive at the imaging sensor <NUM>,<NUM> the required wavelengths in order to provide the hyperspectral image raw data at <NUM>. At step <NUM> a hyperspectral data cube is calculated from the RGB or monochromatic image sensor raw image data. In an embodiment, the calculation is carried out for example using the calibration carried out for the hyperspectral imaging arrangement as explained in <CIT>.

Without in any way limiting the scope, interpretation, or application of the claims appearing below, a technical effect of one or more of the example embodiments disclosed herein is a low-cost arrangement for hyperspectral imaging. Another technical effect of one or more of the example embodiments disclosed herein is the provision of an arrangement applicable with common imaging sensors such as smartphone camera imaging sensors. Another technical effect of one or more of the example embodiments disclosed herein is the provision of hyperspectral imaging with sufficient spectral bands in ambient light.

Claim 1:
A hyperspectral imaging arrangement, comprising
an imaging sensor (<NUM>,<NUM>);
a band-pass filter element (<NUM>,<NUM>);
at least one imaging optics element (<NUM>,<NUM>,<NUM>,<NUM>) configured to form an image on the imaging sensor (<NUM>,<NUM>); and
a first adjustable multi passband filter (150a,<NUM>) and a second adjustable multi passband filter (150b,<NUM>); characterized in that the first adjustable multi passband filter (150a,<NUM>) and the second adjustable multi passband filter (150b,<NUM>) are positioned consecutively on the optical path;
the first (150a) and the second (150b) multi passband filter comprise an adjustable Fabry-Perot interferometer; and in that
both the first (150a) and the second (150b) adjustable Fabry-Perot interferometer is configured to have a fixed gap and to be adjusted by tilting in the same angle in opposite directions in order to adjust the transmission properties.