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Add languages parameter to hOCR output metadata #4531

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cebd193
Add languages parameter to hOCR output metadata
mvanhorn Mar 20, 2026
fbec60b
fix: use ISO 639-1 codes and separate script models in hOCR metadata
mvanhorn Mar 24, 2026
43706b8
fix: handle compound model names and address review feedback
mvanhorn Mar 25, 2026
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3 changes: 3 additions & 0 deletions include/tesseract/renderer.h
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Original file line number Diff line number Diff line change
Expand Up @@ -173,13 +173,16 @@ class TESS_API TessHOcrRenderer : public TessResultRenderer {
explicit TessHOcrRenderer(const char *outputbase, bool font_info);
explicit TessHOcrRenderer(const char *outputbase);

void SetInputLanguages(const char *languages);

protected:
bool BeginDocumentHandler() override;
bool AddImageHandler(TessBaseAPI *api) override;
bool EndDocumentHandler() override;

private:
bool font_info_; // whether to print font information
std::string input_languages_;
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Adding std::string input_languages_ to TessHOcrRenderer changes the size/layout of this exported (TESS_API) C++ class, which can break binary compatibility for downstream code that links against libtesseract and instantiates TessHOcrRenderer. If ABI stability is a concern, consider storing the new state behind an indirection (pimpl/opaque pointer) or in a separate internal structure to minimize ABI impact.

Suggested change
std::string input_languages_;
// NOTE: Additional per-instance state (e.g. input languages) is stored
// out-of-line to avoid changing the ABI-visible layout of this class.

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};

/**
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120 changes: 119 additions & 1 deletion src/api/hocrrenderer.cpp
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Expand Up @@ -18,9 +18,12 @@
**********************************************************************/

#include <tesseract/baseapi.h> // for TessBaseAPI
#include <cstring> // for strcmp
#include <locale> // for std::locale::classic
#include <memory> // for std::unique_ptr
#include <sstream> // for std::stringstream
#include <unordered_map> // for std::unordered_map
#include <unordered_set> // for std::unordered_set
#include <tesseract/renderer.h>
#include "helpers.h" // for copy_string
#include "tesseractclass.h" // for Tesseract
Expand Down Expand Up @@ -477,6 +480,86 @@ TessHOcrRenderer::TessHOcrRenderer(const char *outputbase, bool font_info)
font_info_ = font_info;
}

void TessHOcrRenderer::SetInputLanguages(const char *languages) {
if (languages && languages[0] != '\0') {
input_languages_ = languages;
} else {
input_languages_.clear();
}
}

static const std::unordered_map<std::string, std::string> &Iso639Map() {
static const std::unordered_map<std::string, std::string> map{
{"afr", "af"}, {"amh", "am"}, {"ara", "ar"}, {"asm", "as"},
{"aze", "az"}, {"bel", "be"}, {"ben", "bn"}, {"bod", "bo"},
Comment on lines +491 to +494
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Iso639Map() allocates the map with new and intentionally leaks it for the lifetime of the process. Unless there is a specific reason to avoid static destruction here, prefer a function-local static const std::unordered_map<...> value to avoid heap allocation/leaks and simplify the code.

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{"bos", "bs"}, {"bre", "br"}, {"bul", "bg"}, {"cat", "ca"},
{"ceb", "ceb"}, {"ces", "cs"}, {"chi_sim", "zh"}, {"chi_tra", "zh"},
{"chr", "chr"}, {"cos", "co"}, {"cym", "cy"}, {"dan", "da"},
{"deu", "de"}, {"div", "dv"}, {"dzo", "dz"}, {"ell", "el"},
{"eng", "en"}, {"enm", "en"}, {"epo", "eo"}, {"est", "et"},
{"eus", "eu"}, {"fao", "fo"}, {"fas", "fa"}, {"fil", "fil"},
{"fin", "fi"}, {"fra", "fr"}, {"frk", "de"}, {"frm", "fr"},
{"fry", "fy"}, {"gla", "gd"}, {"gle", "ga"}, {"glg", "gl"},
{"grc", "el"}, {"guj", "gu"}, {"hat", "ht"}, {"heb", "he"},
{"hin", "hi"}, {"hrv", "hr"}, {"hun", "hu"}, {"hye", "hy"},
{"iku", "iu"}, {"ind", "id"}, {"isl", "is"}, {"ita", "it"},
{"jav", "jv"}, {"jpn", "ja"}, {"kan", "kn"}, {"kat", "ka"},
{"kaz", "kk"}, {"khm", "km"}, {"kir", "ky"}, {"kmr", "ku"},
{"kor", "ko"}, {"lao", "lo"}, {"lat", "la"}, {"lav", "lv"},
{"lit", "lt"}, {"ltz", "lb"}, {"mal", "ml"}, {"mar", "mr"},
{"mkd", "mk"}, {"mlt", "mt"}, {"mon", "mn"}, {"mri", "mi"},
{"msa", "ms"}, {"mya", "my"}, {"nep", "ne"}, {"nld", "nl"},
{"nor", "no"}, {"oci", "oc"}, {"ori", "or"}, {"pan", "pa"},
{"pol", "pl"}, {"por", "pt"}, {"pus", "ps"}, {"que", "qu"},
{"ron", "ro"}, {"rus", "ru"}, {"san", "sa"}, {"sin", "si"},
{"slk", "sk"}, {"slv", "sl"}, {"snd", "sd"}, {"spa", "es"},
{"sqi", "sq"}, {"srp", "sr"}, {"sun", "su"}, {"swa", "sw"},
{"swe", "sv"}, {"syr", "syr"}, {"tam", "ta"}, {"tat", "tt"},
{"tel", "te"}, {"tgk", "tg"}, {"tha", "th"}, {"tir", "ti"},
{"ton", "to"}, {"tur", "tr"}, {"uig", "ug"}, {"ukr", "uk"},
{"urd", "ur"}, {"uzb", "uz"}, {"vie", "vi"}, {"yid", "yi"},
{"yor", "yo"}, {"zho", "zh"},
};
return map;
}

// Look up a model name in the ISO 639 map, trying progressively shorter
// prefixes by stripping trailing _suffix parts. This handles compound
// model names like deu_latf -> deu -> "de", chi_tra_vert -> chi_tra -> "zh".
static std::string LookupIso639(const std::string &model) {
const auto &iso_map = Iso639Map();
auto it = iso_map.find(model);
if (it != iso_map.end()) {
return it->second;
}
std::string prefix = model;
while (true) {
auto pos = prefix.rfind('_');
if (pos == std::string::npos) {
break;
}
prefix = prefix.substr(0, pos);
it = iso_map.find(prefix);
if (it != iso_map.end()) {
return it->second;
}
}
return model;
}

static const std::unordered_set<std::string> &ScriptNames() {
static const std::unordered_set<std::string> set{
"Arabic", "Armenian", "Bengali", "Canadian_Aboriginal", "Cherokee",
"Cyrillic", "Devanagari", "Ethiopic", "Fraktur", "Georgian", "Greek",
Comment on lines +550 to +553
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ScriptNames() also uses new for a function-local static and leaks it. Prefer a function-local static const std::unordered_set<std::string> object unless there's a measured reason to avoid its destructor at shutdown.

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"Gujarati", "Gurmukhi", "HanS", "HanS_vert", "HanT", "HanT_vert",
"Hangul", "Hangul_vert", "Hebrew", "Japanese", "Japanese_vert",
"Kannada", "Khmer", "Lao", "Latin", "Malayalam", "Myanmar", "Oriya",
"Sinhala", "Syriac", "Tamil", "Telugu", "Thaana", "Thai", "Tibetan",
"Vietnamese",
};
return set;
}

bool TessHOcrRenderer::BeginDocumentHandler() {
AppendString(
"<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
Expand All @@ -496,8 +579,43 @@ bool TessHOcrRenderer::BeginDocumentHandler() {
if (font_info_) {
AppendString(" ocrp_font ocrp_fsize");
}
AppendString("'/>\n");
if (!input_languages_.empty()) {
std::string langs;
std::string scripts;
const auto &script_set = ScriptNames();
std::istringstream stream(input_languages_);
std::string token;
while (std::getline(stream, token, '+')) {
if (token.empty()) {
Comment on lines 563 to +590
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The new header metadata behavior (splitting/mapping languages and emitting new meta tags) isn't covered by existing unit tests. Since src/api/hocrrenderer.cpp already has test coverage for other hOCR functionality, it would be good to add a focused test that exercises TessHOcrRenderer::BeginDocumentHandler() output with (1) languages set and (2) languages unset, and asserts the exact meta tag(s) emitted (including proper escaping).

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continue;
}
if (script_set.count(token)) {
if (!scripts.empty()) {
scripts += ' ';
}
scripts += token;
} else {
if (!langs.empty()) {
langs += ' ';
}
langs += LookupIso639(token);
}
Comment on lines +583 to +603
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This implementation transforms the -l string by splitting on +, converting some tokens (e.g. eng->en) and joining with spaces, so the emitted <meta name='ocr-langs' ...> does not preserve the original -l value (e.g. eng+fra). That differs from the PR description/issue request and also makes ocr-langs inconsistent with the existing lang='eng' attributes emitted elsewhere in hOCR. Please either emit the raw -l value (escaped) or update the approach/spec and ensure consistency across the document.

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}
if (!langs.empty()) {
std::string escaped_langs = HOcrEscape(langs.c_str());
AppendString(" <meta name='ocr-langs' content='");
AppendString(escaped_langs.c_str());
AppendString("' />\n");
}
if (!scripts.empty()) {
std::string escaped_scripts = HOcrEscape(scripts.c_str());
AppendString(" <meta name='ocr-scripts' content='");
AppendString(escaped_scripts.c_str());
AppendString("' />\n");
}
}
AppendString(
"'/>\n"
" </head>\n"
" <body>\n");

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1 change: 1 addition & 0 deletions src/tesseract.cpp
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Expand Up @@ -516,6 +516,7 @@ static void PreloadRenderers(tesseract::TessBaseAPI &api,
bool font_info;
api.GetBoolVariable("hocr_font_info", &font_info);
auto renderer = std::make_unique<tesseract::TessHOcrRenderer>(outputbase, font_info);
renderer->SetInputLanguages(api.GetInitLanguagesAsString());
if (renderer->happy()) {
renderers.push_back(std::move(renderer));
} else {
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