关键词: 渐晕, 面阵CCD, 温度校正, 邻域灰度梯度, 稀疏性

Abstract:

Since the CCD-based pyrometer can obtain temperature field of objects, it has attracted more and more attention in academic studies recently. However, due to the existence of vignetting, there is serious photometric distortion in temperature field, and so the accuracy of temperature measurement is degraded badly. In order to improve the accuracy of temperature field measurement, a mathematical model for temperature distortion based on theories of radiation thermometry and geometrical optics is built in this paper, and the influence of optical system parameters on the accuracy of temperature field measurement is analyzed. Based on the sparsity of neighborhood gray gradient distribution (NGD), a method for the calibration of vignetting coefficient is also proposed in this paper. Compared with the calibration method using a integrating sphere, its maximum absolute error for vignetting estimation is only 0.052, and the experiment of temperature field correction for casting billets further validates the effectiveness of this calibration method.

Key words: vignetting, CCD-area, temperature correction, neighborhood gray gradient, sparsity