开集测试。用前20个人的前5张图像作为训练，剩下的图像作为测试。也就是说总共有100张图片和300张测试图像。注意，这时候，后20个人并没有出现在训练集中，需要给出一个合理的拒识方式来判断某张图像是否在训练的20个人中。请设计一个合理的拒识方式（最简单的方式是对测试图像到训练图像的最近距离设定一个阈值），并给出ROC曲线（在a问的前提下选择一个合理的K来做，不一定要考察K的影响）。-Open set tests. 20 individuals with the former image as the first five training image as the rest of the test. That is a total of 100 images and 300 test images. Note that this time, after 20 people did not appear in the training set, you need to give a reasonable way to determine whether a rejection images are in training for 20 individuals. Please design a rational rejection mode (the easiest way to test image is the closest distance to the training image set a threshold), and gives the ROC curve (on the premise of a question choose a reasonable K do not Be sure to examine the impact of K).