Tesseract 3.02

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Public Member Functions | Static Public Member Functions | Protected Member Functions
tesseract::WordUnigrams Class Reference

`#include <word_unigrams.h>`

List of all members.

## Public Member Functions
| WordUnigrams ()
| ~WordUnigrams ()
int | Cost (const char_32 *str32, LangModel *lang_mod, CharSet *char_set) const

## Static Public Member Functions
static WordUnigrams * | Create (const string &data_file_path, const string &lang)

## Protected Member Functions
int | CostInternal (const char *str) const

## Detailed Description

Definition at line 34 of file word_unigrams.h.

## Constructor & Destructor Documentation

tesseract::WordUnigrams::WordUnigrams | ( |  | ) |

Definition at line 32 of file word_unigrams.cpp.

{
costs_ = NULL;
words_ = NULL;
word_cnt_ = 0;
}

tesseract::WordUnigrams::~WordUnigrams | ( |  | ) |

Definition at line 38 of file word_unigrams.cpp.

{
if (words_ != NULL) {
if (words_[0] != NULL) {
delete []words_[0];
}
delete []words_;
words_ = NULL;
}
if (costs_ != NULL) {
delete []costs_;
}
}

## Member Function Documentation

int tesseract::WordUnigrams::Cost | ( | const char_32 * | str32,
|  | LangModel * | lang_mod,
|  | CharSet * | char_set
| ) |  | const

Definition at line 150 of file word_unigrams.cpp.

{
if (!key_str32)
return 0;
// convert string to UTF8 to split into space-separated words
string key_str;
CubeUtils::UTF32ToUTF8(key_str32, &key_str);
vector<string> words;
CubeUtils::SplitStringUsing(key_str, " \t", &words);
// no words => no cost
if (words.size() <= 0) {
return 0;
}
// aggregate the costs of all the words
int cost = 0;
for (int word_idx = 0; word_idx < words.size(); word_idx++) {
// convert each word back to UTF32 for analyzing case and punctuation
string_32 str32;
CubeUtils::UTF8ToUTF32(words[word_idx].c_str(), &str32);
int len = CubeUtils::StrLen(str32.c_str());
// strip all trailing punctuation
string clean_str;
int clean_len = len;
bool trunc = false;
while (clean_len > 0 &&
lang_mod->IsTrailingPunc(str32.c_str()[clean_len - 1])) {
--clean_len;
trunc = true;
}
// If either the original string was not truncated (no trailing
// punctuation) or the entire string was removed (all characters
// are trailing punctuation), evaluate original word as is;
// otherwise, copy all but the trailing punctuation characters
char_32 *clean_str32 = NULL;
if (clean_len == 0 || !trunc) {
clean_str32 = CubeUtils::StrDup(str32.c_str());
} else {
clean_str32 = new char_32[clean_len + 1];
for (int i = 0; i < clean_len; ++i) {
clean_str32[i] = str32[i];
}
clean_str32[clean_len] = '\0';
}
ASSERT_HOST(clean_str32 != NULL);
string str8;
CubeUtils::UTF32ToUTF8(clean_str32, &str8);
int word_cost = CostInternal(str8.c_str());
// if case invariant, get costs of all-upper-case and all-lower-case
// versions and return the min cost
if (clean_len >= kMinLengthNumOrCaseInvariant &&
CubeUtils::IsCaseInvariant(clean_str32, char_set)) {
char_32 *lower_32 = CubeUtils::ToLower(clean_str32, char_set);
if (lower_32) {
string lower_8;
CubeUtils::UTF32ToUTF8(lower_32, &lower_8);
word_cost = MIN(word_cost, CostInternal(lower_8.c_str()));
delete [] lower_32;
}
char_32 *upper_32 = CubeUtils::ToUpper(clean_str32, char_set);
if (upper_32) {
string upper_8;
CubeUtils::UTF32ToUTF8(upper_32, &upper_8);
word_cost = MIN(word_cost, CostInternal(upper_8.c_str()));
delete [] upper_32;
}
}
if (clean_len >= kMinLengthNumOrCaseInvariant) {
// if characters are all numeric, incur 0 word cost
bool is_numeric = true;
for (int i = 0; i < clean_len; ++i) {
if (!lang_mod->IsDigit(clean_str32[i]))
is_numeric = false;
}
if (is_numeric)
word_cost = 0;
}
delete [] clean_str32;
cost += word_cost;
} // word_idx
// return the mean cost
return static_cast<int>(cost / static_cast<double>(words.size()));
}

int tesseract::WordUnigrams::CostInternal | ( | const char * | str | ) | const
| protected

Definition at line 243 of file word_unigrams.cpp.

{
if (strlen(key_str) == 0)
return not_in_list_cost_;
int hi = word_cnt_ - 1;
int lo = 0;
while (lo <= hi) {
int current = (hi + lo) / 2;
int comp = strcmp(key_str, words_[current]);
// a match
if (comp == 0) {
return costs_[current];
}
if (comp < 0) {
// go lower
hi = current - 1;
} else {
// go higher
lo = current + 1;
}
}
return not_in_list_cost_;
}

WordUnigrams * tesseract::WordUnigrams::Create | ( | const string & | data_file_path,
|  | const string & | lang
| ) |  |
| static

Definition at line 55 of file word_unigrams.cpp.

{
string file_name;
string str;
file_name = data_file_path + lang;
file_name += ".cube.word-freq";
// load the string into memory
if (CubeUtils::ReadFileToString(file_name, &str) == false) {
return NULL;
}
// split into lines
vector<string> str_vec;
CubeUtils::SplitStringUsing(str, "\r\n \t", &str_vec);
if (str_vec.size() < 2) {
return NULL;
}
// allocate memory
WordUnigrams *word_unigrams_obj = new WordUnigrams();
if (word_unigrams_obj == NULL) {
fprintf(stderr, "Cube ERROR (WordUnigrams::Create): could not create "
"word unigrams object.\n");
return NULL;
}
int full_len = str.length();
int word_cnt = str_vec.size() / 2;
word_unigrams_obj->words_ = new char*[word_cnt];
word_unigrams_obj->costs_ = new int[word_cnt];
if (word_unigrams_obj->words_ == NULL ||
word_unigrams_obj->costs_ == NULL) {
fprintf(stderr, "Cube ERROR (WordUnigrams::Create): error allocating "
"word unigram fields.\n");
delete word_unigrams_obj;
return NULL;
}
word_unigrams_obj->words_[0] = new char[full_len];
if (word_unigrams_obj->words_[0] == NULL) {
fprintf(stderr, "Cube ERROR (WordUnigrams::Create): error allocating "
"word unigram fields.\n");
delete word_unigrams_obj;
return NULL;
}
// construct sorted list of words and costs
word_unigrams_obj->word_cnt_ = 0;
char *char_buff = word_unigrams_obj->words_[0];
word_cnt = 0;
int max_cost = 0;
for (int wrd = 0; wrd < str_vec.size(); wrd += 2) {
word_unigrams_obj->words_[word_cnt] = char_buff;
strcpy(char_buff, str_vec[wrd].c_str());
char_buff += (str_vec[wrd].length() + 1);
if (sscanf(str_vec[wrd + 1].c_str(), "%d",
word_unigrams_obj->costs_ + word_cnt) != 1) {
fprintf(stderr, "Cube ERROR (WordUnigrams::Create): error reading "
"word unigram data.\n");
delete word_unigrams_obj;
return NULL;
}
// update max cost
max_cost = MAX(max_cost, word_unigrams_obj->costs_[word_cnt]);
word_cnt++;
}
word_unigrams_obj->word_cnt_ = word_cnt;
// compute the not-in-list-cost by assuming that a word not in the list
// [ahmadab]: This can be computed as follows:
// - Given that the distribution of words follow Zipf's law:
// (F = K / (rank ^ S)), where s is slightly > 1.0
// - Number of words in the list is N
// - The mean frequency of a word that did not appear in the list is the
// area under the rest of the Zipf's curve divided by 2 (the mean)
// - The area would be the bound integral from N to infinity =
// (K * S) / (N ^ (S + 1)) ~= K / (N ^ 2)
// - Given that cost = -LOG(prob), the cost of an unlisted word would be
// = max_cost + 2*LOG(N)
word_unigrams_obj->not_in_list_cost_ = max_cost +
(2 * CubeUtils::Prob2Cost(1.0 / word_cnt));
// success
return word_unigrams_obj;
}

The documentation for this class was generated from the following files:

- /mnt/data/src/tesseract-ocr/cube/word_unigrams.h
- /mnt/data/src/tesseract-ocr/cube/word_unigrams.cpp