private void FilterRowPaeth()
{
int i, j, imax;
imax = ImgInfo.BytesPerRow;
for (j = 1 - ImgInfo.BytesPixel, i = 1; i <= imax; i++, j++) {
rowbfilter[i] = (byte)(rowb[i] - PngHelperInternal.FilterPaethPredictor(j > 0 ? rowb[j] : (byte)0,
rowbprev[i], j > 0 ? rowbprev[j] : (byte)0));
}
}