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$$PA$$

PA（pixel accuracy）:像素精确度

这是最简单的指标，用来计算被正确分类的像素个数和总像素数之间的比例

实例

gt_image = np.array([    [0,1,2,4],    [0,0,0,0],    [0,0,0,0],    [0,0,0,0]])pre_image = np.array([    [0,1,2,4],    [0,1,0,0],    [0,1,0,0],    [0,0,1,0]])def generate_matrix(gt_image, pre_image,num_class=8):        mask = (gt_image >= 0) & (gt_image < num_class)#ground truth中所有正确(值在[0, classe_num])的像素label的mask                label = num_class * gt_image[mask].astype('int') + pre_image[mask]         # np.bincount计算了从0到n**2-1这n**2个数中每个数出现的次数，返回值形状(n, n)        count = np.bincount(label, minlength=num_class**2)        confusion_matrix = count.reshape(num_class, num_class)#21 * 21(for pascal)        return confusion_matrix        matrix =generate_matrix(gt_image,pre_image)matrix

def Pixel_Accuracy(confusion_matrix):    Acc = np.diag(confusion_matrix).sum() / confusion_matrix.sum()    return AccPixel_Accuracy(matrix)