warp_mbyte_projective_bilinear
Tcl_Obj* imageObj
Tcl_Obj* forwardObj
/*
* Warp image using the given specified transform. The result is made large
* enough to contain all of the warped image, and will contain meta data about
* the location of the actual (0,0) origin point relative to the physical top
* left corner of the result. This last is required because translations in
* the transform may move pixels to negative positions which we cannot express
* with the regular memory grid.
*/
crimp_image* image;
crimp_image* forward;
crimp_image* backward;
crimp_image* result;
int x, y, xt, yt, origx, origy, c;
double xf, yf;
crimp_input_any (imageObj, image);
CRIMP_ASSERT_NOTIMGTYPE (image, float);
CRIMP_ASSERT_NOTIMGTYPE (image, grey16);
CRIMP_ASSERT_NOTIMGTYPE (image, grey32);
crimp_input (forwardObj, forward, float);
if (!crimp_require_dim (forward, 3, 3)) {
Tcl_SetResult(interp, "bad matrix dimensions, expected 3x3", TCL_STATIC);
return TCL_ERROR;
}
backward = crimp_la_invert_matrix_3x3 (forward);
if (!backward) {
Tcl_SetResult(interp, "Unable to invert singular matrix", TCL_STATIC);
return TCL_ERROR;
}
/*
* Determine size of the result, and the location of the origin point inside
* based on the four corners of the input image and the forward transformation.
*/
result = crimp_geo_warp_init (image, forward, &origx, &origy);
for (y = 0, yt = origy; y < crimp_h (result); y++, yt++) {
for (x = 0, xt = origx; x < crimp_w (result); x++, xt++) {
int ixw, iyw;
xf = xt;
yf = yt;
crimp_geo_warp_point (backward, &xf, &yf);
/*
* Perform bilinear interpolation (1) using the nearest 2x2 pixels
* around the sampling location.
*
* (Ad 1) http://en.wikipedia.org/wiki/Bilinear_interpolation
*/
ixw = xf;
iyw = yf;
xf -= ixw;
yf -= iyw;
for (c = 0; c < 4; ++c) {
float val = 0;
int ix, iy;
double yft = yf;
for (iy = MAX(iyw, 0); iy < MIN(iyw + 2, crimp_h (image)); iy++) {
yft = 1 - yft;
double xft = xf;
for (ix = MAX(ixw, 0); ix < MIN(ixw + 2, crimp_w (image)); ix++) {
xft = 1 - xft;
val += CH (image, c, ix, iy) * yft * xft;
}
}
CH (result, c, x, y) = val;
}
}
}
crimp_del (backward);
Tcl_SetObjResult(interp, crimp_new_image_obj (result));
return TCL_OK;
/* vim: set sts=4 sw=4 tw=80 et ft=c: */
/*
* Local Variables:
* mode: c
* c-basic-offset: 4
* fill-column: 78
* End:
*/