add some documentation

docs/image.md

 ## Image
 
-This module provides some image processing methods.
+This module provides some image processing methods, which requires `opencv` to
+to be installed.
 
 ### Read/Write/Show
 To read or write images files, use `imread` or `imwrite`.
@@ -26,16 +27,33 @@ To show an image file or a loaded image
 
 ```python
 mmcv.imshow('tests/data/color.jpg')
+# this is equivalent to 
 
 for i in range(10):
     img = np.random.randint(256, size=(100, 100, 3), dtype=np.uint8)
     mmcv.imshow(img, win_name='test image', wait_time=200)
 ```
 
+### Color space conversion
+Supported conversion methods:
+- bgr2gray
+- gray2bgr
+- bgr2rgb
+- rgb2bgr
+- bgr2hsv
+- hsv2bgr
+
+```python
+img = mmcv.imread('tests/data/color.jpg')
+img1 = mmcv.bgr2rgb(img)
+img2 = mmcv.rgb2gray(img1)
+img3 = mmcv.bgr2hsv(img)
+```
+
 ### Resize
-There are three resize methods. All `imresize_*` methods have a parameter `return_scale`,
-if this param is `False`, then the return value is merely the resized image, otherwise
-is a tuple (resized_img, scale).
+There are three resize methods. All `imresize_*` methods have an argument `return_scale`,
+if this argument is `False`, then the return value is merely the resized image, otherwise
+is a tuple `(resized_img, scale)`.
 
 ```python
 # resize to a given size
@@ -52,47 +70,79 @@ mmcv.imrescale(img, 0.5)
 mmcv.imrescale(img, (1000, 800))
 ```
 
-### Color space conversion
-Supported conversion methods:
-- bgr2gray
-- gray2bgr
-- bgr2rgb
-- rgb2bgr
-- bgr2hsv
-- hsv2bgr
+### Rotate
+To rotate an image by some angle, use `imrotate`. The center can be specified,
+which is the center of original image by default. There are two modes of rotating,
+one is to keep the image size unchanged so that some parts of the image will be
+cropped after rotating, the other is to extend the image size to fit the rotated
+image.
 
 ```python
 img = mmcv.imread('tests/data/color.jpg')
-img1 = mmcv.bgr2rgb(img)
-img2 = mmcv.rgb2gray(img1)
-img3 = mmcv.bgr2hsv(img)
+
+# rotate the image clockwise by 30 degrees.
+img_ = mmcv.imrotate(img, 30)
+
+# rotate the image counterclockwise by 90 degrees.
+img_ = mmcv.imrotate(img, -90)
+
+# rotate the image clockwise by 30 degrees, and rescale it by 1.5x at the same time.
+img_ = mmcv.imrotate(img, 30, scale=1.5)
+
+# rotate the image clockwise by 30 degrees, with (100, 100) as the center.
+img_ = mmcv.imrotate(img, 30, center=(100, 100))
+
+# rotate the image clockwise by 30 degrees, and extend the image size.
+img_ = mmcv.imrotate(img, 30, auto_bound=True)
+```
+
+### Flip
+To flip an image, use `imflip`.
+
+```python
+img = mmcv.imread('tests/data/color.jpg')
+
+# flip the image horizontally
+mmcv.imflip(img)
+
+# flip the image vertically
+mmcv.imflip(img, direction='vertical')
 ```
 
 ### Crop
-Support single/multiple crop.
+`imcrop` can crop the image with one or some regions, represented as (x1, y1, x2, y2).
 
 ```python
 import mmcv
 import numpy as np
 
 img = mmcv.read_img('tests/data/color.jpg')
-bboxes = np.array([10, 10, 100, 120])  # x1, y1, x2, y2
+
+# crop the region (10, 10, 100, 120)
+bboxes = np.array([10, 10, 100, 120])
 patch = mmcv.crop_img(img, bboxes)
+
+# crop two regions (10, 10, 100, 120) and (0, 0, 50, 50)
 bboxes = np.array([[10, 10, 100, 120], [0, 0, 50, 50]])
 patches = mmcv.crop_img(img, bboxes)
-```
 
-Resizing cropped patches.
-```python
-# upsample patches by 1.2x
+# crop two regions, and rescale the patches by 1.2x
 patches = mmcv.crop_img(img, bboxes, scale_ratio=1.2)
 ```
 
 ### Padding
-Pad an image to specific size with given values.
+There are two methods `impad` and `impad_to_multiple` to pad an image to the
+specific size with given values.
 
 ```python
 img = mmcv.read_img('tests/data/color.jpg')
-img = mmcv.pad_img(img, (1000, 1200), pad_val=0)
-img = mmcv.pad_img(img, (1000, 1200), pad_val=[100, 50, 200])
+
+# pad the image to (1000, 1200) with all zeros
+img_ = mmcv.pad_img(img, (1000, 1200), pad_val=0)
+
+# pad the image to (1000, 1200) with different values for three channels.
+img_ = mmcv.pad_img(img, (1000, 1200), pad_val=[100, 50, 200])
+
+# pad an image so that each edge is a multiple of some value.
+img_ = mmcv.impad_to_multiple(img, 32)
 ```
\ No newline at end of file

docs/intro.md

-# Introduction
+## Introduction
 
 `mmcv` is a foundational python library for computer vision research and supports many
 research projects in MMLAB, such as [mmdetection](https://github.com/open-mmlab/mmdetection).
@@ -16,7 +16,7 @@ It provides the following functionalities.
 See the [documentation](http://mmcv.readthedocs.io/en/latest) for more features and usage.
 
 
-## Installation
+### Installation
 
 Try and start with
 

docs/io.md

@@ -12,20 +12,73 @@ import mmcv
 # load data from a file
 data = mmcv.load('test.json')
 data = mmcv.load('test.yaml')
-data = mmcv.load('test.pickle')
+data = mmcv.load('test.pkl')
 # load data from a file-like object
 with open('test.json', 'r') as f:
     data = mmcv.load(f)
 
 # dump data to a string
 json_str = mmcv.dump(data, format='json')
+
 # dump data to a file with a filename (infer format from file extension)
-mmcv.dump(data, 'out.pickle')
+mmcv.dump(data, 'out.pkl')
+
 # dump data to a file with a file-like object
 with open('test.yaml', 'w') as f:
     data = mmcv.dump(data, f, format='yaml')
 ```
 
+It is also very convenient to extend the api to support more file formats.
+All you need to do is to write a file handler inherited from `BaseFileHandler`
+and register it with one or several file formats.
+
+You need to implement at least 3 methods.
+
+```python
+import mmcv
+
+# To register multiple file formats, a list can be used as the argument.
+# @mmcv.register_handler(['txt', 'log'])
+@mmcv.register_handler('txt')
+class TxtHandler1(mmcv.BaseFileHandler):
+
+    def load_from_fileobj(self, file):
+        return file.read()
+
+    def dump_to_fileobj(self, obj, file):
+        file.write(str(obj))
+
+    def dump_to_str(self, obj, **kwargs):
+        return str(obj)
+```
+
+Here is an example of `PickleHandler`.
+
+```python
+from six.moves import cPickle as pickle
+
+class PickleHandler(mmcv.BaseFileHandler):
+
+    def load_from_fileobj(self, file, **kwargs):
+        return pickle.load(file, **kwargs)
+
+    def load_from_path(self, filepath, **kwargs):
+        return super(PickleHandler, self).load_from_path(
+            filepath, mode='rb', **kwargs)
+
+    def dump_to_str(self, obj, **kwargs):
+        kwargs.setdefault('protocol', 2)
+        return pickle.dumps(obj, **kwargs)
+
+    def dump_to_fileobj(self, obj, file, **kwargs):
+        kwargs.setdefault('protocol', 2)
+        pickle.dump(obj, file, **kwargs)
+
+    def dump_to_path(self, obj, filepath, **kwargs):
+        super(PickleHandler, self).dump_to_path(
+            obj, filepath, mode='wb', **kwargs)
+```
+
 ### Load a text file as a list or dict
 
 For example `a.txt` is a text file with 5 lines.
@@ -40,16 +93,14 @@ e
 Then use `list_from_file` to load the list from a.txt.
 
 ```python
-import mmcv
-
-mmcv.list_from_file('a.txt')
-# output ['a', 'b', 'c', 'd', 'e']
-mmcv.list_from_file('a.txt', offset=2)
-# output ['c', 'd', 'e']
-mmcv.list_from_file('a.txt', max_num=2)
-# output ['a', 'b']
-mmcv.list_from_file('a.txt', prefix='/mnt/')
-# output ['/mnt/a', '/mnt/b', '/mnt/c', '/mnt/d', '/mnt/e']
+>>> mmcv.list_from_file('a.txt')
+['a', 'b', 'c', 'd', 'e']
+>>> mmcv.list_from_file('a.txt', offset=2)
+['c', 'd', 'e']
+>>> mmcv.list_from_file('a.txt', max_num=2)
+['a', 'b']
+>>> mmcv.list_from_file('a.txt', prefix='/mnt/')
+['/mnt/a', '/mnt/b', '/mnt/c', '/mnt/d', '/mnt/e']
 ```
 
 For example `b.txt` is a text file with 5 lines.
@@ -62,10 +113,8 @@ For example `b.txt` is a text file with 5 lines.
 Then use `dict_from_file` to load the list from a.txt.
 
 ```python
-import mmcv
-
-mmcv.dict_from_file('b.txt')
-# output {'1': 'cat', '2': ['dog', 'cow'], '3': 'panda'}
-mmcv.dict_from_file('b.txt', key_type=int)
-# output {1: 'cat', 2: ['dog', 'cow'], 3: 'panda'}
+>>> mmcv.dict_from_file('b.txt')
+{'1': 'cat', '2': ['dog', 'cow'], '3': 'panda'}
+>>> mmcv.dict_from_file('b.txt', key_type=int)
+{1: 'cat', 2: ['dog', 'cow'], 3: 'panda'}
 ```

docs/utils.md

@@ -3,7 +3,7 @@
 ### Config
 
 `Config` class is used for manipulating config and config files. It supports
-loading configs from multiple file formats including python scripts, json file and yaml file.
+loading configs from multiple file formats including **python**, **json** and **yaml**.
 It provides dict-like apis to get and set values.
 
 Here is an example of the config file `test.py`.

mmcv/runner/priority.py

@@ -2,13 +2,33 @@ from enum import Enum
 
 
 class Priority(Enum):
+    """Hook priority levels.
+
+    +------------+------------+
+    | Level      | Value      |
+    +============+============+
+    | HIGHEST    | 0          |
+    +------------+------------+
+    | VERY_HIGH  | 10         |
+    +------------+------------+
+    | HIGH       | 30         |
+    +------------+------------+
+    | NORMAL     | 50         |
+    +------------+------------+
+    | LOW        | 70         |
+    +------------+------------+
+    | VERY_LOW   | 90         |
+    +------------+------------+
+    | LOWEST     | 100        |
+    +------------+------------+
+    """
 
     HIGHEST = 0
-    VERY_HIGH = 20
-    HIGH = 40
+    VERY_HIGH = 10
+    HIGH = 30
     NORMAL = 50
-    LOW = 60
-    VERY_LOW = 80
+    LOW = 70
+    VERY_LOW = 90
     LOWEST = 100