Study on the influence of internal modulation parameters on the temperature calculation performance of matrix-searching CCD pyrometer

Matrix-searching CCD temperature measurement technology can integrate the complex signal modulation process of CCD because of its forward solution of inverse problem. But in the existing research, there is still a lack of discussion on the temperature calculation ability of this technology in the internal modulation process. Therefore, the research on the influence of temperature calculation performance of matrix-searching CCD pyrometer is carried out. Based on the three-channel temperature equation and the radiation acquisition theory of the detector, the evaluation model of effective measurement range and temperature resolution is defined and constructed. Combined with the calibration experiment, the effects of gain and gamma internal modulation parameters on the effective temperature measurement range and temperature resolution are discussed. Through the analysis of the simulation results, the use and effects of the two internal modulation parameters are obtained, which not only improves the theoretical system of the matrix-seeking temperature measurement method, but also provides theoretical guidance for the parameter selection of the method under different conditions.


Introduction
Radiation thermometry, with its characteristics of non-contact and long-distance measurement, has become an effective Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence.Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.method for high-temperature measurement.It involves collecting and calculating the thermal radiation signals from the high-temperature object to determine its temperature.However, due to the Wien's displacement law, which states that the wavelength of maximum intensity of radiation shifts towards shorter wavelengths as temperature increases, the response range of the high-temperature radiation detector should be closer to the shortwave region.As a result, infrared radiation thermometry methods do not perform optimally in high-temperature measurements [1].Based on its advantages in shortwave detection, capture of transient spatial information of temperature field and complete post-data processing ability, CCD pyrometer is widely used in high temperature measurement in laser cleaning [2], metal processing [3,4], furnace flame testing [5]and other fields, and it has also become an important part of high temperature measurement field.
In the 1990s, after the development of CCD reached maturity, people began to introduce CCD devices into hightemperature measurement applications.In 1996, Renier et al [6] proposed a method that combines narrowband filters with CCD grayscale signals to perform global temperature measurements of a temperature field.This method was pioneering as it incorporated transient spatial information of temperature into the temperature measurement process.In 2003, Sutter et al improved and applied this method to the field of high-speed metal processing, specifically for measuring temperatures during metal cutting processes.Their successful application effectively demonstrated the practical value of this method.However, the approximation of emissivity in this method still has a significant impact on measurement accuracy [7].With the subsequent maturity of colour CCD technology, in 2008, Fu et al combined CCD grayscale temperature measurement theory with colorimetric temperature measurement principles and conducted research on dual-channel colorimetric temperature measurement based on CCD devices [8][9][10].This method not only obtained the transient spatial distribution of temperature fields but also used the ratio calculation of two closely wavelength thermal radiation signal intensities to eliminate the influence of device calibration parameters, effectively ensuring the accuracy of temperature measurement.However, this method is greatly affected by dual-channel wavelength selection, and the temperature calculation is different in the case of different channel calculation.In addition, the method is combined with Wien approximation and needs to be completed by solving the logarithmic equation of the pixel output signal, so that the accuracy of the solution is affected.With the deepening of the research of visible band radiation text method and the development of application research in this direction, the theory of CCD temperature measurement method has gradually matured.
To improve the temperature measurement performance, the research on the influence of CCD temperature measurement performance parameters has gradually been conducted.In 2010, A three-channel wide-band temperature measurement method based on colour CCD camera is proposed by Fu et al, which is called spectral colour temperature measurement method [11].This method utilizes a CCD detector based on Bayer filter technology [12] to capture the RGB three-channel thermal radiation signals.The logarithmic equation constructed from normalized channel signals is then solved to achieve temperature inversion.On this basis, the team further carried out the study of the influence of the spectral response curve and the dynamic range of the detector on temperature measurement, and improved the measurement theory.In recent years, with the increasing application of feature wavelength methods, Zhang et al evaluated the temperature measurement method based on feature wavelength methods.Their study discussed the measurement range, temperature responsiveness, and other aspects, contributing to the improvement of feature wavelength methods [13].According to the previous research, the proposal of temperature measurement method and the theoretical perfection and influence analysis of method performance parameters are the inherent research mode of radiation temperature measurement, and it is also the best research path to realize engineering application.
In 2023, Li et al proposed a method to calculate the radiation temperature of CCD pyrometer based on matrix search [14].This method transforms the inverse solving process into a forward process for temperature calculation, resolving the difficulties associated with handling integral equations in traditional solving methods.Additionally, the forward-solving enables the internal modulation of the detector to be applied in CCD temperature measurement.However, the influence of internal modulation parameters on system temperature measurement is not systematically described in this study.Considering the necessity of this part of the research on the practical application of the method, the research in this area is carried out in this paper.Based on the theory of matrixsearching CCD temperature measurement, the conditions for judging the effective measurement range and the mathematical model for characterizing the temperature resolution are established.Combined with the equipment calibration results, the effects of different internal modulation parameters are simulated and discussed, and the selection methods of modulation parameters for different measurement conditions are further discussed.This study provides a theoretical basis for improving the matrix-searching CCD temperature measurement technology, and provides theoretical guidance for the parameter selection of measurement methods.

Matrix seeking method for temperature calculation
The matrix-searching CCD temperature measurement method is based on the preparation phase and the solution phase to achieve temperature measurement as shown in the figure 1.
In the preparation stage, the specific environment of temperature measurement needs to be determined first.It includes the spectral response function s i (λ), clear imaging focal length f and aperture d of the selected camera, emissivity model ε(λ) of the material to be measured, spectral absorption k(λ) of the transmission medium and radiative transmission length l.
Based on this, it can be simulated that there is a following integral relation-ship between the receiving radiation intensity of CCD pixels and the actual temperature T of the object [9,15].
where D represents the dark noise of the detector, λ 1 and λ 2 represent the upper and lower spectral limits of the response of the detector, respectively.P(f, d, ∆t) is an instrument parameter that describes the effect of optical system on radiation attenuation.I b is Planck blackbody radiation intensity.The specific expressions of the two are [1]: (2) The simulation temperature range is constructed by taking the Draper point [16] as the lower limit of the simulation temperature and setting a high enough temperature upper limit.Using equation (1) by traversing the temperature range, the signal values of each channel under different simulated temperatures can be obtained.By normalizing the signal in the following form, the mapping relationship between simulated temperature T and R, G can be obtained Taking R and G values as horizontal and vertical coordinates, the temperature map-ping surface in R and G space is obtained by using the nearest difference algorithm [17].If the coordinate values in R and G space are divided into sufficient cells, each unit is: R max represents the theoretically maximum normalized R component, while R min represents the minimum value of that.Similarly, G max and G min have the same meaning and interpretation.∆R and ∆G are defined as the normalized chromatic intervals of the R and G channels, respectively.The values of ∆R and ∆G are determined by the parameters q and p. Taking the R channel signal value as the column vector index and the G channel signal value as the row vector index, the p × q dimensional temperature mapping matrix can be established according to the temperature mapping relationship in R and G space [14] In the solving stage, the camera is used to collect the measured temperature field.If the image dimension is r × c, the normalized R, G and B channel signal values of the image to be solved can be obtained The search address i, j is obtained by performing the following operation on the normalized signal ∆R and ∆G are set in equation (5).Where i mn and j mn are the search addresses of the temperature mapping matrix of the mth row and nth column pixels, respectively.Equations ( 7) and (8) essentially convert the numerical images output by each channel into multiples of the normalized chromatic intervals ∆R, ∆G.This transformation allows the numerical images to be converted into matrices composed of retrieval addresses.Based on the obtained search address of each pixel to call the corresponding matrix element in the temperature mapping matrix equation ( 6), the value is the temperature solution result of the corresponding point of the pixel, and ultimately can obtain the temperature calculation result that corresponds to the pixel point one by one and output the result in the form of data.

Principle of effective measurement range evaluation
The temperature measurement range is an important performance parameter of radiation thermometer, the determination of the temperature solving range and the improvement of the range are crucial for temperature measuring equipment.CCD pyrometer is a temperature measurement based on digital image processing, which makes its temperature measurement range limited by hardware output conditions.For CCD measurement devices with 8 bit colour depth, the measurement can only be achieved when the output grey level of the channel is in the range of 0-255 [18].
Figure 2 is a schematic diagram defining the temperature solution range.In three channels, the temperature interval covered from the grey level just greater than zero to the grey level saturation of a channel is defined as the effective change interval of normalized grey level.It is considered that this area is an effective measurement range, and the temperature range determined by each channel is shown in the corresponding colour area in the figure 2. For the 8 bit colour depth acquisition device, the chromaticity within the effective temperature interval should satisfy the constraint that the grey scale of the output value of any channel is within the open interval (0, 255).That is, if the three-channel signal is represented by R pq , G pq and B pq , it should satisfy the condition in the effective measurement range: (10) where & represents the 'and' operation, substituting into the equation (1) to get: According to Schwarz's inequality, this can be rewritten as: where C T is a parameter affected by the spectral response curve and the imaging parameter P, which is denoted as: After the object to be measured has been determined, the only parameter that can affect the upper and lower temperature limits of the device is C T , which is affected by the spectral response curve s i (λ) and the imaging parameter P. Theoretically, an increase in C T will result in an increase in the effective upper and lower temperature limits of the system, and a decrease in C T will result in a decrease in the upper and lower temperature limits.The imaging parameter that can directly contribute to an increase in C T are the aperture, exposure time and the gain of the amplification circuit.

Evaluation principle for measuring temperature resolution
The temperature resolution is an important index to characterize the accuracy of the system, which is defined as the smallest temperature change that can be resolved by the CCD temperature measurement system, and it is the minimum temperature unit that the system can distinguish.
In the matrix-searching CCD pyrometer, although the a priori calculation of the chromaticity value is based on a preset temperature step ∆T, this does not mean that the temperature resolution of the solution method is exactly equal to the temperature step ∆T.This is because the chromaticity value R, G, which is operated through T forward, is not linearly related to T, as shown in figure 3. Figure 3 shows the grey values output from the CCD image element when the temperature is at 1200-1600 K.At low grey value levels, the temperature change ∆t corresponding to a ∆R grey change in the R channel is relatively large.While at higher grey levels, the temperature change ∆t corresponding to the ∆R grey level change occurring in the R channel is smaller the same phenomenon exists in the G channel.Therefore, the system temperature resolution based on CCD devices is not fixed, and the discussion of its variation relationship is necessary.
For an acquisition system with a colour depth of 8 bit, the minimum chromaticity change that the system can distinguish is 1 grey scale.That is, when the grey level of any channel increases or decreases by 1, the corresponding temperature change is the system temperature resolution.The rate of change of channel grey scale with temperature is expressed by: After rewriting, the temperature resolution satisfies the expression That is, the temperature resolution is a quantity affected by the temperature T at which it is located, and there is a difference in the temperature resolution at different temperatures, in other words the temperature required for the chromaticity to grow by one grey scale at a lower level of temperature is different from that at a higher level of temperature.It is worth noting that according to the description of equation ( 15), on the one hand, the temperature resolution is influenced by the imaging parameter; on the other hand, the temperature resolution is influenced by the temperature rate of the thermal radiation intensity integral.In practice, the imaging parameter is controlled by parameters such as gain, exposure time and aperture, while the temperature change rate of the integral are affected by Gamma modulation.
Theoretically, the temperature resolution of each channel can be calculated for each of the three channels.Considering that the increase of grey scale of any channel in the three channels can cause the change of pixel chromaticity, the temperature value that can cause the change of grey scale of any channel is the temperature resolution of the system at that temperature level.

Effect of internal modulation parameters on temperature solving capability
The purpose of discussing the effective temperature measurement range and temperature resolution is to improve the value by changing the acquisition setting, so as to improve the temperature calculation ability.Considering that this study is based on the establishment of the mapping matrix based on the grey scale of the normalised channels.The same instrumental coefficients P in the simultaneous acquisition of the channels will be eliminated in normalisation, so that the effective measurement range cannot be affected and improved by changing the parameters of instrument coefficient, such as aperture, focal length, exposure time and so on.Therefore, in this study, only the effects of two internal modulation parameters, channel gain and Gamma value, on the temperature resolution capability are discussed.In the process of forward calculation of equation ( 1), the CCD spectral response curve s i (λ) and the grey scale-radiance transfer relationship g i need to be obtained first.

CCD spectral response curves and grey-radiance transfer relationship acquisition
In order to verify the correctness of the theoretically discussed effective temperature measurement range and the temperature resolution, and to discuss the modulation effects of both linear and nonlinear modulation methods, calibration experiments are carried out in this study.The LS1050 blackbody (Electro-optical) is used as the standard source to calibrate the CCD camera, and it is used as the high emissivity source to verify the accuracy of the solution of the lower limit of temperature measurement.DAHENG IMAGING MER2-134-90GC camera as the acquisition equipment, the experimental setup is shown in figure 4.
The CCD acquisition data were transferred to a computer, the image in the blackbody standard source cavity was adjusted to be located in the central position of the CCD screen.The parameters of CCD colour depth, exposure time, lens aperture and lens focal length were fixed to acquire the blackbody at different temperatures.In order to facilitate the subsequent solving, the gain and gamma values were set to the unmodulated state in the experiment.To avoid the influence of Bayer filtering, the RAW format images are collected for interpretation [19].The experimental parameters are summarised in table 1.
The blackbody image in RAW format acquired based on the parameters in the table is shown in figure 5.
The spectral response curves s i (λ) of each channel of the camera and the calibration results of the grey-radiance conversion coefficient g i are shown in figure 6.The experimental results will be used as the basis for the subsequent effective measurement range and temperature resolution studies.The area enclosed by each spectral response curve is a characterisation of the sensitivity of the channel's signal, and the more sensitive R channel has a significant change in output grey scale as the radiated signal grows.The B Channel, which is less sensitive, grows more slowly.To facilitate the comparative analysis of the effect of gain and gamma on the resolution, the effective measurement range and temperature resolution of the system should be given in the standard state, that is, when the gain and gamma coefficients are both 1.

Analysis of temperature solving capability at standard conditions
The calibration results of spectral response curve and grey radiance conversion factor of each channel are substituted into equations ( 12) and (13) to discuss the effective measurement range of the equipment.Considering that the emissivity can affect the effective measurement range of the system.In the standard acquisition state, the effect of effective measurement range on emissivity is shown in figure 7.
The green area in the figure 7 is the effective temperature measurement range.Upper temperature measurement limit close to 1600 K can be obtained at lower emissivity, while a lower temperature limit can be obtained at higher emissivity levels, and the lower limit of measurement is 990 K when the emissivity is at the maximum value of 1.As a standard source of emissivity with 1, the calibration image of blackbody radiation is used to verify the correctness of the simulation.According to the results of the 983 K blackbody acquisition image in figure 7(b), a faint red light appears in the visible radiation region under the acquisition parameter settings in table 1, and the grey level of each channel is exactly greater than zero, which is consistent with the simulation results and meets the solution conditions.
It is worth noting that when discussing the absolute effective measurement range for the case shown in the figure 7, the intersection of the high and low emissivity cases should be chosen, i.e. the intermediate region consisting of the lower temperature limit for the high emissivity case and the upper temperature limit for the low emissivity case.Therefore, in the study of the absolute measuring range, it is sufficient to discuss only the lower temperature limit in the case of high emissivity and the upper temperature limit in the case of low emissivity.Regarding the temperature resolution, based on the discussion of equation ( 15) and the results of calibration experiments, numerical simulations are carried out for the threechannel measurement resolution corresponding to different temperature values under the standard condition with a temperature step of 0.2 K.The results are shown in figure 8.
Temperature resolution of the three channels shows a clear trend, the temperature difference corresponding to one degree of chromaticity change is higher at the high temperature position, and this temperature difference decreases with the increase of temperature.At the same temperature level, the temperature corresponding to a chromaticity change in the green channel is the highest, the blue channel is the second, and the red channel is the smallest.This also indicates that the red channel is relatively responsive to temperature, and only a small temperature change is required to cause an increase in the output grey scale of the channel.

Effect of channel gain on temperature solving capability
Among the internal modulation parameters, gain modulation is a typical linear modulation method, which achieves brightness adjustment of the output image by scaling the detector output signal without difference.If G i is defined as the gain coefficient, the output signal of each image element of CCD pyrometer after gain modulation is where H ′ gain is the gain modulated output signal.The relationship between the detector output signal and the output grey level is shown in figure 9(a) for gain coefficients from 0.2 to 1. Figure 9(b) shows the variation of the grey level of the R channel of the detector image element for different gain conditions in the temperature interval of 1100-1500.
The temperature change corresponding to the same grey scale change ∆R is not the same under different gain modulations, so the channel gain can have an effect on the system temperature resolution.Under different gain conditions.The temperature corresponding to the maximum grey value of each curve is also different under different gain conditions, which further shows that the channel gain has an effect on the effective measurement range.Based on this, the effect of channel gain on the system will be investigated by the effect of channel gain on the performance parameters of effective temperature measurement range and temperature resolution.
The effective temperature measurement range for different channel gain cases and different global gain cases are solved, and the results are shown in figure 10.
Under two different gain modulations, the trend of the measurement range with the variation of emissivity still follows the trend under the standard condition (Gain = 1, Gamma = 1).No notable variation is observed in the lower limit of measurement under different gain modulations.The upper limit of measurement increases with the enhancement of gain modulation.This is because the smaller the gain, the higher the thermal radiation flux required for the camera to reach saturation, allowing it to measure higher temperatures.In channel gain modulation, there is a limit to the upper temperature limit, where the upper temperature limit no longer increases with increasing modulation depth when the gain is below 0.4.This phenomenon occurs due to the collective determination of the measurement range by the three channels in a three-channel system.When the gain falls below 0.4, modulation in the R channel ceases to have a decisive influence on setting the upper limit of the system.This is precisely why alterations in the gain of the G and B channels fail to induce any changes in the temperature measurement range.Therefore, the outcomes from these two channels were not presented.In figure 10(a), with modulation of only the R channel gain, the system achieves a maximum absolute measurement range of 1400 K.In figure 10(b), the system obtains the maximum absolute measurement range when the global gain parameter is set to 0.2, indicated by the white box.Under any emissivity condition, the system has the ability to calculate targets in the range of 1148-1486 K.In the study of the influence of channel gain on the temperature resolution situation, the relationship between the temperature resolution of each channel with the temperature level at different gains is shown in figure 11.The temperature resolution with temperature change relationship at different gains for all three channels shows a clear trend, which is the same as the no modulation case.As shown in figure 11(a), for the R channel, the temperature resolution is affected by the gain modulation in a nonlinear way, and the increase of one chromaticity with the corresponding temperature change is the highest in the low gain case, while the curve is in a relatively low position in the gain of 0.6.Figure 11(b) shows that the effect of the G channel on the temperature resolution is low and does not change significantly at different gains.Figure 11(c) shows that the effect of the B channel on the temperature re-solving ability is clearly linear, as the gain decreases, the temperature change corresponding to the chromaticity change shows a significant increase in the trend, and the temperature range moves to higher temperatures in line with the previous discussion of the effective temperature range.It is worth noting that the effect of three-channel gain modulation on temperature resolution is not uniform.This is naturally determined by the thermal radiation behaviour within the spectral range of each channel.Essentially, temperature resolution is determined by the changing rate of the channel thermal radiation signal intensity with temperature.The greater the rate of change, the larger the incremental increase in the channel signal corresponding to minor temperature changes, leading to a higher temperature resolution capability.Conversely, the lower the temperature resolution capability.

Effect of gamma correction on temperature solving ability
Gamma correction of the CCD system is a nonlinear modulation method that simulates the human eye's processing of radiation signals, the purpose of which is to raise the imaging contrast, so that small changes in radiation intensity in the low-light background are accentuated, and small changes in radiation intensity in the strong-light background are eliminated.This modulation method is a commonly used means of background light filtering in current CCD temperature measurement techniques.Radiation intensity is converted to a nonlinear grey scale signal by Gamma modulation, when there is a Gamma modulation process, the RGB value and the image received power from the linear relationship into a power function relationship, the exponent of this function is called the Gamma value is expressed as γ, and the modulation relationship is: where H ′ γ is the gamma-corrected output signal.The temperature resolution expression equation (15) in this modulation state, transforms to That is, the Gamma parameter will cause the change of the imaging coefficient P and the derivative term.Theoretically, the change of both of them will affect the effective measurement interval and the temperature resolution.The effect of the Gamma parameter on the modulation of the signal and the change of the grey level with the temperature in the different Gamma values are shown in figure 12.
For the R channel, under different Gamma parameters, the temperature intervals corresponding to the same ∆R grey scale interval are not the same, which indicates that the Gamma parameter has an effect on the temperature resolution of the system.At the same time, it can be clearly seen that the grey scale of the channel reaches saturation first when the Gamma is 1.5, that is, reaches the upper limit of temperature measurement under this condition, which indicates that the Gamma has an influence on the effective measurement range.
In the study of the effect of the Gamma parameter on the effective measurement range, in order to contrast with the simulation results of the standard case, the effective measurement range versus emissivity was simulated for different Gamma parameters, and the results are shown in figure 13.
At low gamma values, the effective measurement range is extended to quite a high level and that the upper limit of the effective measurement range decreases dramatically with  increasing gamma values.The lower limit of the temperature measurement cannot be changed by the gamma modulation.Combined with the gain modulation simulation results, the post-processing does not contribute to the lower limit of the temperature measurement.
In the study of the effect of Gamma parameter on temperature resolution, the variation of temperature resolution with temperature level under different Gamma parameter modulation are also simulated and the results are shown in figure 14.
According to the three-channel results, the overall trend of the temperature resolution ability changes due to the nonlinear modulation of the Gamma correction, and the influence of the Gamma parameter on the temperature resolution shows a fluctuating type compared to the linear modulation result of the gain.Under different Gamma values, the temperature resolution of the three channels is basically the same with the temperature change trend.That is, with the increase of Gamma value, the unit chromaticity change corresponds to the temperature change gradually decreases.At a Gamma value of 2.5, the temperature difference of the chromaticity change is lower than 1 K in the whole temperature range, which means that the temperature resolution of the temperature measurement system is significantly improved by the modulation of the Gamma parameter.
There are commonalities in the results of gamma modulation and gain modulation, namely the complementary relationship between temperature resolution and measurement range.A larger measurement range often corresponds to poorer temperature resolution, and vice versa.This is due to hardware limitations that restrict the overall computational capacity of the system.In theory, all colours are capable of obtaining a computational result.However, when the total number of hues that the hardware can recognize is determined, the total number of computations that the system can complete is also determined.In the case when the total number is determined, expanding the computational range through modulation means results in an increased computational interval, thus leading to a loss of temperature resolution.
The above results show that both gain modulation and gamma modulation can affect the temperature resolution and the effective temperature measurement range, and both means can effectively improve the temperature measurement performance.In contrast, the influence of gain modulation on the two indicators is relatively low, and the effect of gamma is more significant.At the same time, the effect of the two indicators is opposite under the same modulation, that is, the increase of the effective measurement range means the decrease of temperature resolution, and vice versa.Through the modulation with high gamma value, a better temperature resolution can be obtained, but the effective solution range of the response is also reduced seriously, and the minimum range can be compressed to 100 K.While the gain modulation is relatively mild, which not only improves the temperature resolution but also has little effect on the temperature solution range.Therefore, for the lower range of temperature variation and high accuracy of temperature measurement, it is more feasible to use gamma modulation to improve the performance of the system, while for the large range and low accuracy, it is more suitable for the use of gain modulation.

Conclusions
In this paper, the influence of CCD internal modulation parameters on the temperature calculation performance of matrix seeking radiation pyrometer is studied.To quantitatively characterize the temperature calculation ability, the effective measurement range and temperature resolution parameters of the system are defined, and the theoretical models for their evaluation are constructed.Combined with the modulation principle of CCD channel gain and Gamma correction, the effects of two internal modulation parameters on the effective measurement range and temperature resolution of the system are studied.In the blackbody calibration experiment, the simulation results of the effective temperature measurement range are verified.The results show that the modulation of the Gamma parameter significantly improves the effective resolution range of the system, but it also brings a larger temperature resolution and reduce the accuracy of the solution.The reduction of channel gain can slightly improve the effective temperature measurement range, and has a relatively stable temperature resolution.Based on the simulation results, the applicability of the two modulation methods is discussed.This study further improves the theory of matrix-searching CCD temperature measurement and provides theoretical support for the selection of internal modulation parameters in practical engineering measurements.

Figure 1 .
Figure 1.Matrix-seeking CCD temperature measurement technology implementation process.

Figure 2 .
Figure 2. Schematic diagram of the temperature resolution range.

Table 1 .Figure 5 .
Figure 5. Acquisition of RAW images for calibration experiments.

Figure 6 .
Figure 6.Spectral response curves and current-to-grey conversion factor calibration results.

Figure 7 .
Figure 7. Acquisition of images without modulation of the effective measuring range and at the position of the minimum range of the blackbody.

Figure 9 .
Figure 9.The modulation effect of channel gain coefficients on signals and their effect on radiation intensity.

Figure 10 .
Figure 10.Effect of channel gain and global gain on effective measurement range.

Figure 11 .
Figure 11.Results of three-channel temperature resolution change under channel gain modulation.

Figure 12 .
Figure 12.The modulation effect of the Gamma coefficient on the signal and its effect on the intensity of radiation.

Figure 13 .
Figure 13.Effect of gamma modulation on effective measurement range.

Figure 14 .
Figure 14.Results of temperature resolution change of each channel under gamma modulation.