BitmapUtil工具类：

import java.io.ByteArrayOutputStream;
 
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.CompressFormat;
import android.graphics.BitmapFactory;
import android.graphics.BitmapFactory.Options;
import android.graphics.Canvas;
import android.graphics.PixelFormat;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.media.ThumbnailUtils;
import android.text.TextUtils;
 
/**
 * Bitmap工具类，获取Bitmap对象
 */
public class BitmapUtil {
	
	private BitmapUtil(){}
	
	/**
	 * 根据资源id获取指定大小的Bitmap对象
	 * @param context	应用程序上下文
	 * @param id		资源id
	 * @param height	高度
	 * @param width		宽度
	 * @return
	 */
	public static Bitmap getBitmapFromResource(Context context, int id, int height, int width){
		Options options = new Options();
		options.inJustDecodeBounds = true;//只读取图片，不加载到内存中
		BitmapFactory.decodeResource(context.getResources(), id, options);
		options.inSampleSize = calculateSampleSize(height, width, options);
		options.inJustDecodeBounds = false;//加载到内存中
		Bitmap bitmap = BitmapFactory.decodeResource(context.getResources(), id, options);
		return bitmap;
	}
	
	/**
	 * 根据文件路径获取指定大小的Bitmap对象
	 * @param path		文件路径
	 * @param height	高度
	 * @param width		宽度
	 * @return
	 */
	public static Bitmap getBitmapFromFile(String path, int height, int width){
		if (TextUtils.isEmpty(path)) {
			throw new IllegalArgumentException("参数为空，请检查你选择的路径:" + path);
		}
		Options options = new Options();
		options.inJustDecodeBounds = true;//只读取图片，不加载到内存中
		BitmapFactory.decodeFile(path, options);
		options.inSampleSize = calculateSampleSize(height, width, options);
		options.inJustDecodeBounds = false;//加载到内存中
		Bitmap bitmap = BitmapFactory.decodeFile(path, options);
		return bitmap;
	}
	
	/**
	 * 获取指定大小的Bitmap对象
	 * @param bitmap	Bitmap对象
	 * @param height	高度
	 * @param width		宽度
	 * @return
	 */
	public static Bitmap getThumbnailsBitmap(Bitmap bitmap, int height, int width){
		if (bitmap == null) {
			throw new IllegalArgumentException("图片为空，请检查你的参数");
		}
		return ThumbnailUtils.extractThumbnail(bitmap, width, height);
	}
	
	/**
	 * 将Bitmap对象转换成Drawable对象
	 * @param context	应用程序上下文
	 * @param bitmap	Bitmap对象
	 * @return	返回转换后的Drawable对象
	 */
	public static Drawable bitmapToDrawable(Context context, Bitmap bitmap){
		if (context == null || bitmap == null) {
			throw new IllegalArgumentException("参数不合法，请检查你的参数");
		}
		Drawable drawable = new BitmapDrawable(context.getResources(), bitmap);
		return drawable;
	}
	
	/**
	 * 将Drawable对象转换成Bitmap对象
	 * @param drawable	Drawable对象
	 * @return	返回转换后的Bitmap对象
	 */
	public static Bitmap drawableToBitmap(Drawable drawable) {
		if (drawable == null) {
			throw new IllegalArgumentException("Drawable为空，请检查你的参数");
		}
		Bitmap bitmap = 
				Bitmap.createBitmap(drawable.getIntrinsicWidth(), 
						drawable.getIntrinsicHeight(), 
						drawable.getOpacity() != PixelFormat.OPAQUE? Bitmap.Config.ARGB_8888 : Bitmap.Config.RGB_565);
		Canvas canvas = new Canvas(bitmap);
		drawable.setBounds(0, 0, drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight());
		drawable.draw(canvas);
		return bitmap;
	}
	
	/**
	 * 将Bitmap对象转换为byte[]数组
	 * @param bitmap	Bitmap对象
	 * @return		返回转换后的数组
	 */
	public static byte[] bitmapToByte(Bitmap bitmap){
		if (bitmap == null) {
			throw new IllegalArgumentException("Bitmap为空，请检查你的参数");
		}
		ByteArrayOutputStream baos = new ByteArrayOutputStream();
		bitmap.compress(CompressFormat.PNG, 100, baos);
		return baos.toByteArray();
	}
	
	/**
	 * 计算所需图片的缩放比例
	 * @param height	高度
	 * @param width		宽度
	 * @param options	options选项
	 * @return
	 */
	private static int calculateSampleSize(int height, int width, Options options){
		int realHeight = options.outHeight;
		int realWidth = options.outWidth;
		int heigthScale = realHeight / height;
		int widthScale = realWidth / width;
		if(widthScale > heigthScale){
			return widthScale;
		}else{
			return heigthScale;
		}
	}
}