Guide To Hyperspectral Imaging Measurement 16/09/2021

Hyperspectral imaging (HSI) is a non-invasive technique that utilizes both spectroscopy and digital imaging. It divides the spectrum into hundreds of thousands of bands, much broader than our human eyes can see (three bands of red, green, and blue). An image is created for each band and coded with greyscale levels to form a hyperspectral data cube for processing and analysis. The full-spectrum capability of HSI enables accurate identification and separation of materials through their physical properties, chemical, and biological differences.

HSI is used increasingly across various industries and research applications. For example, they can be used to study and inspect foods and pharmaceutical products, sort waste and recycled plastic, map vegetation growth, health, and nutritional status, classify skin lesions, etc. The first step towards an effective HSI solution is to have the right hyperspectral camera and setup. Below are some points to consider before setting up an HSI solution.

Wavelength Range

Different materials and compounds have spectral features (signatures) in different wavelength. The selection of HSI cameras should be based on their wavelength range that can cover and identify the spectral features of your target. As illustrated in figure 1, the quartz mineral exhibits spectral features peaks and shape after 8000 nm hence an HSI camera with LWIR (Long-Wave Infrared) wavelength would be more suitable.

Figure 1 – Quartz Wavelength

Watch this video to find out more about how to select the right HSI camera for your application.

Illumination

Light is an important element in HSI as it affects the quality of the hyperspectral image. The first thing to consider is the strength of illumination. The illumination power required depends on the distance between the light source and the target, the geometry of the illuminating beam, and the integration time based on the required frame rate and line speed. Check out this video to understand more.

Next, the selected illumination must be capable of covering the wavelength of the HSI camera you are using. Below is a general guide to help you in the selection of illumination.

HSI Wavelength Range Illumination
Visible · Halogen (spots or linear)

· LED

· Supercontinuum lasers

NIR (Near-Infrared)
SWIR (Short-Wave Infrared) · Halogen
MWIR (Medium-Wave Infrared) and LWIR Range · Thermal

It is also important to ensure the intensity and spectral range of illumination are uniform with minimum shadows or specular reflections.

Image Rate and Integration Time

For industrial sorting and quality inspection applications, image rate and integration time are important factors to consider aside from the sample size and the speed of the conveyer. Image rate refers to the number of measurements per second, while integration time refers to the time it takes for the HSI camera to captures photons. It is important to note that integration time multiplied with image rate should be less or equal to 1. Watch this video to understand more about how to determine the correct image rate for your application.

Besides the factors mentioned above, other factors like light collection efficiency, etc., should also be considered. Check out this guide to learn more.

Keen to find out more about HSI or need help developing and implementing HSI for your application? Contact us for a free consultation now.