Android图片缩放总结及比较

在Android中对大图片进行缩放真的很不尽如人意，不知道是不是我的方法不对。下面我列出3种对图片缩放的方法，并给出相应速度。请高人指教。

第一种是BitmapFactory和BitmapFactory.Options。
首先，BitmapFactory.Options有几个Fields很有用：
inJustDecodeBounds：If set to true, the decoder will return null (no bitmap), but the out...
也就是说，当inJustDecodeBounds设成true时，bitmap并不加载到内存，这样效率很高哦。而这时，你可以获得bitmap的高、宽等信息。
outHeight：The resulting height of the bitmap, set independent of the state of inJustDecodeBounds.
outWidth：The resulting width of the bitmap, set independent of the state of inJustDecodeBounds. 
看到了吧，上面3个变量是相关联的哦。
inSampleSize ： If set to a value > 1, requests the decoder to subsample the original image, returning a smaller image to save memory.
这就是用来做缩放比的。这里有个技巧：
inSampleSize=（outHeight/Height+outWidth/Width）/2
实践证明，这样缩放出来的图片还是很好的。
最后用BitmapFactory.decodeFile(path, options)生成。
由于只是对bitmap加载到内存一次，所以效率比较高。解析速度快。

第二种是使用Bitmap加Matrix来缩放。

首先要获得原bitmap，再从原bitmap的基础上生成新图片。这样效率很低。

第三种是用2.2新加的类ThumbnailUtils来做。
让我们新看看这个类，从API中来看，此类就三个静态方法：createVideoThumbnail、extractThumbnail(Bitmap source, int width, int height, int options)、extractThumbnail(Bitmap source, int width, int height)。
我这里使用了第三个方法。再看看它的源码，下面会附上。是上面我们用到的BitmapFactory.Options和Matrix等经过人家一阵加工而成。
效率好像比第二种方法高一点点。

下面是我的例子：

 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:orientation="vertical"
     android:layout_width="fill_parent"
     android:layout_height="fill_parent"
     >

 <ImageView
     android:id="@+id/imageShow"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
 />
 <ImageView
     android:id="@+id/image2"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
 />
 <TextView
     android:id="@+id/text"
     android:layout_width="fill_parent"
     android:layout_height="wrap_content"
     android:text="@string/hello"
     />
 </LinearLayout>

 package com.linc.ResolvePicture;

 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.FileOutputStream;
 import java.io.IOException;

 import android.app.Activity;
 import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
 import android.graphics.Matrix;
 import android.graphics.drawable.BitmapDrawable;
 import android.graphics.drawable.Drawable;
 import android.media.ThumbnailUtils;
 import android.os.Bundle;
 import android.util.Log;
 import android.widget.ImageView;
 import android.widget.TextView;

 public class ResolvePicture extends Activity {
     private static String tag="ResolvePicture";
     Drawable bmImg;
     ImageView imView;
     ImageView imView2;
     TextView text;
     String theTime;
     long start, stop;
     /** Called when the activity is first created. */
     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.main);

         text=(TextView)findViewById(R.id.text);

         imView=(ImageView) findViewById(R.id.imageShow);
         imView2=(ImageView) findViewById(R.id.image2);

         Bitmap bitmap = BitmapFactory.decodeResource(getResources(),
                 R.drawable.pic);

         start=System.currentTimeMillis();

 //        imView.setImageDrawable(resizeImage(bitmap, 300, 100));

         imView2.setImageDrawable(resizeImage2("/sdcard/2.jpeg", 200, 100));

         stop=System.currentTimeMillis();

         String theTime= String.format("\n1 iterative: (%d msec)",
                 stop - start);

         start=System.currentTimeMillis();
         imView.setImageBitmap(ThumbnailUtils.extractThumbnail(bitmap,200,100));//2.2才加进来的新类，简单易用
 //        imView.setImageDrawable(resizeImage(bitmap, 30, 30));
         stop=System.currentTimeMillis();

          theTime+= String.format("\n2 iterative: (%d msec)",
                 stop - start);

         text.setText(theTime);
     }

     //使用Bitmap加Matrix来缩放
     public static Drawable resizeImage(Bitmap bitmap, int w, int h)
     {
         Bitmap BitmapOrg = bitmap;
         int width = BitmapOrg.getWidth();
         int height = BitmapOrg.getHeight();
         int newWidth = w;
         int newHeight = h;

         float scaleWidth = ((float) newWidth) / width;
         float scaleHeight = ((float) newHeight) / height;

         Matrix matrix = new Matrix();
         matrix.postScale(scaleWidth, scaleHeight);
         // if you want to rotate the Bitmap
         // matrix.postRotate(45);
         Bitmap resizedBitmap = Bitmap.createBitmap(BitmapOrg, 0, 0, width,
                         height, matrix, true);
         return new BitmapDrawable(resizedBitmap);
     }

     //使用BitmapFactory.Options的inSampleSize参数来缩放
     public static Drawable resizeImage2(String path,
             int width,int height)
     {
         BitmapFactory.Options options = new BitmapFactory.Options();
         options.inJustDecodeBounds = true;//不加载bitmap到内存中
         BitmapFactory.decodeFile(path,options);
         int outWidth = options.outWidth;
         int outHeight = options.outHeight;
         options.inDither = false;
         options.inPreferredConfig = Bitmap.Config.ARGB_8888;
         options.inSampleSize = 1;

         if (outWidth != 0 && outHeight != 0 && width != 0 && height != 0)
         {
             int sampleSize=(outWidth/width+outHeight/height)/2;
             Log.d(tag, "sampleSize = " + sampleSize);
             options.inSampleSize = sampleSize;
         }

         options.inJustDecodeBounds = false;
         return new BitmapDrawable(BitmapFactory.decodeFile(path, options));
     }

     //图片保存
     private void saveThePicture(Bitmap bitmap)
     {
         File file=new File("/sdcard/2.jpeg");
         try
         {
             FileOutputStream fos=new FileOutputStream(file);
             if(bitmap.compress(Bitmap.CompressFormat.JPEG, 100, fos))
             {
                 fos.flush();
                 fos.close();
             }
         }
         catch(FileNotFoundException e1)
         {
             e1.printStackTrace();
         }
         catch(IOException e2)
         {
             e2.printStackTrace();
         }
     }
 }

ThumbnailUtils源码：

 /*
  * Copyright (C) 2009 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package android.media;

 import android.content.ContentResolver;
 import android.content.ContentUris;
 import android.content.ContentValues;
 import android.database.Cursor;
 import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
 import android.graphics.Canvas;
 import android.graphics.Matrix;
 import android.graphics.Rect;
 import android.media.MediaMetadataRetriever;
 import android.media.MediaFile.MediaFileType;
 import android.net.Uri;
 import android.os.ParcelFileDescriptor;
 import android.provider.BaseColumns;
 import android.provider.MediaStore.Images;
 import android.provider.MediaStore.Images.Thumbnails;
 import android.util.Log;

 import java.io.FileInputStream;
 import java.io.FileDescriptor;
 import java.io.IOException;
 import java.io.OutputStream;

 /**
  * Thumbnail generation routines for media provider.
  */

 public class ThumbnailUtils {
     private static final String TAG = "ThumbnailUtils";

     /* Maximum pixels size for created bitmap. */
     private static final int MAX_NUM_PIXELS_THUMBNAIL = 512 * 384;
     private static final int MAX_NUM_PIXELS_MICRO_THUMBNAIL = 128 * 128;
     private static final int UNCONSTRAINED = -1;

     /* Options used internally. */
     private static final int OPTIONS_NONE = 0x0;
     private static final int OPTIONS_SCALE_UP = 0x1;

     /**
      * Constant used to indicate we should recycle the input in
      * {@link #extractThumbnail(Bitmap, int, int, int)} unless the output is the input.
      */
     public static final int OPTIONS_RECYCLE_INPUT = 0x2;

     /**
      * Constant used to indicate the dimension of mini thumbnail.
      * @hide Only used by media framework and media provider internally.
      */
     public static final int TARGET_SIZE_MINI_THUMBNAIL = 320;

     /**
      * Constant used to indicate the dimension of micro thumbnail.
      * @hide Only used by media framework and media provider internally.
      */
     public static final int TARGET_SIZE_MICRO_THUMBNAIL = 96;

     /**
      * This method first examines if the thumbnail embedded in EXIF is bigger than our target
      * size. If not, then it'll create a thumbnail from original image. Due to efficiency
      * consideration, we want to let MediaThumbRequest avoid calling this method twice for
      * both kinds, so it only requests for MICRO_KIND and set saveImage to true.
      *
      * This method always returns a "square thumbnail" for MICRO_KIND thumbnail.
      *
      * @param filePath the path of image file
      * @param kind could be MINI_KIND or MICRO_KIND
      * @return Bitmap
      *
      * @hide This method is only used by media framework and media provider internally.
      */
     public static Bitmap createImageThumbnail(String filePath, int kind) {
         boolean wantMini = (kind == Images.Thumbnails.MINI_KIND);
         int targetSize = wantMini
                 ? TARGET_SIZE_MINI_THUMBNAIL
                 : TARGET_SIZE_MICRO_THUMBNAIL;
         int maxPixels = wantMini
                 ? MAX_NUM_PIXELS_THUMBNAIL
                 : MAX_NUM_PIXELS_MICRO_THUMBNAIL;
         SizedThumbnailBitmap sizedThumbnailBitmap = new SizedThumbnailBitmap();
         Bitmap bitmap = null;
         MediaFileType fileType = MediaFile.getFileType(filePath);
         if (fileType != null && fileType.fileType == MediaFile.FILE_TYPE_JPEG) {
             createThumbnailFromEXIF(filePath, targetSize, maxPixels, sizedThumbnailBitmap);
             bitmap = sizedThumbnailBitmap.mBitmap;
         }

         if (bitmap == null) {
             try {
                 FileDescriptor fd = new FileInputStream(filePath).getFD();
                 BitmapFactory.Options options = new BitmapFactory.Options();
                 options.inSampleSize = 1;
                 options.inJustDecodeBounds = true;
                 BitmapFactory.decodeFileDescriptor(fd, null, options);
                 if (options.mCancel || options.outWidth == -1
                         || options.outHeight == -1) {
                     return null;
                 }
                 options.inSampleSize = computeSampleSize(
                         options, targetSize, maxPixels);
                 options.inJustDecodeBounds = false;

                 options.inDither = false;
                 options.inPreferredConfig = Bitmap.Config.ARGB_8888;
                 bitmap = BitmapFactory.decodeFileDescriptor(fd, null, options);
             } catch (IOException ex) {
                 Log.e(TAG, "", ex);
             }
         }

         if (kind == Images.Thumbnails.MICRO_KIND) {
             // now we make it a "square thumbnail" for MICRO_KIND thumbnail
             bitmap = extractThumbnail(bitmap,
                     TARGET_SIZE_MICRO_THUMBNAIL,
                     TARGET_SIZE_MICRO_THUMBNAIL, OPTIONS_RECYCLE_INPUT);
         }
         return bitmap;
     }

     /**
      * Create a video thumbnail for a video. May return null if the video is
      * corrupt or the format is not supported.
      *
      * @param filePath the path of video file
      * @param kind could be MINI_KIND or MICRO_KIND
      */
     public static Bitmap createVideoThumbnail(String filePath, int kind) {
         Bitmap bitmap = null;
         MediaMetadataRetriever retriever = new MediaMetadataRetriever();
         try {
             retriever.setMode(MediaMetadataRetriever.MODE_CAPTURE_FRAME_ONLY);
             retriever.setDataSource(filePath);
             bitmap = retriever.captureFrame();
         } catch (IllegalArgumentException ex) {
             // Assume this is a corrupt video file
         } catch (RuntimeException ex) {
             // Assume this is a corrupt video file.
         } finally {
             try {
                 retriever.release();
             } catch (RuntimeException ex) {
                 // Ignore failures while cleaning up.
             }
         }
         if (kind == Images.Thumbnails.MICRO_KIND && bitmap != null) {
             bitmap = extractThumbnail(bitmap,
                     TARGET_SIZE_MICRO_THUMBNAIL,
                     TARGET_SIZE_MICRO_THUMBNAIL,
                     OPTIONS_RECYCLE_INPUT);
         }
         return bitmap;
     }

     /**
      * Creates a centered bitmap of the desired size.
      *
      * @param source original bitmap source
      * @param width targeted width
      * @param height targeted height
      */
     public static Bitmap extractThumbnail(
             Bitmap source, int width, int height) {
         return extractThumbnail(source, width, height, OPTIONS_NONE);
     }

     /**
      * Creates a centered bitmap of the desired size.
      *
      * @param source original bitmap source
      * @param width targeted width
      * @param height targeted height
      * @param options options used during thumbnail extraction
      */
     public static Bitmap extractThumbnail(
             Bitmap source, int width, int height, int options) {
         if (source == null) {
             return null;
         }

         float scale;
         if (source.getWidth() < source.getHeight()) {
             scale = width / (float) source.getWidth();
         } else {
             scale = height / (float) source.getHeight();
         }
         Matrix matrix = new Matrix();
         matrix.setScale(scale, scale);
         Bitmap thumbnail = transform(matrix, source, width, height,
                 OPTIONS_SCALE_UP | options);
         return thumbnail;
     }

     /*
      * Compute the sample size as a function of minSideLength
      * and maxNumOfPixels.
      * minSideLength is used to specify that minimal width or height of a
      * bitmap.
      * maxNumOfPixels is used to specify the maximal size in pixels that is
      * tolerable in terms of memory usage.
      *
      * The function returns a sample size based on the constraints.
      * Both size and minSideLength can be passed in as IImage.UNCONSTRAINED,
      * which indicates no care of the corresponding constraint.
      * The functions prefers returning a sample size that
      * generates a smaller bitmap, unless minSideLength = IImage.UNCONSTRAINED.
      *
      * Also, the function rounds up the sample size to a power of 2 or multiple
      * of 8 because BitmapFactory only honors sample size this way.
      * For example, BitmapFactory downsamples an image by 2 even though the
      * request is 3. So we round up the sample size to avoid OOM.
      */
     private static int computeSampleSize(BitmapFactory.Options options,
             int minSideLength, int maxNumOfPixels) {
         int initialSize = computeInitialSampleSize(options, minSideLength,
                 maxNumOfPixels);

         int roundedSize;
         if (initialSize <= 8 ) {
             roundedSize = 1;
             while (roundedSize < initialSize) {
                 roundedSize <<= 1;
             }
         } else {
             roundedSize = (initialSize + 7) / 8 * 8;
         }

         return roundedSize;
     }

     private static int computeInitialSampleSize(BitmapFactory.Options options,
             int minSideLength, int maxNumOfPixels) {
         double w = options.outWidth;
         double h = options.outHeight;

         int lowerBound = (maxNumOfPixels == UNCONSTRAINED) ? 1 :
                 (int) Math.ceil(Math.sqrt(w * h / maxNumOfPixels));
         int upperBound = (minSideLength == UNCONSTRAINED) ? 128 :
                 (int) Math.min(Math.floor(w / minSideLength),
                 Math.floor(h / minSideLength));

         if (upperBound < lowerBound) {
             // return the larger one when there is no overlapping zone.
             return lowerBound;
         }

         if ((maxNumOfPixels == UNCONSTRAINED) &&
                 (minSideLength == UNCONSTRAINED)) {
             return 1;
         } else if (minSideLength == UNCONSTRAINED) {
             return lowerBound;
         } else {
             return upperBound;
         }
     }

     /**
      * Make a bitmap from a given Uri, minimal side length, and maximum number of pixels.
      * The image data will be read from specified pfd if it's not null, otherwise
      * a new input stream will be created using specified ContentResolver.
      *
      * Clients are allowed to pass their own BitmapFactory.Options used for bitmap decoding. A
      * new BitmapFactory.Options will be created if options is null.
      */
     private static Bitmap makeBitmap(int minSideLength, int maxNumOfPixels,
             Uri uri, ContentResolver cr, ParcelFileDescriptor pfd,
             BitmapFactory.Options options) {
             Bitmap b = null;
         try {
             if (pfd == null) pfd = makeInputStream(uri, cr);
             if (pfd == null) return null;
             if (options == null) options = new BitmapFactory.Options();

             FileDescriptor fd = pfd.getFileDescriptor();
             options.inSampleSize = 1;
             options.inJustDecodeBounds = true;
             BitmapFactory.decodeFileDescriptor(fd, null, options);
             if (options.mCancel || options.outWidth == -1
                     || options.outHeight == -1) {
                 return null;
             }
             options.inSampleSize = computeSampleSize(
                     options, minSideLength, maxNumOfPixels);
             options.inJustDecodeBounds = false;

             options.inDither = false;
             options.inPreferredConfig = Bitmap.Config.ARGB_8888;
             b = BitmapFactory.decodeFileDescriptor(fd, null, options);
         } catch (OutOfMemoryError ex) {
             Log.e(TAG, "Got oom exception ", ex);
             return null;
         } finally {
             closeSilently(pfd);
         }
         return b;
     }

     private static void closeSilently(ParcelFileDescriptor c) {
       if (c == null) return;
       try {
           c.close();
       } catch (Throwable t) {
           // do nothing
       }
     }

     private static ParcelFileDescriptor makeInputStream(
             Uri uri, ContentResolver cr) {
         try {
             return cr.openFileDescriptor(uri, "r");
         } catch (IOException ex) {
             return null;
         }
     }

     /**
      * Transform source Bitmap to targeted width and height.
      */
     private static Bitmap transform(Matrix scaler,
             Bitmap source,
             int targetWidth,
             int targetHeight,
             int options) {
         boolean scaleUp = (options & OPTIONS_SCALE_UP) != 0;
         boolean recycle = (options & OPTIONS_RECYCLE_INPUT) != 0;

         int deltaX = source.getWidth() - targetWidth;
         int deltaY = source.getHeight() - targetHeight;
         if (!scaleUp && (deltaX < 0 || deltaY < 0)) {
             /*
             * In this case the bitmap is smaller, at least in one dimension,
             * than the target.  Transform it by placing as much of the image
             * as possible into the target and leaving the top/bottom or
             * left/right (or both) black.
             */
             Bitmap b2 = Bitmap.createBitmap(targetWidth, targetHeight,
             Bitmap.Config.ARGB_8888);
             Canvas c = new Canvas(b2);

             int deltaXHalf = Math.max(0, deltaX / 2);
             int deltaYHalf = Math.max(0, deltaY / 2);
             Rect src = new Rect(
             deltaXHalf,
             deltaYHalf,
             deltaXHalf + Math.min(targetWidth, source.getWidth()),
             deltaYHalf + Math.min(targetHeight, source.getHeight()));
             int dstX = (targetWidth  - src.width())  / 2;
             int dstY = (targetHeight - src.height()) / 2;
             Rect dst = new Rect(
                     dstX,
                     dstY,
                     targetWidth - dstX,
                     targetHeight - dstY);
             c.drawBitmap(source, src, dst, null);
             if (recycle) {
                 source.recycle();
             }
             return b2;
         }
         float bitmapWidthF = source.getWidth();
         float bitmapHeightF = source.getHeight();

         float bitmapAspect = bitmapWidthF / bitmapHeightF;
         float viewAspect   = (float) targetWidth / targetHeight;

         if (bitmapAspect > viewAspect) {
             float scale = targetHeight / bitmapHeightF;
             if (scale < .9F || scale > 1F) {
                 scaler.setScale(scale, scale);
             } else {
                 scaler = null;
             }
         } else {
             float scale = targetWidth / bitmapWidthF;
             if (scale < .9F || scale > 1F) {
                 scaler.setScale(scale, scale);
             } else {
                 scaler = null;
             }
         }

         Bitmap b1;
         if (scaler != null) {
             // this is used for minithumb and crop, so we want to filter here.
             b1 = Bitmap.createBitmap(source, 0, 0,
             source.getWidth(), source.getHeight(), scaler, true);
         } else {
             b1 = source;
         }

         if (recycle && b1 != source) {
             source.recycle();
         }

         int dx1 = Math.max(0, b1.getWidth() - targetWidth);
         int dy1 = Math.max(0, b1.getHeight() - targetHeight);

         Bitmap b2 = Bitmap.createBitmap(
                 b1,
                 dx1 / 2,
                 dy1 / 2,
                 targetWidth,
                 targetHeight);

         if (b2 != b1) {
             if (recycle || b1 != source) {
                 b1.recycle();
             }
         }

         return b2;
     }

     /**
      * SizedThumbnailBitmap contains the bitmap, which is downsampled either from
      * the thumbnail in exif or the full image.
      * mThumbnailData, mThumbnailWidth and mThumbnailHeight are set together only if mThumbnail
      * is not null.
      *
      * The width/height of the sized bitmap may be different from mThumbnailWidth/mThumbnailHeight.
      */
     private static class SizedThumbnailBitmap {
         public byte[] mThumbnailData;
         public Bitmap mBitmap;
         public int mThumbnailWidth;
         public int mThumbnailHeight;
     }

     /**
      * Creates a bitmap by either downsampling from the thumbnail in EXIF or the full image.
      * The functions returns a SizedThumbnailBitmap,
      * which contains a downsampled bitmap and the thumbnail data in EXIF if exists.
      */
     private static void createThumbnailFromEXIF(String filePath, int targetSize,
             int maxPixels, SizedThumbnailBitmap sizedThumbBitmap) {
         if (filePath == null) return;

         ExifInterface exif = null;
         byte [] thumbData = null;
         try {
             exif = new ExifInterface(filePath);
             if (exif != null) {
                 thumbData = exif.getThumbnail();
             }
         } catch (IOException ex) {
             Log.w(TAG, ex);
         }

         BitmapFactory.Options fullOptions = new BitmapFactory.Options();
         BitmapFactory.Options exifOptions = new BitmapFactory.Options();
         int exifThumbWidth = 0;
         int fullThumbWidth = 0;

         // Compute exifThumbWidth.
         if (thumbData != null) {
             exifOptions.inJustDecodeBounds = true;
             BitmapFactory.decodeByteArray(thumbData, 0, thumbData.length, exifOptions);
             exifOptions.inSampleSize = computeSampleSize(exifOptions, targetSize, maxPixels);
             exifThumbWidth = exifOptions.outWidth / exifOptions.inSampleSize;
         }

         // Compute fullThumbWidth.
         fullOptions.inJustDecodeBounds = true;
         BitmapFactory.decodeFile(filePath, fullOptions);
         fullOptions.inSampleSize = computeSampleSize(fullOptions, targetSize, maxPixels);
         fullThumbWidth = fullOptions.outWidth / fullOptions.inSampleSize;

         // Choose the larger thumbnail as the returning sizedThumbBitmap.
         if (thumbData != null && exifThumbWidth >= fullThumbWidth) {
             int width = exifOptions.outWidth;
             int height = exifOptions.outHeight;
             exifOptions.inJustDecodeBounds = false;
             sizedThumbBitmap.mBitmap = BitmapFactory.decodeByteArray(thumbData, 0,
                     thumbData.length, exifOptions);
             if (sizedThumbBitmap.mBitmap != null) {
                 sizedThumbBitmap.mThumbnailData = thumbData;
                 sizedThumbBitmap.mThumbnailWidth = width;
                 sizedThumbBitmap.mThumbnailHeight = height;
             }
         } else {
             fullOptions.inJustDecodeBounds = false;
             sizedThumbBitmap.mBitmap = BitmapFactory.decodeFile(filePath, fullOptions);
         }
     }
 }