今天我们将制作一个Android应用程序，在OpenCV的帮助下将图像转换为铅笔素描。在我们开始之前:我假设您的android项目中已经安装了Open CV。

步骤1：打开activity_main。添加一个ImageView和3个按钮(第一个按钮用于从手机图库中选择图像，另两个按钮用于将图像转换为素描和彩色素描。

<RelativeLayout
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:layout_marginLeft="10dp"
 android:layout_marginRight="10dp">
 <ImageView
 android:id="@+id/image"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:src="@mipmap/ic_launcher"
 android:layout_above="@id/btn_contain"
 android:layout_marginBottom="10dp"/>
 <LinearLayout
 android:id="@+id/btn_contain"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_alignParentBottom="true"
 android:layout_marginBottom="40dp">
 <Button
 android:id="@+id/select_img"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:text="Select Image "/>
 <Button
 android:id="@+id/sketch"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:text="Sketch"/>
 <Button
 android:id="@+id/colored_sketch"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:text="Colored Sketch"/>
 </LinearLayout>
</RelativeLayout>

欢迎大家来到IT世界,在知识的湖畔探索吧!

步骤2：打开MainActivity.java，再onCreate中添加如下java代码。

欢迎大家来到IT世界,在知识的湖畔探索吧!private ImageView image;
private Button select, sketch, colored
@Override
protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 OpenCVLoader.initDebug();
 image = findViewById(R.id.image);
 select = findViewById(R.id.select_img);
 sketch = findViewById(R.id.sketch);
 colored = findViewById(R.id.colored_sketch);
}

步骤3：创建一个ImageChooser函数，从图库中选择图像并显示在ImageView中。

为图像选择器声明几个变量。

private final int SELECT_PHOTO = 1;
private Bitmap originBitmap = null;
private File tempFile = new File("/sdcard/a.jpg");
private Bitmap processImg;

显示图像选择器的函数

欢迎大家来到IT世界,在知识的湖畔探索吧!private void showImageChooser() {
 Intent photoPickerIntent = new Intent(Intent.ACTION_PICK);
 photoPickerIntent.setType("image/*");
 startActivityForResult(photoPickerIntent, SELECT_PHOTO);
}
@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
 super.onActivityResult(requestCode, resultCode, data);
 if (requestCode == SELECT_PHOTO && resultCode == RESULT_OK && null != data) {
 Uri selectedImage = data.getData();
 InputStream imageStream;
 try {
 imageStream = getContentResolver().openInputStream(selectedImage);
 originBitmap = BitmapFactory.decodeStream(imageStream);
 } catch (FileNotFoundException e) {
 e.printStackTrace();
 }
 if (originBitmap != null) {
 tempFile.delete();
 this.image.setImageBitmap(originBitmap);
 }
 }
}

将OnClickListener设置为图像选择按钮

select.setOnClickListener(new View.OnClickListener() {
 @Override
 public void onClick(View view) {
 showImageChooser();
 }
});

步骤4：让我们将效果应用到选定的图像。

为了将图像转换为素描，我们需要制作3个不同的图像层

1. 灰度（第1层）
2. 反转灰度图像（第2层）
3. 将高斯模糊应用于inverted image（第3层）
4. 用于铅笔素描的颜色减淡和混合（第3层，第1层），用于彩色素描的颜色减淡（原始图像，第1层）。

素描函数的java代码如下：

public void Sketch(Bitmap bitmap, String type){
 bitmap=bitmap.copy(Bitmap.Config.ARGB_8888, true);
 Mat src = new Mat(bitmap.getHeight(), bitmap.getWidth(), CvType.CV_8UC4);
 Mat dest = new Mat(bitmap.getHeight(), bitmap.getWidth(), CvType.CV_8UC4);
 Mat grey = new Mat(bitmap.getHeight(), bitmap.getWidth(), CvType.CV_8UC4);
 Mat invert = new Mat(bitmap.getHeight(), bitmap.getWidth(), CvType.CV_8UC4);
 Bitmap inv, gray;
 Utils.bitmapToMat(bitmap, src);
 Imgproc.cvtColor(src, grey, Imgproc.COLOR_BGR2GRAY);
 Imgproc.cvtColor(grey, grey, Imgproc.COLOR_GRAY2RGBA, 4);
 Core.bitwise_not( grey, invert);
 Imgproc.GaussianBlur(invert,invert, new Size(11,11),0);
 inv = Bitmap.createBitmap(invert.cols(),invert.rows(),Bitmap.Config.ARGB_8888);
 gray = Bitmap.createBitmap(invert.cols(),invert.rows(),Bitmap.Config.ARGB_8888);
 Utils.matToBitmap(invert, inv);
 Utils.matToBitmap(grey, gray);
 Bitmap b = null;
 if (type.equals("normal")) {
 b = ColorDodgeBlend(inv, gray);
 }else if(type.equals("colored")){
 b = ColorDodgeBlend(inv, bitmap);
 }
 processImg = Bitmap.createBitmap(dest.cols(),dest.rows(),Bitmap.Config.ARGB_8888);
 Utils.matToBitmap(dest, processImg);
 image.setImageBitmap(b);
}

颜色减淡和混合的java代码：

private static int colordodge(int in1, int in2) {
 float image = (float)in2;
 float mask = (float)in1;
 return ((int) ((image == 255) ? image:Math.min(255, (((long)mask << 8 ) / (255 - image)))));
}
public static Bitmap ColorDodgeBlend(Bitmap source, Bitmap layer) {
 Bitmap base = source.copy(Bitmap.Config.ARGB_8888, true);
 Bitmap blend = layer.copy(Bitmap.Config.ARGB_8888, false);
 IntBuffer buffBase = IntBuffer.allocate(base.getWidth() * base.getHeight());
 base.copyPixelsToBuffer(buffBase);
 buffBase.rewind();
 IntBuffer buffBlend = IntBuffer.allocate(blend.getWidth() * blend.getHeight());
 blend.copyPixelsToBuffer(buffBlend);
 buffBlend.rewind();
 IntBuffer buffOut = IntBuffer.allocate(base.getWidth() * base.getHeight());
 buffOut.rewind();
 while (buffOut.position() < buffOut.limit()) {
 int filterInt = buffBlend.get();
 int srcInt = buffBase.get();
 int redValueFilter = Color.red(filterInt);
 int greenValueFilter = Color.green(filterInt);
 int blueValueFilter = Color.blue(filterInt);
 int redValueSrc = Color.red(srcInt);
 int greenValueSrc = Color.green(srcInt);
 int blueValueSrc = Color.blue(srcInt);
 int redValueFinal = colordodge(redValueFilter, redValueSrc);
 int greenValueFinal = colordodge(greenValueFilter, greenValueSrc);
 int blueValueFinal = colordodge(blueValueFilter, blueValueSrc);
 int pixel = Color.argb(255, redValueFinal, greenValueFinal, blueValueFinal);
 buffOut.put(pixel);
 }
 buffOut.rewind();
 base.copyPixelsFromBuffer(buffOut);
 blend.recycle();
 return base;
}

将OnClickListener添加到按钮

sketch.setOnClickListener(new View.OnClickListener() {
 @Override
 public void onClick(View view) {
 
 if (originBitmap != null) {
 Sketch(originBitmap, "normal");
 }
 }
});
colored.setOnClickListener(new View.OnClickListener() {
 @Override
 public void onClick(View view) {
 if (originBitmap != null) {
 Sketch(originBitmap, "colored");
 }
 }
});

步骤5：在模拟器中构建和测试应用程序。