Shulou(Shulou.com)06/01 Report--

It is believed that many inexperienced people have no idea about how to use mobile phone camera to get the edge of Canny in OpenCV4Android. Therefore, this paper summarizes the causes and solutions of the problem. Through this article, I hope you can solve this problem.

It is widely used to obtain the edge of the main influence in the image, so the effect of Canny edge is used.

The process of Canny Edge extraction

Gaussian blur

Gradient calculation

Non-maximum information suppression

High and low threshold link

Display

Still use our Demo.

But this time we added something new, because we just learned how to call the camera function in OpenCV to get picture information, and it took us a whole day to get into the door.

First of all, add a button to the original MainActivity

Corresponding to the increase in events

Camera page

First, we added an opencvcarema.xml page and an activity for OpenCVCarema

Opencvcarema.xml

You can add org.opencv.android.JavaCameraView directly to this, and then add a button at the bottom

OpenCvCarema

This class we need to inherit from Activity and refer to the

CameraBridgeViewBase.CvCameraViewListener2

There are several methods in it.

Button to get the edge of the current image

It is to create a bitbmp image based on the acquired image, and then use Gaussian blur to convert the acquired image mRgbaF into a grayscale image, then use the edge of Canny to extract the new Mat, and then convert the extracted image back to bmp image. Because we need to return data, we convert the bmp image to byte [] when we return. It turns out that the returned camera data is added to the onActivityResult in our MainActivity.

The judgment of horizontal and vertical screen is added when the camera acquires the image.

When OpenCV calls the camera, the default is horizontal screen, so when our vertical screen phone is turned on, it will be a 90 rotation, which is very unfriendly. I often find information and test many times. I have modified the onCameraFrame function myself.

The red one is to judge whether the current mobile phone screen is horizontal and vertical. By comparing the width and height, when the width is greater than the height, it is the horizontal screen, and when it is smaller, it is the vertical screen.

If it is a vertical screen, we will perform the following steps:

First change the horizontal image to vertical.

After turning, the image is scaled to its original size.

Then flip the image along the Y axis (if you don't flip, the image you see is interadjusted from left to right)

The following is our video effect, and finally we have the code for the whole class of OpenCVCarema.java.

The following classes for the entire OpenCvCarema.java

Package dem.vaccae.opencvdemo

Import android.app.Activity

Import android.content.Intent

Import android.graphics.Bitmap

Import android.graphics.Camera

Import android.os.Bundle

Import android.os.PersistableBundle

Import android.support.annotation.Nullable

Import android.util.DisplayMetrics

Import android.util.Log

Import android.view.Menu

Import android.view.MenuItem

Import android.view.View

Import android.view.WindowManager

Import android.widget.Button

Import org.opencv.android.CameraBridgeViewBase

Import org.opencv.android.OpenCVLoader

Import org.opencv.android.Utils

Import org.opencv.core.Core

Import org.opencv.core.CvType

Import org.opencv.core.Mat

Import org.opencv.core.Size

Import org.opencv.imgproc.Imgproc

Import java.io.ByteArrayOutputStream

/ * *

* Created by Administrator on 2018-01-01.

, /

Public class OpenCvCarema extends Activity implements CameraBridgeViewBase.CvCameraViewListener2 {

Private static final String TAG = "OpenCvCameraActivity"

Static {

OpenCVLoader.initDebug ()

}

Private Mat mRgba

Private Mat mRgbaF

Private Mat mFlipRgba

Private Camera mCamera

Private CameraBridgeViewBase mOpenCvCameraView

Private Button btnCanny

/ / whether to press the button or not

Private boolean isbtn = false

Private Bitmap bmp

Public OpenCvCarema () {

Log.i (TAG, "Instantiated new" + this.getClass ())

}

@ Override

Public void onCreate (Bundle savedInstanceState) {

Log.i (TAG, "called onCreate")

Super.onCreate (savedInstanceState)

GetWindow () addFlags (WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)

SetContentView (R.layout.opencvcarema)

MOpenCvCameraView = findViewById (R.id.opencvcaremaview)

MOpenCvCameraView.enableView ()

MOpenCvCameraView.setCvCameraViewListener (this)

/ / Rear camera

MOpenCvCameraView.setCameraIndex (CameraBridgeViewBase.CAMERA_ID_BACK)

BtnCanny = findViewById (R.id.btnCanny)

BtnCanny.setOnClickListener (new View.OnClickListener () {

@ Override

Public void onClick (View view) {

Isbtn = true

Bmp = Bitmap.createBitmap (mRgbaF.width (), mRgbaF.height (), Bitmap.Config.ARGB_8888)

/ / perform Gaussian blur first

Imgproc.GaussianBlur (mRgbaF, mRgbaF, new Size (3,3), 0,0, Imgproc.BORDER_DEFAULT)

/ / change to grayscale image first

Imgproc.cvtColor (mRgbaF, mRgbaF, Imgproc.COLOR_BGRA2GRAY)

/ / t represents a low threshold, and a high threshold is generally twice as high as a low threshold, so threshold can use tasking 2 or tasking 3.

/ / apertureSize enter 3 here, which is the eye mask representing 333.

/ / L2gradient this is the precision requirement, if it is true, the precision will be high, but it will be slow, so generally speaking, we can use false.

Imgproc.Canny (mRgbaF, mFlipRgba, 112,112 * 2,3, false)

Utils.matToBitmap (mFlipRgba, bmp)

/ / compress the picture into byte [] and pass it back

ByteArrayOutputStream baos = new ByteArrayOutputStream ()

Bmp.compress (Bitmap.CompressFormat.PNG, 100,100, baos)

Byte [] bitmapByte = baos.toByteArray ()

Intent rtnintent = new Intent ()

Rtnintent.putExtra ("bitmap", bitmapByte)

OpenCvCarema.this.setResult (Activity.RESULT_OK, rtnintent)

Finish ()

}

});

}

@ Override

Protected void onPause () {

Super.onPause ()

If (mOpenCvCameraView! = null)

MOpenCvCameraView.disableView ()

}

@ Override

Protected void onResume () {

Super.onResume ()

}

@ Override

Protected void onDestroy () {

Super.onDestroy ()

MOpenCvCameraView.disableView ()

}

@ Override

Public void onCameraViewStarted (int width, int height) {

MRgba = new Mat ()

MRgbaF = new Mat ()

MFlipRgba = new Mat ()

}

@ Override

Public void onCameraViewStopped () {

MFlipRgba.release ()

MRgbaF.release ()

}

@ Override

Public Mat onCameraFrame (CameraBridgeViewBase.CvCameraViewFrame inputFrame) {

If (! isbtn) {

/ / pay attention

MRgba = inputFrame.rgba ()

/ / get the width and height of the screen to determine whether the screen is horizontal or vertical.

DisplayMetrics dm = getResources () .getDisplayMetrics ()

If (dm.widthPixels

< dm.heightPixels) { //转置函数，可以水平的图像变为垂直 Core.transpose(mRgba, mFlipRgba); //将转置后的图像缩放为mRgbaF的大小 Imgproc.resize(mFlipRgba, mRgbaF, mRgba.size(), 0.0D, 0.0D, 0); //flipCode>

0 flip mRgbaF horizontally (flip along the Y axis) to get mRgba

Core.flip (mRgbaF, mRgbaF, 1)

} else {

MRgbaF = mRgba

}

}

Return mRgbaF

}

@ Override

Public boolean onCreateOptionsMenu (Menu menu) {

Return true

}

@ Override

Public boolean onOptionsItemSelected (MenuItem item) {

Return true

}

}

After reading the above, have you mastered how to use the mobile camera to get the edge of Canny in OpenCV4Android? If you want to learn more skills or want to know more about it, you are welcome to follow the industry information channel, thank you for reading!

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