自動計算BitmapFactory.Options 的inSampleSize 引數。程式碼如下：

public static Bitmap decodeSampledBitmapFromResource(Resources res,int resId,
				int reqWidth,int reqHeight) {
	// First decode with inJustDecodeBounds=true to check dimensions
	final BitmapFactory.Options options = new BitmapFactory.Options();
	options.inJustDecodeBounds = true;
	BitmapFactory.decodeResource(res,resId,options);
	// Calculate inSampleSize
	options.inSampleSize = calculateInSampleSize(options,reqWidth,reqHeight);
	// Decode bitmap with inSampleSize set
	options.inJustDecodeBounds = false;
	return BitmapFactory.decodeResource(res,resId,options);
}
public static int calculateInSampleSize(
		BitmapFactory.Options options,int reqWidth,int reqHeight) {
	// Raw height and width of image
	final int height = options.outHeight;
	final int width = options.outWidth;
	int inSampleSize = 1;
	if (height > reqHeight || width > reqWidth) {
		final int halfHeight = height / 2;
		final int halfWidth = width / 2;
		// Calculate the largest inSampleSize value that is a power of 2 and
		keeps both
		// height and width larger than the requested height and width.
		while ((halfHeight / inSampleSize) => reqHeight
			&& (halfWidth / inSampleSize) => reqWidth) {
		inSampleSize *= 2;
		}
	}
	return inSampleSize;
}