/**
*
* Function to upsample the image
*
**/
void zoom_in(
const float *I, // input image
float *Iout, // output image
int nx, // width of the original image
int ny, // height of the original image
int nxx, // width of the zoomed image
int nyy // height of the zoomed image
)
{
// compute the zoom factor
const float factorx = ((float)nxx / nx);
const float factory = ((float)nyy / ny);
// re-sample the image using bicubic interpolation
#pragma omp parallel for
for (int i1 = 0; i1 < nyy; i1++)
for (int j1 = 0; j1 < nxx; j1++)
{
float i2 = (float) i1 / factory;
float j2 = (float) j1 / factorx;
float g = bicubic_interpolation_at(I, j2, i2, nx, ny, false);
Iout[i1 * nxx + j1] = g;
}
}
/**
*
* Compute the bicubic interpolation of an image.
*
**/
static void bicubic_interpolation_warp(
const float *input, //image to be warped
const float *u, //x component of the vector field
const float *v, //y component of the vector field
float *output, //warped output image with bicubic interpolation
const int nx, //image width
const int ny, //image height
bool border_out//if true, put zeros outside the region
)
{
#ifdef _OPENMP
#pragma omp parallel for
#endif
for(int i = 0; i < ny; i++)
for(int j = 0; j < nx; j++)
{
const int p = i * nx + j;
const float uu = (float) (j + u[p]);
const float vv = (float) (i + v[p]);
//obtain the bicubic interpolation at position (uu, vv)
output[p] = bicubic_interpolation_at(input,
uu, vv, nx, ny, border_out);
}
}
/**
*
* Downsample an image
*
**/
static void zoom_out(
const float *I, // input image
float *Iout, // output image
const int nx, // image width
const int ny, // image height
const float factor // zoom factor between 0 and 1
)
{
// temporary working image
float *Is = xmalloc(nx * ny * sizeof(float));
for(int i = 0; i < nx * ny; i++)
Is[i] = I[i];
// compute the size of the zoomed image
int nxx, nyy;
zoom_size(nx, ny, &nxx, &nyy, factor);
// compute the Gaussian sigma for smoothing
const float sigma = ZOOM_SIGMA_ZERO * sqrt(1.0/(factor*factor) - 1.0);
// pre-smooth the image
gaussian_smoothing_in_place(Is, nx, ny, sigma);
// re-sample the image using bicubic interpolation
#ifdef _OPENMP
#pragma omp parallel for
#endif
for (int i1 = 0; i1 < nyy; i1++)
for (int j1 = 0; j1 < nxx; j1++)
{
const float i2 = (float) i1 / factor;
const float j2 = (float) j1 / factor;
float g = bicubic_interpolation_at(Is, j2, i2, nx, ny, false);
Iout[i1 * nxx + j1] = g;
}
free(Is);
}