图片有各种形状和大小。在很多情况下这些图片是远远大于我们的用户界面(UI)且占领着极大的内存空间，假设我们不正确位图进行压缩处理，我们的程序会发生内存泄露的错误。

MainActivity的代码

package com.example.g08_bitmap;import android.os.Bundle;import android.app.Activity;import android.content.res.Resources;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.widget.ImageView;public class MainActivity extends Activity {	private ImageView imageView;	@Override	protected void onCreate(Bundle savedInstanceState) {		super.onCreate(savedInstanceState);		setContentView(R.layout.activity_main);		imageView = (ImageView) this.findViewById(R.id.imageView1);		imageView.setImageBitmap(decodeSampledBitmapFromResource(				getResources(), R.drawable.a, 300, 300));	}	public static Bitmap decodeSampledBitmapFromResource(Resources res,			int resId, int reqWidth, int reqHeight) {		final BitmapFactory.Options options = new BitmapFactory.Options();		//先将inJustDecodeBounds属性设置为true,解码避免内存分配		options.inJustDecodeBounds = true;		// 将图片传入选择器中		BitmapFactory.decodeResource(res, resId, options);		// 对图片进行指定比例的压缩		options.inSampleSize = calculateInSampleSize(options, reqWidth,				reqHeight);		//待图片处理完毕后再进行内存的分配，避免内存泄露的发生		options.inJustDecodeBounds = false;		return BitmapFactory.decodeResource(res, resId, options);	}	// 计算图片的压缩比例	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 heightRatio = Math.round((float) height					/ (float) reqHeight);			final int widthRatio = Math.round((float) width / (float) reqWidth);			// 选择长宽高较小的比例，成为压缩比例			inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;		}		return inSampleSize;	}}