88 lines
2.5 KiB
C++
88 lines
2.5 KiB
C++
#include <math.h>
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#include <assert.h>
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#include <string.h>
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#include "mex.h"
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#define round(x) ((x-floor(x))>0.5 ? ceil(x) : floor(x))
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// reduce(im) resizes im to half its size, using a 5-tap binomial filter for anti-aliasing
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// (see Burt & Adelson's Laplacian Pyramid paper)
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// reduce each column
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// result is transposed, so we can apply it twice for a complete reduction
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void reduce1dtran(double *src, int sheight, double *dst, int dheight,
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int width, int chan) {
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// resize each column of each color channel
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//bzero(dst, chan*width*dheight*sizeof(double));
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memset(dst, 0, chan*width*dheight*sizeof(double));
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int y;
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double *s, *d;
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for (int c = 0; c < chan; c++) {
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for (int x = 0; x < width; x++) {
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s = src + c*width*sheight + x*sheight;
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d = dst + c*dheight*width + x;
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// First row
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*d = s[0]*.6875 + s[1]*.2500 + s[2]*.0625;
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for (y = 1; y < dheight-2; y++) {
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s += 2;
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d += width;
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*d = s[-2]*0.0625 + s[-1]*.25 + s[0]*.375 + s[1]*.25 + s[2]*.0625;
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}
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// Last two rows
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s += 2;
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d += width;
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if (dheight*2 <= sheight) {
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*d = s[-2]*0.0625 + s[-1]*.25 + s[0]*.375 + s[1]*.25 + s[2]*.0625;
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} else {
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*d = s[1]*.3125 + s[0]*.3750 + s[-1]*.2500 + s[-2]*.0625;
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}
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s += 2;
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d += width;
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*d = s[0]*.6875 + s[-1]*.2500 + s[-2]*.0625;
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}
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}
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}
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// main function
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// takes a double color image and a scaling factor
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// returns resized image
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mxArray *reduce(const mxArray *mxsrc) {
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double *src = (double *)mxGetPr(mxsrc);
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const int *sdims = mxGetDimensions(mxsrc);
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if (mxGetNumberOfDimensions(mxsrc) != 3 ||
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mxGetClassID(mxsrc) != mxDOUBLE_CLASS)
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mexErrMsgTxt("Invalid input");
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int ddims[3];
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ddims[0] = (int)round(sdims[0]*.5);
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ddims[1] = (int)round(sdims[1]*.5);
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ddims[2] = sdims[2];
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mxArray *mxdst = mxCreateNumericArray(3, ddims, mxDOUBLE_CLASS, mxREAL);
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double *dst = (double *)mxGetPr(mxdst);
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double *tmp = (double *)mxCalloc(ddims[0]*sdims[1]*sdims[2], sizeof(double));
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reduce1dtran(src, sdims[0], tmp, ddims[0], sdims[1], sdims[2]);
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reduce1dtran(tmp, sdims[1], dst, ddims[1], ddims[0], sdims[2]);
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mxFree(tmp);
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return mxdst;
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}
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// matlab entry point
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// dst = resize(src, scale)
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// image should be color with double values
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void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) {
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if (nrhs != 1)
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mexErrMsgTxt("Wrong number of inputs");
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if (nlhs != 1)
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mexErrMsgTxt("Wrong number of outputs");
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plhs[0] = reduce(prhs[0]);
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}
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