OUR TECHNOLOGY | HYPERSPECTRAL IMAGING

Figure 1 : Spectra at differents points of the Photon etc logo made of plastic beads

WHAT IS HYPERSPECTRAL IMAGING?

Hyperspectral imaging is a technique combining spectroscopy and imaging, where each image is acquired at a narrow band of the electromagnetic spectrum. As an example, the human eye sees light in three bands (red, green and blue) of the visible spectrum while hyperspectral imaging divides the spectrum in more bands, typically covering the visible and near-infrared range.

The term hyperspectral imaging refers to the continuous acquisition of narrow bands (< 10 nm) across the electromagnetic spectrum. With our unique technology we are able to obtain bands of 2nm-4nm wide and even 0.3nm. On the contrary, multispectral imaging covers only a discrete number of bands, and is often performed with a filter wheel.

Through the analysis of the spectral and spatial information contained in each pixel of the image, it is possible to identify unique spectral signatures and assign them to the components of the sample under investigation. For example, the material or tissue analyzed can be mapped according to its molecular components.

Figure 2 : Schematic of a hyperspectral data cube

HYPERSPECTRAL DATA CUBE

The monochromatic images acquired form what we call a hyperspectral data cube, which contains both the spatial and spectral information of a sample. In the hyperspectral cube, the first two dimensions are spatial (x,y axis) while the third dimension (z axis) is the wavelength. Depending on the size of the sensor used, one single cube can represent many gigabytes of data representing an extremely rich source of information for material scientists or biomedical researchers. This data can be analysed using our proprietary software, PHySpec™.

RASTER SCANNING VS GLOBAL IMAGING

Raster scanning is done by taking sequential measurements of the spectra of adjacent regions of a sample by moving the sample point by point or line by line until the region of interest has been covered. On the other hand, imaging consists of focusing the image of a sample on an array detector and measuring for each pixel the intensity of light at one particular wavelength, much like taking a photograph, but at a single wavelength. In some applications, the power of the laser used in imaging can be orders of magnitude stronger than in mapping, since the power is spread on the whole region instead of a single point or line, thus avoiding the damaging of a sample. Imaging also permits a higher resolution, reduces the acquisition time by orders of magnitude and requires no prior knowledge of the sample contrary to mapping.

Photon Etc.'s Global Imaging Technology

This video shows the conceptual difference between hyperspectral global imaging and raster scan (line-scan, push- broom). With global imaging, the gain in acquiring 3D data, 2D spatial and 1D spectral, is important since only a few monochromatic images are required to cover the complete spectral range where one needs to take the full spectrum for each point or line in the image with other technologies.

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