function halfSample(inImgWrapper, outImgWrapper) {
    var inImg = inImgWrapper.data;
    var inWidth = inImgWrapper.size.x;
    var outImg = outImgWrapper.data;
    var topRowIdx = 0;
    var bottomRowIdx = inWidth;
    var endIdx = inImg.length;
    var outWidth = inWidth / 2;
    var outImgIdx = 0;
    while (bottomRowIdx < endIdx) {
        for (var i = 0; i < outWidth; i++) {
            outImg[outImgIdx] = Math.floor((inImg[topRowIdx] + inImg[topRowIdx + 1] + inImg[bottomRowIdx] + inImg[bottomRowIdx + 1]) / 4);
            outImgIdx++;
            topRowIdx = topRowIdx + 2;
            bottomRowIdx = bottomRowIdx + 2;
        }
        topRowIdx = topRowIdx + inWidth;
        bottomRowIdx = bottomRowIdx + inWidth;
    }
}
@param inImg {ImageWrapper} input image to be sampled
@param outImg {ImageWrapper} to be stored in