Function thresholdTo2bppLow

deps/leptonica/src/grayquant.c:1436–1462

! * \brief thresholdTo2bppLow() * * Low-level function for thresholding from 8 bpp (datas) to * 2 bpp (datad), using thresholds implicitly defined through %tab, * a 256-entry lookup table that gives a 2-bit output value * for each possible input. * * For each line, unroll the loop so that for each 32 bit src word, * representing four consecutive 8-bit pixels, we compose one byte

 *  of output consisiting of four 2-bit pixels.
 */
static void
thresholdTo2bppLow(l_uint32  *datad,
                   l_int32    h,
                   l_int32    wpld,
                   l_uint32  *datas,
                   l_int32    wpls,
                   l_int32   *tab)
{
l_uint8    sval1, sval2, sval3, sval4, dval;
l_int32    i, j, k;
l_uint32  *lines, *lined;

    for (i = 0; i < h; i++) {
        lines = datas + i * wpls;
        lined = datad + i * wpld;
        for (j = 0; j < wpls; j++) {
            k = 4 * j;
            sval1 = GET_DATA_BYTE(lines, k);
            sval2 = GET_DATA_BYTE(lines, k + 1);
            sval3 = GET_DATA_BYTE(lines, k + 2);
            sval4 = GET_DATA_BYTE(lines, k + 3);
            dval = (tab[sval1] << 6) | (tab[sval2] << 4) |
                   (tab[sval3] << 2) | tab[sval4];
            SET_DATA_BYTE(lined, j, dval);
        }
    }
}


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