Function makeGrayQuantTargetTable

deps/leptonica/src/grayquant.c:1894–1921

! * \brief makeGrayQuantTargetTable() * * \param[in] nlevels number of output levels * \param[in] depth of dest pix, in bpp; 2, 4 or 8 bpp * \return table maps input gray level to thresholded gray level, * or NULL on error * * * Notes: * (1) nlevels is some number between 2 and 2^(depth) * (2) The table is used in two similar ways: *

 * </pre>
 */
static l_int32 *
makeGrayQuantTargetTable(l_int32  nlevels,
                         l_int32  depth)
{
l_int32   *tab;
l_int32    i, j, thresh, maxval, quantval;

    PROCNAME("makeGrayQuantTargetTable");

    if ((tab = (l_int32 *)LEPT_CALLOC(256, sizeof(l_int32))) == NULL)
        return (l_int32 *)ERROR_PTR("calloc fail for tab", procName, NULL);

    maxval = (1 << depth) - 1;
    if (depth < 8)
        nlevels = 1 << depth;
    for (i = 0; i < 256; i++) {
        for (j = 0; j < nlevels; j++) {
            thresh = 255 * (2 * j + 1) / (2 * nlevels - 2);
            if (i <= thresh) {
                quantval = maxval * j / (nlevels - 1);
                tab[i] = quantval;
/*                fprintf(stderr, "tab[%d] = %d\n", i, tab[i]); */
                break;
            }
        }
    }
    return tab;
}


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