1.输入一张图片转化成一张新图（只适用单通道图片）

def convert_image_size1(img,size):#size=[width,height]
    img = np.array(img)
    height, width = img.shape[0],img.shape[1]
    ratio = width / height
    mask_image = []
    channel = 1
    if len(img.shape) == 3:
        channel = 3
    if width > height:
        w = size[0]
        h = int(w / ratio)
        img1 = cv2.resize(img, (w, h))
        h1, w1 = img1.shape[0],img1.shape[1]

        if h1 % 2 == 0:
            c1 = int((size[1] - h1) / 2)
            c2 = int((size[1]- h1) / 2)

            mask1 = np.zeros([c1, w,channel], dtype=np.uint8)
            mask2 = np.zeros([c2, w,channel], dtype=np.uint8)
            # img2=cv2.vconcat([mask1,img1,mask2])
            img2 = np.concatenate([mask1, img1, mask2], axis=0)
            mask_image.append(img2)
            # print("*****", img2.shape)

        elif h1 % 2 == 1:
            c1 = int(((size[1] - h1) / 2) + 1)
            c2 = int((size[1] - h1) / 2)
            mask1 = np.zeros([c1, w,channel], dtype=np.uint8)
            mask2 = np.zeros([c2, w,channel], dtype=np.uint8)
            # img2 = cv2.vconcat([mask1, img1, mask2])
            img2 = np.concatenate([mask1, img1, mask2], axis=0)
            mask_image.append(img2)

    elif width < height:
        h = size[1]
        w = int(h * ratio)
        img1 = cv2.resize(img, (w, h))
        h1, w1 = img1.shape
        if w1 % 2 == 0:
            c1 = int((size[0] - w1) / 2)
            c2 = int((size[0] - w1) / 2)
            mask1 = np.zeros([h, c1,channel], dtype=np.uint8)
            mask2 = np.zeros([h, c2,channel], dtype=np.uint8)
            # img2 = cv2.hconcat([mask1, img1, mask2])
            img2 = np.concatenate([mask1, img1, mask2], axis=1)
            mask_image.append(img2)
            # print(">>>>>>>>>", img2.shape)
            # cv2.imwrite("", img2)

        elif w1 % 2 == 1:
            c1 = int((size[0] - w1) / 2) + 1
            c2 = int((size[0] - w1) / 2)
            print("c1c2:", c1, c2)
            mask1 = np.zeros([h, c1,channel], dtype=np.uint8)
            mask2 = np.zeros([h, c2,channel], dtype=np.uint8)
            # img2 = cv2.hconcat([mask1, img1, mask2])
            img2 = np.concatenate([mask1, img1, mask2], axis=1)
            print(">>>>>>>>>", img2.shape)
            mask_image.append(img2)

    else:
        img1 = cv2.resize(img, (size[0], size[1],channel))
        mask_image.append(img1)

    return mask_image[0]

2.输入一张图片转化成一张新图（适用单通道和3通道图片）

def convert_image_size(img,size):#size=[width,height]
    img=np.array(img)
    new_shape = list(img.shape)
    new_shape[0] = size[0]
    new_shape[1] = size[1]
    mask_image = np.zeros(new_shape, dtype=np.uint8)

    height, width= img.shape[0],img.shape[1]
    ratio = width / height
    if width > height:
        img2 = cv2.resize(img, (size[0],  int(size[0] / ratio)))
        start=int((size[1]-img2.shape[0])/2)
        mask_image[start:start+img2.shape[0], 0:size[0]] = img2
    elif width < height:
        img2 = cv2.resize(img, (int(size[1] * ratio), size[1]))
        start = int((size[0] - img2.shape[1]) / 2)
        mask_image[0:size[1],start:start+img2.shape[1]] = img2
    else:
        mask_image = cv2.resize(img, (size[0], size[1]))
    return mask_image

3.案例

import os
from PIL import Image
import numpy as np
import cv2


def convert_image_size1(img,size):#size=[width,height]
    img = np.array(img)
    height, width = img.shape
    ratio = width / height
    mask_image = []
    if width > height:
        w = size[0]
        h = int(w / ratio)
        img1 = cv2.resize(img, (w, h))
        h1, w1 = img1.shape
        c1 = int(((size[1] - h1) / 2)+0.5)
        c2 = int((size[1]- h1) / 2)
        mask1 = np.zeros([c1, w], dtype=np.uint8)
        mask2 = np.zeros([c2, w], dtype=np.uint8)
        # img2=cv2.vconcat([mask1,img1,mask2])
        img2 = np.concatenate([mask1, img1, mask2], axis=0)
        mask_image.append(img2)
        print("*****", img2.shape)

    elif width < height:
        h = size[1]
        w = int(h * ratio)
        img1 = cv2.resize(img, (w, h))
        h1, w1 = img1.shape
        c1 = int(((size[0] - w1) / 2)+0.5)
        c2 = int((size[0] - w1) / 2)
        mask1 = np.zeros([h, c1], dtype=np.uint8)
        mask2 = np.zeros([h, c2], dtype=np.uint8)
        # img2 = cv2.hconcat([mask1, img1, mask2])
        img2 = np.concatenate([mask1, img1, mask2], axis=1)
        mask_image.append(img2)
        print(">>>>>>>>>", img2.shape)
        # cv2.imwrite("", img2)

    else:
        img1 = cv2.resize(img, (size[0], size[1]))
        mask_image.append(img1)

    return mask_image[0]


def convert_image_size(img,size):#size=[width,height]800,800
    img=np.array(img)

    new_shape = list(img.shape)
    new_shape[0] = size[0]
    new_shape[1] = size[1]
    mask_image = np.zeros(new_shape, dtype=np.uint8)

    height, width= img.shape[0],img.shape[1]
    ratio = width / height
    if width > height:
        img2 = cv2.resize(img, (size[0],  int(size[0] / ratio)))
        start=int((size[1]-img2.shape[0])/2)
        mask_image[start:start+img2.shape[0], 0:size[0]] = img2
    elif width < height:
        img2 = cv2.resize(img, (int(size[1] * ratio), size[1]))
        start = int((size[0] - img2.shape[1]) / 2)
        mask_image[0:size[1],start:start+img2.shape[1]] = img2
    else:
        mask_image = cv2.resize(img, (size[0], size[1]))
    return mask_image

if __name__ == '__main__':
    #图片转化固定大小
    dir="/media/tianhailong/新加卷/coco_seg/image1"
    out_dir="/media/tianhailong/新加卷/coco_seg/out"
    for path in os.listdir(dir):
        path1=os.path.join(dir,path)
        print(path1)
        img = Image.open(path1)
        mask_image=convert_image_size(img,(640,640))
        cv2.imwrite(os.path.join(out_dir,path),mask_image)

# 将待贴图片贴到原始图片上