CLI: Unexpected handling of parameters using -c VAR=VALUE

[sdubinsky]

Note by @amitdo. The original title was: Inconsistency Between --oem and -c "tessedit_ocr_engine_mode"

Current Behavior

As far as I can tell, these two options should be identical, however the attached image produces different output. With --oem it says 11, with the config var it says 1. I should add that with any --oem value other than 0, it returns '1' not '11'.

Full command:

tesseract -l eng --oem 0 --psm 7  -c "tessedit_char_whitelist=0123456789"  ramdisk/test_0.png  -
tesseract -l eng --psm 7  -c "tessedit_char_whitelist=0123456789" -c "tessedit_ocr_engine_mode=0" ramdisk/test_0.png  -

Expected Behavior

Both commands should return the same result, ideally 11.

Suggested Fix

They should either return the same information or the docs should be updated to clarify the difference.

tesseract -v

tesseract 5.4.1
leptonica-1.84.1
libgif 5.2.2 : libjpeg 6b (libjpeg-turbo 3.0.2) : libpng 1.6.40 : libtiff 4.6.0 : zlib 1.3.1.zlib-ng : libwebp 1.4.0
Found AVX2
Found AVX
Found FMA
Found SSE4.1
Found libcurl/8.9.1 OpenSSL/3.2.2 zlib/1.3.1.zlib-ng libidn2/2.3.7 nghttp2/1.62.1

Operating System

No response

Other Operating System

Fedora 42.

uname -a

Linux deux-ex 6.11.7-300.fc41.x86_64 #1 SMP PREEMPT_DYNAMIC Fri Nov 8 19:23:10 UTC 2024 x86_64 GNU/Linux

Compiler

No response

CPU

Intel(R) Core(TM) i7-9850H CPU @ 2.60GHz (12)

Virtualization / Containers

None.

Other Information

No response

[zdenop]

Which tessdata you use?

[sdubinsky]

eng.traineddata

[sdubinsky]

I'm not sure how to find the version

[zdenop]

Check filesize of eng.traineddata and compare it with https://github.com/tesseract-ocr/tessdata, https://github.com/tesseract-ocr/tessdata_best, https://github.com/tesseract-ocr/tessdata_fast

• make sure you use the latest tessract (5.5.0)

[sdubinsky]

I am using the first version linked.

[zdenop]

OK. I think I know ( ;-) ) the reason:
tessedit_ocr_engine_mode is INIT variable

tesseract/src/ccmain/tesseractclass.cpp

Lines 119 to 123 in 43b8d74

	, INT_INIT_MEMBER(tessedit_ocr_engine_mode, tesseract::OEM_DEFAULT,
	"Which OCR engine(s) to run (Tesseract, LSTM, both)."
	" Defaults to loading and running the most accurate"
	" available.",
	this->params())

e.g. it must be set during initialisation of API/language model (see enginemode variable in init ):

tesseract/src/tesseract.cpp

Lines 736 to 741 in 43b8d74

	const int init_failed = api.Init(datapath, lang, enginemode, &(argv[arg_i]), argc - arg_i,
	&vars_vec, &vars_values, false);
	if (!SetVariablesFromCLArgs(api, argc, argv)) {
	return EXIT_FAILURE;
	}

But variables speficied via "-c" argument are setup by function SetVariablesFromCLArgs after init phase. E.g. -c "tessedit_ocr_engine_mode=0" has no effect and OEM_DEFAULT is used....

[stweil]

Yes, that's the right explanation.

[sdubinsky]

Thanks!

[amitdo]

7dcfd02

@sdubinsky,
Congrats! You've just found a 11.5 years old bug :-)

[zdenop]

@amitdo : why do you claim it is a bug? Can you elaborate on this?

[amitdo]

@zdenop,
Is your question is about the referenced commit or in general?

[zdenop]

@amitdo : My question is about your claims (bug, wrong handling of parameters).

[amitdo]

You already analyzed what's wrong in the code which makes any init parameter set with -c a no-op.

I don't see how this can not be classified as a bug.

[stweil]

Not any. It depends on the parameter. Many parameters are used after init, and these parameters work fine. Examples: debug output, thresholding, ...

[amitdo]

Yes, I know, but 'wrong handling of parameters' is still true, because the code wrongly defers the task of parsing the -c VAR=VALUE (and pushing them to vectors to be used by init()).

[stweil]

So ideally Tesseract should

• Set all parameters to default values.
• Optionally read parameter values from a global configuration file (missing implementation).
• Optionally read parameter values from a user's configuration file (missing implementation).
• Apply parameters which are given with -c on the command line. That's currently wrong.
• Set parameters which are implicitly given with command line arguments like --psm or --dpi.
• Read parameters given by config files on the command line.
• Run init.

[amitdo]

Using:

tesseract in.tif out pdf

Works fine when the config file is in the right path.

[amitdo]

I mean, the config files are already given to init() in the current code.

[amitdo]

• Set all parameters to default values.

For the parameters that are set with -c, this is already done by tesseract (with C macros).

[zdenop]

@amitdo: If I understood you correctly, you suggest this kind of modification of tesseract:

diff --git a/src/tesseract.cpp b/src/tesseract.cpp
index 2c27d2a0..a6bd6405 100644
--- a/src/tesseract.cpp
+++ b/src/tesseract.cpp
@@ -273,32 +273,6 @@ static void PrintHelpMessage(const char *program) {
      program, program, program);
}

-static bool SetVariablesFromCLArgs(tesseract::TessBaseAPI &api, int argc, char **argv) {
-  bool success = true;
-  char opt1[256], opt2[255];
-  for (int i = 0; i < argc; i++) {
-    if (strcmp(argv[i], "-c") == 0 && i + 1 < argc) {
-      strncpy(opt1, argv[i + 1], 255);
-      opt1[255] = '\0';
-      char *p = strchr(opt1, '=');
-      if (!p) {
-        fprintf(stderr, "Missing = in configvar assignment\n");
-        success = false;
-        break;
-      }
-      *p = 0;
-      strncpy(opt2, strchr(argv[i + 1], '=') + 1, sizeof(opt2) - 1);
-      opt2[254] = 0;
-      ++i;
-
-      if (!api.SetVariable(opt1, opt2)) {
-        fprintf(stderr, "Could not set option: %s=%s\n", opt1, opt2);
-      }
-    }
-  }
-  return success;
-}
-
static void PrintLangsList(tesseract::TessBaseAPI &api) {
  std::vector<std::string> languages;
  api.GetAvailableLanguagesAsVector(&languages);
@@ -485,7 +459,16 @@ static bool ParseArgs(int argc, char **argv, const char **lang, const char **ima
      *print_fonts_table = true;
#endif  // ndef DISABLED_LEGACY_ENGINE
    } else if (strcmp(argv[i], "-c") == 0 && i + 1 < argc) {
-      // handled properly after api init
+      std::string argument(argv[i + 1]);
+      auto equal_pos = argument.find('=');
+      if (equal_pos == std::string::npos) {
+          throw std::invalid_argument("Missing '=' in configvar assignment");
+      }
+      // Extract key and value
+      std::string key = argument.substr(0, equal_pos);
+      std::string value = argument.substr(equal_pos + 1);
+      vars_vec->push_back(key);
+      vars_values->push_back(value);
      ++i;
    } else if (*image == nullptr) {
      *image = argv[i];
@@ -736,10 +719,6 @@ int main(int argc, char **argv) {
  const int init_failed = api.Init(datapath, lang, enginemode, &(argv[arg_i]), argc - arg_i,
                                   &vars_vec, &vars_values, false);

-  if (!SetVariablesFromCLArgs(api, argc, argv)) {
-    return EXIT_FAILURE;
-  }
-
  // SIMD settings might be overridden by config variable.
  tesseract::SIMDDetect::Update();

Right?

I am just wandering about that comment (handled properly after api init). Maybe some parameter should be set after init??? At least tesseract -l eng --psm 7 -c "tessedit_char_whitelist=0123456789" -c "tessedit_ocr_engine_mode=0" test_0.png - works after above modification.

[amitdo]

Zdenko,

About your patch - LGTM.

About that comment. I think you added it. You just didn't take into account the INIT parameters.

Maybe some parameter should be set after init???

I don't think there is a good reason to do this.

[amitdo]

BTW, the number of INIT parameters is very small.