iOS & OpenCV: Image Registration / Alignment

问题

I am doing a project of combining multiple images similar to HDR in iOS. I have managed to get 3 images of different exposures through the Camera and now I want to align them because during the capture, one's hand must have shaken and resulted in all 3 images having slightly different alignment.

I have imported OpenCV framework and I have been exploring functions in OpenCV to align/register images, but found nothing. Is there actually a function in OpenCV to achieve this? If not, is there any other alternatives?

Thanks!

回答1:

There is no single function called something like align, you need to do/implement it yourself, or find an already implemented one.

Here is a one solution.

You need to extract keypoints from all 3 images and try to match them. Be sure that your keypoint extraction technique is invariant to illumination changes since all have different intensity values because of different exposures. You need to match your keypoints and find some disparity. Then you can use disparity to align your images.

Remember this answer is so superficial, for details first you need to do some research about keypoint/descriptor extraction, and keypoint/descriptor matching.

Good luck!

回答2:

In OpenCV 3.0 you can use findTransformECC. I have copied this ECC Image Alignment code from LearnOpenCV.com where a very similar problem is solved for aligning color channels. The post also contains code in Python. Hope this helps.

// Read the images to be aligned
Mat im1 = imread("images/image1.jpg");
Mat im2 = imread("images/image2.jpg");

// Convert images to gray scale;
Mat im1_gray, im2_gray;
cvtColor(im1, im1_gray, CV_BGR2GRAY);
cvtColor(im2, im2_gray, CV_BGR2GRAY);

// Define the motion model
const int warp_mode = MOTION_EUCLIDEAN;

// Set a 2x3 or 3x3 warp matrix depending on the motion model.
Mat warp_matrix;

// Initialize the matrix to identity
if ( warp_mode == MOTION_HOMOGRAPHY )
   warp_matrix = Mat::eye(3, 3, CV_32F);
else
    warp_matrix = Mat::eye(2, 3, CV_32F);

// Specify the number of iterations.
int number_of_iterations = 5000;

// Specify the threshold of the increment
// in the correlation coefficient between two iterations
double termination_eps = 1e-10;

// Define termination criteria
TermCriteria criteria (TermCriteria::COUNT+TermCriteria::EPS,   number_of_iterations, termination_eps);

// Run the ECC algorithm. The results are stored in warp_matrix.
findTransformECC(
             im1_gray,
             im2_gray,
             warp_matrix,
             warp_mode,
             criteria
          );

// Storage for warped image.
Mat im2_aligned;

if (warp_mode != MOTION_HOMOGRAPHY)
    // Use warpAffine for Translation, Euclidean and Affine
    warpAffine(im2, im2_aligned, warp_matrix, im1.size(), INTER_LINEAR + WARP_INVERSE_MAP);
else
    // Use warpPerspective for Homography
    warpPerspective (im2, im2_aligned, warp_matrix, im1.size(),INTER_LINEAR + WARP_INVERSE_MAP);

// Show final result
imshow("Image 1", im1);
imshow("Image 2", im2);
imshow("Image 2 Aligned", im2_aligned);
waitKey(0);

来源：https://stackoverflow.com/questions/20584527/ios-opencv-image-registration-alignment

标签

ios

image

OpenCV

alignment

registration