PDFlibPas: text, image, and font extraction in Delphi

losLab PDF Library ger Delphi- och C++Builder-team en PDF-motor med tillgänglig källkod för skrivbord, server, DLL, ActiveX och Dylib, med inbyggda PDF/A- och PDF/UA-kontroller, PAdES-signering och valbara renderare utan extern PDF-tjänst.

Den här artikeln är skriven för teams building PDF analysis, migration, search, evidence capture, or support-inspection tools. Den behandlar text, image, and font extraction som produktionsnära dokumentteknik, inte som ett isolerat komponentanrop.

Den praktiska risken är att extraction output is easy to over-trust even though PDF content order, font encoding, image color spaces, and page resources rarely match user-visible reading order exactly. Därför behöver flödet ett skrivet kontrakt, observerbar diagnostik och realistiska regressionsfiler.

Arkitekturbeslut

Separate extraction facts from interpretation. whether output needs visual order, content-stream order, or search-oriented order / image extraction format, color conversion, compression retention, and naming

whether output needs visual order, content-stream order, or search-oriented order
image extraction format, color conversion, compression retention, and naming
font subset naming, encoding diagnostics, and missing ToUnicode handling
confidence flags for OCR layers, hidden text, clipped content, and rotated pages

Implementeringsflöde

Preserve page and resource context. Ordningen nedan gör arbetsflödet granskbart för Delphi- och C++Builder-team.

scan page resources and content streams while preserving object references
extract text runs with coordinates, font identity, Unicode mapping, and style signals
extract images with page location, dimensions, color space, and original object data when needed
classify fonts by subset, embedded status, and encoding behavior
produce an analysis report that distinguishes facts from inferred reading order

Valideringsbevis

Extraction evidence that remains explainable. Behåll dessa fält tillsammans med utdata eller supportunderlaget.

page number, object reference, coordinates, decoded text, font, and confidence
image size, color space, compression, mask, and export filename
font subset name, embedded state, encoding map, and ToUnicode status
warnings for hidden, clipped, rotated, or overlapping content

Extracted text is not always authored text

A professional extraction workflow should record where each text run, image, and font resource came from, how it was decoded, and which assumptions were used to group it into searchable or reviewable content.

Support package design

Once PDFlibPas is deployed, the most valuable support package is the one that explains the input, profile, output, and exact stage that failed.

page number, object reference, coordinates, decoded text, font, and confidence
image size, color space, compression, mask, and export filename
font subset name, embedded state, encoding map, and ToUnicode status
warnings for hidden, clipped, rotated, or overlapping content
terminology snapshot: text extraction, image extraction, font resource, ToUnicode

Tekniska granskningsnoteringar för text, image, and font extraction

Använd dessa granskningsnoteringar för att säkerställa att funktionen har passerat demo-nivån och kan försvaras under leverans, support och kundeskalering.

Beslut: whether output needs visual order, content-stream order, or search-oriented order. Implementeringspresspunkt: extract text runs with coordinates, font identity, Unicode mapping, and style signals. Acceptansbevis: font subset name, embedded state, encoding map, and ToUnicode status. Regressionsutlösare: OCR layers can contain stale or misaligned text over scanned pages
Beslut: image extraction format, color conversion, compression retention, and naming. Implementeringspresspunkt: extract images with page location, dimensions, color space, and original object data when needed. Acceptansbevis: warnings for hidden, clipped, rotated, or overlapping content. Regressionsutlösare: PDF drawing order may not equal human reading order
Beslut: font subset naming, encoding diagnostics, and missing ToUnicode handling. Implementeringspresspunkt: classify fonts by subset, embedded status, and encoding behavior. Acceptansbevis: page number, object reference, coordinates, decoded text, font, and confidence. Regressionsutlösare: ligatures and custom encodings can make copied text differ from visible text
Beslut: confidence flags for OCR layers, hidden text, clipped content, and rotated pages. Implementeringspresspunkt: produce an analysis report that distinguishes facts from inferred reading order. Acceptansbevis: image size, color space, compression, mask, and export filename. Regressionsutlösare: images may be masks, soft masks, or repeated resources rather than standalone pictures
Beslut: whether output needs visual order, content-stream order, or search-oriented order. Implementeringspresspunkt: scan page resources and content streams while preserving object references. Acceptansbevis: font subset name, embedded state, encoding map, and ToUnicode status. Regressionsutlösare: OCR layers can contain stale or misaligned text over scanned pages
Beslut: image extraction format, color conversion, compression retention, and naming. Implementeringspresspunkt: extract text runs with coordinates, font identity, Unicode mapping, and style signals. Acceptansbevis: warnings for hidden, clipped, rotated, or overlapping content. Regressionsutlösare: PDF drawing order may not equal human reading order
Beslut: font subset naming, encoding diagnostics, and missing ToUnicode handling. Implementeringspresspunkt: extract images with page location, dimensions, color space, and original object data when needed. Acceptansbevis: page number, object reference, coordinates, decoded text, font, and confidence. Regressionsutlösare: ligatures and custom encodings can make copied text differ from visible text

Gränsfall

PDF drawing order may not equal human reading order
ligatures and custom encodings can make copied text differ from visible text
images may be masks, soft masks, or repeated resources rather than standalone pictures
OCR layers can contain stale or misaligned text over scanned pages

Delphi / C++Builder notes

PDFlibPas should sit behind a small service boundary that receives files, streams, profiles, and credentials, then returns output paths, warnings, metrics, and validation status. Important terms include text extraction, image extraction, font resource, ToUnicode, content stream, coordinates.

Delphi-kodexempel

Följande Delphi-skiss visar en praktisk servicegräns för detta ämne. Håll policykontroller, loggning och validering utanför det smala produktanropet så att arbetsflödet går att testa.

procedure ExtractForIndexing(const FileName, OutputDir: string);
var
  Pdf: TPDFlib;
begin
  Pdf := TPDFlib.Create;
  try
    Pdf.LoadFromFile(FileName, '');
    SaveExtractedText(OutputDir, ExtractDocumentText(Pdf));
    SaveEmbeddedImages(OutputDir, ExtractDocumentImages(Pdf));
    SaveFontInventory(OutputDir, BuildFontInventory(Pdf));
  finally
    Pdf.Free;
  end;
end;

Produktionschecklista

Kör arbetsflödet på en tom fil, en normal kundfil och en värstafallfil
Öppna den genererade PDF-filen med rätt visare, validator, skrivare eller nedströmsapplikation
Logga produktversion, profilversion, inmatningshash, utdatasökväg, förfluten tid och antal varningar
Håll lösenord, certifikat, tillfälliga filer och kunddata under tydliga lagringsregler
Lägg till regressionsdokument när en kundfil avslöjar ett nytt gränsfall

Produktdokumentation

PDFlibPas

Fler kodexempel

var
  ImgList, I: Integer;
begin
  Pdf.SelectPage(1);
  ImgList := Pdf.GetPageImageList(0);
  for I := 0 to Pdf.GetImageListCount(ImgList) - 1 do
  begin
    Writeln(Pdf.GetImageListItemFormatDesc(ImgList, I, 0));
    Pdf.SaveImageListItemDataToFile(ImgList, I, 0,
      Format('page1-img%.2d.bin', [I]));
  end;
  Pdf.ReleaseImageList(ImgList);
end;

var
  I: Integer;
begin
  Pdf.FindFonts;
  for I := 1 to Pdf.FontCount do        // font indexes start at 1, not 0
    if Pdf.SelectFont(Pdf.GetFontID(I)) = 1 then
      Writeln(Format('%s  type=%d  embedded=%d  subset=%d',
        [Pdf.FontName, Pdf.FontType,
         Pdf.GetFontIsEmbedded, Pdf.GetFontIsSubsetted]));
end;