向图像添加填充以使它们具有相同的形状

Question

我有一组不同大小的图像(45,50,3), (69,34,3), (34,98,3)。我想为这些图像添加填充，如下所示：

取整张图片的最大宽度和长度，然后把图片放在那个尺寸

import os
import glob
import cv2

input_path="/home/images"
os.chdir(indput_path)
images=glob.glob("*.png")
Length=[]
Width=[]
for img in images:
    img=cv2.imread(img)
    width,length=img.shape[0:2]
    Length.append(length)
    Width.append(width)
W=max(Width)
L=max(Length)

如何在 opencv 中添加填充以使所有图像具有相同的大小？在示例中我给出的图像将得到(69,98,3)的形状

Answer 1

只需使用 Pillow 的 crop_pad()。它会自动调整大小并在需要的地方添加“零”填充 (rgb=(0,0,0) / black)，无需图片缩放。

from PIL import Image

img = Image.open(your_file_path)
img.crop_pad((width, height))

Answer 2

这是在 Python/OpenCV/Numpy 中执行此操作的另一种方法。它使用 Numpy 切片将输入图像复制到具有所需输出大小和给定偏移量的新图像中。在这里，我计算偏移量以进行中心填充。我认为这更容易使用宽度、高度、xoffset、yoffset，而不是每边填充多少。

输入：

import cv2
import numpy as np

# read image
img = cv2.imread('lena.jpg')
old_image_height, old_image_width, channels = img.shape

# create new image of desired size and color (blue) for padding
new_image_width = 300
new_image_height = 300
color = (255,0,0)
result = np.full((new_image_height,new_image_width, channels), color, dtype=np.uint8)

# compute center offset
x_center = (new_image_width - old_image_width) // 2
y_center = (new_image_height - old_image_height) // 2

# copy img image into center of result image
result[y_center:y_center+old_image_height, 
       x_center:x_center+old_image_width] = img

# view result
cv2.imshow("result", result)
cv2.waitKey(0)
cv2.destroyAllWindows()

# save result
cv2.imwrite("lena_centered.jpg", result)

Answer 3

你可以使用：

image = cv2.copyMakeBorder(src, top, bottom, left, right, borderType)

src 是您的源图像，top、bottom、left、right 是图像周围的填充。

您可以在 while 循环中使用 max(sizes) - 图像的大小值来为每个图像添加填充。 边框类型可以是以下之一：

• cv2.BORDER_CONSTANT
• cv2.BORDER_REFLECT
• cv2.BORDER_REFLECT_101
• cv2.BORDER_DEFAULT
• cv2.BORDER_REPLICATE
• cv2.BORDER_WRAP

cv2.copyMakeBorder tutorial

Answer 4

尝试使用此功能：

from PIL import Image, ImageOps


def padding(img, expected_size):
    desired_size = expected_size
    delta_width = desired_size - img.size[0]
    delta_height = desired_size - img.size[1]
    pad_width = delta_width // 2
    pad_height = delta_height // 2
    padding = (pad_width, pad_height, delta_width - pad_width, delta_height - pad_height)
    return ImageOps.expand(img, padding)


def resize_with_padding(img, expected_size):
    img.thumbnail((expected_size[0], expected_size[1]))
    # print(img.size)
    delta_width = expected_size[0] - img.size[0]
    delta_height = expected_size[1] - img.size[1]
    pad_width = delta_width // 2
    pad_height = delta_height // 2
    padding = (pad_width, pad_height, delta_width - pad_width, delta_height - pad_height)
    return ImageOps.expand(img, padding)


if __name__ == "__main__":
    img = Image.open("./demo.jpg")
    print(img)
    img = resize_with_padding(img, (500, 400))
    print(img.size)
    img.show()
    img.save("resized_img.jpg")

原始图像

使用填充调整大小后

见https://gist.github.com/BIGBALLON/cb6ab73f6aaaa068ab6756611bb324b2

Answer 5

这是一个为你做所有事情的函数：

import cv2


def pad_images_to_same_size(images):
    """
    :param images: sequence of images
    :return: list of images padded so that all images have same width and height (max width and height are used)
    """
    width_max = 0
    height_max = 0
    for img in images:
        h, w = img.shape[:2]
        width_max = max(width_max, w)
        height_max = max(height_max, h)

    images_padded = []
    for img in images:
        h, w = img.shape[:2]
        diff_vert = height_max - h
        pad_top = diff_vert//2
        pad_bottom = diff_vert - pad_top
        diff_hori = width_max - w
        pad_left = diff_hori//2
        pad_right = diff_hori - pad_left
        img_padded = cv2.copyMakeBorder(img, pad_top, pad_bottom, pad_left, pad_right, cv2.BORDER_CONSTANT, value=0)
        assert img_padded.shape[:2] == (height_max, width_max)
        images_padded.append(img_padded)

    return images_padded

Answer 6

像这样（填充在openCV上称为边框）：

BLUE = [255,255,255]
constant= cv2.copyMakeBorder(image.copy(),10,10,10,10,cv2.BORDER_CONSTANT,value=BLUE)

蓝色甚至可以变成白色

来源： https://docs.opencv.org/3.4/da/d0c/tutorial_bounding_rects_circles.html

Answer 7

由于我没有看到可接受的答案，而且必须确定函数的顶部、底部、左侧、右侧这一事实，所以我很容易知道什么对我有用。取自：https://jdhao.github.io/2017/11/06/resize-image-to-square-with-padding/

import cv2

desired_size = 368
im_pth = "/home/jdhao/test.jpg"

im = cv2.imread(im_pth)
old_size = im.shape[:2] # old_size is in (height, width) format

ratio = float(desired_size)/max(old_size)
new_size = tuple([int(x*ratio) for x in old_size])

# new_size should be in (width, height) format

im = cv2.resize(im, (new_size[1], new_size[0]))

delta_w = desired_size - new_size[1]
delta_h = desired_size - new_size[0]
top, bottom = delta_h//2, delta_h-(delta_h//2)
left, right = delta_w//2, delta_w-(delta_w//2)

color = [0, 0, 0]
new_im = cv2.copyMakeBorder(im, top, bottom, left, right, cv2.BORDER_CONSTANT,
    value=color)

cv2.imshow("image", new_im)
cv2.waitKey(0)
cv2.destroyAllWindows()