[Feature]add CLAHE transform (open-mmlab#229)

* add CLAHE transform

* fix syntax error

* fix syntax error

* restore

* add a test

* modify cv2 to mmcv

* add docstring

* modify

* restore

* fix mmcv.clahe error

* change mmcv version to 1.3.0

* fix bugs

* add all data transformers to __init__

* fix __init__

* fix test_transform

Author: yamengxi

mmseg/datasets/pipelines/__init__.py

@@ -3,14 +3,14 @@
                         Transpose, to_tensor)
 from .loading import LoadAnnotations, LoadImageFromFile
 from .test_time_aug import MultiScaleFlipAug
-from .transforms import (Normalize, Pad, PhotoMetricDistortion, RandomCrop,
-                         RandomFlip, RandomRotate, Rerange, Resize, RGB2Gray,
-                         SegRescale)
+from .transforms import (CLAHE, AdjustGamma, Normalize, Pad,
+                         PhotoMetricDistortion, RandomCrop, RandomFlip,
+                         RandomRotate, Rerange, Resize, RGB2Gray, SegRescale)
 
 __all__ = [
     'Compose', 'to_tensor', 'ToTensor', 'ImageToTensor', 'ToDataContainer',
     'Transpose', 'Collect', 'LoadAnnotations', 'LoadImageFromFile',
     'MultiScaleFlipAug', 'Resize', 'RandomFlip', 'Pad', 'RandomCrop',
     'Normalize', 'SegRescale', 'PhotoMetricDistortion', 'RandomRotate',
-    'Rerange', 'RGB2Gray'
+    'AdjustGamma', 'CLAHE', 'Rerange', 'RGB2Gray'
 ]

mmseg/datasets/pipelines/transforms.py

@@ -1,6 +1,6 @@
 import mmcv
 import numpy as np
-from mmcv.utils import deprecated_api_warning
+from mmcv.utils import deprecated_api_warning, is_tuple_of
 from numpy import random
 
 from ..builder import PIPELINES
@@ -415,7 +415,6 @@ def __call__(self, results):
 
         Args:
             results (dict): Result dict from loading pipeline.
-
         Returns:
             dict: Reranged results.
         """
@@ -439,6 +438,51 @@ def __repr__(self):
         return repr_str
 
 
+@PIPELINES.register_module()
+class CLAHE(object):
+    """Use CLAHE method to process the image.
+
+    See `ZUIDERVELD,K. Contrast Limited Adaptive Histogram Equalization[J].
+    Graphics Gems, 1994:474-485.` for more information.
+
+    Args:
+        clip_limit (float): Threshold for contrast limiting. Default: 40.0.
+        tile_grid_size (tuple[int]): Size of grid for histogram equalization.
+            Input image will be divided into equally sized rectangular tiles.
+            It defines the number of tiles in row and column. Default: (8, 8).
+    """
+
+    def __init__(self, clip_limit=40.0, tile_grid_size=(8, 8)):
+        assert isinstance(clip_limit, (float, int))
+        self.clip_limit = clip_limit
+        assert is_tuple_of(tile_grid_size, int)
+        assert len(tile_grid_size) == 2
+        self.tile_grid_size = tile_grid_size
+
+    def __call__(self, results):
+        """Call function to Use CLAHE method process images.
+
+        Args:
+            results (dict): Result dict from loading pipeline.
+
+        Returns:
+            dict: Processed results.
+        """
+
+        for i in range(results['img'].shape[2]):
+            results['img'][:, :, i] = mmcv.clahe(
+                np.array(results['img'][:, :, i], dtype=np.uint8),
+                self.clip_limit, self.tile_grid_size)
+
+        return results
+
+    def __repr__(self):
+        repr_str = self.__class__.__name__
+        repr_str += f'(clip_limit={self.clip_limit}, '\
+                    f'tile_grid_size={self.tile_grid_size})'
+        return repr_str
+
+
 @PIPELINES.register_module()
 class RandomCrop(object):
     """Random crop the image & seg.

tests/test_data/test_transform.py

@@ -409,6 +409,46 @@ def test_rerange():
     assert str(transform) == f'Rerange(min_value={0}, max_value={255})'
 
 
+def test_CLAHE():
+    # test assertion if clip_limit is None
+    with pytest.raises(AssertionError):
+        transform = dict(type='CLAHE', clip_limit=None)
+        build_from_cfg(transform, PIPELINES)
+
+    # test assertion if tile_grid_size is illegal
+    with pytest.raises(AssertionError):
+        transform = dict(type='CLAHE', tile_grid_size=(8.0, 8.0))
+        build_from_cfg(transform, PIPELINES)
+
+    # test assertion if tile_grid_size is illegal
+    with pytest.raises(AssertionError):
+        transform = dict(type='CLAHE', tile_grid_size=(9, 9, 9))
+        build_from_cfg(transform, PIPELINES)
+
+    transform = dict(type='CLAHE', clip_limit=2)
+    transform = build_from_cfg(transform, PIPELINES)
+    results = dict()
+    img = mmcv.imread(
+        osp.join(osp.dirname(__file__), '../data/color.jpg'), 'color')
+    original_img = copy.deepcopy(img)
+    results['img'] = img
+    results['img_shape'] = img.shape
+    results['ori_shape'] = img.shape
+    # Set initial values for default meta_keys
+    results['pad_shape'] = img.shape
+    results['scale_factor'] = 1.0
+
+    results = transform(results)
+
+    converted_img = np.empty(original_img.shape)
+    for i in range(original_img.shape[2]):
+        converted_img[:, :, i] = mmcv.clahe(
+            np.array(original_img[:, :, i], dtype=np.uint8), 2, (8, 8))
+
+    assert np.allclose(results['img'], converted_img)
+    assert str(transform) == f'CLAHE(clip_limit={2}, tile_grid_size={(8, 8)})'
+
+
 def test_seg_rescale():
     results = dict()
     seg = np.array(