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- 实验方案
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Nonuniformity Correction for Variable-Integration-Time Infrared Camera
摘要： A two-dimensional calibration technique is proposed to correct the spatial nonuniformity in infrared imaging systems adapting to different integration time and time-varying offset with one-time calibration. Differing from traditional calibration-based nonuniformity correction, this method calibrates nonuniformity with two-dimensional information from two integration time besides different irradiance, which conquers drawbacks of traditional calibration-based correction. First, it eliminates the dependence on integration time in calibration process and dramatically suppresses fixed pattern noise by a large attenuation factor. In addition, time-varying offset is real-time canceled by the subtraction of images integrated with normal and short time. Correction error of two-point correction and the proposed method are analyzed in detail. In experiments with cooled infrared camera, the proposed method provides enhanced uniformity even for seven-time variation of integration time using same correction coefficients. Both quantitative and qualitative comparisons to two-point correction demonstrate its superiority. The one-time calibration and shutterless correction scheme avoids interruption of the normal operation for real scene, extending the application range in practical engineering for infrared imaging systems with low complexity of computation and hardware.
关键词： Infrared imaging,nonuniformity correction
更新于2025-09-23 15:22:29
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Ultraviolet exposure of Gafchromic XR-RV3 and XR-SP2 films
摘要： Gafchromic film has been used for X-ray dose measurement in diagnostic examinations. Their use has been initiated for three-dimensional X-ray dose measurement by using the high-resolution characteristics of Gafchromic films in computed tomography. However, it is necessary to solve the problem of nonuniform thickness in the active layers of Gafchromic films. A double exposure technique using X-rays is performed in therapeutic radiology; it is difficult to use in a diagnostic examination because of the heel effect. Therefore, it is suggested that ultraviolet (UV) rays be substituted for X-rays. However, the appropriate UV wavelength is unknown. In this study, we aimed to determine which UV wavelengths are effective to expose Gafchromic XR-RV3 and XR-SP2. UV lamps with peak wavelengths of 245 nm, 310 nm, and 365 nm were used. The three UV wavelengths were used to irradiate Gafchromic XR-RV3 and XR-SP2 films for 60 min, and irradiation was repeated every 60 min for 600 min thereafter. Films were scanned after each irradiation period on a flatbed scanner. The images were split into their red-green-blue components, and red images were stored using ImageJ version 1.44o image analysis software. Regions of interest (ROI), 0.5 inches in diameter, were placed at the centers of the subtracted Gafchromic film images, and graphs of UV irradiation duration and mean pixel values were plotted. There were reactions to UV-A on both Gafchromic XR-RV3 and XR-SP2; those to UV-B were moderate. However, UV-C demonstrated few reactions with Gafchromic XR-RV3 and XR-SP2. From these results, irradiation with UV-A may be able to correct nonuniformity errors. Uniform UV-A irradiation of Gafchromic films with large areas is possible, and UV rays can be used as a substitute for X-rays in the double exposure technique.
关键词： Gafchromic film,nonuniformity,high-resolution measurement,ultraviolet rays,computed tomography
更新于2025-09-23 15:22:29
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Total Variation Based Neural Network Regression for Nonuniformity Correction of Infrared Images
摘要： Many existing scene-adaptive nonuniformity correction (NUC) methods suffer from slow convergence rate together with ghosting effects. In this paper, an improved NUC algorithm based on total variation penalized neural network regression is presented. Our work mainly focuses on solving the overfitting problem in least mean square (LMS) regression of traditional neural network NUC methods, which is realized by employing a total variation penalty in the cost function and redesigning the processing architecture. Moreover, an adaptive gated learning rate is presented to further reduce the ghosting artifacts and guarantee fast convergence. The performance of the proposed algorithm is comprehensively investigated with artificially corrupted test sequences and real infrared image sequences, respectively. Experimental results show that the proposed algorithm can effectively accelerate the convergence speed, suppress ghosting artifacts, and promote correction precision.
关键词： total variation,neural network,infrared imaging,nonuniformity correction
更新于2025-09-04 15:30:14