feat(optical_flow): add stitching optical flow example

Author: AmitMY

assets/example/optical_flow.pdf

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+from pathlib import Path
+
+from matplotlib import pyplot as plt
+from pose_format import Pose
+from pose_format.numpy.representation.distance import DistanceRepresentation
+from pose_format.utils.optical_flow import OpticalFlowCalculator
+from spoken_to_signed.gloss_to_pose.concatenate import concatenate_poses
+
+plt.rcParams["font.family"] = "Times New Roman"
+plt.rcParams["font.size"] = 13
+
+example_dir = Path(__file__).parent.parent / "assets" / "example"
+
+fig = plt.figure(figsize=(8, 2))
+
+for directory in [example_dir / "original", example_dir / "anonymized"]:
+    poses = []
+    for word in ["kleine", "kinder", "essen", "pizza"]:
+        with open(directory / f"{word}.pose", 'rb') as pose_file:
+            poses.append(Pose.read(pose_file.read()))
+
+    concatenated = concatenate_poses(poses).get_components(["FACE_LANDMARKS"])
+    calculator = OpticalFlowCalculator(fps=30, distance=DistanceRepresentation())
+    flow = calculator(concatenated.body.data).sum(-1).squeeze()
+
+    # Plot the flow on the main plot, (173, 1)
+    plt.plot(flow, label=directory.name.capitalize())
+
+plt.yticks([])
+plt.legend(loc='upper left')
+plt.ylabel("Optical Flow")
+plt.tight_layout()
+fig.show()
+fig.savefig(example_dir / "optical_flow.pdf")