Thermal Imaging overview

Thermal Imaging overview

Geometric, Photometric and Morphological - Image transformations

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Harshvardhan

Published on Aug 17, 2021

3 min read

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Thermal imaging is a non-destructive, non-contact and rapid system. It reports temperature through measuring infrared radiation emanated by an object/material surface. Automated thermal imaging system involves thermal camera equipped with infrared detectors, signal processing unit and image acquisition system supported by computer. It is elaborated in wide domains applications. Extensive focus is directed to the thermal imaging in the medical domain especially breast cancer detection. This chapter provided the main concept and the different applications of thermal imaging. It explores and analyses several works in the light of studding the thermograph. It is an effective screening tool for breast cancer prediction. Studies justify that thermography can be considered a complementary tool to detect breast diseases. The current chapter reviews many usages and limitations of thermography in biomedical field. Extensive recommendations for future directions are summarized to provide a structured vision of breast thermography.

Thermal imaging background

All materials/ objects that are at temperature above -273 degrees C (0 degrees Kelvin) emanate infrared energy. The emitted infrared (IR) energy from the measured object is converted into an electrical signal by imaging sensor. This imaging sensor is in the camera which connected to computer for displaying on a monitor the converted signal as a color or monochrome thermal image. The IR is a form of electromagnetic radiation that has wavelength band of 0.78 to 1000µm, which are longer than the wavelength of visible light and shorter than the radio waves. Several characteristics of the infrared radiation are similar to visible light, such as: the IR radiation can be refracted, focused, reflected and transmitted. The absorptivity, emissivity, transmissivity, and reflectivity of infrared radiation vary for different objects/ materials. Good absorber objects for the infrared radiation are also good emitters.

Equipment that produces thermal image (Camera)

Thermal imaging refers to improve objects visibility even in a dark environment by recognizing the objects' infrared radiation as well as creating an image based on that information. Since, all objects emit heat (infrared energy) as a function of their temperature. This emitted infrared energy is known as the object‘s heat signature (Gaussorgues,& Chomet, 2012). Generally, the emitted radiation is directly proportional to the object temperature (i.e. the hotter an object is, the more radiation it emits). Therefore, a heat sensor is required to detect tiny differences in temperature. This thermal sensor is essentially a thermal infrared (IR) camera (thermal camera) that collects the infrared radiation on the surface of the objects under investigation and produces an electronic image based on the temperature differences information. Additionally, thermal camera can detect different objects in the same view based on the object's different temperature, which make them appear as distinct objects in a thermal image.

Thermal Imaging in Medical Science

Geometric, Photometric and Morphological transformations

Geometric transformation

The functions in this section perform various geometrical transformations of 2D images. They do not change the image content but deform the pixel grid and map this deformed grid to the destination image. In fact, to avoid sampling artifacts, the mapping is done in the reverse order, from destination to the source. That is, for each pixel (x, y) of the destination image, the functions compute coordinates of the corresponding “donor” pixel in the source image and copy the pixel value:

{dst} (x,y)= {src} (f_x(x,y), f_y(x,y))

Library for Such operation

OpenCV
  1. getAffineTransform
  2. getPerspectiveTransform
  3. getRectSubPix
  4. getRotationMatrix2D
  5. invertAffineTransform
  6. LinearPolar
  7. LogPolar
  8. remap
  9. resize
  10. warpAffine
  11. warpPerspective
  12. initUndistortRectifyMap
  13. getDefaultNewCameraMatrix
  14. undistortPoints
  15. undistort
 
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