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Machine Vision Newsletter

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Part Two: What is provided by a pushbroom camera?

Go to Part One
Go to Specim
Go to Hyperspectral Cameras

 

 

 

  Hyperspectral imaging
What does it provide?
   
   

In Part One of this two-part series, we examined how a hyperspectral camera works. We discussed the key components and how they contribute to producing hyperspectral data.

This Part Two will investigate how the data captured by a hyperspectral camera is structured and how the spectral signatures of individual pixels can be accessed. Articles in a future new series will investigate how the data is analysed to determine chemical features.

A hyperspectral camera collects a data cube. Hyperspectral imaging produces a spectrum for each pixel in the image and so produces a three-dimensional data set that we call a data cube.

To describe a hyperspectral data cube we will image a leaf and use a book as a simile for the data captured.

   
   
   

Let's first examine how a hyperspectral camera compares to a standard digital camera or smart phone. A digital camera captures 3 colours for each pixel in an image; Red, Green and Blue and matches it to the way our eyes see colour.

Each of these three colours is made up from a broad set of wavelengths. For example the Red channel in a digitial camera captures wavelengths from around 570nm to 700nm, Green from 430nm to 620nm and Blue from 400 to 550nm. If we imagine each of these colour channels is a page in our book, the result is a small book or leaflet with three pages. The colour image that we humans can see is the combination of colours from these pages as shown on the cover of the book in the image above.

   
 

 

 
   

However, with a hyperspectral camera, our target leaf is imaged with hundreds of narrow wavelength channels (bands). The number of bands depends on the model of hyperspectral camera being used but each band may be only a few nanometres (nm) wide. In this example the leaf is imaged with 220 bands i.e. each pixel in the image has 220 bands. Using the book simile again, this translates to 220 pages in the book.

 

   
 
 
   
It is clear when comparing the books produced by the hyperspectral camera and the digital RGB camera, the book produced by the hyperspectral camera is much thicker and contains a lot more detailed information about our leaf.
   
 
 
   
   

A signficant difference between a hyperspectral camera and standard digital RGB camera is that in most cases a hyperspectral camera captures bands that are invisible to the human eye. Hyperspectral camera models can range from Ultraviolet light that is shorter than visible wavelengths to wavelengths in the thermal range that are far longer than what is visible i.e. 12,000nm.

 

   
 
 
   
The book cover showing our image leaf is constructed from many wavelength bands. As said, every page of the book presents its own information. By combining different pages we are able to process different qualities of our target.
   
   
   
We are also able to choose any point of the leaf from the book cover and obtain its full, accurate, and contiguous spectrum. This requires that we use all the information of that specific point in every page of the book. It's comparable to drilling into the book at that pixel location and collecting a spectrum of that pixel.
   
   
 
 
   

The full spectral information that is collected becomes very versatile for the analysis, detection, and identification of chemical features. For the example above we mentioned plant disease. Other examples are detection of minerals or soil contituents, protein and fat in seeds, fat and the pH of meat, contamination of soil, detection of explosives .... and many many more.

The raw data collected by a hyperspectral camera still requires a significant amount of processing (cleaning up) to be useful. Non-linearities in the sensor of the camera need to be corrected, dark noise needs to be removed to enhance SNR, spatial distortions need to be corrected, signal needs to be converted to engineering units, and if imaging from a distance, atmospheric conditions need to be allowed for. Once all of these have been calibrated for, then the data can be analysed with the many mathematical techniques available to extract cheimical features. This will be discussed in the future series of articles.

   
   

 

Specim FX

The Specim FX series of hyperspectral imagers currently consists of three robust hyperspectral cameras that offer a range of features which are suited to industrial imaging applications. The FX camera series produce images with intensity measurements at hundreds of wavelengths for every pixel to provide a non-destructive measurement of a target's chemical composition.

Specim FX in the field

The FX series cameras are used for a wide variety of product inspection tasks including the inspection and grading of fruit and vegetables. Packing houses require robust, fast and accurate sensors to fit to their automated packing lines and the ability to non-destructively image a product for its chemical makeup gives them a valuable tool to guarantee quality to their customers.

FX series cameras can detect blemishes and bruising under the skin, define ripeness and chemical quality independent of the fruit color and size and find foreign materials like plastic, wood, paper, metal, or insects. Specim FX cameras can reveal much more than traditional colour and filter cameras or point spectrometers. They allow a producer to achieve better quality, ripe products with optimized shelf life, and reduce loss and waste.

 

 
     
 

Need a price or more information? Please email or call us
Adept Turnkey Pty Ltd are 'The Machine Vision and Imaging Specialists and distributor for Specim products in Australia and New Zealand.

To find out more about the Specim options or any Specim product, please contact us or call:
Perth (08) 9242 5411 / Sydney (02) 9979 2599 / Melbourne (03) 9384 1775

 

 

 

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