使用嵌入字体的 iText 提取文本
Extract text with iText with embedded fonts
我正在尝试使用 iTextSharp (v5.5.12.1) 从以下 PDF 中提取文本：
https://structure.mil.ru/files/morf/military/files/ENGV_1929.pdf
不幸的是，他们似乎使用了一些嵌入式自定义字体，这让我很沮丧。
目前，我有一个使用 OCR 的可行解决方案，但 OCR 可能不精确，会错误地读取某些字符并在字符之间添加额外的空格。如果能直接把文字提取出来就好了
public static string ExtractTextFromPdf(Stream pdfStream, bool addNewLineBetweenPages = false)
{
using (PdfReader reader = new PdfReader(pdfStream))
{
string text = "";
for (int i = 1; i <= reader.NumberOfPages; i++)
{
text += PdfTextExtractor.GetTextFromPage(reader, i);
if (addNewLineBetweenPages && i != reader.NumberOfPages)
{
text += Environment.NewLine;
}
}
return text;
}
}
这里的问题是嵌入字体程序中的字形具有非标准字形名称（G00、G01、.. .) 并且仅由字形名称标识。因此，必须建立从这些字形名称到 Unicode 字符的映射。可以这样做，例如通过检查 PDF 中的字体程序（例如使用 font forge）并通过名称视觉识别字形。例如。喜欢这里
（如您所知，手头文档中未使用的相关字体字形存在一些空白。您可以猜到一些缺失的字形，有些则没有。）
然后你必须将这些映射注入到 iText 中。由于映射是隐藏的（GlyphList class 的 private static 成员），您要么必须修补 iText 本身，要么使用反射：
void InitializeGlyphs()
{
FieldInfo names2unicodeFiled = typeof(GlyphList).GetField("names2unicode", BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Static);
Dictionary<string, int[]> names2unicode = (Dictionary<string, int[]>) names2unicodeFiled.GetValue(null);
names2unicode["G03"] = new int[] { ' ' };
names2unicode["G0A"] = new int[] { '\'' };
names2unicode["G0B"] = new int[] { '(' };
names2unicode["G0C"] = new int[] { ')' };
names2unicode["G0F"] = new int[] { ',' };
names2unicode["G10"] = new int[] { '-' };
names2unicode["G11"] = new int[] { '.' };
names2unicode["G12"] = new int[] { '/' };
names2unicode["G13"] = new int[] { '0' };
names2unicode["G14"] = new int[] { '1' };
names2unicode["G15"] = new int[] { '2' };
names2unicode["G16"] = new int[] { '3' };
names2unicode["G17"] = new int[] { '4' };
names2unicode["G18"] = new int[] { '5' };
names2unicode["G19"] = new int[] { '6' };
names2unicode["G1A"] = new int[] { '7' };
names2unicode["G1B"] = new int[] { '8' };
names2unicode["G1C"] = new int[] { '9' };
names2unicode["G1D"] = new int[] { ':' };
names2unicode["G23"] = new int[] { '@' };
names2unicode["G24"] = new int[] { 'A' };
names2unicode["G25"] = new int[] { 'B' };
names2unicode["G26"] = new int[] { 'C' };
names2unicode["G27"] = new int[] { 'D' };
names2unicode["G28"] = new int[] { 'E' };
names2unicode["G29"] = new int[] { 'F' };
names2unicode["G2A"] = new int[] { 'G' };
names2unicode["G2B"] = new int[] { 'H' };
names2unicode["G2C"] = new int[] { 'I' };
names2unicode["G2D"] = new int[] { 'J' };
names2unicode["G2E"] = new int[] { 'K' };
names2unicode["G2F"] = new int[] { 'L' };
names2unicode["G30"] = new int[] { 'M' };
names2unicode["G31"] = new int[] { 'N' };
names2unicode["G32"] = new int[] { 'O' };
names2unicode["G33"] = new int[] { 'P' };
names2unicode["G34"] = new int[] { 'Q' };
names2unicode["G35"] = new int[] { 'R' };
names2unicode["G36"] = new int[] { 'S' };
names2unicode["G37"] = new int[] { 'T' };
names2unicode["G38"] = new int[] { 'U' };
names2unicode["G39"] = new int[] { 'V' };
names2unicode["G3A"] = new int[] { 'W' };
names2unicode["G3B"] = new int[] { 'X' };
names2unicode["G3C"] = new int[] { 'Y' };
names2unicode["G3D"] = new int[] { 'Z' };
names2unicode["G42"] = new int[] { '_' };
names2unicode["G44"] = new int[] { 'a' };
names2unicode["G45"] = new int[] { 'b' };
names2unicode["G46"] = new int[] { 'c' };
names2unicode["G46._"] = new int[] { 'c' };
names2unicode["G47"] = new int[] { 'd' };
names2unicode["G48"] = new int[] { 'e' };
names2unicode["G49"] = new int[] { 'f' };
names2unicode["G4A"] = new int[] { 'g' };
names2unicode["G4B"] = new int[] { 'h' };
names2unicode["G4C"] = new int[] { 'i' };
names2unicode["G4D"] = new int[] { 'j' };
names2unicode["G4E"] = new int[] { 'k' };
names2unicode["G4F"] = new int[] { 'l' };
names2unicode["G50"] = new int[] { 'm' };
names2unicode["G51"] = new int[] { 'n' };
names2unicode["G52"] = new int[] { 'o' };
names2unicode["G53"] = new int[] { 'p' };
names2unicode["G54"] = new int[] { 'q' };
names2unicode["G55"] = new int[] { 'r' };
names2unicode["G56"] = new int[] { 's' };
names2unicode["G57"] = new int[] { 't' };
names2unicode["G58"] = new int[] { 'u' };
names2unicode["G59"] = new int[] { 'v' };
names2unicode["G5A"] = new int[] { 'w' };
names2unicode["G5B"] = new int[] { 'x' };
names2unicode["G5C"] = new int[] { 'y' };
names2unicode["G5D"] = new int[] { 'z' };
names2unicode["G62"] = new int[] { 'Ш' };
names2unicode["G63"] = new int[] { 'Р' };
names2unicode["G6A"] = new int[] { 'И' };
names2unicode["G6B"] = new int[] { 'А' };
names2unicode["G6C"] = new int[] { 'М' };
names2unicode["G6D"] = new int[] { 'в' };
names2unicode["G6E"] = new int[] { 'Ф' };
names2unicode["G70"] = new int[] { 'Е' };
names2unicode["G72"] = new int[] { 'Б' };
names2unicode["G73"] = new int[] { 'Н' };
names2unicode["G76"] = new int[] { 'С' };
names2unicode["G7A"] = new int[] { 'К' };
names2unicode["G7B"] = new int[] { 'В' };
names2unicode["G7C"] = new int[] { 'О' };
names2unicode["G7D"] = new int[] { 'к' };
names2unicode["G7E"] = new int[] { 'З' };
names2unicode["G80"] = new int[] { 'Г' };
names2unicode["G81"] = new int[] { 'П' };
names2unicode["G82"] = new int[] { 'у' };
names2unicode["G85"] = new int[] { '»' };
names2unicode["G88"] = new int[] { 'т' };
names2unicode["G8D"] = new int[] { '’' };
names2unicode["G90"] = new int[] { 'У' };
names2unicode["G91"] = new int[] { 'Т' };
names2unicode["GA1"] = new int[] { 'Ц' };
names2unicode["GA2"] = new int[] { '№' };
names2unicode["GAA"] = new int[] { 'э' };
names2unicode["GAB"] = new int[] { 'я' };
names2unicode["GAC"] = new int[] { 'і' };
names2unicode["GAD"] = new int[] { 'б' };
names2unicode["GAE"] = new int[] { 'й' };
names2unicode["GAF"] = new int[] { 'р' };
names2unicode["GB0"] = new int[] { 'с' };
names2unicode["GB2"] = new int[] { 'х' };
names2unicode["GB5"] = new int[] { '“' };
names2unicode["GB9"] = new int[] { 'п' };
names2unicode["GBA"] = new int[] { 'о' };
names2unicode["GBD"] = new int[] { '«' };
names2unicode["GC1"] = new int[] { 'ф' };
names2unicode["GC8"] = new int[] { 'а' };
names2unicode["GCB"] = new int[] { 'е' };
names2unicode["GCE"] = new int[] { 'ж' };
names2unicode["GCF"] = new int[] { 'з' };
names2unicode["GD2"] = new int[] { 'и' };
names2unicode["GD3"] = new int[] { 'н' };
names2unicode["GDC"] = new int[] { '–' };
names2unicode["GE3"] = new int[] { 'л' };
}
执行该方法后，您可以使用您的方法提取文本：
InitializeGlyphs();
using (FileStream pdfStream = new FileStream(@"ENGV_1929.pdf", FileMode.Open))
{
string result = ExtractTextFromPdf(pdfStream, true);
File.WriteAllText(@"ENGV_1929.txt", result);
Console.WriteLine("\n\nENGV_1929.pdf\n");
Console.WriteLine(result);
}
结果：
From Notices to Mariners
Edition No 29/2019
(English version)
Notiсes to Mariners from Seсtion II «Сharts Сorreсtion», based on the original sourсe information, and
NAVAREA XIII, XX and XXI navigational warnings are reprinted hereunder in English. Original Notiсes to
Mariners from Seсtion I «Misсellaneous Navigational Information» and from Seсtion III «Nautiсal
Publiсations Сorreсtion» may be only briefly annotated and/or a referenсe may be made to Notiсes from
other Seсtions. Information from Seсtion IV «Сatalogues of Сharts and Nautiсal Publiсations Сorreсtion»
сonсerning the issue of сharts and publiсations is presented with details.
Digital analogue of English version of the extracts from original Russian Notices to Mariners is available
by: http://structure.mil.ru/structure/forces/hydrographic/info/notices.htm
СНАRTS СОRRЕСTIОN
Вarents Sea
3493 Сharts 18012, 17052, 15005, 15004
Amend 1. Light to light Fl G 4s 1M at
front leading lightbeacon 69111’32.2“N 33129’48.0“E
2. Light to light Fl G 4s 1M at
rear leading lightbeacon 69111’34.85“N 33129’44.25“E
Cancel coastal warning
MURMANSK 71/19
...
请注意，您会经常看到使用看起来相似的西里尔字符代替拉丁字符。显然该文档是由不认为印刷正确性非常重要的人手动创建的..
因此，如果您想在文本中进行搜索，您应该首先规范化文本和您的搜索词（例如，对拉丁语 'c' 和西里尔语 'с' 使用相同的字符）。
我正在尝试使用 iTextSharp (v5.5.12.1) 从以下 PDF 中提取文本： https://structure.mil.ru/files/morf/military/files/ENGV_1929.pdf
不幸的是，他们似乎使用了一些嵌入式自定义字体，这让我很沮丧。
目前，我有一个使用 OCR 的可行解决方案，但 OCR 可能不精确，会错误地读取某些字符并在字符之间添加额外的空格。如果能直接把文字提取出来就好了
public static string ExtractTextFromPdf(Stream pdfStream, bool addNewLineBetweenPages = false)
{
using (PdfReader reader = new PdfReader(pdfStream))
{
string text = "";
for (int i = 1; i <= reader.NumberOfPages; i++)
{
text += PdfTextExtractor.GetTextFromPage(reader, i);
if (addNewLineBetweenPages && i != reader.NumberOfPages)
{
text += Environment.NewLine;
}
}
return text;
}
}
这里的问题是嵌入字体程序中的字形具有非标准字形名称（G00、G01、.. .) 并且仅由字形名称标识。因此，必须建立从这些字形名称到 Unicode 字符的映射。可以这样做，例如通过检查 PDF 中的字体程序（例如使用 font forge）并通过名称视觉识别字形。例如。喜欢这里
（如您所知，手头文档中未使用的相关字体字形存在一些空白。您可以猜到一些缺失的字形，有些则没有。）
然后你必须将这些映射注入到 iText 中。由于映射是隐藏的（GlyphList class 的 private static 成员），您要么必须修补 iText 本身，要么使用反射：
void InitializeGlyphs()
{
FieldInfo names2unicodeFiled = typeof(GlyphList).GetField("names2unicode", BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Static);
Dictionary<string, int[]> names2unicode = (Dictionary<string, int[]>) names2unicodeFiled.GetValue(null);
names2unicode["G03"] = new int[] { ' ' };
names2unicode["G0A"] = new int[] { '\'' };
names2unicode["G0B"] = new int[] { '(' };
names2unicode["G0C"] = new int[] { ')' };
names2unicode["G0F"] = new int[] { ',' };
names2unicode["G10"] = new int[] { '-' };
names2unicode["G11"] = new int[] { '.' };
names2unicode["G12"] = new int[] { '/' };
names2unicode["G13"] = new int[] { '0' };
names2unicode["G14"] = new int[] { '1' };
names2unicode["G15"] = new int[] { '2' };
names2unicode["G16"] = new int[] { '3' };
names2unicode["G17"] = new int[] { '4' };
names2unicode["G18"] = new int[] { '5' };
names2unicode["G19"] = new int[] { '6' };
names2unicode["G1A"] = new int[] { '7' };
names2unicode["G1B"] = new int[] { '8' };
names2unicode["G1C"] = new int[] { '9' };
names2unicode["G1D"] = new int[] { ':' };
names2unicode["G23"] = new int[] { '@' };
names2unicode["G24"] = new int[] { 'A' };
names2unicode["G25"] = new int[] { 'B' };
names2unicode["G26"] = new int[] { 'C' };
names2unicode["G27"] = new int[] { 'D' };
names2unicode["G28"] = new int[] { 'E' };
names2unicode["G29"] = new int[] { 'F' };
names2unicode["G2A"] = new int[] { 'G' };
names2unicode["G2B"] = new int[] { 'H' };
names2unicode["G2C"] = new int[] { 'I' };
names2unicode["G2D"] = new int[] { 'J' };
names2unicode["G2E"] = new int[] { 'K' };
names2unicode["G2F"] = new int[] { 'L' };
names2unicode["G30"] = new int[] { 'M' };
names2unicode["G31"] = new int[] { 'N' };
names2unicode["G32"] = new int[] { 'O' };
names2unicode["G33"] = new int[] { 'P' };
names2unicode["G34"] = new int[] { 'Q' };
names2unicode["G35"] = new int[] { 'R' };
names2unicode["G36"] = new int[] { 'S' };
names2unicode["G37"] = new int[] { 'T' };
names2unicode["G38"] = new int[] { 'U' };
names2unicode["G39"] = new int[] { 'V' };
names2unicode["G3A"] = new int[] { 'W' };
names2unicode["G3B"] = new int[] { 'X' };
names2unicode["G3C"] = new int[] { 'Y' };
names2unicode["G3D"] = new int[] { 'Z' };
names2unicode["G42"] = new int[] { '_' };
names2unicode["G44"] = new int[] { 'a' };
names2unicode["G45"] = new int[] { 'b' };
names2unicode["G46"] = new int[] { 'c' };
names2unicode["G46._"] = new int[] { 'c' };
names2unicode["G47"] = new int[] { 'd' };
names2unicode["G48"] = new int[] { 'e' };
names2unicode["G49"] = new int[] { 'f' };
names2unicode["G4A"] = new int[] { 'g' };
names2unicode["G4B"] = new int[] { 'h' };
names2unicode["G4C"] = new int[] { 'i' };
names2unicode["G4D"] = new int[] { 'j' };
names2unicode["G4E"] = new int[] { 'k' };
names2unicode["G4F"] = new int[] { 'l' };
names2unicode["G50"] = new int[] { 'm' };
names2unicode["G51"] = new int[] { 'n' };
names2unicode["G52"] = new int[] { 'o' };
names2unicode["G53"] = new int[] { 'p' };
names2unicode["G54"] = new int[] { 'q' };
names2unicode["G55"] = new int[] { 'r' };
names2unicode["G56"] = new int[] { 's' };
names2unicode["G57"] = new int[] { 't' };
names2unicode["G58"] = new int[] { 'u' };
names2unicode["G59"] = new int[] { 'v' };
names2unicode["G5A"] = new int[] { 'w' };
names2unicode["G5B"] = new int[] { 'x' };
names2unicode["G5C"] = new int[] { 'y' };
names2unicode["G5D"] = new int[] { 'z' };
names2unicode["G62"] = new int[] { 'Ш' };
names2unicode["G63"] = new int[] { 'Р' };
names2unicode["G6A"] = new int[] { 'И' };
names2unicode["G6B"] = new int[] { 'А' };
names2unicode["G6C"] = new int[] { 'М' };
names2unicode["G6D"] = new int[] { 'в' };
names2unicode["G6E"] = new int[] { 'Ф' };
names2unicode["G70"] = new int[] { 'Е' };
names2unicode["G72"] = new int[] { 'Б' };
names2unicode["G73"] = new int[] { 'Н' };
names2unicode["G76"] = new int[] { 'С' };
names2unicode["G7A"] = new int[] { 'К' };
names2unicode["G7B"] = new int[] { 'В' };
names2unicode["G7C"] = new int[] { 'О' };
names2unicode["G7D"] = new int[] { 'к' };
names2unicode["G7E"] = new int[] { 'З' };
names2unicode["G80"] = new int[] { 'Г' };
names2unicode["G81"] = new int[] { 'П' };
names2unicode["G82"] = new int[] { 'у' };
names2unicode["G85"] = new int[] { '»' };
names2unicode["G88"] = new int[] { 'т' };
names2unicode["G8D"] = new int[] { '’' };
names2unicode["G90"] = new int[] { 'У' };
names2unicode["G91"] = new int[] { 'Т' };
names2unicode["GA1"] = new int[] { 'Ц' };
names2unicode["GA2"] = new int[] { '№' };
names2unicode["GAA"] = new int[] { 'э' };
names2unicode["GAB"] = new int[] { 'я' };
names2unicode["GAC"] = new int[] { 'і' };
names2unicode["GAD"] = new int[] { 'б' };
names2unicode["GAE"] = new int[] { 'й' };
names2unicode["GAF"] = new int[] { 'р' };
names2unicode["GB0"] = new int[] { 'с' };
names2unicode["GB2"] = new int[] { 'х' };
names2unicode["GB5"] = new int[] { '“' };
names2unicode["GB9"] = new int[] { 'п' };
names2unicode["GBA"] = new int[] { 'о' };
names2unicode["GBD"] = new int[] { '«' };
names2unicode["GC1"] = new int[] { 'ф' };
names2unicode["GC8"] = new int[] { 'а' };
names2unicode["GCB"] = new int[] { 'е' };
names2unicode["GCE"] = new int[] { 'ж' };
names2unicode["GCF"] = new int[] { 'з' };
names2unicode["GD2"] = new int[] { 'и' };
names2unicode["GD3"] = new int[] { 'н' };
names2unicode["GDC"] = new int[] { '–' };
names2unicode["GE3"] = new int[] { 'л' };
}
执行该方法后，您可以使用您的方法提取文本：
InitializeGlyphs();
using (FileStream pdfStream = new FileStream(@"ENGV_1929.pdf", FileMode.Open))
{
string result = ExtractTextFromPdf(pdfStream, true);
File.WriteAllText(@"ENGV_1929.txt", result);
Console.WriteLine("\n\nENGV_1929.pdf\n");
Console.WriteLine(result);
}
结果：
From Notices to Mariners
Edition No 29/2019
(English version)
Notiсes to Mariners from Seсtion II «Сharts Сorreсtion», based on the original sourсe information, and
NAVAREA XIII, XX and XXI navigational warnings are reprinted hereunder in English. Original Notiсes to
Mariners from Seсtion I «Misсellaneous Navigational Information» and from Seсtion III «Nautiсal
Publiсations Сorreсtion» may be only briefly annotated and/or a referenсe may be made to Notiсes from
other Seсtions. Information from Seсtion IV «Сatalogues of Сharts and Nautiсal Publiсations Сorreсtion»
сonсerning the issue of сharts and publiсations is presented with details.
Digital analogue of English version of the extracts from original Russian Notices to Mariners is available
by: http://structure.mil.ru/structure/forces/hydrographic/info/notices.htm
СНАRTS СОRRЕСTIОN
Вarents Sea
3493 Сharts 18012, 17052, 15005, 15004
Amend 1. Light to light Fl G 4s 1M at
front leading lightbeacon 69111’32.2“N 33129’48.0“E
2. Light to light Fl G 4s 1M at
rear leading lightbeacon 69111’34.85“N 33129’44.25“E
Cancel coastal warning
MURMANSK 71/19
...
请注意，您会经常看到使用看起来相似的西里尔字符代替拉丁字符。显然该文档是由不认为印刷正确性非常重要的人手动创建的..
因此，如果您想在文本中进行搜索，您应该首先规范化文本和您的搜索词（例如，对拉丁语 'c' 和西里尔语 'с' 使用相同的字符）。