Merge pull request #240 from chsasank/master

Refactor of transforms 

torchvision/transforms.py

@@ -13,43 +13,35 @@ import types
 import collections
 
 
-class Compose(object):
-    """Composes several transforms together.
+def _is_pil_image(img):
+    if accimage is not None:
+        return isinstance(img, (Image.Image, accimage.Image))
+    else:
+        return isinstance(img, Image.Image)
 
-    Args:
-        transforms (list of ``Transform`` objects): list of transforms to compose.
 
-    Example:
-        >>> transforms.Compose([
-        >>>     transforms.CenterCrop(10),
-        >>>     transforms.ToTensor(),
-        >>> ])
-    """
+def _is_tensor_image(img):
+    return torch.is_tensor(img) and img.ndimension() == 3
 
-    def __init__(self, transforms):
-        self.transforms = transforms
 
-    def __call__(self, img):
-        for t in self.transforms:
-            img = t(img)
-        return img
+def _is_numpy_image(img):
+    return isinstance(img, np.ndarray) and (img.ndim in {2, 3})
 
 
-class ToTensor(object):
+def to_tensor(pic):
     """Convert a ``PIL.Image`` or ``numpy.ndarray`` to tensor.
 
-    Converts a PIL.Image or numpy.ndarray (H x W x C) in the range
-    [0, 255] to a torch.FloatTensor of shape (C x H x W) in the range [0.0, 1.0].
-    """
+    See ``ToTensor`` for more details.
 
-    def __call__(self, pic):
-        """
     Args:
         pic (PIL.Image or numpy.ndarray): Image to be converted to tensor.
 
     Returns:
         Tensor: Converted image.
     """
+    if not(_is_pil_image(pic) or _is_numpy_image(pic)):
+        raise TypeError('pic should be PIL Image or ndarray. Got {}'.format(type(pic)))
+
     if isinstance(pic, np.ndarray):
         # handle numpy array
         img = torch.from_numpy(pic.transpose((2, 0, 1)))
@@ -85,29 +77,27 @@ class ToTensor(object):
         return img
 
 
-class ToPILImage(object):
-    """Convert a tensor to PIL Image.
+def to_pil_image(pic):
+    """Convert a tensor or an ndarray to PIL Image.
 
-    Converts a torch.*Tensor of shape C x H x W or a numpy ndarray of shape
-    H x W x C to a PIL.Image while preserving the value range.
-    """
+    See ``ToPIlImage`` for more details.
 
-    def __call__(self, pic):
-        """
     Args:
         pic (Tensor or numpy.ndarray): Image to be converted to PIL.Image.
 
     Returns:
         PIL.Image: Image converted to PIL.Image.
-
     """
+    if not(_is_numpy_image(pic) or _is_tensor_image(pic)):
+        raise TypeError('pic should be Tensor or ndarray. Got {}.'.format(type(pic)))
+
     npimg = pic
     mode = None
     if isinstance(pic, torch.FloatTensor):
         pic = pic.mul(255).byte()
     if torch.is_tensor(pic):
         npimg = np.transpose(pic.numpy(), (1, 2, 0))
-        assert isinstance(npimg, np.ndarray), 'pic should be Tensor or ndarray'
+    assert isinstance(npimg, np.ndarray)
     if npimg.shape[2] == 1:
         npimg = npimg[:, :, 0]
 
@@ -129,6 +119,212 @@ class ToPILImage(object):
     return Image.fromarray(npimg, mode=mode)
 
 
+def normalize(tensor, mean, std):
+    """Normalize an tensor image with mean and standard deviation.
+
+    See ``Normalize`` for more details.
+
+    Args:
+        tensor (Tensor): Tensor image of size (C, H, W) to be normalized.
+        mean (sequence): Sequence of means for R, G, B channels respecitvely.
+        std (sequence): Sequence of standard deviations for R, G, B channels
+            respecitvely.
+
+    Returns:
+        Tensor: Normalized image.
+    """
+    if not _is_tensor_image(tensor):
+        raise TypeError('tensor is not a torch image.')
+    # TODO: make efficient
+    for t, m, s in zip(tensor, mean, std):
+        t.sub_(m).div_(s)
+    return tensor
+
+
+def scale(img, size, interpolation=Image.BILINEAR):
+    """Rescale the input PIL.Image to the given size.
+
+    Args:
+        img (PIL.Image): Image to be scaled.
+        size (sequence or int): Desired output size. If size is a sequence like
+            (h, w), output size will be matched to this. If size is an int,
+            smaller edge of the image will be matched to this number.
+            i.e, if height > width, then image will be rescaled to
+            (size * height / width, size)
+        interpolation (int, optional): Desired interpolation. Default is
+            ``PIL.Image.BILINEAR``
+
+    Returns:
+        PIL.Image: Rescaled image.
+    """
+    if not _is_pil_image(img):
+        raise TypeError('img should be PIL Image. Got {}'.format(type(img)))
+    if not (isinstance(size, int) or (isinstance(size, collections.Iterable) and len(size) == 2)):
+        raise TypeError('Got inappropriate size arg: {}'.format(size))
+
+    if isinstance(size, int):
+        w, h = img.size
+        if (w <= h and w == size) or (h <= w and h == size):
+            return img
+        if w < h:
+            ow = size
+            oh = int(size * h / w)
+            return img.resize((ow, oh), interpolation)
+        else:
+            oh = size
+            ow = int(size * w / h)
+            return img.resize((ow, oh), interpolation)
+    else:
+        return img.resize(size[::-1], interpolation)
+
+
+def pad(img, padding, fill=0):
+    """Pad the given PIL.Image on all sides with the given "pad" value.
+
+    Args:
+        img (PIL.Image): Image to be padded.
+        padding (int or tuple): Padding on each border. If a single int is provided this
+            is used to pad all borders. If tuple of length 2 is provided this is the padding
+            on left/right and top/bottom respectively. If a tuple of length 4 is provided
+            this is the padding for the left, top, right and bottom borders
+            respectively.
+        fill: Pixel fill value. Default is 0. If a tuple of
+            length 3, it is used to fill R, G, B channels respectively.
+
+    Returns:
+        PIL.Image: Padded image.
+    """
+    if not _is_pil_image(img):
+        raise TypeError('img should be PIL Image. Got {}'.format(type(img)))
+
+    if not isinstance(padding, (numbers.Number, tuple)):
+        raise TypeError('Got inappropriate padding arg')
+    if not isinstance(fill, (numbers.Number, str, tuple)):
+        raise TypeError('Got inappropriate fill arg')
+
+    if isinstance(padding, collections.Sequence) and len(padding) not in [2, 4]:
+        raise ValueError("Padding must be an int or a 2, or 4 element tuple, not a " +
+                         "{} element tuple".format(len(padding)))
+
+    return ImageOps.expand(img, border=padding, fill=fill)
+
+
+def crop(img, i, j, h, w):
+    """Crop the given PIL.Image.
+
+    Args:
+        img (PIL.Image): Image to be cropped.
+        i: Upper pixel coordinate.
+        j: Left pixel coordinate.
+        h: Height of the cropped image.
+        w: Width of the cropped image.
+
+    Returns:
+        PIL.Image: Cropped image.
+    """
+    if not _is_pil_image(img):
+        raise TypeError('img should be PIL Image. Got {}'.format(type(img)))
+
+    return img.crop((j, i, j + w, i + h))
+
+
+def scaled_crop(img, i, j, h, w, size, interpolation=Image.BILINEAR):
+    """Crop the given PIL.Image and scale it to desired size.
+
+    Notably used in RandomSizedCrop.
+
+    Args:
+        img (PIL.Image): Image to be cropped.
+        i: Upper pixel coordinate.
+        j: Left pixel coordinate.
+        h: Height of the cropped image.
+        w: Width of the cropped image.
+        size (sequence or int): Desired output size. Same semantics as ``scale``.
+        interpolation (int, optional): Desired interpolation. Default is
+            ``PIL.Image.BILINEAR``.
+    Returns:
+        PIL.Image: Cropped image.
+    """
+    assert _is_pil_image(img), 'img should be PIL Image'
+    img = crop(img, i, j, h, w)
+    img = scale(img, size, interpolation)
+    return img
+
+
+def hflip(img):
+    """Horizontally flip the given PIL.Image.
+
+    Args:
+        img (PIL.Image): Image to be flipped.
+
+    Returns:
+        PIL.Image:  Horizontall flipped image.
+    """
+    if not _is_pil_image(img):
+        raise TypeError('img should be PIL Image. Got {}'.format(type(img)))
+
+    return img.transpose(Image.FLIP_LEFT_RIGHT)
+
+
+class Compose(object):
+    """Composes several transforms together.
+
+    Args:
+        transforms (list of ``Transform`` objects): list of transforms to compose.
+
+    Example:
+        >>> transforms.Compose([
+        >>>     transforms.CenterCrop(10),
+        >>>     transforms.ToTensor(),
+        >>> ])
+    """
+
+    def __init__(self, transforms):
+        self.transforms = transforms
+
+    def __call__(self, img):
+        for t in self.transforms:
+            img = t(img)
+        return img
+
+
+class ToTensor(object):
+    """Convert a ``PIL.Image`` or ``numpy.ndarray`` to tensor.
+
+    Converts a PIL.Image or numpy.ndarray (H x W x C) in the range
+    [0, 255] to a torch.FloatTensor of shape (C x H x W) in the range [0.0, 1.0].
+    """
+
+    def __call__(self, pic):
+        """
+        Args:
+            pic (PIL.Image or numpy.ndarray): Image to be converted to tensor.
+
+        Returns:
+            Tensor: Converted image.
+        """
+        return to_tensor(pic)
+
+
+class ToPILImage(object):
+    """Convert a tensor or an ndarray to PIL Image.
+
+    Converts a torch.*Tensor of shape C x H x W or a numpy ndarray of shape
+    H x W x C to a PIL.Image while preserving the value range.
+    """
+
+    def __call__(self, pic):
+        """
+        Args:
+            pic (Tensor or numpy.ndarray): Image to be converted to PIL.Image.
+
+        Returns:
+            PIL.Image: Image converted to PIL.Image.
+
+        """
+        return to_pil_image(pic)
+
+
 class Normalize(object):
     """Normalize an tensor image with mean and standard deviation.
 
@@ -154,10 +350,7 @@ class Normalize(object):
         Returns:
             Tensor: Normalized image.
         """
-        # TODO: make efficient
-        for t, m, s in zip(tensor, self.mean, self.std):
-            t.sub_(m).div_(s)
-        return tensor
+        return normalize(tensor, self.mean, self.std)
 
 
 class Scale(object):
@@ -186,20 +379,7 @@ class Scale(object):
         Returns:
             PIL.Image: Rescaled image.
         """
-        if isinstance(self.size, int):
-            w, h = img.size
-            if (w <= h and w == self.size) or (h <= w and h == self.size):
-                return img
-            if w < h:
-                ow = self.size
-                oh = int(self.size * h / w)
-                return img.resize((ow, oh), self.interpolation)
-            else:
-                oh = self.size
-                ow = int(self.size * w / h)
-                return img.resize((ow, oh), self.interpolation)
-        else:
-            return img.resize(self.size[::-1], self.interpolation)
+        return scale(img, self.size, self.interpolation)
 
 
 class CenterCrop(object):
@@ -217,6 +397,23 @@ class CenterCrop(object):
         else:
             self.size = size
 
+    @staticmethod
+    def get_params(img, output_size):
+        """Get parameters for ``crop`` for center crop.
+
+        Args:
+            img (PIL.Image): Image to be cropped.
+            output_size (tuple): Expected output size of the crop.
+
+        Returns:
+            tuple: params (i, j, h, w) to be passed to ``crop`` for center crop.
+        """
+        w, h = img.size
+        th, tw = output_size
+        i = int(round((h - th) / 2.))
+        j = int(round((w - tw) / 2.))
+        return i, j, th, tw
+
     def __call__(self, img):
         """
         Args:
@@ -225,11 +422,8 @@ class CenterCrop(object):
         Returns:
             PIL.Image: Cropped image.
         """
-        w, h = img.size
-        th, tw = self.size
-        x1 = int(round((w - tw) / 2.))
-        y1 = int(round((h - th) / 2.))
-        return img.crop((x1, y1, x1 + tw, y1 + th))
+        i, j, h, w = self.get_params(img, self.size)
+        return crop(img, i, j, h, w)
 
 
 class Pad(object):
@@ -263,7 +457,7 @@ class Pad(object):
         Returns:
             PIL.Image: Padded image.
         """
-        return ImageOps.expand(img, border=self.padding, fill=self.fill)
+        return pad(img, self.padding, self.fill)
 
 
 class Lambda(object):
@@ -301,6 +495,26 @@ class RandomCrop(object):
             self.size = size
         self.padding = padding
 
+    @staticmethod
+    def get_params(img, output_size):
+        """Get parameters for ``crop`` for a random crop.
+
+        Args:
+            img (PIL.Image): Image to be cropped.
+            output_size (tuple): Expected output size of the crop.
+
+        Returns:
+            tuple: params (i, j, h, w) to be passed to ``crop`` for random crop.
+        """
+        w, h = img.size
+        th, tw = output_size
+        if w == tw and h == th:
+            return img
+
+        i = random.randint(0, h - th)
+        j = random.randint(0, w - tw)
+        return i, j, th, tw
+
     def __call__(self, img):
         """
         Args:
@@ -310,16 +524,11 @@ class RandomCrop(object):
             PIL.Image: Cropped image.
         """
         if self.padding > 0:
-            img = ImageOps.expand(img, border=self.padding, fill=0)
+            img = pad(img, self.padding)
 
-        w, h = img.size
-        th, tw = self.size
-        if w == tw and h == th:
-            return img
+        i, j, h, w = self.get_params(img, self.size)
 
-        x1 = random.randint(0, w - tw)
-        y1 = random.randint(0, h - th)
-        return img.crop((x1, y1, x1 + tw, y1 + th))
+        return crop(img, i, j, h, w)
 
 
 class RandomHorizontalFlip(object):
@@ -334,7 +543,7 @@ class RandomHorizontalFlip(object):
             PIL.Image: Randomly flipped image.
         """
         if random.random() < 0.5:
-            return img.transpose(Image.FLIP_LEFT_RIGHT)
+            return hflip(img)
         return img
 
 
@@ -347,15 +556,25 @@ class RandomSizedCrop(object):
     This is popularly used to train the Inception networks.
 
     Args:
-        size: size of the smaller edge
+        size: expected output size of each edge
         interpolation: Default: PIL.Image.BILINEAR
     """
 
     def __init__(self, size, interpolation=Image.BILINEAR):
-        self.size = size
+        self.size = (size, size)
         self.interpolation = interpolation
 
-    def __call__(self, img):
+    @staticmethod
+    def get_params(img):
+        """Get parameters for ``crop`` for a random sized crop.
+
+        Args:
+            img (PIL.Image): Image to be cropped.
+
+        Returns:
+            tuple: params (i, j, h, w) to be passed to ``crop`` for a random
+                sized crop.
+        """
         for attempt in range(10):
             area = img.size[0] * img.size[1]
             target_area = random.uniform(0.08, 1.0) * area
@@ -368,15 +587,23 @@ class RandomSizedCrop(object):
                 w, h = h, w
 
             if w <= img.size[0] and h <= img.size[1]:
-                x1 = random.randint(0, img.size[0] - w)
-                y1 = random.randint(0, img.size[1] - h)
+                i = random.randint(0, img.size[1] - h)
+                j = random.randint(0, img.size[0] - w)
+                return i, j, h, w
 
-                img = img.crop((x1, y1, x1 + w, y1 + h))
-                assert(img.size == (w, h))
+        # Fallback
+        w = min(img.size[0], img.shape[1])
+        i = (img.shape[1] - w) // 2
+        j = (img.shape[0] - w) // 2
+        return i, j, w, w
 
-                return img.resize((self.size, self.size), self.interpolation)
+    def __call__(self, img):
+        """
+        Args:
+            img (PIL.Image): Image to be flipped.
 
-        # Fallback
-        scale = Scale(self.size, interpolation=self.interpolation)
-        crop = CenterCrop(self.size)
-        return crop(scale(img))
+        Returns:
+            PIL.Image: Randomly cropped and scaled image.
+        """
+        i, j, h, w = self.get_params(img)
+        return scaled_crop(img, i, j, h, w, self.size, self.interpolation)