There are 2 alternatives to save the (x,y,score) body part locations. The write_keypoint flag uses the OpenCV cv::FileStorage default formats (JSON, XML and YML). However, the JSON format is only available after OpenCV 3.0. Hence, write_keypoint_json saves the people pose data using a custom JSON writer. For the latter, each JSON file has a people array of objects, where each object has an array pose_keypoints containing the body part locations and detection confidence formatted as x1,y1,c1,x2,y2,c2,.... The coordinates x and y can be normalized to the range [0,1], [-1,1], [0, source size], [0, output size], etc., depending on the flag keypoint_scale. In addition, c is the confidence in the range [0,1].
{
"version":0.1,
"people":[
{"pose_keypoints":[1114.15,160.396,0.846207,...]},
{"pose_keypoints":[...]},
]
}
The body part order of the COCO (18 body parts) and MPI (15 body parts) keypoints is described in POSE_BODY_PART_MAPPING in include/openpose/pose/poseParameters.hpp. E.g., for COCO:
POSE_COCO_BODY_PARTS {
{0, "Nose"},
{1, "Neck"},
{2, "RShoulder"},
{3, "RElbow"},
{4, "RWrist"},
{5, "LShoulder"},
{6, "LElbow"},
{7, "LWrist"},
{8, "RHip"},
{9, "RKnee"},
{10, "RAnkle"},
{11, "LHip"},
{12, "LKnee"},
{13, "LAnkle"},
{14, "REye"},
{15, "LEye"},
{16, "REar"},
{17, "LEar"},
{18, "Bkg"},
}
For the heat maps storing format, instead of individually saving each of the 67 heatmaps (18 body parts + background + 2 x 19 PAFs) individually, the library concatenates them into a huge (width x #heat maps) x (height) matrix, i.e. it concats the heat maps by columns. E.g., columns [0, individual heat map width] contains the first heat map, columns [individual heat map width + 1, 2 * individual heat map width] contains the second heat map, etc. Note that some image viewers are not able to display the resulting images due to the size. However, Chrome and Firefox are able to properly open them.
The saving order is body parts + background + PAFs. Any of them can be disabled with program flags. If background is disabled, then the final image will be body parts + PAFs. The body parts and background follow the order of POSE_COCO_BODY_PARTS or POSE_MPI_BODY_PARTS, while the PAFs follow the order specified on POSE_BODY_PART_PAIRS in poseParameters.hpp. E.g., for COCO:
POSE_COCO_PAIRS {1,2, 1,5, 2,3, 3,4, 5,6, 6,7, 1,8, 8,9, 9,10, 1,11, 11,12, 12,13, 1,0, 0,14, 14,16, 0,15, 15,17, 2,16, 5,17};
Where each index is the key value corresponding to each body part in POSE_COCO_BODY_PARTS, e.g., 0 for "Neck", 1 for "RShoulder", etc.
The output format is analogous for hand (hand_left_keypoints and hand_right_keypoints) and face (face_keypoints) JSON files.
We use standard formats (JSON, XML, PNG, JPG, ...) to save our results, so there will be lots of frameworks to read them later, but you might also directly use our functions in include/openpose/filestream.hpp. In particular, loadData (for JSON, XML and YML files) and loadImage (for image formats such as PNG or JPG) to load the data into cv::Mat format.
