perspective-transform/opencv-perspective-transform.c

   1 #include <stdio.h>
   2 #include <errno.h>
   3 #include <opencv2/core/core_c.h>
   4 #include <opencv2/highgui/highgui_c.h>
   5 #include <opencv2/imgproc/imgproc_c.h>
   6
   7 #define WIDTH 800
   8 #define HEIGHT 480
   9
  10 #define X_CORRECTION 200
  11
  12 int main(int argc, char *argv[])
  13 {
  14         int ret;
  15         IplImage *image;
  16         IplImage *transformed_image;
  17         CvRect viewport;
  18         CvPoint2D32f src[4];
  19         CvPoint2D32f dst[4];
  20         CvMat *perspective_matrix;
  21
  22         if (argc != 2) {
  23                 fprintf(stderr, "usage: %s <image>\n", argv[0]);
  24                 ret = -EINVAL;
  25                 goto out;
  26         }
  27
  28         image = cvLoadImage(argv[1], CV_LOAD_IMAGE_COLOR);
  29         if (!image) {
  30                 fprintf(stderr, "Cannot load image\n");
  31                 ret = -EINVAL;
  32                 goto out;
  33         }
  34
  35         cvNamedWindow("Viewport", 0);
  36         cvResizeWindow("Viewport", WIDTH, HEIGHT);
  37
  38         /* Trasform only a part of the whole image */
  39         viewport.x = 0;
  40         viewport.y = 0;
  41         viewport.width = WIDTH;
  42         viewport.height = HEIGHT;
  43         cvSetImageROI(image, viewport);
  44
  45         /* Calculate the prospective tranformation */
  46         src[0].x = 0;
  47         src[0].y = 0;
  48         src[1].x = WIDTH;
  49         src[1].y = 0;
  50         src[2].x = WIDTH;
  51         src[2].y = HEIGHT;
  52         src[3].x = 0;
  53         src[3].y = HEIGHT;
  54
  55         dst[0].x = X_CORRECTION;
  56         dst[0].y = 0;
  57         dst[1].x = WIDTH - X_CORRECTION;
  58         dst[1].y = 0;
  59         dst[2].x = WIDTH;
  60         dst[2].y = HEIGHT;
  61         dst[3].x = 0;
  62         dst[3].y = HEIGHT;
  63
  64         perspective_matrix = cvCreateMat(3, 3, CV_64F);
  65         if (!perspective_matrix) {
  66                 fprintf(stderr, "Cannot create matrix\n");
  67                 ret = -EINVAL;
  68                 goto out_destroy_window;
  69         }
  70
  71         perspective_matrix = cvGetPerspectiveTransform(src, dst,
  72                                                        perspective_matrix);
  73
  74         /* Create a new image and apply the prospective transformation */
  75         transformed_image = cvCreateImage(cvSize(WIDTH, HEIGHT), image->depth,
  76                                           image->nChannels);
  77         if (!transformed_image) {
  78                 fprintf(stderr, "Cannot create trasnformed image\n");
  79                 ret = -EINVAL;
  80                 goto out_release_mat;
  81         }
  82
  83         cvWarpPerspective(image, transformed_image, perspective_matrix,
  84                           CV_INTER_LINEAR | CV_WARP_FILL_OUTLIERS,
  85                           cvScalarAll(0));
  86
  87         cvShowImage("Viewport", transformed_image);
  88
  89         cvWaitKey(0);
  90
  91         ret = 0;
  92
  93 out_release_mat:
  94         cvReleaseMat(&perspective_matrix);
  95 out_destroy_window:
  96         cvDestroyWindow("Viewport");
  97         cvReleaseImage(&image);
  98 out:
  99         return ret;
 100 }