# Copyright (c) Open-MMLab. All rights reserved.
from __future__ import division
import cv2
def _scale_size(size, scale):
"""Rescale a size by a ratio.
Args:
size (tuple): w, h.
scale (float): Scaling factor.
Returns:
tuple[int]: scaled size.
"""
w, h = size
return int(w * float(scale) + 0.5), int(h * float(scale) + 0.5)
interp_codes = {
'nearest': cv2.INTER_NEAREST,
'bilinear': cv2.INTER_LINEAR,
'bicubic': cv2.INTER_CUBIC,
'area': cv2.INTER_AREA,
'lanczos': cv2.INTER_LANCZOS4
}
[docs]def imresize(img,
size,
return_scale=False,
interpolation='bilinear',
out=None):
"""Resize image to a given size.
Args:
img (ndarray): The input image.
size (tuple): Target (w, h).
return_scale (bool): Whether to return `w_scale` and `h_scale`.
interpolation (str): Interpolation method, accepted values are
"nearest", "bilinear", "bicubic", "area", "lanczos".
out (ndarray): The output destination.
Returns:
tuple or ndarray: (`resized_img`, `w_scale`, `h_scale`) or
`resized_img`.
"""
h, w = img.shape[:2]
resized_img = cv2.resize(
img, size, dst=out, interpolation=interp_codes[interpolation])
if not return_scale:
return resized_img
else:
w_scale = size[0] / w
h_scale = size[1] / h
return resized_img, w_scale, h_scale
[docs]def imresize_like(img, dst_img, return_scale=False, interpolation='bilinear'):
"""Resize image to the same size of a given image.
Args:
img (ndarray): The input image.
dst_img (ndarray): The target image.
return_scale (bool): Whether to return `w_scale` and `h_scale`.
interpolation (str): Same as :func:`resize`.
Returns:
tuple or ndarray: (`resized_img`, `w_scale`, `h_scale`) or
`resized_img`.
"""
h, w = dst_img.shape[:2]
return imresize(img, (w, h), return_scale, interpolation)
[docs]def rescale_size(old_size, scale, return_scale=False):
"""Calculate the new size to be rescaled to.
Args:
old_size (tuple[int]): The old size of image.
scale (float or tuple[int]): The scaling factor or maximum size.
If it is a float number, then the image will be rescaled by this
factor, else if it is a tuple of 2 integers, then the image will
be rescaled as large as possible within the scale.
return_scale (bool): Whether to return the scaling factor besides the
rescaled image size.
Returns:
tuple[int]: The new rescaled image size.
"""
w, h = old_size
if isinstance(scale, (float, int)):
if scale <= 0:
raise ValueError(
'Invalid scale {}, must be positive.'.format(scale))
scale_factor = scale
elif isinstance(scale, tuple):
max_long_edge = max(scale)
max_short_edge = min(scale)
scale_factor = min(max_long_edge / max(h, w),
max_short_edge / min(h, w))
else:
raise TypeError(
'Scale must be a number or tuple of int, but got {}'.format(
type(scale)))
new_size = _scale_size((w, h), scale_factor)
if return_scale:
return new_size, scale_factor
else:
return new_size
[docs]def imrescale(img, scale, return_scale=False, interpolation='bilinear'):
"""Resize image while keeping the aspect ratio.
Args:
img (ndarray): The input image.
scale (float or tuple[int]): The scaling factor or maximum size.
If it is a float number, then the image will be rescaled by this
factor, else if it is a tuple of 2 integers, then the image will
be rescaled as large as possible within the scale.
return_scale (bool): Whether to return the scaling factor besides the
rescaled image.
interpolation (str): Same as :func:`resize`.
Returns:
ndarray: The rescaled image.
"""
h, w = img.shape[:2]
new_size, scale_factor = rescale_size((w, h), scale, return_scale=True)
rescaled_img = imresize(img, new_size, interpolation=interpolation)
if return_scale:
return rescaled_img, scale_factor
else:
return rescaled_img