Relabel support for Darknet (YOLO) annotation files

README.md

@@ -213,6 +213,23 @@ $ cvdata_filter --format darknet \
     --boxes_per_class car:6000 truck:6000
 ```
 
+## Relabel annotations
+The module/script `cvdata/relabel.py` or the corresponding script entry point `cvdata_relabel` 
+can be used to filter the number of image/annotation files of a dataset. For example, 
+to relabel all PASCAL annotation files in a directory from "dog" to "beagle":
+```bash
+$ cvdata_relabel --labels_dir /data/cvdata/pascal \
+  --old dog --new beagle --format pascal
+```
+Since Darknet (YOLO) annotation files use index values that correspond to entries 
+in a class labels file we would use integer values for the `--old` and `--new` 
+arguments:
+```bash
+$ cvdata_relabel --labels_dir /data/cvdata/darknet \
+  --old 1 --new 4 --format darknet
+```
+This function currently supports `darknet`, `kitti`, and `pascal` formats.
+
 ## Remove duplicates
 The module/script `cvdata/duplicates.py`  or the corresponding script entry point 
 `cvdata_duplicates` can be used to remove duplicate images from a directory. This 

src/cvdata/relabel.py

@@ -20,6 +20,35 @@
 _logger = logging.getLogger(__name__)
 
 
+# ------------------------------------------------------------------------------
+def relabel_darknet(
+        file_path: str,
+        old_index: int,
+        new_index: int,
+):
+    """
+    Replaces the label index values of a Darknet (YOLO) annotation file.
+
+    :param file_path: path of the Darknet (YOLO) file
+    :param old_index: label index value which if found will be replaced by the
+        new label index
+    :param new_index: new label index value
+    """
+
+    # arguments validation
+    if (old_index < 0) or (new_index < 0):
+        raise ValueError("Invalid label index argument, must be equal or greater than zero")
+
+    # replace the label indices in-place
+    with fileinput.FileInput(file_path, inplace=True) as file_input:
+        for line in file_input:
+            line = line.rstrip("\r\n")
+            parts = line.split()
+            if (len(parts) > 0) and (parts[0] == str(old_index)):
+                parts[0] = str(new_index)
+            print(" ".join(parts))
+
+
 # ------------------------------------------------------------------------------
 def relabel_kitti(
         file_path: str,
@@ -29,7 +58,7 @@ def relabel_kitti(
     """
     Replaces the label values of a KITTI annotation file.
 
-    :param file_path: path of the KITTI file to have labels replaced
+    :param file_path: path of the KITTI file
     :param old_label: label value which if found will be replaced by the new label
     :param new_label: new label value
     """
@@ -53,7 +82,7 @@ def relabel_pascal(
     """
     Replaces the label values of a PASCAL VOC annotation file.
 
-    :param file_path: path of the PASCAL VOC file to have labels replaced
+    :param file_path: path of the PASCAL VOC file
     :param old_label: label value which if found will be replaced by the new label
     :param new_label: new label value
     """
@@ -92,6 +121,21 @@ def _validate_args(
         raise ValueError(f"File path argument {file_path} is not a valid file path")
 
 
+# ------------------------------------------------------------------------------
+def _relabel_darknet(arguments: Dict):
+    """
+    Unpacks a dictionary of arguments and calls the function for replacing the
+    labels of a Darknet (YOLO) annotation file.
+
+    :param arguments: dictionary of function arguments, should include:
+         "file_path": path of the Darknet (YOLO) file to have labels renamed
+         "old": label index which if found will be renamed
+         "new": new label index value
+    """
+
+    relabel_darknet(arguments["file_path"], arguments["old"], arguments["new"])
+
+
 # ------------------------------------------------------------------------------
 def _relabel_kitti(arguments: Dict):
     """
@@ -161,6 +205,9 @@ def main():
     elif args["format"] == "pascal":
         file_ext = ".xml"
         relabel_function = _relabel_pascal
+    elif args["format"] == "darknet":
+        file_ext = ".txt"
+        relabel_function = _relabel_darknet
     else:
         raise ValueError("Only KITTI and PASCAL annotation files are supported")
 

tests/test_relabel.py

@@ -11,6 +11,57 @@
 logging.disable(logging.CRITICAL)
 
 
+# ------------------------------------------------------------------------------
+@pytest.mark.usefixtures(
+    "data_dir",
+)
+def test_relabel_darknet(
+        data_dir,
+):
+    """
+    Test for the cvdata.relabel.relabel_darknet() function
+
+    :param data_dir: temporary directory into which test files will be loaded
+    """
+    darknet_file_name = "darknet_1.txt"
+    darknet_file_path = str(data_dir.join(darknet_file_name))
+
+    # confirm that a relabeling won't occur if the old value is not present
+    relabel.relabel_darknet(darknet_file_path, 58, 59)
+    expected_darknet_file_name = "expected_darknet_1.txt"
+    expected_darknet_file_path = str(data_dir.join(expected_darknet_file_name))
+    assert text_files_equal(
+        darknet_file_path,
+        expected_darknet_file_path,
+    )
+
+    # confirm that relabeling occurred as expected
+    relabel.relabel_darknet(darknet_file_path, 3, 2)
+    expected_darknet_file_name = "expected_darknet_2.txt"
+    expected_darknet_file_path = str(data_dir.join(expected_darknet_file_name))
+    assert text_files_equal(
+        darknet_file_path,
+        expected_darknet_file_path,
+    )
+
+    # confirm that various invalid arguments raise an error
+    with pytest.raises(TypeError):
+        relabel.relabel_darknet(darknet_file_path, None, 0)
+        relabel.relabel_darknet(darknet_file_path, 0, None)
+        relabel.relabel_darknet(1, 0, 1)
+        relabel.relabel_darknet(None, 1, 0)
+        relabel.relabel_darknet("/not/present", 0, 1)
+        relabel.relabel_darknet(1.0, "strings won't work", 0)
+        relabel.relabel_darknet(darknet_file_path, 1, "strings won't work")
+        relabel.relabel_darknet(darknet_file_path, 1.0, 0)
+        relabel.relabel_darknet(darknet_file_path, 2, 1.0)
+        relabel.relabel_darknet(darknet_file_path, True, 0)
+        relabel.relabel_darknet(darknet_file_path, 1, True)
+    with pytest.raises(ValueError):
+        relabel.relabel_darknet(darknet_file_path, -5, 1)
+        relabel.relabel_darknet(darknet_file_path, 1, -4)
+
+
 # ------------------------------------------------------------------------------
 @pytest.mark.usefixtures(
     "data_dir",
@@ -44,7 +95,7 @@ def test_relabel_kitti(
         expected_kitti_file_path,
     )
 
-    # confirm that invalid argument types raise an error
+    # confirm that various invalid arguments raise an error
     with pytest.raises(ValueError):
         relabel.relabel_kitti(None, "don't care", "don't care")
         relabel.relabel_kitti(kitti_file_path, None, "don't care")
@@ -95,7 +146,7 @@ def test_relabel_pascal(
         etree_after_relabel.getroot(),
     )
 
-    # confirm that invalid argument types raise an error
+    # confirm that various invalid arguments raise an error
     with pytest.raises(ValueError):
         relabel.relabel_pascal(None, "don't care", "don't care")
         relabel.relabel_pascal(pascal_file_path, None, "don't care")

tests/test_relabel/darknet_1.txt

@@ -0,0 +1 @@
+3 0.4995 0.2012 0.3994 0.0456

tests/test_relabel/expected_darknet_1.txt

@@ -0,0 +1 @@
+3 0.4995 0.2012 0.3994 0.0456

tests/test_relabel/expected_darknet_2.txt

@@ -0,0 +1 @@
+2 0.4995 0.2012 0.3994 0.0456