problem in cvtColor function

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Hi,I have a native methode which play frame so i retreive the pixels of the image into a byte [] buffer and call a java methode to proceed the processing :

 public void processCameraImage(byte[] buffer, int width, int height)  {
    System.out.println("setRGB565CameraImage....intent received..."); 
    Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565);
    Mat inputFrame= new Mat();
    inputFrame.put(0, 0, buffer);
    if(inputFrame.channels()==1)
    {      /* Grayscale */  Log.i("grayscale", "grayscale"); 
   Imgproc.cvtColor(inputFrame, mGray, Imgproc.COLOR_GRAY2BGR565); // i have a problem here//
    }
    else if (inputFrame.channels()==4)
    {      /* ARGB or RGBA image */      Log.i("ARGB or RGBA", "ARGB or RGBA");                               }
    else
    {      /* RGB, BGR, HSV, or any other 3-channel representation */Log.i("RGB, BGR, HSV", "RGB, BGR, HSV");   }
  //ect
   }

i have this in logcat:

03-24 11:23:45.322: I/System.out(9915): setRGB565CameraImage....intent received...
03-24 11:23:45.362: D/dalvikvm(9915): GC_CONCURRENT freed <1K, 22% free 8108K/10311K, paused 1ms+3ms   
03-24 11:23:45.372: I/grayscale(9915): grayscale    
03-24 11:23:45.372: W/dalvikvm(9915): JNI WARNING: JNI method called with exception pending

03-24 11:23:45.372: W/dalvikvm(9915):  in Lcom/qualcomm/ar/pl/CameraPreview;.newFrameAvailable:       (IIII[B)V (CallIntMethodV)
03-24 11:23:45.372: W/dalvikvm(9915): Pending exception is:
03-24 11:23:45.372: I/dalvikvm(9915): java.lang.NullPointerException:
03-24 11:23:45.372: I/dalvikvm(9915):   at   org.opencv.imgproc.Imgproc.cvtColor(Imgproc.java:4354)
03-24 11:23:45.372: I/dalvikvm(9915): at   com.qualcomm.QCARSamples.ImageTargets.ImageTargets.processCameraImage(ImageTargets.java:524)
03-24 11:23:45.372: I/dalvikvm(9915): at com.qualcomm.ar.pl.CameraPreview.newFrameAvailable(Native Method)

Please i need help as soon as possible i'm stucked here.