static void threshold16(const uint8_t *iin, const uint8_t *tthreshold, const uint8_t *ffirst, const uint8_t *ssecond, uint8_t *oout, ptrdiff_t ilinesize, ptrdiff_t tlinesize, ptrdiff_t flinesize, ptrdiff_t slinesize, ptrdiff_t olinesize, int w, int h)
static void threshold8(const uint8_t *in, const uint8_t *threshold, const uint8_t *min, const uint8_t *max, uint8_t *out, ptrdiff_t ilinesize, ptrdiff_t tlinesize, ptrdiff_t flinesize, ptrdiff_t slinesize, ptrdiff_t olinesize, int w, int h)