learnopencv/WarpTriangle/warpTriangle.py

#!/usr/bin/env python

# Copyright (c) 2016 Satya Mallick <spmallick@learnopencv.com>
# All rights reserved. No warranty, explicit or implicit, provided.

import cv2
import numpy as np


# Warps and alpha blends triangular regions from img1 and img2 to img
def warpTriangle(img1, img2, tri1, tri2) :
    
    # Find bounding rectangle for each triangle
    r1 = cv2.boundingRect(tri1)
    r2 = cv2.boundingRect(tri2)
    
    # Offset points by left top corner of the respective rectangles
    tri1Cropped = []
    tri2Cropped = []
    
    for i in xrange(0, 3):
        tri1Cropped.append(((tri1[0][i][0] - r1[0]),(tri1[0][i][1] - r1[1])))
        tri2Cropped.append(((tri2[0][i][0] - r2[0]),(tri2[0][i][1] - r2[1])))

    # Crop input image
    img1Cropped = img1[r1[1]:r1[1] + r1[3], r1[0]:r1[0] + r1[2]]

    # Given a pair of triangles, find the affine transform.
    warpMat = cv2.getAffineTransform( np.float32(tri1Cropped), np.float32(tri2Cropped) )
    
    # Apply the Affine Transform just found to the src image
    img2Cropped = cv2.warpAffine( img1Cropped, warpMat, (r2[2], r2[3]), None, flags=cv2.INTER_LINEAR, borderMode=cv2.BORDER_REFLECT_101 )

    # Get mask by filling triangle
    mask = np.zeros((r2[3], r2[2], 3), dtype = np.float32)
    cv2.fillConvexPoly(mask, np.int32(tri2Cropped), (1.0, 1.0, 1.0), 16, 0);

    img2Cropped = img2Cropped * mask
    
    # Copy triangular region of the rectangular patch to the output image
    img2[r2[1]:r2[1]+r2[3], r2[0]:r2[0]+r2[2]] = img2[r2[1]:r2[1]+r2[3], r2[0]:r2[0]+r2[2]] * ( (1.0, 1.0, 1.0) - mask )
    
    img2[r2[1]:r2[1]+r2[3], r2[0]:r2[0]+r2[2]] = img2[r2[1]:r2[1]+r2[3], r2[0]:r2[0]+r2[2]] + img2Cropped


if __name__ == '__main__' :

    # Read input image
    imgIn = cv2.imread("robot.jpg")
    
    # Output image is set to white
    imgOut = 255 * np.ones(imgIn.shape, dtype = imgIn.dtype)
    
    # Input triangle
    triIn = np.float32([[[360,200], [60,250], [450,400]]])
    
    # Output triangle
    triOut = np.float32([[[400,200], [160,270], [400,400]]])
    
    # Warp all pixels inside input triangle to output triangle
    warpTriangle(imgIn, imgOut, triIn, triOut)

    # Draw triangle using this color
    color = (255, 150, 0)

    # Draw triangles in input and output images.
    cv2.polylines(imgIn, triIn.astype(int), True, color, 2, 16)
    cv2.polylines(imgOut, triOut.astype(int), True, color, 2, 16)

    cv2.imshow("Input", imgIn)
    cv2.imshow("Output", imgOut)
    
    
    cv2.waitKey(0)