Convert Mat to Blob and then back to Mat

问题:

Basically I am trying facial recognition using OpenCV Android. I need to convert a Mat image that is received during face detection via inputFrame.gray(); in CvCameraViewFrame into a blob that is a byte[] to save into an SQLite database. Then, during recognition, convert this byte[] back to a Mat file that can be used in .cpp files in the jni folder, as recognition code is native.

回答1:

[edit]

it turned out to be quite easy with androids onboard methods:

import org.opencv.core.Mat;  import android.content.Context; import android.content.ContentValues; import android.database.Cursor; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteDatabase.CursorFactory; import android.database.sqlite.SQLiteOpenHelper;  class SqTable extends SQLiteOpenHelper {     String table = "mydb";      public SqlTable(Context context, String name, CursorFactory factory, int version) {         super(context, name, factory, version);          }      @Override     public void onCreate(SQLiteDatabase db) {         db.execSQL("create table "+table+" (name TEXT UNIQUE, t INTEGER, w INTEGER, h INTEGER, pix BLOB);");     }      @Override     public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {     }      public void dbput(String name, Mat m) {         long nbytes = m.total() * m.elemSize();         byte[] bytes = new byte[ (int)nbytes ];         m.get(0, 0,bytes);          dbput(name, m.type(), m.cols(), m.rows(), bytes);      }      public void dbput(String name, int t, int w, int h, byte[] bytes) {         Log.d("dbput", name + " " + t + " " + w + "x" + h);         SQLiteDatabase db = this.getWritableDatabase();         ContentValues values = new ContentValues();         values.put("name", name);         values.put("t", t);          values.put("w", w);          values.put("h", h);          values.put("pix", bytes);         db.insert(table, null, values);         db.close();     }       public Mat dbget(String name) {         SQLiteDatabase db = this.getReadableDatabase();         String [] columns = {"t","w","h","pix"};         Cursor cursor = db.query(table,columns," name = ?",                  new String[] { name }, // d. selections args                 null, // e. group by                 null, // f. having                 null, // g. order by                 null); // h. limit          if (cursor != null)             cursor.moveToFirst();          int t = cursor.getInt(0);         int w = cursor.getInt(1);         int h = cursor.getInt(2);         byte[] p = cursor.getBlob(3);         Mat m = new Mat(h,w,t);         m.put(0,0,p);         Log.d("dbget("+name+")", m.toString());         return m;     } };  // later use in your Activity: SqlTable sql = new SqlTable(this,"imgs",null,1); Mat m = new Mat(200,400, CvType.CV_8UC3,new Scalar(0,100,0)); Core.putText(m, "world (~)", new Point(30,80), Core.FONT_HERSHEY_SCRIPT_SIMPLEX, 2.2, new          Scalar(200,200,200)); sql.dbput("hello",m); // Mat m = sql.dbget("hello"); 

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