FileStorage for OpenCV Python API

Question

I\'m currently using FileStorage class for storing matrices XML/YAML using OpenCV C++ API.

However, I have to writ

Answer 1

To improve on the previous answer by @Roy_Shilkrot I added support for numpy vectors as well as matrices:

# A yaml constructor is for loading from a yaml node.
# This is taken from @misha 's answer: http://stackoverflow.com/a/15942429
def opencv_matrix_constructor(loader, node):
    mapping = loader.construct_mapping(node, deep=True)
    mat = np.array(mapping["data"])
    if mapping["cols"] > 1:
        mat.resize(mapping["rows"], mapping["cols"])
    else:
        mat.resize(mapping["rows"], )
    return mat
yaml.add_constructor(u"tag:yaml.org,2002:opencv-matrix", opencv_matrix_constructor)


# A yaml representer is for dumping structs into a yaml node.
# So for an opencv_matrix type (to be compatible with c++'s FileStorage) we save the rows, cols, type and flattened-data
def opencv_matrix_representer(dumper, mat):
    if mat.ndim > 1:
        mapping = {'rows': mat.shape[0], 'cols': mat.shape[1], 'dt': 'd', 'data': mat.reshape(-1).tolist()}
    else:
        mapping = {'rows': mat.shape[0], 'cols': 1, 'dt': 'd', 'data': mat.tolist()}
    return dumper.represent_mapping(u"tag:yaml.org,2002:opencv-matrix", mapping)
yaml.add_representer(np.ndarray, opencv_matrix_representer)

Example:

with open('output.yaml', 'w') as f:
    yaml.dump({"a matrix": np.zeros((10,10)), "another_one": np.zeros((5,))}, f)

with open('output.yaml', 'r') as f:
    print yaml.load(f)

Output:

a matrix: !!opencv-matrix
  cols: 10
  data: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
    0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
    0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
    0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
    0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
    0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
    0.0, 0.0, 0.0, 0.0, 0.0]
  dt: d
  rows: 10
another_one: !!opencv-matrix
  cols: 1
  data: [0.0, 0.0, 0.0, 0.0, 0.0]
  dt: d
  rows: 5

Though I could not control the order of rows, cols, dt, data.