python双三次插值

opencv双三次插值方法

import cv2
import numpy as np
import math


def S(x):
    x = np.abs(x)
    if 0 <= x < 1:
        return 1 - 2 * x * x + x * x * x
    if 1 <= x < 2:
        return 4 - 8 * x + 5 * x * x - x * x * x
    else:
        return 0
def function(img,m,n):
    height,width,channels =img.shape
    emptyImage=np.zeros((m,n,channels),np.uint8)
    sh=m/height
    sw=n/width
    for i in range(m):
        for j in range(n):
            x = i/sh
            y = j/sw
            p=(i+0.0)/sh-x
            q=(j+0.0)/sw-y
            x=int(x)-2
            y=int(y)-2
            A = np.array([
                [S(1 + p), S(p), S(1 - p), S(2 - p)]
            ])
            if x>=m-3:
                m-1
            if y>=n-3:
                n-1
            if x>=1 and x<=(m-3) and y>=1 and y<=(n-3):
                B = np.array([
                    [img[x-1, y-1], img[x-1, y],
                     img[x-1, y+1],
                     img[x-1, y+1]],
                    [img[x, y-1], img[x, y],
                     img[x, y+1], img[x, y+2]],
                    [img[x+1, y-1], img[x+1, y],
                     img[x+1, y+1], img[x+1, y+2]],
                    [img[x+2, y-1], img[x+2, y],
                     img[x+2, y+1], img[x+2, y+1]],

                    ])
                C = np.array([
                    [S(1 + q)],
                    [S(q)],
                    [S(1 - q)],
                    [S(2 - q)]
                ])
                blue = np.dot(np.dot(A, B[:, :, 0]), C)[0, 0]
                green = np.dot(np.dot(A, B[:, :, 1]), C)[0, 0]
                red = np.dot(np.dot(A, B[:, :, 2]), C)[0, 0]

                # ajust the value to be in [0,255]
                def adjust(value):
                    if value > 255:
                        value = 255
                    elif value < 0:
                        value = 0
                    return value

                blue = adjust(blue)
                green = adjust(green)
                red = adjust(red)
                emptyImage[i, j] = np.array([blue, green, red], dtype=np.uint8)


    return emptyImage

img=cv2.imread("e:\\lena.bmp")
zoom=function(img,1024,1024)
cv2.imshow("cubic",zoom)
cv2.imshow("image",img)
cv2.waitKey(0)