Android中Bitmap常见的一些操作：缩放、裁剪、旋转和偏移

/**
  * 根据给定的宽和高进行拉伸
  *
  * @param origin 原图
  * @param newWidth 新图的宽
  * @param newHeight 新图的高
  * @return new Bitmap
  */
 private Bitmap scaleBitmap(Bitmap origin, int newWidth, int newHeight) {
  if (origin == null) {
   return null;
  }
  int height = origin.getHeight();
  int width = origin.getWidth();
  float scaleWidth = ((float) newWidth) / width;
  float scaleHeight = ((float) newHeight) / height;
  Matrix matrix = new Matrix();
  matrix.postScale(scaleWidth, scaleHeight);// 使用后乘
  Bitmap newBM = Bitmap.createBitmap(origin, 0, 0, width, height, matrix, false);
  if (!origin.isRecycled()) {
   origin.recycle();
  }
  return newBM;
 }

 /**
  * 按比例缩放图片
  *
  * @param origin 原图
  * @param ratio 比例
  * @return 新的bitmap
  */
 private Bitmap scaleBitmap(Bitmap origin, float ratio) {
  if (origin == null) {
   return null;
  }
  int width = origin.getWidth();
  int height = origin.getHeight();
  Matrix matrix = new Matrix();
  matrix.preScale(ratio, ratio);
  Bitmap newBM = Bitmap.createBitmap(origin, 0, 0, width, height, matrix, false);
  if (newBM.equals(origin)) {
   return newBM;
  }
  origin.recycle();
  return newBM;
 }

 /**
  * 裁剪
  *
  * @param bitmap 原图
  * @return 裁剪后的图像
  */
 private Bitmap cropBitmap(Bitmap bitmap) {
  int w = bitmap.getWidth(); // 得到图片的宽，高
  int h = bitmap.getHeight();
  int cropWidth = w >= h ? h : w;// 裁切后所取的正方形区域边长
  cropWidth /= 2;
  int cropHeight = (int) (cropWidth / 1.2);
  return Bitmap.createBitmap(bitmap, w / 3, 0, cropWidth, cropHeight, null, false);
 }

 /**
  * 选择变换
  *
  * @param origin 原图
  * @param alpha 旋转角度，可正可负
  * @return 旋转后的图片
  */
 private Bitmap rotateBitmap(Bitmap origin, float alpha) {
  if (origin == null) {
   return null;
  }
  int width = origin.getWidth();
  int height = origin.getHeight();
  Matrix matrix = new Matrix();
  matrix.setRotate(alpha);
  // 围绕原地进行旋转
  Bitmap newBM = Bitmap.createBitmap(origin, 0, 0, width, height, matrix, false);
  if (newBM.equals(origin)) {
   return newBM;
  }
  origin.recycle();
  return newBM;
 }

 /**
  * 偏移效果
  * @param origin 原图
  * @return 偏移后的bitmap
  */
 private Bitmap skewBitmap(Bitmap origin) {
  if (origin == null) {
   return null;
  }
  int width = origin.getWidth();
  int height = origin.getHeight();
  Matrix matrix = new Matrix();
  matrix.postSkew(-0.6f, -0.3f);
  Bitmap newBM = Bitmap.createBitmap(origin, 0, 0, width, height, matrix, false);
  if (newBM.equals(origin)) {
   return newBM;
  }
  origin.recycle();
  return newBM;
 }

@Override
 public void onClick(View v) {
  Bitmap originBM = BitmapFactory.decodeResource(getResources(),
    R.drawable.littleboygreen_x128);
  switch (v.getId()) {
   case R.id.btn1: {// 按尺寸缩放
    effectTextView.setText(R.string.scale);
    Bitmap nBM = scaleBitmap(originBM, 100, 72);
    effectView.setImageBitmap(nBM);
    break;
   }
   case R.id.btn2: {// 按比例缩放，每次点击缩放比例都会不同
    effectTextView.setText(R.string.scale_ratio);
    if (ratio < 3) {
     ratio += 0.05f;
    } else {
     ratio = 0.1f;
    }
    Bitmap nBM = scaleBitmap(originBM, ratio);
    effectView.setImageBitmap(nBM);
    break;
   }
   case R.id.btn3: {// 裁剪
    effectTextView.setText("剪个头");
    Bitmap cropBitmap = cropBitmap(originBM);
    effectView.setImageBitmap(cropBitmap);
    break;
   }
   case R.id.btn4: {// 顺时针旋转效果；每次点击更新旋转角度
    if (alpha < 345) {
     alpha += 15;
    } else {
     alpha = 0;
    }
    effectTextView.setText("旋转");
    Bitmap rotateBitmap = rotateBitmap(originBM, alpha);
    effectView.setImageBitmap(rotateBitmap);
    break;
   }
   case R.id.btn5: {// 逆时针旋转效果；每次点击更新旋转角度
    if (beta > 15) {
     beta -= 15;
    } else {
     beta = 360;
    }
    effectTextView.setText("旋转");
    Bitmap rotateBitmap = rotateBitmap(originBM, beta);
    effectView.setImageBitmap(rotateBitmap);
    break;
   }
   case R.id.btn6: {// 偏移效果；偏移量在方法中
    Bitmap skewBM = skewBitmap(originBM);
    effectView.setImageBitmap(skewBM);
    break;
   }
  }
 }

Matrix matrix = new Matrix();
matrix.preScale(ratio, ratio);// 当 ratio=1，下面的 newBM 将会等价于 origin
Bitmap newBM = Bitmap.createBitmap(origin, 0, 0, width, height, matrix, false);
if (!origin.isRecycled()) {
origin.recycle();
}