Android 图片相关操作

1、将 Uri 转化为 path

public String uriToPath(Uri uri,Activity context) {
    // 新建一个字符串数组用于存储图片地址数据。
    String[] proj = { MediaStore.Images.Media.DATA };
    // android系统提供的接口，用于根据uri获取数据
    // Cursor cursor = context.managedQuery(uri, proj, null, null, null);
    Cursor cursor = context.getContentResolver().query(uri, proj, null, null, null);
    // 获得用户选择图片的索引值
    int column_index = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);
    // 将游标移至开头 ，防止引起队列越界
    cursor.moveToFirst();
    // 根据索引值获取图片路径
    String path = cursor.getString(column_index);
    return path;
}

2、根据Uri生成Bitmap

public Bitmap getBitmap(Uri uri,Activity context) {
    Bitmap bm = null;
    // 外界的程序访问ContentProvider所提供数据 可以通过ContentResolver接口
    ContentResolver resolver = context.getContentResolver();
    try {
        //根据图片的URi生成bitmap
        bm = MediaStore.Images.Media.getBitmap(resolver, uri);
    } catch (IOException e) {
        Log.e("getImg", e.toString());
    }
    return bm;
}

3、将彩色图片转化为黑白色

public Bitmap convertToBlackWhite(Bitmap bmp) {
    int width = bmp.getWidth(); // 获取位图的宽
    int height = bmp.getHeight(); // 获取位图的高
    int[] pixels = new int[width * height]; // 通过位图的大小创建像素点数组

    bmp.getPixels(pixels, 0, width, 0, 0, width, height);
    int alpha = 0xFF << 24;
    for (int i = 0; i < height; i++) {
        for (int j = 0; j < width; j++) {
            int grey = pixels[width * i + j];

            //分离三原色
            int red = ((grey & 0x00FF0000) >> 16);
            int green = ((grey & 0x0000FF00) >> 8);
            int blue = (grey & 0x000000FF);

            //转化成灰度像素
            grey = (int) (red * 0.3 + green * 0.59 + blue * 0.11);
            grey = alpha | (grey << 16) | (grey << 8) | grey;
            pixels[width * i + j] = grey;
        }
    }
    //新建图片
    Bitmap newBmp = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565);
    //设置图片数据
    newBmp.setPixels(pixels, 0, width, 0, 0, width, height);

    Bitmap bitmap = ThumbnailUtils.extractThumbnail(newBmp, 380, 460);
    return bitmap;
}