Python-OpenCV 中头部姿势的仰角如何工作？

Question

我正在尝试估计主要遵循本指南的单张图像的头部姿势： https://towardsdatascience.com/real-time-head-pose-estimation-in-python-e52db1bc606a

面部检测工作正常 - 如果我绘制图像和检测到的地标，它们会很好地对齐。

我正在根据图像估计相机矩阵，并假设没有镜头失真：

    size = image.shape
    focal_length = size[1]
    center = (size[1]/2, size[0]/2)
    camera_matrix = np.array([[focal_length, 0, center[0]],
                             [0, focal_length, center[1]],
                             [0, 0, 1]], dtype="double")
    dist_coeffs = np.zeros((4, 1))  # Assuming no lens distortion

我正在尝试通过使用 solvePNP 将图像中的点与 3D 模型中的点进行匹配来获得头部姿势：

    # 3D-model points to which the points extracted from an image are matched:
    model_points = np.array([
                                (0.0, 0.0, 0.0),             # Nose tip
                                (0.0, -330.0, -65.0),        # Chin
                                (-225.0, 170.0, -135.0),     # Left eye corner
                                (225.0, 170.0, -135.0),      # Right eye corner
                                (-150.0, -150.0, -125.0),    # Left Mouth corner
                                (150.0, -150.0, -125.0)      # Right mouth corner
                            ])
    
    image_points = np.array([
                            shape[30],     # Nose tip
                            shape[8],     # Chin
                            shape[36],     # Left eye left corner
                            shape[45],     # Right eye right corne
                            shape[48],     # Left Mouth corner
                            shape[54]      # Right mouth corner
                            ], dtype="double")
    
    success, rotation_vec, translation_vec) = \
            cv2.solvePnP(model_points, image_points, camera_matrix, dist_coeffs)

最后，我得到了旋转的欧拉角：

rotation_mat, _ = cv2.Rodrigues(rotation_vec)
pose_mat = cv2.hconcat((rotation_mat, translation_vec))
_, _, _, _, _, _, angles = cv2.decomposeProjectionMatrix(pose_mat)

现在方位角是我所期望的 - 如果我向左看，它是负的，中间是零，向右看是正的。

但是海拔很奇怪 - 如果我在中间看它有一个恒定值但符号是随机的 - 从图像到图像变化（值大约为 170）。

当我向上看时，符号是正的，越往上看值越小，往下看符号是负的，越往下看数值越低

有人可以向我解释一下这个输出吗？

Answer 1

好的，看来我找到了解决方案 - 模型点（我在几个关于该主题的博客中找到的）似乎是错误的。该代码似乎适用于这种模型和图像点的组合（不知道为什么要反复试验）：

model_points = np.float32([[6.825897, 6.760612, 4.402142],
                         [1.330353, 7.122144, 6.903745],
                         [-1.330353, 7.122144, 6.903745],
                         [-6.825897, 6.760612, 4.402142],
                         [5.311432, 5.485328, 3.987654],
                         [1.789930, 5.393625, 4.413414],
                         [-1.789930, 5.393625, 4.413414],
                         [-5.311432, 5.485328, 3.987654],
                         [2.005628, 1.409845, 6.165652],
                         [-2.005628, 1.409845, 6.165652],
                         [2.774015, -2.080775, 5.048531],
                         [-2.774015, -2.080775, 5.048531],
                         [0.000000, -3.116408, 6.097667],
                         [0.000000, -7.415691, 4.070434]])

image_points = np.float32([shape[17], shape[21], shape[22], shape[26],
                           shape[36], shape[39], shape[42], shape[45],
                           shape[31], shape[35], shape[48], shape[54],
                           shape[57], shape[8]])

Python-OpenCV 中头部姿势的仰角如何工作？

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