opencv保存和读入图片的结果不一致的问题

今天用python读取和保存图像时，发现读取jpg的图像，在保存为jpg，再读取时，两个图像的差会有很大不同。原因是，jpeg在保存的时会有损失，png格式为无损保存。

import cv2

img1 = cv2.imread("test.jpg")
cv2.imwrite("test1.jpg",img1)

img2 = cv2.imread("test1.jpg")
img_diff = img1 - img2
cv2.imwrite("diff1.png",img_diff)
cv2.imshow("imgdiff1",img_diff)
cv2.waitKey(100)


cv2.imwrite("test2.png",img1)
img3 = cv2.imread("test2.png")
img_diff = img1 - img3
cv2.imwrite("diff2.png",img_diff)
cv2.imshow("imgdiff2",img_diff)
cv2.waitKey(100)

test.jpg

diff1.png

diff2.png