[Feature] Add min_size arg in Resize to keep the shape after resize bigger than slide window

mmseg/datasets/pipelines/transforms.py

@@ -99,13 +99,18 @@ class Resize(object):
             Default: None
         keep_ratio (bool): Whether to keep the aspect ratio when resizing the
             image. Default: True
+        crop_size (int, optional): The minimum size for input and the shape
+            of the image and seg map will not be less than ``crop_szie``.
+            It always be used in ``SETR`` algorithm to keep the shape.
+            Default: None
     """
 
     def __init__(self,
                  img_scale=None,
                  multiscale_mode='range',
                  ratio_range=None,
-                 keep_ratio=True):
+                 keep_ratio=True,
+                 crop_size=None):
         if img_scale is None:
             self.img_scale = None
         else:
@@ -126,6 +131,7 @@ def __init__(self,
         self.multiscale_mode = multiscale_mode
         self.ratio_range = ratio_range
         self.keep_ratio = keep_ratio
+        self.crop_size = crop_size
 
     @staticmethod
     def random_select(img_scales):
@@ -240,6 +246,20 @@ def _random_scale(self, results):
     def _resize_img(self, results):
         """Resize images with ``results['scale']``."""
         if self.keep_ratio:
+            if self.crop_size is not None:
+                # keep the shape is not less than crop_size
+                if min(results['scale']) < self.crop_size:
+                    new_short = self.crop_size
+                else:
+                    new_short = min(results['scale'])
+
+                h, w = results['img'].shape[:2]
+                if h > w:
+                    new_h, new_w = new_short * h / w, new_short
+                else:
+                    new_h, new_w = new_short, new_short * w / h
+                results['scale'] = (new_h, new_w)
+
             img, scale_factor = mmcv.imrescale(
                 results['img'], results['scale'], return_scale=True)
             # the w_scale and h_scale has minor difference

tests/test_data/test_transform.py

@@ -123,6 +123,12 @@ def test_resize():
     assert int(288 * 0.5) <= resized_results['img_shape'][0] <= 288 * 2.0
     assert int(512 * 0.5) <= resized_results['img_shape'][1] <= 512 * 2.0
 
+    # test crop_size=640
+    transform = dict(type='Resize', img_scale=(2560, 640), crop_size=640)
+    resize_module = build_from_cfg(transform, PIPELINES)
+    resized_results = resize_module(results.copy())
+    assert resized_results['img_shape'] == (640, 1138, 3)
+
 
 def test_flip():
     # test assertion for invalid prob