diff --git a/CMakeLists.txt b/CMakeLists.txt
index d1954cb..278aad8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -53,13 +53,10 @@ include(CheckCXXCompilerFlag)
 include(CheckCXXSourceCompiles)
 include(CheckCXXSourceRuns)
 
-set(CMAKE_C_FLAGS "-std=gnu99")
-set(CMAKE_CXX_FLAGS "-ansi -pedantic -Wall -Wextra -Wno-long-long")
+set(CMAKE_CXX_FLAGS "-ansi -pedantic -Wall -Wextra -Wno-long-long -std=gnu++11 -DINVERT_IMAGES")
 
 set(CMAKE_CXX_FLAGS_RELEASE "-O3 -mtune=native -march=native -DNDEBUG -fomit-frame-pointer -ffast-math") # TODO -Ofast GCC 4.6
-set(CMAKE_C_FLAGS_RELEASE ${CMAKE_CXX_FLAGS_RELEASE})
 set(CMAKE_CXX_FLAGS_DEBUG "-g3 -DDEBUG")
-set(CMAKE_C_FLAGS_DEBUG ${CMAKE_CXX_FLAGS_DEBUG})
 # TODO RelWithDebInfo MinSizeRel? maybe move -march=native -ffast-math etc. to a different build type
 
 find_package(Threads)
diff --git a/src/vobsub2srt.c++ b/src/vobsub2srt.c++
index 2f9e1a0..5cba42f 100644
--- a/src/vobsub2srt.c++
+++ b/src/vobsub2srt.c++
@@ -92,6 +92,19 @@ using namespace tesseract;
 #define TESSERACT_DATA_PATH TESSERACT_DEFAULT_PATH
 #endif
 
+struct ImageInverter {
+    ImageInverter(const unsigned char* image, size_t image_size)
+      : inverted_image(new unsigned char[image_size])
+    {
+      for (size_t i = 0; i < image_size; ++i) {
+        inverted_image[i] = 255 - image[i];
+      }
+    }
+    ~ImageInverter() { delete[] inverted_image; }
+
+    unsigned char* inverted_image;
+};
+
 int main(int argc, char **argv) {
   bool dump_images = false;
   bool verb = false;
@@ -265,6 +278,18 @@ int main(int argc, char **argv) {
              << start_pts << ")\n";
       }
 
+      // While tesseract version 3.05 (and older) handle inverted image (dark
+      // background and light text) without problem, for 4.x version use dark
+      // text on light background.
+      // https://github.com/tesseract-ocr/tesseract/wiki/ImproveQuality#inverting-images
+
+      #ifdef INVERT_IMAGES
+
+      ImageInverter inverter(image, width*height);
+      image = inverter.inverted_image;
+
+      #endif // INVERT_IMAGES
+
       if(dump_images) {
         dump_pgm(subname, sub_counter, width, height, stride, image, image_size);
       }