android 合成两张图片，上层图片设置透明度

private Bitmap mergeThumbnailBitmap(Bitmap firstBitmap, Bitmap secondBitmap) {

Bitmap bitmap = Bitmap.createBitmap(firstBitmap.getWidth(), firstBitmap

.getHeight(), firstBitmap.getConfig());

Canvas canvas = new Canvas(bitmap);

Paint paint = new Paint();

paint.setAlpha(150);

canvas.drawBitmap(firstBitmap, new Matrix(), null);

canvas.drawBitmap(secondBitmap, 0, 0, paint);

return bitmap;

}