Artifact 5eb6c030647e52f047fe5f48ea54fe9223437250:

• File operator/downsampley-float.crimp — part of check-in [122bdc7d78] at 2011-12-14 21:53:28 on branch infinite-plane — Continued from previous commit. Left to check/modify are

  unary: ahe, convolve, region_sum, rof

  binary: atan2, hypot, pow, cannyinternal, complex div/multiply, join, joint-bilateral, threshold

  other: warp-field, cut (*)

  (*) Currently done via 'crop', semantic mismatch. Better as their own operator. (user: andreask size: 1365) [more...]

downsampley_float
Tcl_Obj* imageObj
int      factor

/*
 * The input image is downsampled in the y direction by storing only every
 * 'factor' pixel into the result. Note that this method of shrinking an image
 * causes image frequencies above the nyquist threshold of the result to be
 * aliased into the range.
 *
 * The input image has to be convolved with a low-pass filter first, to avoid
 * such artefacts. The integrated combination of such a filter with
 * downsampling is called 'decimation'. This is but one step in the generation
 * of image pyramids.
 */

crimp_image* image;
crimp_image* result;
int          x, yo, yi;

crimp_input (imageObj, image, float);
if (factor < 1) {
    Tcl_SetResult(interp, "bad sampling factor, expected integer > 0", TCL_STATIC);
    return TCL_ERROR;
}

if (factor == 1) {
    Tcl_SetObjResult(interp, imageObj);
    return TCL_OK;
}

result = crimp_new_at (image->itype, crimp_x (image), crimp_y (image), crimp_w (image), crimp_h (image)/factor);

for (yo = 0, yi = 0; yo < crimp_h (result); yo++, yi += factor) {
    for (x = 0; x < crimp_w (result); x++) {

	FLOATP (result, x, yo) = FLOATP (image, x, yi);
    }
}

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:
 */