Android Bitmap 加载与像素操作

一：加载与像素读写
在Android SDK中，图像的像素读写可以通过getPixel与setPixel两个Bitmap的API实现。Bitmap API读取像素的代码如下：

int pixel = bitmap.getPixel(col, row);// ARGBint red = Color.red(pixel); // same as (pixel >> 16) &0xffint green = Color.green(pixel); // same as (pixel >> 8) &0xffint blue = Color.blue(pixel); // same as (pixel & 0xff)int alpha = Color.alpha(pixel); // same as (pixel >>> 24)

得到像素pixel是32位的整数，四个字节分别对应透明通道、红色、绿色、蓝色通道。Bitmap API 写入像素,代码如下：

bm.setPixel(col, row, Color.argb(alpha, red, green, blue));

通过Color.argb重新组装成一个int的像素值。
使用BitmapFactory.decodeFile或者decodeResource等方法实现加载图像的Bitmap对象时，这些方法就会为要构建的Bitmap对象分配合适大小的内存，如果原始的图像文件数据很大，就会导致DVM不能分配请求的内存大小，从而导致OOM(out of memory)问题。而通过配置BitmapFactory.Option预先读取图像高度与宽带，图像进行适当的下采样，就可以避免OOM问题的发生。预先只获取图像高度与宽带的代码如下：

        // 获取Bitmap图像大小与类型属性        BitmapFactory.Options options = new BitmapFactory.Options();        options.inJustDecodeBounds = true;        BitmapFactory.decodeResource(getResources(),                                         R.drawable.shar_03, options);        int height = options.outHeight;        int width = options.outWidth;        String imageType = options.outMimeType;

基于下采样加载超大Bitmap图像的缩小版本：

        // 下采样        int inSampleSize = 1;        if (height > reqHeight || width > reqWidth) {            final int halfHeight = height / 2;            final int halfWidth = width / 2;            // Calculate the largest inSampleSize value             // that is a power of 2 and keeps both            // height and width larger than the requested height and width.            while ((halfHeight / inSampleSize) > reqHeight                    && (halfWidth / inSampleSize) > reqWidth) {                inSampleSize *= 2;            }        }        // 获取采样后的图像显示，避免OOM问题        options.inJustDecodeBounds = false;        srcImage = BitmapFactory.decodeResource(getResources(), R.drawable.shar_03, options);

二：像素操作
android彩色图像灰度化的三个简单方法
灰度化方法一：
灰度值GRAY = (max(red, green, blue) + min(red, green, blue))/2
灰度化方法二：
灰度值GRAY = (red + green + blue)/3
灰度化方法三：
灰度值GRAY = red*0.3 + green*0.59 + blue*0.11
代码实现如下：

public Bitmap gray(Bitmap bitmap, int schema){    Bitmap bm = Bitmap.createBitmap(bitmap.getWidth(),bitmap.getHeight(), bitmap.getConfig());    int width = bitmap.getWidth();    int height = bitmap.getHeight();    for(int row=0; row<height; row++){       for(int col=0; col<width; col++){          int pixel = bitmap.getPixel(col, row);// ARGB          int red = Color.red(pixel); // same as (pixel >> 16) &0xff          int green = Color.green(pixel); // same as (pixel >> 8) &0xff          int blue = Color.blue(pixel); // same as (pixel & 0xff)          int alpha = Color.alpha(pixel); // same as (pixel >>> 24)          int gray = 0;          if(schema == 0)          {              gray = (Math.max(blue, Math.max(red, green)) +                           Math.min(blue, Math.min(red, green))) / 2;          }          else if(schema == 1)          {              gray = (red + green + blue) / 3;          }          else if(schema == 2)          {              gray = (int)(0.3 * red + 0.59 * green + 0.11 * blue);          }          bm.setPixel(col, row, Color.argb(alpha, gray, gray, gray));       }    }    return bm;}

Bitmap图像镜像映射与亮度调整的代码实现如下：

public Bitmap brightness(Bitmap bitmap, double depth){    Bitmap bm = Bitmap.createBitmap(bitmap.getWidth(),bitmap.getHeight(), bitmap.getConfig());    int width = bitmap.getWidth();    int height = bitmap.getHeight();    for(int row=0; row<height; row++){       for(int col=0; col<width; col++){          int pixel = bitmap.getPixel(col, row);// ARGB          int red = Color.red(pixel); // same as (pixel >> 16) &0xff          int green = Color.green(pixel); // same as (pixel >> 8) &0xff          int blue = Color.blue(pixel); // same as (pixel & 0xff)          int alpha = Color.alpha(pixel); // same as (pixel >>> 24)          double gray = (0.3 * red + 0.59 * green + 0.11 * blue);          red += (depth * gray);          if(red > 255) { red = 255; }          green += (depth * gray);          if(green > 255) { green = 255; }          blue += (depth * gray);          if(blue > 255) { blue = 255; }          bm.setPixel(col, row, Color.argb(alpha, red, green, blue));       }    }    return bm;}public Bitmap flip(Bitmap bitmap){    Bitmap bm = Bitmap.createBitmap(bitmap.getWidth(),bitmap.getHeight(), bitmap.getConfig());    int width = bitmap.getWidth();    int height = bitmap.getHeight();    for(int row=0; row<height; row++){       for(int col=0; col<width; col++){          int pixel = bitmap.getPixel(col, row);// ARGB          int red = Color.red(pixel); // same as (pixel >> 16) &0xff          int green = Color.green(pixel); // same as (pixel >> 8) &0xff          int blue = Color.blue(pixel); // same as (pixel & 0xff)          int alpha = Color.alpha(pixel); // same as (pixel >>> 24)          int ncol = width - col - 1;          bm.setPixel(ncol, row, Color.argb(alpha, red, green, blue));       }    }    return bm;}

运行截图：

布局XML文件内容如下：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical"    android:paddingBottom="@dimen/activity_vertical_margin"    android:paddingLeft="@dimen/activity_horizontal_margin"    android:paddingRight="@dimen/activity_horizontal_margin"    android:paddingTop="@dimen/activity_vertical_margin"    tools:context="com.example.imageprocess1.MainActivity" >    <RelativeLayout        android:layout_width="wrap_content"        android:layout_height="wrap_content">        <Button            android:id="@+id/button_gray_3"            android:layout_width="100dp"            android:layout_height="wrap_content"            android:text="@string/process" />        <Button            android:id="@+id/button_inverse"            android:layout_width="100dp"            android:layout_height="wrap_content"            android:layout_toRightOf="@+id/button_gray_3"            android:layout_alignTop="@+id/button_gray_3"            android:text="@string/inverse" />        <Button            android:id="@+id/button_gray_1"            android:layout_width="100dp"            android:layout_height="wrap_content"            android:layout_toRightOf="@+id/button_inverse"            android:layout_alignTop="@+id/button_gray_3"            android:text="@string/nored" />        <Button            android:id="@+id/button_gray_2"            android:layout_width="100dp"            android:layout_below="@+id/button_gray_3"            android:layout_height="wrap_content"            android:text="@string/noblue" />        <Button            android:id="@+id/button_flip"            android:layout_width="100dp"            android:layout_height="wrap_content"            android:layout_below="@+id/button_inverse"            android:layout_toRightOf="@+id/button_gray_2"            android:text="@string/flip" />        <Button            android:id="@+id/button_save"            android:layout_width="100dp"            android:layout_height="wrap_content"            android:layout_below="@+id/button_gray_3"            android:layout_toRightOf="@+id/button_flip"            android:text="@string/save" />    </RelativeLayout>    <ImageView        android:id="@+id/image_content"        android:layout_width="fill_parent"        android:layout_height="fill_parent"        android:scaleType="fitCenter"        android:src="@drawable/ic_launcher" /></LinearLayout>

MainActivity中的onCreate方法的代码如下：

super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);ImageView iView = (ImageView) this.findViewById(R.id.image_content);Bitmap b = Bitmap.createBitmap(400, 400, Bitmap.Config.ARGB_8888);Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);paint.setColor(Color.BLACK);Canvas c = new Canvas(b);c.drawText("Load Image from here...", 50, 200, paint);iView.setImageBitmap(b);Button saveBtn = (Button) this.findViewById(R.id.button_save);saveBtn.setOnClickListener(new OnClickListener() {    @Override    public void onClick(View view) {        Toast toast = Toast.makeText(getApplicationContext(), "Please load the image firstly...", Toast.LENGTH_SHORT);        toast.show();        loadImage();        ImageView iView = (ImageView) findViewById(R.id.image_content);        iView.setImageBitmap(srcImage);        if(srcImage != null)        {            //saveFile(srcImage);        }    }});Button processBtn = (Button) this.findViewById(R.id.button_gray_3);processBtn.setOnClickListener(new OnClickListener() {    @Override    public void onClick(View view) {        if(srcImage == null)        {            loadImage();        }        ImagePixelsProcessor processor = new ImagePixelsProcessor();        Bitmap bm = processor.gray(srcImage, 2); // 有不同的灰度化策略        final ImageView iView = (ImageView) findViewById(R.id.image_content);        iView.setImageBitmap(bm);    }});Button inverseBtn = (Button) this.findViewById(R.id.button_inverse);inverseBtn.setOnClickListener(new OnClickListener() {    @Override    public void onClick(View view) {        if(srcImage == null)        {            loadImage();        }        ImagePixelsProcessor processor = new ImagePixelsProcessor();        Bitmap bm = processor.brightness(srcImage, 0.3);        final ImageView iView = (ImageView) findViewById(R.id.image_content);        iView.setImageBitmap(bm);    }});Button noRedBtn = (Button) this.findViewById(R.id.button_gray_1);noRedBtn.setOnClickListener(new OnClickListener() {    @Override    public void onClick(View view) {        if(srcImage == null)        {            loadImage();        }        ImagePixelsProcessor processor = new ImagePixelsProcessor();        Bitmap bm = processor.gray(srcImage, 0); // 有不同的灰度化策略        final ImageView iView = (ImageView) findViewById(R.id.image_content);        iView.setImageBitmap(bm);    }});Button gray2Btn = (Button) this.findViewById(R.id.button_gray_2);gray2Btn.setOnClickListener(new OnClickListener() {    @Override    public void onClick(View view) {        if(srcImage == null)        {            loadImage();        }        ImagePixelsProcessor processor = new ImagePixelsProcessor();        Bitmap bm = processor.gray(srcImage, 1); // 有不同的灰度化策略        final ImageView iView = (ImageView) findViewById(R.id.image_content);        iView.setImageBitmap(bm);    }});Button flipBtn = (Button) this.findViewById(R.id.button_flip);flipBtn.setOnClickListener(new OnClickListener() {    @Override    public void onClick(View view) {        if(srcImage == null)        {            loadImage();        }        ImagePixelsProcessor processor = new ImagePixelsProcessor();        Bitmap bm = processor.flip(srcImage);        final ImageView iView = (ImageView) findViewById(R.id.image_content);        iView.setImageBitmap(bm);    }});

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