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An implementation of the hough transform for demonstration purpose.
/*
* hough_impl.cpp
*
* Created on: Dec 11, 2012
* Author: tan
*
* Related blog post at:
* http://sidekick.windforwings.com/2012/12/implementing-hough-transform.html
*/
#include <opencv/cv.h>
#include <opencv/highgui.h>
#include <opencv2/core/types_c.h>
#include <math.h>
#include <stdlib.h>
#define WINDOW_NAME "Hough Transformation"
#define THETA_GRANULARITY (4*100)
#define RHO_GRANULARITY 1
IplImage *img_read;
IplImage *img_edges;
IplImage *img_sine;
int *img_sine_arr;
int threshold;
CvSize img_attrib_dim;
CvSize img_attrib_sine;
int max_rho;
/*****************************************************************
* create and destroy gui items
*****************************************************************/
void create_gui() {
cvNamedWindow(WINDOW_NAME);
max_rho = sqrt(img_attrib_dim.width*img_attrib_dim.width + img_attrib_dim.height*img_attrib_dim.height);
printf("Image diagonal size (max rho): %d\n", max_rho);
img_attrib_sine.width = THETA_GRANULARITY;
img_attrib_sine.height = RHO_GRANULARITY * max_rho * 2;
img_sine_arr = (int *)malloc(img_attrib_sine.width*img_attrib_sine.height*sizeof(int));
img_edges = cvCreateImage(img_attrib_dim, IPL_DEPTH_8U, 1);
img_sine = cvCreateImage(img_attrib_sine, IPL_DEPTH_8U, 1);
cvZero(img_sine);
}
void destroy_gui() {
cvDestroyWindow(WINDOW_NAME);
cvReleaseImage(&img_read);
cvReleaseImage(&img_edges);
cvReleaseImage(&img_sine);
}
/*****************************************************************
* display a message and wait for escape key to continue
*****************************************************************/
void disp_msg(const char *msg) {
printf("%s. Press escape to continue.\n", msg);
char c;
do {
c = cvWaitKey(500);
} while (27 != c);
}
/*****************************************************************
* main.
* 1. read image
* 2. detect edges
* 3. hough transform to detect lines
*****************************************************************/
int main(int argc, char **argv) {
if(argc < 3) {
printf("Usage: %s <image> <threshold>\n", argv[0]);
return 1;
}
img_read = cvLoadImage(argv[1]);
if(NULL == img_read) {
printf("Error loading image %s\n", argv[1]);
return -1;
}
img_attrib_dim = cvGetSize(img_read);
threshold = atoi(argv[2]);
create_gui();
cvShowImage(WINDOW_NAME, img_read);
printf("Original image size: %d x %d\n", img_attrib_dim.width, img_attrib_dim.height);
disp_msg("This is the original image");
// detect edges
cvCvtColor(img_read, img_edges, CV_BGR2GRAY);
cvLaplace(img_edges, img_edges, 3);
cvThreshold(img_edges, img_edges, 200, 255, CV_THRESH_BINARY);
cvShowImage(WINDOW_NAME, img_edges);
disp_msg("This is the edge detected image");
printf("working...\n");
// for each pixel in the edge
int max_dest = 0;
int min_dest = INT_MAX;
for(int y=0; y < img_edges->height; y++) {
uchar *row_ptr = (uchar*) (img_edges->imageData + y*img_edges->widthStep);
for(int x=0; x < img_edges->width; x++) {
if(*(row_ptr+x) > 0) {
for(int theta_div=0; theta_div < THETA_GRANULARITY; theta_div++) {
double theta = (CV_PI * theta_div / THETA_GRANULARITY) - (CV_PI / 2);
int rho = (int)round(cos(theta)*x + sin(theta)*y + max_rho);
int *dest = img_sine_arr + rho*img_attrib_sine.width + theta_div;
int d_val = *dest = *dest + 1;
if(d_val > max_dest) max_dest = d_val;
if(d_val < min_dest) min_dest = d_val;
}
}
}
}
// scale the intensity for contrast
float div = ((float)max_dest)/255;
printf("max_dest: %d, min_dest: %d, scale: %f\n", max_dest, min_dest, div);
for(int y=0; y < img_sine->height; y++) {
uchar *row_ptr = (uchar*) (img_sine->imageData + y*img_sine->widthStep);
for(int x=0; x < img_sine->width; x++) {
int val = (*((img_sine_arr + y*img_attrib_sine.width) + x))/div;
if (val < 0) val = 0;
*(row_ptr + x) = val;
}
}
// find rho and theta at maximum positions (within the threshold)
int possible_edge = round((float)max_dest/div) - threshold;
printf("possible edges beyond %d\n", possible_edge);
for(int y=0; y < img_sine->height; y++) {
uchar *row_ptr = (uchar*) (img_sine->imageData + y*img_sine->widthStep);
for(int x=0; x < img_sine->width; x++) {
int val = *(row_ptr + x);
if(possible_edge <= val) {
float theta_rad = (CV_PI * x / THETA_GRANULARITY) - (CV_PI/2);
float theta_deg = theta_rad * 180 / CV_PI;
printf("val: %d at rho %d, theta %f (%f degrees)\n", val, y-max_rho, theta_rad, theta_deg);
}
}
}
// display the plotted intensity graph of the hough space
cvShowImage(WINDOW_NAME, img_sine);
disp_msg("this is the hough space image");
destroy_gui();
return 0;
}
@lavenderziyi

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@lavenderziyi lavenderziyi commented Mar 21, 2013

I managed to solve the sqrt problem and run the program. Unfortunately nothing came out. I guess it's because I didn't load any images. Where shall I load it? What are argv[0], argv[1] and argv[2]?

@lavenderziyi

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@lavenderziyi lavenderziyi commented Mar 21, 2013

Can you plesae email me at lavenderziyi@hotmail.com? Thank you so much

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