tesseract-ocr/dict/context.cpp

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/* -*-C-*-
 ********************************************************************************
 *
 * File:        context.c  (Formerly context.c)
 * Description:  Context checking functions
 * Author:       Mark Seaman, OCR Technology
 * Created:      Thu Feb 15 11:18:24 1990
 * Modified:     Tue Jul  9 17:38:16 1991 (Mark Seaman) marks@hpgrlt
 * Language:     C
 * Package:      N/A
 * Status:       Experimental (Do Not Distribute)
 *
 * (c) Copyright 1990, Hewlett-Packard Company.
 ** Licensed under the Apache License, Version 2.0 (the "License");
 ** you may not use this file except in compliance with the License.
 ** You may obtain a copy of the License at
 ** http://www.apache.org/licenses/LICENSE-2.0
 ** Unless required by applicable law or agreed to in writing, software
 ** distributed under the License is distributed on an "AS IS" BASIS,
 ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 ** See the License for the specific language governing permissions and
 ** limitations under the License.
 *
 *********************************************************************************/

#include "dict.h"
#include "tprintf.h"
#include "unicharset.h"

namespace tesseract {

static const int kMinAbsoluteGarbageWordLength = 10;
static const float kMinAbsoluteGarbageAlphanumFrac = 0.5f;

const int case_state_table[6][4] = { {
                                  /*  0. Begining of word        */
    /*    P   U   L   D                                          */
                                  /* -1. Error on case           */
      0, 1, 5, 4
    },
    {                            /*  1. After initial capital    */
      0, 3, 2, 4
    },
    {                            /*  2. After lower case         */
      0, -1, 2, -1
    },
    {                            /*  3. After upper case         */
      0, 3, -1, 4
    },
    {                            /*  4. After a digit            */
      0, -1, -1, 4
    },
    {                            /*  5. After initial lower case */
      5, -1, 2, -1
    },
  };

int Dict::case_ok(const WERD_CHOICE &word, const UNICHARSET &unicharset) {
  int last_state = 0;
  int state = 0;
  int x;
  for (x = 0; x < word.length(); ++x) {
    UNICHAR_ID ch_id = word.unichar_id(x);
    if (unicharset.get_isupper(ch_id))
      state = case_state_table[state][1];
    else if (unicharset.get_islower(ch_id))
      state = case_state_table[state][2];
    else if (unicharset.get_isdigit(ch_id))
      state = case_state_table[state][3];
    else
      state = case_state_table[state][0];
    if (state == -1) return false;
    last_state = state;
  }
  return state != 5; // single lower is bad
}

bool Dict::absolute_garbage(const WERD_CHOICE &word,
                            const UNICHARSET &unicharset) {
  if (word.length() < kMinAbsoluteGarbageWordLength) return false;
  int num_alphanum = 0;
  for (int x = 0; x < word.length(); ++x) {
    num_alphanum += (unicharset.get_isalpha(word.unichar_id(x)) ||
                     unicharset.get_isdigit(word.unichar_id(x)));
  }
  return (static_cast<float>(num_alphanum) /
          static_cast<float>(word.length()) < kMinAbsoluteGarbageAlphanumFrac);
}

}  // namespace tesseract