Android中图片处理

加载图片

• 加载大图: 3648 * 2736

  总像素的个数: 9980928
  每一个像素占用的空间: ARGB_4444(2bytes), ARGB_8888(4bytes), RGB_565(2bytes)
  
  图片占用的空间 = 总像素的个数 * 像素的单位.
  9980928 * 2bytes = 19961856bytes = 19.037109375MB
  

• 缩放加载.

  • 图片的宽和高: 3648 * 2736

  • 屏幕的宽和高: 320 * 480

  • 计算缩放比例

    • 宽度缩放比例: 3648 / 320 = 11;

    • 高度缩放比例: 2736 / 480 = 5;

    • 比较宽和高的缩放比例, 哪一个大用哪一个进行缩放.

  • 进行缩放: 331 * 248 = 82088 * 2bytes = 164176bytes = 160KB

    3648 / 11 = 331; 2736 / 11 = 248;

    核心代码：
    String picpath = et_picpath.getText().toString().trim();
    
    Options opts = new Options();
    opts.inJustDecodeBounds = true;
    
    BitmapFactory.decodeFile(picpath, opts);
    int picHeight = opts.outHeight;
    int picWidth = opts.outWidth;
    
    WindowManager manager = getWindowManager();
    int screenHeight = manager.getDefaultDisplay().getHeight();
    int screenWidth = manager.getDefaultDisplay().getWidth();
    
    int heightScale = picHeight / screenHeight;
    int widthScale = picWidth / screenWidth;
    int scale = heightScale > widthScale ? heightScale : widthScale;
    opts.inJustDecodeBounds = false;
    opts.inSampleSize = scale;
    Bitmap bitmap = BitmapFactory.decodeFile(picpath, opts);
    iv_image.setImageBitmap(bitmap);