Android Bitmap 载入与像素操作

一：载入与像素读写
在Android SDK中，图像的像素读写能够通过getPixel与setPixel两个Bitmap的API实现。

Bitmap API读取像素的代码例如以下：

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)

得到像素pixel是32位的整数，四个字节分别相应透明通道、红色、绿色、蓝色通道。

Bitmap API 写入像素,代码例如以下：

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

通过Color.argb又一次组装成一个int的像素值。

使用BitmapFactory.decodeFile或者decodeResource等方法实现载入图像的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。假设原始的图像文件数据非常大，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，图像进行适当的下採样，就能够避免OOM问题的发生。预先仅仅获取图像高度与宽带的代码例如以下：

        // 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;

基于下採样载入超大Bitmap图像的缩小版本号：

        // 下採样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;}}// 获取採样后的图像显示。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
代码实现例如以下：

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);// 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)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例如以下：

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);// 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)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);// 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)int ncol = width - col - 1;bm.setPixel(ncol, row, Color.argb(alpha, red, green, blue));}}return bm;
}

执行截图：

布局XML文件内容例如以下：

<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方法的代码例如以下：

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() {@Overridepublic 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() {@Overridepublic 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() {@Overridepublic 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() {@Overridepublic 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() {@Overridepublic 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() {@Overridepublic 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);}
});

-第一次尝试用CSDN-markdown编辑器写文章。发现这个东西真好用！赞。。！
-gloomyfish@2015-07-02