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https://github.com/tesseract-ocr/tesseract.git
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4523ce9f7d
git-svn-id: https://tesseract-ocr.googlecode.com/svn/trunk@526 d0cd1f9f-072b-0410-8dd7-cf729c803f20
233 lines
7.4 KiB
C++
233 lines
7.4 KiB
C++
/**********************************************************************
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* File: search_node.cpp
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* Description: Implementation of the Beam Search Node Class
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* Author: Ahmad Abdulkader
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* Created: 2008
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*
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* (C) Copyright 2008, Google Inc.
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** Licensed under the Apache License, Version 2.0 (the "License");
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** you may not use this file except in compliance with the License.
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** You may obtain a copy of the License at
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** http://www.apache.org/licenses/LICENSE-2.0
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** Unless required by applicable law or agreed to in writing, software
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** distributed under the License is distributed on an "AS IS" BASIS,
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** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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** See the License for the specific language governing permissions and
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** limitations under the License.
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*
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**********************************************************************/
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#include "search_node.h"
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namespace tesseract {
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// The constructor updates the best paths and costs:
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// mean_char_reco_cost_ (returned by BestRecoCost()) is the mean
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// char_reco cost of the best_path, including this node.
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// best_path_reco_cost is the total char_reco_cost of the best_path,
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// but excludes the char_reco_cost of this node.
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// best_cost is the mean mixed cost, i.e., mean_char_reco_cost_ +
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// current language model cost, all weighted by the cube context's
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// RecoWgt parameter
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SearchNode::SearchNode(CubeRecoContext *cntxt, SearchNode *parent_node,
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int char_reco_cost, LangModEdge *edge, int col_idx) {
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// copy data members
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cntxt_ = cntxt;
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lang_mod_edge_ = edge;
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col_idx_ = col_idx;
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parent_node_ = parent_node;
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char_reco_cost_ = char_reco_cost;
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// the string of this node is the same as that of the language model edge
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str_ = (edge == NULL ? NULL : edge->EdgeString());
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// compute best path total reco cost
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best_path_reco_cost_ = (parent_node_ == NULL) ? 0 :
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parent_node_->CharRecoCost() + parent_node_->BestPathRecoCost();
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// update best path length
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best_path_len_ = (parent_node_ == NULL) ?
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1 : parent_node_->BestPathLength() + 1;
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if (edge != NULL && edge->IsRoot() && parent_node_ != NULL) {
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best_path_len_++;
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}
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// compute best reco cost mean cost
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mean_char_reco_cost_ = static_cast<int>(
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(best_path_reco_cost_ + char_reco_cost_) /
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static_cast<double>(best_path_len_));
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// get language model cost
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int lm_cost = LangModCost(lang_mod_edge_, parent_node_);
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// compute aggregate best cost
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best_cost_ = static_cast<int>(cntxt_->Params()->RecoWgt() *
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(best_path_reco_cost_ + char_reco_cost_) /
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static_cast<double>(best_path_len_)
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) + lm_cost;
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}
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SearchNode::~SearchNode() {
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if (lang_mod_edge_ != NULL) {
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delete lang_mod_edge_;
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}
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}
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// update the parent_node node if provides a better (less) cost
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bool SearchNode::UpdateParent(SearchNode *new_parent, int new_reco_cost,
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LangModEdge *new_edge) {
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if (lang_mod_edge_ == NULL) {
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if (new_edge != NULL) {
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return false;
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}
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} else {
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// to update the parent_node, we have to have the same target
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// state and char
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if (new_edge == NULL || !lang_mod_edge_->IsIdentical(new_edge) ||
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!SearchNode::IdenticalPath(parent_node_, new_parent)) {
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return false;
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}
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}
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// compute the path cost and combined cost of the new path
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int new_best_path_reco_cost;
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int new_cost;
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int new_best_path_len;
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new_best_path_reco_cost = (new_parent == NULL) ?
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0 : new_parent->BestPathRecoCost() + new_parent->CharRecoCost();
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new_best_path_len =
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(new_parent == NULL) ? 1 : new_parent->BestPathLength() + 1;
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// compute the new language model cost
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int new_lm_cost = LangModCost(new_edge, new_parent);
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new_cost = static_cast<int>(cntxt_->Params()->RecoWgt() *
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(new_best_path_reco_cost + new_reco_cost) /
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static_cast<double>(new_best_path_len)
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) + new_lm_cost;
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// update if it is better (less) than the current one
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if (best_cost_ > new_cost) {
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parent_node_ = new_parent;
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char_reco_cost_ = new_reco_cost;
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best_path_reco_cost_ = new_best_path_reco_cost;
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best_path_len_ = new_best_path_len;
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mean_char_reco_cost_ = static_cast<int>(
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(best_path_reco_cost_ + char_reco_cost_) /
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static_cast<double>(best_path_len_));
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best_cost_ = static_cast<int>(cntxt_->Params()->RecoWgt() *
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(best_path_reco_cost_ + char_reco_cost_) /
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static_cast<double>(best_path_len_)
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) + new_lm_cost;
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return true;
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}
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return false;
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}
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char_32 *SearchNode::PathString() {
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SearchNode *node = this;
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// compute string length
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int len = 0;
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while (node != NULL) {
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if (node->str_ != NULL) {
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len += CubeUtils::StrLen(node->str_);
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}
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// if the edge is a root and does not have a NULL parent, account for space
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LangModEdge *lm_edge = node->LangModelEdge();
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if (lm_edge != NULL && lm_edge->IsRoot() && node->ParentNode() != NULL) {
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len++;
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}
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node = node->parent_node_;
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}
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char_32 *char_ptr = new char_32[len + 1];
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if (char_ptr == NULL) {
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return NULL;
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}
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int ch_idx = len;
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node = this;
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char_ptr[ch_idx--] = 0;
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while (node != NULL) {
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int str_len = ((node->str_ == NULL) ? 0 : CubeUtils::StrLen(node->str_));
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while (str_len > 0) {
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char_ptr[ch_idx--] = node->str_[--str_len];
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}
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// if the edge is a root and does not have a NULL parent, insert a space
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LangModEdge *lm_edge = node->LangModelEdge();
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if (lm_edge != NULL && lm_edge->IsRoot() && node->ParentNode() != NULL) {
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char_ptr[ch_idx--] = (char_32)' ';
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}
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node = node->parent_node_;
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}
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return char_ptr;
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}
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// compares the path of two nodes and checks if its identical
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bool SearchNode::IdenticalPath(SearchNode *node1, SearchNode *node2) {
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if (node1 != NULL && node2 != NULL &&
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node1->best_path_len_ != node2->best_path_len_) {
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return false;
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}
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// backtrack until either a root or a NULL edge is reached
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while (node1 != NULL && node2 != NULL) {
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if (node1->str_ != node2->str_) {
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return false;
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}
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// stop if either nodes is a root
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if (node1->LangModelEdge()->IsRoot() || node2->LangModelEdge()->IsRoot()) {
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break;
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}
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node1 = node1->parent_node_;
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node2 = node2->parent_node_;
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}
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return ((node1 == NULL && node2 == NULL) ||
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(node1 != NULL && node1->LangModelEdge()->IsRoot() &&
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node2 != NULL && node2->LangModelEdge()->IsRoot()));
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}
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// Computes the language model cost of a path
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int SearchNode::LangModCost(LangModEdge *current_lm_edge,
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SearchNode *parent_node) {
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int lm_cost = 0;
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int node_cnt = 0;
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do {
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// check if root
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bool is_root = ((current_lm_edge != NULL && current_lm_edge->IsRoot()) ||
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parent_node == NULL);
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if (is_root) {
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node_cnt++;
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lm_cost += (current_lm_edge == NULL ? 0 : current_lm_edge->PathCost());
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}
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// continue until we hit a null parent
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if (parent_node == NULL) {
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break;
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}
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// get the previous language model edge
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current_lm_edge = parent_node->LangModelEdge();
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// back track
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parent_node = parent_node->ParentNode();
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} while (true);
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return static_cast<int>(lm_cost / static_cast<double>(node_cnt));
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}
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} // namespace tesseract
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