CN115931142A - Colorimetric temperature measuring black body calibration method - Google Patents
Colorimetric temperature measuring black body calibration method Download PDFInfo
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Abstract
The application provides a method for calibrating a colorimetric temperature measurement black body, which uses a first camera and a second camera which are respectively superposed with a first wavelength infrared filter and a second wavelength infrared filter, wherein the first camera and the second camera are visible light cameras, and the calibration of the colorimetric temperature measurement black body comprises the following steps: respectively carrying out camera lens distortion correction and image registration on the first camera and the second camera, and calculating an internal parameter matrix and a distortion matrix of the cameras and a coordinate conversion matrix of the first camera image and the second camera image; calibrating the gray scales of the first camera and the second camera respectively by using a black body; correcting a colorimetric temperature measurement formula, and establishing a model relation between the temperature and the gray levels of the first wavelength image and the first wavelength image; and establishing a thread pool to acquire images of the first camera and the second camera, processing the images by using a temperature measurement model, and transmitting temperature data.
Description
Technical Field
The application relates to the field of infrared temperature measurement, in particular to a method for calibrating a colorimetric temperature measurement black body.
Background
The temperature is the basic physical quantity for describing the state of an object, the infrared temperature measurement has an important role in the production of aerospace, materials, energy, metallurgy and the like, and the infrared temperature measurement device has the advantages of no damage to the temperature field of the object to be measured, high reaction speed, high sensitivity, wide temperature measurement range and the like. At present, the infrared temperature measurement at home and abroad mainly comprises the following methods: total radiation thermometry, luminance thermometry, colorimetric thermometry.
A so-called total radiation thermometry method, in which the radiation temperature of an object is determined by measuring the thermal radiation of the object at its full wavelength; the method is called brightness thermometry, which determines the brightness temperature of an object by measuring the monochromatic radiation brightness of the object under a certain wavelength; the colorimetric thermometry is used for determining the temperature by the change of the ratio of the monochromatic radiance of a measured object under two wavelengths along with the temperature.
The precision of the total radiation temperature measurement method and the brightness temperature measurement method is greatly influenced by the emissivity of an object, and although the temperature measurement precision of a black body is higher after calibration in a laboratory, the precision often cannot meet the requirement in practical production and use.
The colorimetric temperature measurement method can reduce the influence of the emissivity of an object, and is characterized in that a relation model between the temperature of the object and the gray level of a camera is established after blackbody calibration according to the ratio of the radiation power of two given wavelengths, so that the influence of the emissivity on the temperature measurement precision can be reduced, and the colorimetric temperature measurement method has important application value.
Disclosure of Invention
The embodiment of the invention provides a method for calibrating colorimetric temperature measurement, which can greatly increase the speed and the precision of temperature measurement.
The invention provides a calibration method of a colorimetric temperature measurement black body, which uses a first camera and a second camera which are respectively superposed with a first wavelength infrared filter and a second wavelength infrared filter, wherein the first camera and the second camera are both visible light cameras, and the calibration of the colorimetric temperature measurement black body comprises the following steps:
s101: respectively carrying out camera lens distortion correction and image registration on the first camera and the second camera, and calculating an internal reference matrix and a distortion matrix of the cameras and a coordinate conversion matrix of the first camera image and the second camera image;
s102: calibrating the gray scales of the first camera and the second camera respectively by using a black body, thereby completing the calculation of temperature resolution, time domain noise and nonuniformity;
s103: correcting a colorimetric temperature measurement formula, and establishing a model relation between the temperature and the gray levels of the first wavelength image and the first wavelength image;
s104: and establishing a thread pool to acquire images of the first camera and the second camera, processing the images by using a temperature measurement model, and transmitting temperature data.
According to one embodiment of the present invention, a method is provided, wherein,
the lens distortion correction comprises radial distortion correction and tangential distortion correction;
the internal reference matrix is a conversion matrix for converting an image coordinate system into a pixel coordinate system;
the distortion matrix is a conversion matrix for solving radial distortion and tangential distortion so as to calculate the corresponding relation of pixel positions before and after the conversion of the image matrix.
According to the method provided by one embodiment of the invention, in the image registration, corresponding control points are uniformly selected on two images, and an image conversion homography matrix is calculated, so that an image lookup table is calculated.
According to the method provided by an embodiment of the present invention, in step S102, the calibration of the gray scales of the first camera and the second camera respectively by using a black body includes: the method comprises the steps of collecting black body gray scale of the same pixel position, calculating a pixel window gray scale mean value and a standard deviation by taking the pixel as a center, calculating time domain noise by the pixel window gray scale mean value and the standard deviation, continuously collecting N frames of images in a fixed temperature section, waiting for the temperature rise of a black body, and collecting the pixel window mean value of the N frames of images at N degrees per liter, so that the calculation of temperature resolution is completed, and the gray scale offset and the nonuniformity of the black body when a camera collects the images are removed.
According to one embodiment of the present invention, there is provided a method wherein N is equal to or greater than 50.
According to one embodiment of the present invention, there is provided a method, wherein n is 20 or less.
According to one embodiment of the present invention, the step of establishing a model relationship between the temperature and the gray scale of the first and second wavelength images in step S103 includes: obtaining two wavelengths within the near infrared range as lambda 1 ，λ 2 The ratio of the thermal radiation energy of the light source to the light source, and the relationship between the gray scale ratio and the temperature is established.
According to the method provided by an embodiment of the present invention, in step S103, the colorimetric temperature measurement formula is modified, and consideration of environmental factors is added.
According to the method provided by an embodiment of the present invention, in step S103, the colorimetric temperature measurement formula is
Wherein λ is 1 At a first wavelength, λ 2 At a second wavelength, C 1 Is a first radiation constant, C 2 Is the second radiation constant, T is the temperature, and K is the correction parameter.
According to the method provided by one embodiment of the present invention, in step S104, the thread pool is a Buffer that takes the maximum size of the image as the collection thread pool, image collection is performed according to the SDK packet provided by the manufacturer, and the image is taken from the thread pool to complete image algorithm processing; transmitting the temperature data to a server side by using a UDT protocol; the server side software receives the data result for using the UDT protocol and stores the data result in a fixed position.
The invention has the following beneficial effects: the method adds a surface temperature measurement function through image registration on the basis of the prior point colorimetric thermodetector, loads a conversion matrix generated by camera distortion correction and image registration into a memory in the form of an image lookup table, and provides correction for a fitting formula of gray scale and temperature. The method can provide an implementation scheme for industrial application of colorimetric temperature measurement, rebuilds the object surface temperature field, and greatly improves the temperature measurement speed and precision.
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The above features, technical features, advantages and modes of realisation of the present application will be further described in the following detailed description of preferred embodiments in a clearly understandable manner, in conjunction with the accompanying drawings. The drawings are only for purposes of illustrating and explaining the present application and are not to be construed as limiting the scope of the present application. Wherein:
fig. 1 is a flowchart of a colorimetric temperature measurement calibration method disclosed in an embodiment of the present invention.
Detailed Description
In order to more clearly understand the technical features, objects, and effects of the present application, embodiments of the present application will now be described with reference to the accompanying drawings.
The invention provides a method for calibrating a colorimetric temperature measurement black body, which increases a surface temperature measurement function through image registration on the basis of a traditional point colorimetric thermometer, uses two visible light cameras to respectively superpose infrared filters with different wave bands, carries out distortion correction and image registration on the cameras, loads a conversion matrix into a memory in the form of an image lookup table, and provides correction for a fitting formula of gray scale and temperature. The method can provide an implementation scheme for industrial application of colorimetric temperature measurement, and greatly improves the temperature measurement speed and precision.
As shown in fig. 1, the method for calibrating a colorimetric temperature measuring black body according to the present invention uses a first camera and a second camera respectively superimposed with a first band infrared filter and a second band infrared filter, where the first camera and the second camera are both visible light cameras, and the method includes:
s101: and respectively carrying out camera lens distortion correction and image registration on the first camera and the second camera, and calculating an internal reference matrix and a distortion matrix of the cameras and a coordinate conversion matrix of the first camera image and the second camera image.
The distortion correction of the camera lens is the correction of an image coordinate system, and comprises the solving of an internal parameter matrix and a distortion coefficient of the camera. The internal reference matrix of the camera is a conversion matrix for converting an image coordinate system into a pixel coordinate system. Distortion is image distortion caused by a manufacturing process, and distortion of a lens is divided into radial distortion and tangential distortion.
In the image registration step, a single camera is first calibrated. Establishing a camera coordinate system by taking a visible light camera as an origin, and coinciding the camera coordinate system with a world coordinate system, wherein the camera coordinate system is considered to rotate to an imaging physical coordinate system to a certain extent
In fact, the final image results in a pixel point (x) on the display pix ，y pix ) Then, then
Wherein s is the number of pixel points in unit distance, and t is the translation amount.
Combine (1) and (2), then
Writing in matrix form:
r and T of the first visible light camera a and the second visible light camera B are obtained, respectively.
Then there are:
elimination of X in the formula (5) c Then, there are:
X vi pix ＝R vi (R in ) -1 X in pix -R vi (R in ) -1 T in +T vi
R i2v ＝R vi (R in ) -1 X in pix
T i2v ＝-R vi (R in ) -1 T in +T vi (6)
through the formula (6), the rotation R from the pixel point B of the second visible light camera to the pixel point A of the first visible light camera can be obtained i2v And translation T i2v And (5) matrix, calculating an image lookup table, and storing the image lookup table into an xml file.
S102: calibrating the gray scales of the first camera and the second camera respectively by using a black body, thereby completing the calculation of temperature resolution, time domain noise and nonuniformity;
the calculation process of the temperature resolution ratio is as follows: calculating a temperature resolution by testing the output of the camera at high and low temperatures;
temperature resolution = (T) high -T low )/(AD high –AD low )
T is the object temperature and AD is the grey scale value.
The calculation process of the time domain noise is as follows: the camera is aimed at the radiation target after stabilization, 50 images are continuously acquired, and the average value and the standard deviation are calculated.
The non-uniformity calculation procedure is as follows: aligning the whole target surface of the camera to a stable black body target surface, calculating a pixel window gray level mean value, continuously acquiring 50 frames of images in a fixed temperature section, waiting for the temperature rise of the black body, and acquiring the pixel window mean value of 50 frames of images at 20 degrees per liter, thereby removing the gray level offset and the nonuniformity of the black body when the camera acquires the images;
s103: correcting a colorimetric temperature measurement formula, and establishing a model relation between the temperature and the gray levels of the first and second band images;
wherein the colorimetric temperature measurement formula is
According to Planck's law, a black body has a radiance of at least
In the formula C 1 ＝3.742x10 -16 W.m 2 Is a first radiation constant, C 2 ＝1.439x10 -2 m.K is the second radiation constant, T is the temperature, and lambda is the wavelength of the filter plate of the visible light camera
Since the measured object is not black body, the radiation brightness is
In the formula, epsilon (lambda, T) is the emissivity of the object, and the radiance of the object to be measured under two cameras provided with filters of different wave bands is L 1 And L 2 According to the ratio of the two
The emissivity difference can be approximately obtained by taking logarithms at two sides because the emissivity of the object can be approximately equal in a narrow wave band range
K is a correction parameter, the consideration of some environmental factors such as background stray light, field dust and the like is considered, the temperature is measured only by a single correction parameter through field working condition verification, the universality is avoided, the temperature measurement error is larger, the method adopts least square iterative solution, logarithms are taken from the gray levels of two different wave bands of the same object measured by black body calibration, polynomial fitting is carried out on the logarithms and the temperature, and the measured temperature formula is
The temperature calculation formula is as follows:
T＝-2915.37048379764+532.743896708742*Ln(x)+(-31.2652960687133)*(Ln(x))^2+2218.64173796713*Ln(y)+(-780.956006517218)*(Ln(y))^2+119.68436894504*(Ln(y))^3+(-8.72389262816654)*(Ln(y))^4+0.254978292499841*(Ln(y))^5
wherein: x is the gray value of the measured object under 780nm wavelength, and y is the gray value of the measured object under 840nm wavelength
S104: establishing a thread pool to collect two camera images with different wave bands, processing the images by using a temperature measurement model, and transmitting temperature data to a server terminal through a UDT protocol.
The image acquisition thread pool is a Buffer taking the maximum size of an image as an acquisition thread pool, image acquisition is carried out according to an SDK (software development kit) packet provided by a manufacturer, image data is placed into the thread pool, and the image is taken from the thread pool to complete colorimetric temperature measurement algorithm processing; the temperature result transmission is to transmit a data result to a server end by using a UDT protocol; and the server-side software receives the temperature data result in a multithreading mode by using a UDT protocol.
The invention relates to a colorimetric temperature measurement black body calibration scheme, which aims at the problems that the existing colorimetric temperature measurement product only aims at single points, temperature measurement precision is not enough and the like, and firstly distortion correction and image registration are carried out on two camera lenses; then, calibrating a color temperature measuring camera by using a black body, and establishing a model relation between the temperature and the gray scale ratio of the two different wave band images; and finally, establishing a thread pool to collect two camera images with different wave bands, processing the images by using a temperature measurement model, and transmitting temperature data to a server terminal through a UDT protocol.
The method adds a surface temperature measurement function through image registration on the basis of the prior point colorimetric thermodetector, loads a conversion matrix generated by camera distortion correction and image registration into a memory in the form of an image lookup table, and provides correction for a fitting formula of gray scale and temperature. The method can provide an implementation scheme for industrial application of colorimetric temperature measurement, rebuilds the object surface temperature field, and greatly improves the temperature measurement speed and precision.
It should be understood that although the present description has been described in terms of various embodiments, not every embodiment includes only a single embodiment, and such description is for clarity purposes only, and those skilled in the art will recognize that the embodiments described herein may be combined as suitable to form other embodiments, as will be appreciated by those skilled in the art.
The above description is only illustrative of the present invention and is not intended to limit the scope of the present invention. Any equivalent alterations, modifications and combinations that may be made by those skilled in the art without departing from the spirit and principles of this application shall fall within the scope of this application.
Claims (10)
1. A method for calibrating a colorimetric temperature measurement black body uses a first camera and a second camera which are respectively superposed with a first wavelength infrared filter and a second wavelength infrared filter, wherein the first camera and the second camera are both visible light cameras, and the calibration of the colorimetric temperature measurement black body comprises the following steps:
s101: respectively carrying out camera lens distortion correction and image registration on the first camera and the second camera, and calculating an internal parameter matrix and a distortion matrix of the cameras and a coordinate conversion matrix of the first camera image and the second camera image;
s102: calibrating the gray scales of the first camera and the second camera respectively by using a black body, thereby completing the calculation of temperature resolution, time domain noise and nonuniformity;
s103: correcting a colorimetric temperature measurement formula, and establishing a model relation between the temperature and the gray levels of the first wavelength image and the first wavelength image;
s104: and establishing a thread pool to acquire images of the first camera and the second camera, processing the images by using a temperature measurement model, and transmitting temperature data.
2. The method of claim 1, wherein,
the lens distortion correction comprises radial distortion correction and tangential distortion correction;
the internal reference matrix is a conversion matrix for converting an image coordinate system into a pixel coordinate system;
the distortion matrix is a conversion matrix for solving radial distortion and tangential distortion so as to calculate the corresponding relation of pixel positions before and after the conversion of the image matrix.
3. The method of claim 1, wherein in the image registration, corresponding control points are uniformly selected on two images, and an image transformation homography matrix is calculated, thereby calculating an image lookup table.
4. The method according to claim 1, wherein in the step S102, the calibration of the gray scales of the first camera and the second camera respectively by using the black body comprises: the method comprises the steps of collecting black body gray scale of the same pixel position, calculating a pixel window gray scale mean value and a standard deviation by taking the pixel as a center, calculating time domain noise by the pixel window gray scale mean value and the standard deviation, continuously collecting N frames of images in a fixed temperature section, waiting for the temperature rise of a black body, and collecting the pixel window mean value of the N frames of images at N degrees per liter, so that the calculation of temperature resolution is completed, and the gray scale offset and the nonuniformity of the black body when a camera collects the images are removed.
5. The method of claim 4, wherein N is greater than or equal to 50.
6. The method of claim 4, n is less than or equal to 20.
7. The method of claim 1, wherein the step of modeling the temperature with respect to the gray scale of the first and second wavelength images in step S103 comprises: obtaining two wavelengths respectively lambda in the near infrared range 1 ，λ 2 The ratio of the thermal radiation energy of the light source to the light source, and the relationship between the gray scale ratio and the temperature is established.
8. The method of claim 1, wherein in step S103, the colorimetric thermometry equation is modified to take into account environmental factors.
9. The method of claim 1, wherein in step S103, the colorimetric thermometry formula is
Wherein λ is 1 At a first wavelength, λ 2 At a second wavelength, C 1 Is a first radiation constant, C 2 Is the second radiation constant, T is the temperature, and K is the correction parameter.
10. The method according to claim 1, wherein in step S104, the thread pool is a Buffer with the maximum size of the image as the collection thread pool, the image collection is performed according to the SDK package provided by the manufacturer, and the image is taken from the thread pool to complete the image algorithm processing; transmitting the temperature data to a server side by using a UDT protocol; the server side software receives the data result by using the UDT protocol and stores the data result in a fixed position.
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