Below is an example of a simple module, that rotates a float image
using a bilinear interpolation.
As you can see, the main part of the program is devoted to the algorithm :
only a short header describes the inputs/outputs of the module and only
one line handles memory allocations.
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/*--------------------------- Commande MegaWave -----------------------------*/
/* mwcommand
name = {frot};
version = {"1.0"};
author = {"Lionel Moisan"};
function = {"Rotate a Fimage using bilinear interpolation"};
usage = {
'a':[a=0.0]->a "rotation angle (in degrees, counterclockwise, default 0.0)",
'b':[b=0.0]->b "background grey value (default: 0.0)",
'k'->k_flag "to keep original input image size (keep center position)",
in->in "input Fimage",
out<-out "output Fimage"
};
*/
#include <stdio.h>
#include <math.h>
#include "mw.h"
void bound(x,y,ca,sa,xmin,xmax,ymin,ymax)
int x,y;
float ca,sa;
int *xmin,*xmax,*ymin,*ymax;
{
int rx,ry;
rx = (int)floor(ca*(float)x+sa*(float)y);
ry = (int)floor(-sa*(float)x+ca*(float)y);
if (rx<*xmin) *xmin=rx; if (rx>*xmax) *xmax=rx;
if (ry<*ymin) *ymin=ry; if (ry>*ymax) *ymax=ry;
}
/* NB : calling this module with out=in is nonsense */
void frot(in,out,a,b,k_flag)
Fimage in,out;
float *a,*b;
char *k_flag;
{
int nx,ny,x,y,x1,y1,adr;
float ca,sa,xp,yp,a11,a12,a21,a22,ux,uy,xtrans,ytrans;
int tx1,ty1,tx2,ty2,xmin,xmax,ymin,ymax,sx,sy;
nx = in->ncol;
ny = in->nrow;
ca = (float)cos((double)(*a)*M_PI/180.0);
sa = (float)sin((double)(*a)*M_PI/180.0);
/********** Compute new image location **********/
if (k_flag) {
/* crop image and fix center */
xmin = ymin = 0;
xmax = nx-1;
ymax = ny-1;
xtrans = 0.5*( (float)(nx-1)*(1.0-ca)+(float)(ny-1)*sa );
ytrans = 0.5*( (float)(ny-1)*(1.0-ca)-(float)(nx-1)*sa );
} else {
/* extend image size to include the whole input image */
xmin = xmax = ymin = ymax = 0;
bound(nx-1,0,ca,sa,&xmin,&xmax,&ymin,&ymax);
bound(0,ny-1,ca,sa,&xmin,&xmax,&ymin,&ymax);
bound(nx-1,ny-1,ca,sa,&xmin,&xmax,&ymin,&ymax);
xtrans = ytrans = 0.0;
}
sx = xmax-xmin+1;
sy = ymax-ymin+1;
out = mw_change_fimage(out,sy,sx);
if (!out) mwerror(FATAL,1,"not enough memory\n");
/********** Rotate image **********/
for (x=xmin;x<=xmax;x++)
for (y=ymin;y<=ymax;y++) {
xp = ca*(float)x-sa*(float)y + xtrans;
yp = sa*(float)x+ca*(float)y + ytrans;
x1 = (int)floor(xp);
y1 = (int)floor(yp);
ux = xp-(float)x1;
uy = yp-(float)y1;
adr = y1*nx+x1;
tx1 = (x1>=0 && x1<nx);
tx2 = (x1+1>=0 && x1+1<nx);
ty1 = (y1>=0 && y1<ny);
ty2 = (y1+1>=0 && y1+1<ny);
a11 = (tx1 && ty1? in->gray[adr]:*b);
a12 = (tx1 && ty2? in->gray[adr+nx]:*b);
a21 = (tx2 && ty1? in->gray[adr+1]:*b);
a22 = (tx2 && ty2? in->gray[adr+nx+1]:*b);
out->gray[(y-ymin)*sx+x-xmin] =
(1.0-uy)*((1.0-ux)*a11+ux*a21)+uy*((1.0-ux)*a12+ux*a22);
}
}
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An example of a module written for MegaWave2
