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#define _BSD_SOURCE
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <gdk-pixbuf/gdk-pixbuf.h>
struct mat2 {
float a1, a2, b1, b2;
float mc;
};
static inline float
det(struct mat2 *m)
{
return m->a1 * m->b2 - m->a2 * m->b1;
}
static inline float
trace(struct mat2 *m)
{
return m->a1 + m->b2;
}
static inline void
pixbuf_get(GdkPixbuf *pixbuf, guchar **pixels,
gint *width, gint *height, gint *nch, gint *stride)
{
if (pixels) *pixels = gdk_pixbuf_get_pixels(pixbuf);
if (width) *width = gdk_pixbuf_get_width(pixbuf);
if (height) *height = gdk_pixbuf_get_height(pixbuf);
if (nch) *nch = gdk_pixbuf_get_n_channels(pixbuf);
if (stride) *stride = gdk_pixbuf_get_rowstride(pixbuf);
}
static void
grey_scale(GdkPixbuf *image)
{
gint Y, x, y, width, height, nch, stride;
guchar *p, *row;
pixbuf_get(image, &row, &width, &height, &nch, &stride);
for (y = 0; y < height; ++y, row += stride) {
for (x = 0, p = row; x < width; ++x, p += nch) {
Y = 0.299 * p[0] + 0.587 * p[1] + 0.115 * p[2];
p[0] = p[1] = p[2] = Y;
}
}
}
int *
conv(GdkPixbuf *pixbuf, gint *operator, gint block_size)
{
gint Y, i, j, ci, cj, x, y, width, height, nch, stride;
guchar *p, *row, v;
int *out;
pixbuf_get(pixbuf, &row, &width, &height, &nch, &stride);
out = malloc(width * height * sizeof *out);
if (!out)
return NULL;
for (y = 0; y < height; ++y, row += stride) {
for (x = 0, p = row; x < width; ++x, p += nch) {
Y = 0;
for (j = 0; j < block_size; ++j) {
cj = CLAMP(j - block_size/2, -y, height-1-y);
for (i = 0; i < block_size; ++i) {
ci = CLAMP(i - block_size/2, -x, width-1-x);
v = p[cj * stride + ci * nch + 0];
Y += v * operator[j*block_size + i];
}
}
*out++ = Y/4;
}
}
return out - width*height;
}
struct mat2 *
multiply(int *deriv_x, int *deriv_y, int width, int height)
{
struct mat2 *m, *pm;
int *px, *py;
int i, n;
n = width * height;
m = calloc(n, sizeof *m);
if (!m)
return NULL;
px = deriv_x;
py = deriv_y;
pm = m;
for (i = 0; i < n; ++i) {
pm->a1 = *px * *px;
pm->a2 = pm->b1 = *px * *py;
pm->b2 = *py * *py;
++px; ++py; ++pm;
}
return m;
}
struct mat2 *
calc_window_sum(struct mat2 *m, int width, int height, int wsize)
{
struct mat2 *avg, *v;
float w;
int x, y, i, j;
avg = calloc(width * height, sizeof *avg);
if (!avg)
return NULL;
for (y = 0; y < height; ++y) {
for (x = 0; x < width; ++x) {
for (j = -wsize/2; j < wsize/2; ++j) {
for (i = -wsize/2; i < wsize/2; ++i) {
v = &m[(CLAMP(y+j, 0, height-1) * width
+ CLAMP(x+i, 0, width-1))];
w = (M_1_PI * 1.0 / (2.0 * 0.16) *
exp(- i*i - j*j / 0.16));
avg->a1 += w * v->a1;
avg->a2 += w * v->a2;
avg->b1 += w * v->b1;
avg->b2 += w * v->b2;
}
}
++avg;
}
}
return avg - width*height;
}
gboolean
check_neighbours(struct mat2 *m, int x, int y, int width, int height)
{
int i, j;
gboolean max = TRUE;
int n = 2;
for (j = MAX(0, y-n); j < MIN(y+n, height-1); ++j) {
for (i = MAX(0, x-n); i < MIN(x+n, width-1); ++i) {
if (m[j * width + i].mc > m[y * width + x].mc)
max = FALSE;
}
}
return max;
}
int
main(int argc, char *argv[])
{
GdkPixbuf *image, *grey;
int *deriv_x, *deriv_y;
gint sobel_x[] = {
1, 0, -1,
2, 0, -2,
1, 0, -1
};
gint sobel_y[] = {
1, 2, 1,
0, 0, 0,
-1, -2, -1
};
const float k = 0.04;
int x, y, width, height, size, nch, stride;
struct mat2 *m, *n, *c;
guchar *p, *row;
float max_mc, threshold;
if (argc < 2)
return 1;
g_type_init();
image = gdk_pixbuf_new_from_file(argv[1], NULL);
if (!image)
return 1;
width = gdk_pixbuf_get_width(image);
height = gdk_pixbuf_get_height(image);
grey = gdk_pixbuf_copy(image);
grey_scale(grey);
deriv_x = conv(grey, sobel_x, 3);
deriv_y = conv(grey, sobel_y, 3);
gdk_pixbuf_save(grey, argc > 3 ? argv[3] : "grey.tiff", "tiff",
NULL, NULL);
m = multiply(deriv_x, deriv_y, width, height);
n = calc_window_sum(m, width, height, 9);
free(m);
max_mc = 0;
size = width * height;
for (c = n; c < n+size; ++c) {
c->mc = det(c) - k * trace(c) * trace(c);
if (c->mc > max_mc)
max_mc = c->mc;
}
printf("max_mc: %f\n", max_mc);
threshold = 0.001 * max_mc;
pixbuf_get(grey, &row, &width, &height, &nch, &stride);
for (y = 0; y < height; ++y, row += stride) {
for (x = 0, p = row; x < width; ++x, p += nch) {
if (n[y * width + x].mc > threshold &&
check_neighbours(n, x, y, width, height)) {
p[0] = 255;
p[1] = 0;
p[2] = 0;
printf("corner at: %d, %d\n", x, y);
}
}
}
gdk_pixbuf_save(grey, argc > 2 ? argv[2] : "harris.tiff", "tiff",
NULL, NULL);
free(n);
free(deriv_x);
free(deriv_y);
g_object_unref(image);
g_object_unref(grey);
return 0;
}
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