Thermal imaging apparatus and method of thermal imaging

Patent metadata

Field	Value
Publication number	US-2022187135-A1
Application number	US-202117512776-A
Country	US
Kind code	A1
Filing date	Oct 28, 2021
Priority date	Dec 16, 2020
Publication date	Jun 16, 2022
Grant date	—

Abstract

A thermal imaging apparatus comprising: a thermal detector device (100) comprising an array of thermal sensing pixels (102) and signal processing circuitry (104) coupled to the detector device (100). The circuitry (104) supports a background identifier (110) and a pixel classifier (112), the background identifier (110) comprising a common intensity identifier (114) and an expected background intensity calculator (116). The background identifier (110) receives pixel measurement data captured by the detector device (100) in respect of pixels of the array (102) and the common intensity identifier (114) identifies a largest number of substantially the same pixel intensity values from the pixel measurement data. The expected background intensity calculator (116) uses the largest number of substantially the same pixel intensity values to generate a model of expected background intensity levels. The pixel classifier (112) uses the model to determine whether an intensity measurement by a pixel (118) of the array (102) corresponds to a background or an object in an image.

First claim

What is claimed is:

1 . A thermal imaging apparatus comprising:
a thermal detector device comprising an array of thermal sensing pixels; signal processing circuitry operably coupled to the thermal detector device and comprising a background identifier and a pixel classifier, the background identifier comprising a common intensity identifier and an expected background intensity calculator; the background identifier is configured to receive pixel measurement data of an image captured, when in use, by the thermal detector device in respect of pixels of the array of thermal sensing pixels and the common intensity identifier is configured to identify a largest number of substantially the same pixel intensity values from the pixel measurement data received; the expected background intensity calculator is configured to use the largest number of substantially the same pixel intensity values to generate a model of expected background intensity levels referable by pixel; and the pixel classifier is configured to use the model to determine whether an intensity measurement by a pixel of the array of thermal sensing pixels corresponds to a background of the image or an object in the image.

2 . The apparatus according to claim 1 , wherein
the background identifier further comprises a pixel threshold calculator; the largest number of substantially the same pixel intensity values has a range of measured pixel intensities associated therewith; the expected pixel intensity calculator is configured to calculate a gradient across the range of measured pixel intensities, the model comprising the calculated gradient; the expected pixel intensity calculator is configured to use the calculated gradient in order to generate a plurality of expected pixel background intensity values in respect of the array of thermal sensing pixels; the pixel threshold calculator is configured to compare the plurality of expected pixel intensity values with the pixel measurement data in order to determine a temperature threshold value; and the pixel classifier is configured to classify the intensity measurement by the pixel of the array of thermal sensing pixels as corresponding to the background or the object by comparing the intensity measurement with the temperature threshold value.

3 . The apparatus according to claim 2 , wherein the common intensity identifier is configured to sort the pixel measurement data received into an order to provide sorted pixel intensity measurement data.

4 . The apparatus according to claim 3 , wherein the common intensity identifier is configured to identify the largest number of substantially the same pixel intensity values from the sorted pixel intensity measurement data.

5 . The apparatus according to claim 3 , wherein the common intensity identifier is configured to calculate a plurality of intensity differential values by calculating differences between successive intensity measurements of the sorted pixel intensity measurement data.

6 . The apparatus according to claim 5 , wherein the common intensity identifier is configured to identify the largest number of substantially the same pixel intensity values by identifying ranges of substantially unchanged differential values in the plurality of intensity differential values and identifying a largest of the ranges of substantially unchanged differential values, thereby identifying the largest number of substantially the same pixel intensity values.

7 . The apparatus according to claim 6 , wherein the common intensity identifier is configured to analyse the plurality of intensity differential values and to identify occurrences of a lowest non-zero intensity differential value amongst the plurality of intensity differential values.

8 . The apparatus according to claim 5 , wherein
the pixel measurement data received is stored as a first vector; the plurality of intensity differential values is stored as a second vector; the plurality of expected pixel background intensity values is stored as a third vector; and indexing of each of the first and third vectors maps to indexing of the array of thermal sensing pixels.

9 . The apparatus according to claim 4 , wherein
the pixel classifier is configured to identify a first boundary pixel index in respect of the largest number of substantially the same pixel intensity values of the sorted pixel intensity measurement data and to select first expected pixel intensity values of the plurality of expected pixel intensity values and first pixel measurement data of the pixel measurement data having respective pixel indices incrementing in distance away from the first boundary pixel index; the array of thermal sensing pixels generates a plurality of intensity measurements comprising the intensity measurement; and the pixel classifier is also configured to compare each of the plurality of intensity measurements with the temperature threshold value.

10 . The apparatus according to claim 9 , wherein
the pixel classifier is configured to identify a second boundary pixel index in respect of the largest number of substantially the same pixel intensity values of the sorted pixel intensity measurement data and to select second expected pixel intensity values of the plurality of expected pixel intensity values and second pixel measurement data of the pixel measurement data having respective pixel indices incrementing in distance away from the second boundary pixel index so as to decrement in value; and the pixel classifier is also configured to compare each of the plurality of intensity measurements with another temperature threshold value.

11 . The apparatus according to claim 1 , wherein the temperature threshold value comprises an adjustment by a noise margin.

12 . The apparatus according to claim 11 , wherein the noise margin is a number of standard deviations of a calculated noise level.

13 . The apparatus according to claim 3 , wherein the signal processing circuitry further comprises a filter configured to filter the sorted pixel intensity measurement data.

14 . The apparatus according to claim 3 , wherein the filter is configured to perform sliding window averaging.

15 . The apparatus according to claim 1 , wherein the common intensity identifier is configured to sort the pixel measurement data received into an order to provide sorted pixel intensity measurement data.

16 . The apparatus according to claim 15 , wherein the common intensity identifier is configured to identify the largest number of substantially the same pixel intensity values from the sorted pixel intensity measurement data.

17 . The apparatus according to claim 15 , wherein the common intensity identifier is configured to calculate a plurality of intensity differential values by calculating differences between successive intensity measurements of the sorted pixel intensity measurement data.

18 . The apparatus according to claim 17 , wherein the common intensity identifier is configured to identify the largest number of substantially the same pixel intensity values by identifying ranges of substantially unchanged differential values in the plurality of intensity differential values and identifying a largest of the ranges of substantially unchanged differential values, thereby identifying the largest number of substantially the same pixel intensity values.

19 . The apparatus according to claim 15 , wherein the signal processing circuitry further comprises a filter configured to filter the sorted pixel intensity measurement data.

Assignees

• Melexis Technologies Nv

Inventors

• Rennies Jos
• Reusen Wouter
• Buydens Luc

Classifications

• H04N25/46

  by combining or binning pixels · CPC title

• G01J5/0803 Primary

  Arrangements for time-dependent attenuation of radiation signals · CPC title

• G01J2005/0077

  Imaging · CPC title

• H04N25/706

  Pixels for exposure or ambient light measuring · CPC title

• H04N23/23

  from thermal infrared radiation · CPC title