二维光纤光谱图是天文望远镜系统中的光谱仪的观测结果, 由此又经过一系列的后续处理, 才能生成普遍意义上的一维光谱。 由于光谱仪和CCD相机的光学畸变, 使得二维光纤光谱图像普遍出现了弯曲现象, 尤其是在光纤两端表现得尤为明显, 这个问题一直以来没有很好的解决办法, 也没有在任何参考文献中看到相关工作。 这种弯曲给后续的抽谱工作造成困扰, 处理不好会很大程度上影响波长定标, 从而影响一维谱的准确性。 给出的一种法向映射法可以对这种二维光纤光谱图的弯曲进行有效的校正。 该法把二光纤光谱图中的每一条光纤光谱进行单独处理。 首先做预处理抽取每根光纤中心线, 然后把该中心线当作光滑曲线求取每个点的法线方向, 以整条中心线的某个点(一般是最凸点)为基点作理想竖直线, 光纤中心线所有点沿自身法线方向投影到这条竖直线上, 从而实现了光纤中心线本身的校直。 因光纤宽度在二维光纤光谱图中一般是7个像素, 因此将光纤中心线向左向右各依次平移3个像素, 分别实现上述流程, 即可得到整条光纤光谱的校直结果。 该法实施过程中有两个问题需要注意: 一个是坐标点的均匀化问题, 一个是像素灰度值的精度保持问题。 坐标点的均匀化问题是由于在该法中使用了法向映射, 从而造成形成后的校直线的点的疏密程度不均匀, 这对后续处理不利。 解决办法是在实际操作中采用三次样条插值的方法进行直线上点的密度均匀化, 保证获得一系列的整数点坐标, 以利于后续的处理。 而像素灰度值的精度保持问题, 在插值计算过程中始终保持像素灰度值的64位高精度数, 最终也得到同样精度的结果, 避免造成像素值损失。 该法实施的最后, 还需要进行头尾一致性的截取, 把延伸出图像高度范围的像素去掉, 仅保留图像范围内的像素点。 如果没有这个过程, 由于光纤本身是有宽度的, 映射出来的直线长短不一, 从而给后续处理造成困难。 实验完整处理了整幅的二维光纤光谱图, 用曲线拟合的方法较好地解决了光纤中心线提取过程中的个别地方的亮度偏差问题, 用法向映射法得到了校直后的二维光谱, 并做了后续的抽谱对比。 在一维谱的抽谱对比中可以看到, 校正前后的谱线差值在有弯曲现象存在的光谱两端变化较为明显。 这个实验结果证明了该方法对光谱的弯曲情况可以完全改善——在两端的变化较大, 在中间的变化很小, 这完全符合观测的基本认知。 不仅如此, 由于像素点的错位和像素值的插值计算, 也会造成流量值叠加的效果发生显著变化。 因此, 通过观察抽谱后的谱线在校正前后的移动情况, 验证了对于特征谱线的波长位置的精确获取具有重要影响。 本文创造性地设计的二维光纤光谱的自动弯曲校正的方法。

The two-dimensional optical fiber spectral images are the observation results of a spectrometer in an astronomical telescope system, and they are followed by a series of post-processing steps to produce the common one-dimensional spectra. Owing to the optical distortion caused by the spectrometer and CCD, obvious bending can be seen from the two-dimensional optical fiber spectral images, especially at both ends of the fibers. So far for this bending problem, there has been no good solution, nor in any reference to see any relevant work. And this kind of bending can cause great troubles to the subsequent spectral lines extraction and other works, which will affect the wavelength calibration to a great extent, as well as the accuracy of the one-dimensional spectrum. In this paper, a normal mapping method has been used to correct the bending phenomenon of the two-dimensional optical fiber spectral images. The method deals with each optical fiber spectrum in the images separately, and corrects the spectrum into vertical straight. The first step is preprocessing, which is to extract each fiber’s centerline. Then the centerline is taken as a smooth curve to obtain the normal direction at each point. The ideal vertical line is based on a point (usually the most salient point) of the whole centerline, and all the points of the optical fiber centerline are projected onto the ideal vertical line along the relevant normal directions, so as to realize the alignment of the optical fiber centerline points, which is the second step. The third step is to handle the whole fiber spectrum. Because the fiber’s width is 7 pixels in the two-dimensional optical fiber spectral image, the fiber’s centerline moves 3 pixels one by one to the left and right, respectively, realizing the above 2 steps and obtaining the straightening result of the whole fiber spectrum. In the whole process, there are two key problems to be noticed: one is the homogenization problem of the coordinate points, and the other is the accuracy maintenance problem of pixels’ values. The uniformity of the sitting punctuation is due to the use of the normal mapping in this method, which results in uneven density of the points after the formation of the alignment, which is unfavorable to the subsequent processing. The solution is to use the cubic spline interpolation method to achieve the density uniformity of the point on the line, to ensure a series of integer coordinates to facilitate the subsequent processing. To maintain the accuracy of pixels’ gray values, the 64-bit high precision number of pixels’ gray values is always kept in the process of the interpolation calculation. At the end of the implementation of the method, it is necessary to intercept both of the two ends of the spectrum to keep the end-to-end consistency, removing the pixels extending out of the height range of the image, and retaining only the pixel points in the image range. If without this process, the mapped vertical lines are different in length, so that causing difficulties in subsequent processing. This paper deals with the two-dimensional optical fiber spectral images, solves the problem of brightness deviation in the process of extracting optical fiber centerlines by using curve fitting method, obtains the corrected two-dimensional spectra after straightening, and makes a follow-up comparison between the one-dimensional spectra. In the comparison, it can be seen that the spectral line differences before and after correction are more obvious than those of the spectra at both ends of the curve. The experimental results show that this method can completely improve the bending of the spectra. It can be seen that the changes at both ends are large and the changes in the middle are very small, which accords with the basic understanding of the observation. Furthermore, due to the dislocation of pixels and the interpolation of pixels’ values, the effect of the superposition of the pixels’ values changes significantly. Therefore, by observing the movement of the spectral lines after the calibration, it is proved that this method has an important influence on the precise acquisition of the wavelength positions of the characteristic spectral lines. This paper creatively designs the method of automatic bending correction of two-dimensional optical fiber spectra and verifies the validity of the method by experiments.