Prise en charge de la compression JBIG2

Vue d’ensemble

HotPDF inclut désormais une prise en charge complète de la compression JBIG2 (Joint Bi-level Image Experts Group 2), une norme de compression avec ou sans perte conçue spécialement pour les images bichromes (monochromes), souvent utilisée dans les documents PDF pour les pages de texte numérisé et les tracés au trait

Fonctionnalités clés

High-efficiency compression for bilevel images
Support for both lossy and lossless compression modes
Optimized for text and line art compression
Significant file size reduction compared to traditional compression methods
Full PDF/A compliance support
Multi-page document support with shared dictionaries

Avantages de la compression

Superior Compression Ratios: Up to 3-5x better compression than Group 4 CCITT
Pattern Recognition: Intelligent recognition of repeated patterns and symbols
Adaptive Compression: Automatically adjusts compression strategy based on content type
Memory Efficient: Optimized for processing large scanned documents

Cas d'utilisation typiques

Scanned text documents
Technical drawings and blueprints
Forms and invoices
Maps and diagrams
Mixed content documents with text and graphics

Implémentation technique

La prise en charge JBIG2 est implémentée dans l'unité HPDFJBIG2.pas, qui fournit :

THPDFJBIG2Decoder: Core decoder class for JBIG2 compressed data
Stream Processing : Traitement efficace des flux de données JBIG2
Global Dictionary Support: Shared symbol dictionaries for multi-page documents
Scanline Access: Row-by-row data access for memory-efficient processing

Exemple d'utilisation



// Delphi example - Processing JBIG2 compressed data

procedure ProcessJBIG2Data;

var

  PDF: THotPDF;

  Decoder: THPDFJBIG2Decoder;

  ImageData: TBytesArray;

  ScanlineData: TBytesArray;

  Row: Integer;

begin

  PDF := THotPDF.Create(nil);

  Decoder := THPDFJBIG2Decoder.Create;

  try

    PDF.BeginDoc;

    PDF.AddPage;



    // Load JBIG2 compressed image data

    if Decoder.LoadFromByteArray(ImageData) then

    begin

      // Process scanline by scanline for memory efficiency

      for Row := 0 to Decoder.Height - 1 do

      begin

        if Decoder.GetScanline(Row, ScanlineData) then

        begin

          // Process scanline data as needed

          // Add to PDF page

        end;

      end;

    end;



    PDF.EndDoc;

  finally

    Decoder.Free;

    PDF.Free;

  end;

end;

Référence de classe

THPDFJBIG2Decoder

LoadFromByteArray: Load JBIG2 data from byte array
GetScanline: Retrieve specific scanline data
Width/Height: Image dimensions properties

Optimisation des performances

Memory-efficient scanline processing
Optimized for large document handling
Minimal memory footprint during decompression
Fast pattern recognition algorithms

Conformité aux normes

ITU-T T.88 standard compliance
ISO/IEC 14492 standard support
PDF/A archival format compatibility
Cross-platform consistency

Voir aussi