/// Subordinate pass of EZW algorithm. see Shapiro, 1993 for info.
bool ezw_decoder::subordinate_pass(ibitstream& in) {
for (size_t i=0; i < sub_list_.size(); i++) {
sub_elt e = sub_list_[i];
if (in.read_bit()) {
if (!in.good()) return false;
// check bounds in case we're creating reduced-size output,
// where we'd ignore things that are out of bounds.
if (matrix_utils::in_bounds(*decoded_, e.row, e.col)) {
if ((*decoded_)(e.row, e.col) < 0) {
(*decoded_)(e.row, e.col) -= threshold_;
} else {
(*decoded_)(e.row, e.col) += threshold_;
}
}
DBG_OUT(1);
} else {
if (!in.good()) return false;
DBG_OUT(0);
}
}
return true;
}
ezw_code ezw_decoder::decode_value(const dom_elt& e, ibitstream& in) {
bool hi = in.read_bit(); // tells whether POS/NEG or not
bool lo = in.read_bit(); // ZERO_TREE or ZERO
if (!in.good()) { // make sure end of file wasn't reached early
return STOP;
}
if (hi) {
sub_list_.push_back(sub_elt(e.row, e.col));
if (lo) {
DBG_OUT('p');
// check size in case of reduced-size output.
if (matrix_utils::in_bounds(*decoded_, e.row, e.col)) {
(*decoded_)(e.row, e.col) = threshold_;
}
return POSITIVE;
} else {
DBG_OUT('n');
// check size in case of reduced-size output.
if (matrix_utils::in_bounds(*decoded_, e.row, e.col)) {
(*decoded_)(e.row, e.col) = -threshold_;
}
return NEGATIVE;
}
} else {
DBG_OUT(lo ? 'z' : 't');
return lo ? ZERO : ZERO_TREE;
}
}