// halfsize.cpp
//
// Scale down an image by a factor of 2 (i.e., to a quarter of its
// original area) by averaging 4 pixels into one.  For images with odd
// width/height, the last column/row of the image is simply ignored.

#include "imageLib.h"
#define VERBOSE 0

void halfsize(CByteImage src, CByteImage& dst)
{
    CShape sh = src.Shape();
    int w = sh.width, h = sh.height, nB = sh.nBands;
    CShape sh2(w/2, h/2, nB);
    dst.ReAllocate(sh2);
    for (int y = 0; y < h-1; y += 2) {
	for (int x = 0; x < w-1; x += 2) {
	    for (int b = 0; b < nB; b++) {
		dst.Pixel(x/2, y/2, b) =
		    (  src.Pixel(x,   y  , b) 
		       + src.Pixel(x+1, y  , b) 
		       + src.Pixel(x  , y+1, b) 
		       + src.Pixel(x+1, y+1, b)
		       + 2) // ROUND!
		    / 4;
	    }
	}
    }
}

int main(int argc, char *argv[])
{
    try {
	if (argc < 3)
	    throw CError("\n  usage: %s in.png out.png [ntimes]\n", argv[0]);

	CByteImage im1, im2;
	int ntimes = 1;
	if (argc > 3)
	    ntimes = atoi(argv[3]);
	ReadImageVerb(im1, argv[1], VERBOSE);
	for (int i=0; i < ntimes; i++) {
	    if (VERBOSE)
		fprintf(stderr, "reducing\n");
	    halfsize(im1, im2);
	    im1 = im2;
	}
	WriteImageVerb(im1, argv[2], VERBOSE);
    }
    catch (CError &err) {
	fprintf(stderr, err.message);
	fprintf(stderr, "\n");
	return -1;
    }

    return 0;
}