title: cverror android assertion failed (scn == 3) Android
body: <p>I'm trying to use adaptive thresholding on an image (Bitmap) I have in android which requires changing it into a Mat and then converting it to grayscale.</p>
  
  <p>Below is my code starting with creating the bitmaps. They are named crop because I just cropped the photo right before this.</p>
  
  <pre><code>            Bitmap bmCrop = BitmapFactory.decodeStream(iStream);
              Bitmap bmThreshed = null;
              /*
               * Initialize the Mats
               */
              Mat threshed = new Mat(bmCrop.getHeight(),bmCrop.getWidth(), CvType.CV_8UC1, new Scalar(4));//, new Scalar(4)
              //Mat crop = new Mat();
              Mat crop = new Mat(bmCrop.getHeight(),bmCrop.getWidth(), CvType.CV_8UC1,new Scalar(4));//, new Scalar(4)
              /*
               * Convert the Mats to Grayscale
               */
              if(!threshed.empty())
                  Imgproc.cvtColor(threshed, threshed, Imgproc.COLOR_RGB2GRAY,1);// CURRENTLY BREAKING HERE
              if(!crop.empty())
                  Imgproc.cvtColor(crop, crop, Imgproc.COLOR_BGR2GRAY,1);         
  
  
              Utils.bitmapToMat(bmCrop, crop);
  
              // Mat src, Mat dst, double maxValue, int adaptiveMethod, int thresholdType, int blockSize, double C
              Imgproc.adaptiveThreshold(crop, threshed, 255, Imgproc.ADAPTIVE_THRESH_MEAN_C, Imgproc.THRESH_BINARY_INV, 15, 8);
  
              Utils.matToBitmap(threshed, bmThreshed);
              bmThreshed = bmCrop;
  </code></pre>
  
  <p>It is currently breaking on the line "Imgproc.cvtColor(threshed, threshed, Imgproc.COLOR_RGB2GRAY,1)" where I attempt to cvtColor on the Mat.</p>
  
  <p>Below is the output of LogCat:</p>
  
  <pre><code>05-28 11:25:21.172: E/cv::error()(32505): OpenCV Error: Assertion failed (scn == 3 || scn == 4) in void cv::cvtColor(cv::InputArray, cv::OutputArray, int, int), file /home/reports/ci/slave/50-SDK/opencv/modules/imgproc/src/color.cpp, line 3414
  05-28 11:25:25.697: D/AndroidRuntime(32505): Shutting down VM
  05-28 11:25:25.707: W/dalvikvm(32505): threadid=1: thread exiting with uncaught exception (group=0x414b1930)
  05-28 11:25:25.747: E/AndroidRuntime(32505): FATAL EXCEPTION: main
  05-28 11:25:25.747: E/AndroidRuntime(32505): CvException [org.opencv.core.CvException: /home/reports/ci/slave/50-SDK/opencv/modules/imgproc/src/color.cpp:3414: error: (-215) scn == 3 || scn == 4 in function void cv::cvtColor(cv::InputArray, cv::OutputArray, int, int)
  05-28 11:25:25.747: E/AndroidRuntime(32505): ]
  05-28 11:25:25.747: E/AndroidRuntime(32505):    at org.opencv.imgproc.Imgproc.cvtColor_0(Native Method)
  05-28 11:25:25.747: E/AndroidRuntime(32505):    at org.opencv.imgproc.Imgproc.cvtColor(Imgproc.java:4017)
  05-28 11:25:25.747: E/AndroidRuntime(32505):    at com.activity.IMGP_Camera$1.onManagerConnected(IMGP_Camera.java:263)
  05-28 11:25:25.747: E/AndroidRuntime(32505):    at org.opencv.android.AsyncServiceHelper$1.onServiceConnected(AsyncServiceHelper.java:318)
  05-28 11:25:25.747: E/AndroidRuntime(32505):    at android.app.LoadedApk$ServiceDispatcher.doConnected(LoadedApk.java:1101)
  05-28 11:25:25.747: E/AndroidRuntime(32505):    at android.app.LoadedApk$ServiceDispatcher$RunConnection.run(LoadedApk.java:1118)
  05-28 11:25:25.747: E/AndroidRuntime(32505):    at android.os.Handler.handleCallback(Handler.java:725)
  05-28 11:25:25.747: E/AndroidRuntime(32505):    at android.os.Handler.dispatchMessage(Handler.java:92)
  05-28 11:25:25.747: E/AndroidRuntime(32505):    at android.os.Looper.loop(Looper.java:137)
  05-28 11:25:25.747: E/AndroidRuntime(32505):    at android.app.ActivityThread.main(ActivityThread.java:5226)
  05-28 11:25:25.747: E/AndroidRuntime(32505):    at java.lang.reflect.Method.invokeNative(Native Method)
  05-28 11:25:25.747: E/AndroidRuntime(32505):    at java.lang.reflect.Method.invoke(Method.java:511)
  05-28 11:25:25.747: E/AndroidRuntime(32505):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
  05-28 11:25:25.747: E/AndroidRuntime(32505):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562)
  05-28 11:25:25.747: E/AndroidRuntime(32505):    at dalvik.system.NativeStart.main(Native Method)
  </code></pre>