E/AndroidRuntime(2128): Caused by: java.lang.OutOfMemoryError
E/dalvikvm-heap(2128): Out of memory on a 30720012-byte allocation.

    //1） 获取手机的宽和高
    WindowManager wm = (WindowManager) getSystemService(WINDOW_SERVICE);
    int screenWidth = wm.getDefaultDisplay().getWidth();
    int screenHeight = wm.getDefaultDisplay().getHeight();
    //2）获取图片的宽和高
    BitmapFactory.Options options = new Options();
    //返回一个null 没有bitmap，不去真正解析位图，但是能返回图片的一些信息。
    options.inJustDecodeBounds = true; 
    BitmapFactory.decodeResource(getResources(), R.drawable.dog,options);
    int imagWidth = options.outWidth;
    int imagHeight = options.outHeight;
    //3)计算缩放比
    int scale =1;
    int scalex = imagWidth / screenWidth;
    int scaley = imagHeight / screenHeight;
    scale = Math.max(scalex, scaley);
    //4）按照缩放比显示图片
    options.inSampleSize = scale;
    //开始真正的解析位图 
    options.inJustDecodeBounds = false;
    Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.dog,options);

 Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);
    bitmap.setPixel(100, 20, Color.RED);

Bitmap bitmap = BitmapFactory.decodeResource(getResources(),
        R.drawable.ic_launcher);
    // bitmap.setPixel(100, 20, Color.RED);
    // 1）创建模板
    Bitmap copybitmap = Bitmap.createBitmap(bitmap.getWidth(),
        bitmap.getHeight(), bitmap.getConfig());
    // 2）创建一个画布以原图作为模板
    Canvas canvas = new Canvas(copybitmap);
    // 3）创建一个画笔
    Paint paint = new Paint();
    // 4）开始拷贝原图
    canvas.drawBitmap(bitmap, new Matrix(), paint);

    // 修改图片
    copybitmap.setPixel(20, 30, Color.RED);