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| #include <math.h>
#include <assert.h>
#include <string.h>
#include "mex.h"
/*
* Fast image subsampling.
* This is used to construct the feature pyramid.
*/
// struct used for caching interpolation values
struct alphainfo {
int si, di;
double alpha;
};
// copy src into dst using pre-computed interpolation values
void alphacopy(double *src, double *dst, struct alphainfo *ofs, int n) {
struct alphainfo *end = ofs + n;
while (ofs != end) {
dst[ofs->di] += ofs->alpha * src[ofs->si];
ofs++;
}
}
// resize along each column
// result is transposed, so we can apply it twice for a complete resize
void resize1dtran(double *src, int sheight, double *dst, int dheight,
int width, int chan) {
double scale = (double)dheight/(double)sheight;
double invscale = (double)sheight/(double)dheight;
// we cache the interpolation values since they can be
// shared among different columns
int len = (int)ceil(dheight*invscale) + 2*dheight;
alphainfo ofs[len];
int k = 0;
for (int dy = 0; dy < dheight; dy++) {
double fsy1 = dy * invscale;
double fsy2 = fsy1 + invscale;
int sy1 = (int)ceil(fsy1);
int sy2 = (int)floor(fsy2);
if (sy1 - fsy1 > 1e-3) {
assert(k < len);
assert(sy-1 >= 0);
ofs[k].di = dy*width;
ofs[k].si = sy1-1;
ofs[k++].alpha = (sy1 - fsy1) * scale;
}
for (int sy = sy1; sy < sy2; sy++) {
assert(k < len);
assert(sy < sheight);
ofs[k].di = dy*width;
ofs[k].si = sy;
ofs[k++].alpha = scale;
}
if (fsy2 - sy2 > 1e-3) {
assert(k < len);
assert(sy2 < sheight);
ofs[k].di = dy*width;
ofs[k].si = sy2;
ofs[k++].alpha = (fsy2 - sy2) * scale;
}
}
// resize each column of each color channel
bzero(dst, chan*width*dheight*sizeof(double));
for (int c = 0; c < chan; c++) {
for (int x = 0; x < width; x++) {
double *s = src + c*width*sheight + x*sheight;
double *d = dst + c*width*dheight + x;
alphacopy(s, d, ofs, k);
}
}
}
// main function
// takes a double color image and a scaling factor
// returns resized image
mxArray *resize(const mxArray *mxsrc, const mxArray *mxscale) {
double *src = (double *)mxGetPr(mxsrc);
const int *sdims = mxGetDimensions(mxsrc);
if (mxGetNumberOfDimensions(mxsrc) != 3 ||
mxGetClassID(mxsrc) != mxDOUBLE_CLASS)
mexErrMsgTxt("Invalid input");
double scale = mxGetScalar(mxscale);
if (scale > 1)
mexErrMsgTxt("Invalid scaling factor");
int ddims[3];
ddims[0] = (int)round(sdims[0]*scale);
ddims[1] = (int)round(sdims[1]*scale);
ddims[2] = sdims[2];
mxArray *mxdst = mxCreateNumericArray(3, ddims, mxDOUBLE_CLASS, mxREAL);
double *dst = (double *)mxGetPr(mxdst);
double *tmp = (double *)mxCalloc(ddims[0]*sdims[1]*sdims[2], sizeof(double));
resize1dtran(src, sdims[0], tmp, ddims[0], sdims[1], sdims[2]);
resize1dtran(tmp, sdims[1], dst, ddims[1], ddims[0], sdims[2]);
mxFree(tmp);
return mxdst;
}
// matlab entry point
// dst = resize(src, scale)
// image should be color with double values
void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) {
if (nrhs != 2)
mexErrMsgTxt("Wrong number of inputs");
if (nlhs != 1)
mexErrMsgTxt("Wrong number of outputs");
plhs[0] = resize(prhs[0], prhs[1]);
} |
