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optical_flow.cpp
/*******************************************************
* Copyright (c) 2014, ArrayFire
* All rights reserved.
*
* This file is distributed under 3-clause BSD license.
* The complete license agreement can be obtained at:
* http://arrayfire.com/licenses/BSD-3-Clause
********************************************************/
#include <string.h>
#include <stdio.h>
#include <math.h>
#include <algorithm>
#include <arrayfire.h>
using namespace af;
static void diffs(array& Ix, array& Iy, array& It, array I1, array I2)
{
// 3x3 derivative kernels
float dx_kernel[] = { -1.0f / 6.0f, -1.0f / 6.0f, -1.0f / 6.0f,
0.0f / 6.0f, 0.0f / 6.0f, 0.0f / 6.0f,
1.0f / 6.0f, 1.0f / 6.0f, 1.0f / 6.0f
};
float dy_kernel[] = { -1.0f / 6.0f, 0.0f / 6.0f, 1.0f / 6.0f,
-1.0f / 6.0f, 0.0f / 6.0f, 1.0f / 6.0f,
-1.0f / 6.0f, 0.0f / 6.0f, 1.0f / 6.0f
};
array dx = array(dim4(3, 3), dx_kernel);
array dy = array(dim4(3, 3), dy_kernel);
array dt = constant(1,1, 2) / 4.0;
Ix = convolve(I1, dx) + convolve(I2, dx);
Iy = convolve(I1, dy) + convolve(I2, dy);
It = convolve(I2, dt) - convolve(I1, dt);
}
static void optical_flow_demo(bool console)
{
af::Window wnd("Horn-Schunck Optical Flow Demo");
wnd.setColorMap(AF_COLORMAP_COLORS);
double time_total = 10; // run for N seconds
const float h_mean_kernel[] = {1.0f / 12.0f, 2.0f / 12.0f, 1.0f / 12.0f,
2.0f / 12.0f, 0.0f, 2.0f / 12.0f,
1.0f / 12.0f, 2.0f / 12.0f, 1.1f / 12.0f
};
array mean_kernel = array(dim4(3, 3), h_mean_kernel, afHost);
array I1 = loadImage(ASSETS_DIR "/examples/images/circle_left.ppm"); // grayscale
array I2 = loadImage(ASSETS_DIR "/examples/images/circle_center.ppm");
array u = constant(0,I1.dims()), v = constant(0,I1.dims());
array Ix, Iy, It; diffs(Ix, Iy, It, I1, I2);
timer time_start, time_last;
time_start = time_last = timer::start();
int iter = 0, iter_last = 0;
double max_rate = 0;
while (true) {
iter++;
array u_ = convolve(u, mean_kernel);
array v_ = convolve(v, mean_kernel);
const float alphasq = 0.1f;
array num = Ix * u_ + Iy * v_ + It;
array den = alphasq + Ix * Ix + Iy * Iy;
array tmp = 0.01 * num;
u = u_ - (Ix * tmp) / den;
v = v_ - (Iy * tmp) / den;
if (!console) {
wnd.grid(2,2);
wnd(0, 0).image(I1, "I1");
wnd(1, 0).image(I2, "I2");
wnd(0, 1).image(u, "u");
wnd(1, 1).image(v, "v");
wnd.show();
}
double elapsed = timer::stop(time_last);
if (elapsed > 1) {
double rate = (iter - iter_last) / elapsed;
double total_elapsed = timer::stop(time_start);
time_last = timer::start();
iter_last = iter;
max_rate = std::max(max_rate, rate);
if (total_elapsed >= time_total) {
break;
}
if (!console)
printf(" iterations per second: %.0f (progress %.0f%%)\n",
rate, 100.0f * total_elapsed / time_total);
}
}
if (console) {
printf(" ### optical_flow %f iterations per second (max)\n", max_rate);
}
}
int main(int argc, char* argv[])
{
int device = argc > 1 ? atoi(argv[1]) : 0;
bool console = argc > 2 ? argv[2][0] == '-' : false;
try {
af::setDevice(device);
af::info();
printf("Horn-Schunck optical flow\n");
optical_flow_demo(console);
} catch (af::exception& e) {
fprintf(stderr, "%s\n", e.what());
throw;
}
#ifdef WIN32 // pause in Windows
if (!console) {
printf("hit [enter]...");
fflush(stdout);
getchar();
}
#endif
return 0;
}