opencv之为图像添加边界

Posted 2021-05-07 sdu20112013

我们经常会有对图像边缘做扩展的需求.比如

• 希望卷积后得到的矩阵大小不变
• 希望改变图像大小,但是不改变宽高比

opencv实现

opencv中使用copyMakeBorder()来完成这一功能
api

• src是原图像矩阵
• dst是新图像矩阵
• top/bottom/left/right是边界扩展的大小(比如5就代表5个像素)
• borderType
• value是扩充的像素填什么值

borderType分两种:

• BORDER_CONSTANT
  边缘填充用固定像素值,比如填充黑边,就用0,白边255
• BORDER_REPLICATE
  用原始图像相应的边缘的像素去做填充,看起来有一种把图像边缘"拉糊了"的效果

opencv示例

import sys
import cv2 as cv

def test():
    src = cv.imread("/home/sc/disk/keepgoing/opencv_test/lights.jpeg") 
    top = int(0.05 * src.shape[0])  # shape[0] = rows
    bottom = top
    left = int(0.04 * src.shape[1])  # shape[1] = cols
    right = left
    
    value = [0,0,0]
    borderType = cv.BORDER_CONSTANT
    dst1 = cv.copyMakeBorder(src, top, bottom, left, right, borderType, None, value)
    
    borderType = cv.BORDER_REPLICATE
    dst2 = cv.copyMakeBorder(src, top, bottom, left, right, borderType, None, value)
    
    cv.imshow("blackborder",dst1)
    cv.imshow("BORDER_REPLICATE",dst2)
    
    if 27 == cv.waitKey():
        cv.destroyAllWindows()
        
test()

效果如下: