OPENCV-NDK-OCR

Android ocr with OpenCV and tess-two
This project is a dead-simple which described how to build an easy off-line OCR system.

Total Process Diagram

This diagram is a dead-simple which described how to build an easy motion identification system.

Effect Comparison

In first step, we use morphological edge detection function to drop text rects in source image.
And then, we use tess-two to identify Chinese characters and print them.

How to use tess-two in Android

Add implementation 'com.rmtheis:tess-two:9.0.0 in your app module gradle, and use tess-two like this.

val tessBaseAPI = TessBaseAPI()
tessBaseAPI.init("/storage/emulated/0/", "chi_sim")
tessBaseAPI.setImage(src)
println(tessBaseAPI.utF8Text)
tessBaseAPI.end()

How to use OpenCV(Native & JAVA) in Android with Android Studio

Follow this link to build your app with OpenCV(NDK & Java).
Don't forget to link jnigraphics in Cmake->target_link_libraries

Use Native Function

The native function are in the native-lib.cpp.

external fun selfBinary(bitmap: Any) //gary and sobel and binary
external fun selfDilate(bitmap: Any, p1: Int = 24, p2: Int = 3) //Dilate
external fun selfErode(bitmap: Any, p1: Int = 30, p2: Int = 9) //Erode
external fun selfRect(bitmap: Any) //Draw rects

Use Java Function

Java OpenCV functions are easy to use, but it is hard to corp Mat.

val temp = Mat()
            
cvtColor(srcMat, temp, COLOR_RGBA2GRAY)
Sobel(temp, temp, CV_8U, 1, 0)
threshold(temp, temp, 0.0, 255.0, THRESH_OTSU + THRESH_BINARY)

val element1 = getStructuringElement(MORPH_RECT, Size(30.0, 9.0))
val element2 = getStructuringElement(MORPH_RECT, Size(24.0, 3.0))

dilate(temp, temp, element2)
dilate(temp, temp, element2)

erode(temp, temp, element1) // optional

dilate(temp, temp, element2)
dilate(temp, temp, element2)

Crop Mat with RotatedRect

Follow this link to crop Mat.

How to use FFMPEG in Android Studio

Pre-build lib can be found at here.
Copy them to your jnilibs dir.

In app-build.gradle add as blow.

      android {
             ...
          defaultConfig {
          ...
              externalNativeBuild {
                  ndk {
                      abiFilters 'armeabi-v7a', 'arm64-v8a'
                  }
              }
          }
          sourceSets {
              main {
                  jniLibs.srcDirs = ['libs']
              }
          }
      }

Config your CmakeList.txt add includes and libraries.

add_library(avcodec SHARED IMPORTED)
set_target_properties(avcodec  PROPERTIES IMPORTED_LOCATION
../../../../libs/${ANDROID_ABI}/libavcodec.so)

...

target_link_libraries( ... avcodec ...)

Cautions

Please give this app WRITE_EXTERNAL_STORAGE permission

You may need to copy tess data to /storage/emulated/0/tessdata

1996scarlet / OPENCV-NDK-OCR