Allow user to specify dpi for input image

src/api/baseapi.cpp

@@ -2320,12 +2320,22 @@ bool TessBaseAPI::Threshold(Pix** pix) {
   if (*pix != nullptr)
     pixDestroy(pix);
   // Zero resolution messes up the algorithms, so make sure it is credible.
+  int user_dpi = 0;
+  bool a = GetIntVariable("user_defined_dpi", &user_dpi);
   int y_res = thresholder_->GetScaledYResolution();
-  if (y_res < kMinCredibleResolution || y_res > kMaxCredibleResolution) {
-    // Use the minimum default resolution, as it is safer to under-estimate
-    // than over-estimate resolution.
-    tprintf("Warning. Invalid resolution %d dpi. Using %d instead.\n", y_res,
-            kMinCredibleResolution);
+  if (user_dpi && (user_dpi < kMinCredibleResolution ||
+      user_dpi > kMaxCredibleResolution)) {
+    tprintf("Warning: User defined image dpi is outside of expected range "
+            "(%d - %d)!\n",
+            kMinCredibleResolution, kMaxCredibleResolution);
+  }
+  // Always use user defined dpi
+  if (user_dpi) {
+    thresholder_->SetSourceYResolution(user_dpi);
+  } else if (y_res < kMinCredibleResolution ||
+             y_res > kMaxCredibleResolution) {
+    tprintf("Warning: Invalid resolution %d dpi. Using %d instead.\n",
+            y_res, kMinCredibleResolution);
     thresholder_->SetSourceYResolution(kMinCredibleResolution);
   }
   PageSegMode pageseg_mode =
@@ -2350,7 +2360,8 @@ bool TessBaseAPI::Threshold(Pix** pix) {
                                   kMinCredibleResolution,
                                   kMaxCredibleResolution);
   if (estimated_res != thresholder_->GetScaledEstimatedResolution()) {
-    tprintf("Estimated resolution %d out of range! Corrected to %d\n",
+    tprintf("Estimated internal resolution %d out of range! "
+            "Corrected to %d.\n",
             thresholder_->GetScaledEstimatedResolution(), estimated_res);
   }
   tesseract_->set_source_resolution(estimated_res);

src/api/tesseractmain.cpp

@@ -165,6 +165,7 @@ static void PrintHelpExtra(const char* program) {
       "  --tessdata-dir PATH   Specify the location of tessdata path.\n"
       "  --user-words PATH     Specify the location of user words file.\n"
       "  --user-patterns PATH  Specify the location of user patterns file.\n"
+      "  --dpi VALUE           Specify DPI for input image.\n"
       "  -l LANG[+LANG]        Specify language(s) used for OCR.\n"
       "  -c VAR=VALUE          Set value for config variables.\n"
       "                        Multiple -c arguments are allowed.\n"
@@ -288,10 +289,9 @@ static void checkArgValues(int arg, const char* mode, int count) {
 // NOTE: arg_i is used here to avoid ugly *i so many times in this function
 static void ParseArgs(const int argc, char** argv, const char** lang,
                       const char** image, const char** outputbase,
-                      const char** datapath,
-                      bool* list_langs, bool* print_parameters,
-                      GenericVector<STRING>* vars_vec,
-                      GenericVector<STRING>* vars_values, int* arg_i,
+                      const char** datapath, l_int32* dpi, bool* list_langs,
+                      bool* print_parameters, GenericVector<STRING>* vars_vec,
+                      GenericVector<STRING>* vars_values, l_int32* arg_i,
                       tesseract::PageSegMode* pagesegmode,
                       tesseract::OcrEngineMode* enginemode) {
   bool noocr = false;
@@ -324,6 +324,9 @@ static void ParseArgs(const int argc, char** argv, const char** lang,
     } else if (strcmp(argv[i], "--tessdata-dir") == 0 && i + 1 < argc) {
       *datapath = argv[i + 1];
       ++i;
+    } else if (strcmp(argv[i], "--dpi") == 0 && i + 1 < argc) {
+      *dpi = atoi(argv[i + 1]);
+      ++i;
     } else if (strcmp(argv[i], "--user-words") == 0 && i + 1 < argc) {
       vars_vec->push_back("user_words_file");
       vars_values->push_back(argv[i + 1]);
@@ -456,6 +459,7 @@ int main(int argc, char** argv) {
   const char* datapath = nullptr;
   bool list_langs = false;
   bool print_parameters = false;
+  l_int32 dpi = 0;
   int arg_i = 1;
   tesseract::PageSegMode pagesegmode = tesseract::PSM_AUTO;
 #ifdef DISABLED_LEGACY_ENGINE
@@ -479,9 +483,9 @@ int main(int argc, char** argv) {
   TIFFSetWarningHandler(Win32WarningHandler);
 #endif /* HAVE_TIFFIO_H &&  _WIN32 */
 
-  ParseArgs(argc, argv, &lang, &image, &outputbase, &datapath, &list_langs,
-            &print_parameters, &vars_vec, &vars_values, &arg_i, &pagesegmode,
-            &enginemode);
+  ParseArgs(argc, argv, &lang, &image, &outputbase, &datapath, &dpi,
+            &list_langs, &print_parameters, &vars_vec, &vars_values, &arg_i,
+            &pagesegmode, &enginemode);
 
   if (lang == nullptr) {
     // Set default language if none was given.
@@ -528,6 +532,11 @@ int main(int argc, char** argv) {
 
   FixPageSegMode(&api, pagesegmode);
 
+  if (dpi) {
+    char dpi_string[255];
+    snprintf(dpi_string, 254, "%d", dpi);
+    api.SetVariable("user_defined_dpi", dpi_string);
+  }
   if (pagesegmode == tesseract::PSM_AUTO_ONLY) {
     int ret_val = EXIT_SUCCESS;
 

src/ccmain/tesseractclass.cpp

@@ -395,6 +395,8 @@ Tesseract::Tesseract()
                   "Create PDF with only one invisible text layer",
                   this->params()),
       INT_MEMBER(jpg_quality, 85, "Set JPEG quality level", this->params()),
+      INT_MEMBER(user_defined_dpi, 0, "Specify DPI for input image",
+                 this->params()),
       STRING_MEMBER(unrecognised_char, "|",
                     "Output char for unidentified blobs", this->params()),
       INT_MEMBER(suspect_level, 99, "Suspect marker level", this->params()),

src/ccmain/tesseractclass.h

@@ -1042,6 +1042,7 @@ class Tesseract : public Wordrec {
   BOOL_VAR_H(textonly_pdf, false,
              "Create PDF with only one invisible text layer");
   INT_VAR_H(jpg_quality, 85, "Set JPEG quality level");
+  INT_VAR_H(user_defined_dpi, 0, "Specify DPI for input image");
   STRING_VAR_H(unrecognised_char, "|",
                "Output char for unidentified blobs");
   INT_VAR_H(suspect_level, 99, "Suspect marker level");