python+opencv 图像金字塔（尺度空间不变性）

1、图像金字塔原理：

reduce = 高斯模糊  +  降采样

降采样：行、列各取偶数行，组成新的图像

expand = 扩大 + 卷积（扩大是升采样）

2、经过reduce的图像是高斯金字塔

L1 = g1 - expand(g2)得到图像的轮廓是拉普拉斯金字塔

import cv2 as cv
import numpy as np


# 金字塔定义
def pyramid_demo(image):
    level = 3
    temp = image.copy()
    pyramid_images = []
    for i in range(level):
        dst = cv.pyrDown(temp)
        pyramid_images.append(dst)
        cv.imshow('pyramid_down_'+str(i), dst)
        temp = dst.copy()
    return pyramid_images


# 拉普拉斯金字塔
def lapalian_demo(image):
    pyramid_images = pyramid_demo(image)
    level = len(pyramid_images)
    for i in range(level-1, -1, -1):
        if (i-1) < 0:
            expand = cv.pyrUp(pyramid_images[i], dstsize=image.shape[:2])
            lpls = cv.subtract(image, expand)
            cv.imshow('lapalian_down_' + str(i), lpls)
        else:
            expand = cv.pyrUp(pyramid_images[i], dstsize=pyramid_images[i-1].shape[:2])
            lpls = cv.subtract(pyramid_images[i-1], expand)
            cv.imshow('lapalian_down_'+str(i), lpls)


# src的大小必须是2的整数幂大小
src = cv.imread('C:/Users/Y/Pictures/Saved Pictures/lena.png')
cv.namedWindow('input image', cv.WINDOW_AUTOSIZE)
cv.imshow('input image', src)
lapalian_demo(src)

cv.waitKey(0)
cv.destroyAllWindows() 

高斯金字塔

拉普拉斯金字塔