Implement invisible text only for PDF

api/capi.cpp

@@ -64,9 +64,10 @@ TESS_API TessResultRenderer* TESS_CALL TessHOcrRendererCreate2(const char* outpu
     return new TessHOcrRenderer(outputbase, font_info);
 }
 
-TESS_API TessResultRenderer* TESS_CALL TessPDFRendererCreate(const char* outputbase, const char* datadir)
+TESS_API TessResultRenderer* TESS_CALL TessPDFRendererCreate(const char* outputbase, const char* datadir,
+                                                             BOOL textonly)
 {
-    return new TessPDFRenderer(outputbase, datadir);
+    return new TessPDFRenderer(outputbase, datadir, textonly);
 }
 
 TESS_API TessResultRenderer* TESS_CALL TessUnlvRendererCreate(const char* outputbase)

api/pdfrenderer.cpp

@@ -178,10 +178,12 @@ const int kCharWidth = 2;
  * PDF Renderer interface implementation
  **********************************************************************/
 
-TessPDFRenderer::TessPDFRenderer(const char* outputbase, const char *datadir)
+TessPDFRenderer::TessPDFRenderer(const char *outputbase, const char *datadir,
+                                 bool textonly)
     : TessResultRenderer(outputbase, "pdf") {
   obj_  = 0;
   datadir_ = datadir;
+  textonly_ = textonly;
   offsets_.push_back(0);
 }
 
@@ -326,7 +328,11 @@ char* TessPDFRenderer::GetPDFTextObjects(TessBaseAPI* api,
   pdf_str.add_str_double("", prec(width));
   pdf_str += " 0 0 ";
   pdf_str.add_str_double("", prec(height));
-  pdf_str += " 0 0 cm /Im1 Do Q\n";
+  pdf_str += " 0 0 cm";
+  if (!textonly_) {
+    pdf_str += " /Im1 Do";
+  }
+  pdf_str += " Q\n";
 
   int line_x1 = 0;
   int line_y1 = 0;
@@ -837,6 +843,7 @@ bool TessPDFRenderer::imageToPDFObj(Pix *pix,
 bool TessPDFRenderer::AddImageHandler(TessBaseAPI* api) {
   size_t n;
   char buf[kBasicBufSize];
+  char buf2[kBasicBufSize];
   Pix *pix = api->GetInputImage();
   char *filename = (char *)api->GetInputName();
   int ppi = api->GetSourceYResolution();
@@ -845,6 +852,9 @@ bool TessPDFRenderer::AddImageHandler(TessBaseAPI* api) {
   double width = pixGetWidth(pix) * 72.0 / ppi;
   double height = pixGetHeight(pix) * 72.0 / ppi;
 
+  snprintf(buf2, sizeof(buf2), "XObject << /Im1 %ld 0 R >>\n", obj_ + 2);
+  const char *xobject = (textonly_) ? "" : buf2;
+
   // PAGE
   n = snprintf(buf, sizeof(buf),
                "%ld 0 obj\n"
@@ -855,19 +865,18 @@ bool TessPDFRenderer::AddImageHandler(TessBaseAPI* api) {
                "  /Contents %ld 0 R\n"
                "  /Resources\n"
                "  <<\n"
-               "    /XObject << /Im1 %ld 0 R >>\n"
+               "    %s"
                "    /ProcSet [ /PDF /Text /ImageB /ImageI /ImageC ]\n"
                "    /Font << /f-0-0 %ld 0 R >>\n"
                "  >>\n"
                ">>\n"
                "endobj\n",
                obj_,
-               2L,            // Pages object
-               width,
-               height,
-               obj_ + 1,      // Contents object
-               obj_ + 2,      // Image object
-               3L);           // Type0 Font
+               2L,  // Pages object
+               width, height,
+               obj_ + 1,  // Contents object
+               xobject,   // Image object
+               3L);       // Type0 Font
   if (n >= sizeof(buf)) return false;
   pages_.push_back(obj_);
   AppendPDFObject(buf);
@@ -904,13 +913,15 @@ bool TessPDFRenderer::AddImageHandler(TessBaseAPI* api) {
   objsize += strlen(b2);
   AppendPDFObjectDIY(objsize);
 
-  char *pdf_object;
-  if (!imageToPDFObj(pix, filename, obj_, &pdf_object, &objsize)) {
-    return false;
+  if (!textonly_) {
+    char *pdf_object = nullptr;
+    if (!imageToPDFObj(pix, filename, obj_, &pdf_object, &objsize)) {
+      return false;
+    }
+    AppendData(pdf_object, objsize);
+    AppendPDFObjectDIY(objsize);
+    delete[] pdf_object;
   }
-  AppendData(pdf_object, objsize);
-  AppendPDFObjectDIY(objsize);
-  delete[] pdf_object;
   return true;
 }
 

api/renderer.h

@@ -186,7 +186,7 @@ class TESS_API TessPDFRenderer : public TessResultRenderer {
  public:
   // datadir is the location of the TESSDATA. We need it because
   // we load a custom PDF font from this location.
-  TessPDFRenderer(const char *outputbase, const char *datadir);
+  TessPDFRenderer(const char* outputbase, const char* datadir, bool textonly);
 
  protected:
   virtual bool BeginDocumentHandler();
@@ -196,20 +196,20 @@ class TESS_API TessPDFRenderer : public TessResultRenderer {
  private:
   // We don't want to have every image in memory at once,
   // so we store some metadata as we go along producing
-  // PDFs one page at a time. At the end that metadata is
+  // PDFs one page at a time. At the end, that metadata is
   // used to make everything that isn't easily handled in a
   // streaming fashion.
   long int obj_;                     // counter for PDF objects
   GenericVector<long int> offsets_;  // offset of every PDF object in bytes
   GenericVector<long int> pages_;    // object number for every /Page object
   const char *datadir_;              // where to find the custom font
+  bool textonly_;                    // skip images if set
   // Bookkeeping only. DIY = Do It Yourself.
   void AppendPDFObjectDIY(size_t objectsize);
   // Bookkeeping + emit data.
   void AppendPDFObject(const char *data);
   // Create the /Contents object for an entire page.
-  static char* GetPDFTextObjects(TessBaseAPI* api,
-                                 double width, double height);
+  char* GetPDFTextObjects(TessBaseAPI* api, double width, double height);
   // Turn an image into a PDF object. Only transcode if we have to.
   static bool imageToPDFObj(Pix *pix, char *filename, long int objnum,
                           char **pdf_object, long int *pdf_object_size);

api/tesseractmain.cpp

@@ -348,8 +348,10 @@ void PreloadRenderers(
 
     api->GetBoolVariable("tessedit_create_pdf", &b);
     if (b) {
-      renderers->push_back(
-          new tesseract::TessPDFRenderer(outputbase, api->GetDatapath()));
+      bool textonly;
+      api->GetBoolVariable("textonly_pdf", &textonly);
+      renderers->push_back(new tesseract::TessPDFRenderer(
+          outputbase, api->GetDatapath(), textonly));
     }
 
     api->GetBoolVariable("tessedit_write_unlv", &b);

ccmain/tesseractclass.cpp

@@ -389,6 +389,8 @@ Tesseract::Tesseract()
                   this->params()),
       BOOL_MEMBER(tessedit_create_pdf, false, "Write .pdf output file",
                   this->params()),
+      BOOL_MEMBER(textonly_pdf, false, "Invisible text only for PDF",
+                  this->params()),
       STRING_MEMBER(unrecognised_char, "|",
                     "Output char for unidentified blobs", this->params()),
       INT_MEMBER(suspect_level, 99, "Suspect marker level", this->params()),

ccmain/tesseractclass.h

@@ -1026,6 +1026,7 @@ class Tesseract : public Wordrec {
   BOOL_VAR_H(tessedit_create_hocr, false, "Write .html hOCR output file");
   BOOL_VAR_H(tessedit_create_tsv, false, "Write .tsv output file");
   BOOL_VAR_H(tessedit_create_pdf, false, "Write .pdf output file");
+  BOOL_VAR_H(textonly_pdf, false, "Invisible text only for PDF");
   STRING_VAR_H(unrecognised_char, "|",
                "Output char for unidentified blobs");
   INT_VAR_H(suspect_level, 99, "Suspect marker level");