android读取sd卡图片并进行缩放操作

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：

[html] view plain copy

<?xmlversion="1.0"encoding="utf-8"?>
<LinearLayoutxmlns: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>

[java] view plain copy

packagecom.linc.ResolvePicture;
importjava.io.File;
importjava.io.FileNotFoundException;
importjava.io.FileOutputStream;
importjava.io.IOException;
importandroid.app.Activity;
importandroid.graphics.Bitmap;
importandroid.graphics.BitmapFactory;
importandroid.graphics.Matrix;
importandroid.graphics.drawable.BitmapDrawable;
importandroid.graphics.drawable.Drawable;
importandroid.media.ThumbnailUtils;
importandroid.os.Bundle;
importandroid.util.Log;
importandroid.widget.ImageView;
importandroid.widget.TextView;
publicclassResolvePictureextendsActivity{
privatestaticStringtag="ResolvePicture";
DrawablebmImg;
ImageViewimView;
ImageViewimView2;
TextViewtext;
StringtheTime;
longstart,stop;
/**Calledwhentheactivityisfirstcreated.*/
@Override
publicvoidonCreate(BundlesavedInstanceState){
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);
Bitmapbitmap=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();
StringtheTime=String.format("\n1iterative:(%dmsec)",
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("\n2iterative:(%dmsec)",
stop-start);
text.setText(theTime);
}
//使用Bitmap加Matrix来缩放
publicstaticDrawableresizeImage(Bitmapbitmap,intw,inth)
{
BitmapBitmapOrg=bitmap;
intwidth=BitmapOrg.getWidth();
intheight=BitmapOrg.getHeight();
intnewWidth=w;
intnewHeight=h;
floatscaleWidth=((float)newWidth)/width;
floatscaleHeight=((float)newHeight)/height;
Matrixmatrix=newMatrix();
matrix.postScale(scaleWidth,scaleHeight);
//ifyouwanttorotatetheBitmap
//matrix.postRotate(45);
BitmapresizedBitmap=Bitmap.createBitmap(BitmapOrg,0,0,width,
height,matrix,true);
returnnewBitmapDrawable(resizedBitmap);
}
//使用BitmapFactory.Options的inSampleSize参数来缩放
publicstaticDrawableresizeImage2(Stringpath,
intwidth,intheight)
{
BitmapFactory.Optionsoptions=newBitmapFactory.Options();
options.inJustDecodeBounds=true;//不加载bitmap到内存中
BitmapFactory.decodeFile(path,options);
intoutWidth=options.outWidth;
intoutHeight=options.outHeight;
options.inDither=false;
options.inPreferredConfig=Bitmap.Config.ARGB_8888;
options.inSampleSize=1;
if(outWidth!=0&&outHeight!=0&&width!=0&&height!=0)
{
intsampleSize=(outWidth/width+outHeight/height)/2;
Log.d(tag,"sampleSize="+sampleSize);
options.inSampleSize=sampleSize;
}
options.inJustDecodeBounds=false;
returnnewBitmapDrawable(BitmapFactory.decodeFile(path,options));
}
//图片保存
privatevoidsaveThePicture(Bitmapbitmap)
{
Filefile=newFile("/sdcard/2.jpeg");
try
{
FileOutputStreamfos=newFileOutputStream(file);
if(bitmap.compress(Bitmap.CompressFormat.JPEG,100,fos))
{
fos.flush();
fos.close();
}
}
catch(FileNotFoundExceptione1)
{
e1.printStackTrace();
}
catch(IOExceptione2)
{
e2.printStackTrace();
}
}
}

ThumbnailUtils源码：
[java] view plain copy

/*
*Copyright(C)2009TheAndroidOpenSourceProject
*
*LicensedundertheApacheLicense,Version2.0(the"License");
*youmaynotusethisfileexceptincompliancewiththeLicense.
*YoumayobtainacopyoftheLicenseat
*
*http://www.apache.org/licenses/LICENSE-2.0
*
*Unlessrequiredbyapplicablelaworagreedtoinwriting,software
*distributedundertheLicenseisdistributedonan"ASIS"BASIS,
*WITHOUTWARRANTIESORCONDITIONSOFANYKIND,eitherexpressorimplied.
*SeetheLicenseforthespecificlanguagegoverningpermissionsand
*limitationsundertheLicense.
*/
packageandroid.media;
importandroid.content.ContentResolver;
importandroid.content.ContentUris;
importandroid.content.ContentValues;
importandroid.database.Cursor;
importandroid.graphics.Bitmap;
importandroid.graphics.BitmapFactory;
importandroid.graphics.Canvas;
importandroid.graphics.Matrix;
importandroid.graphics.Rect;
importandroid.media.MediaMetadataRetriever;
importandroid.media.MediaFile.MediaFileType;
importandroid.net.Uri;
importandroid.os.ParcelFileDescriptor;
importandroid.provider.BaseColumns;
importandroid.provider.MediaStore.Images;
importandroid.provider.MediaStore.Images.Thumbnails;
importandroid.util.Log;
importjava.io.FileInputStream;
importjava.io.FileDescriptor;
importjava.io.IOException;
importjava.io.OutputStream;
/**
*Thumbnailgenerationroutinesformediaprovider.
*/
publicclassThumbnailUtils{
privatestaticfinalStringTAG="ThumbnailUtils";
/*Maximumpixelssizeforcreatedbitmap.*/
privatestaticfinalintMAX_NUM_PIXELS_THUMBNAIL=512*384;
privatestaticfinalintMAX_NUM_PIXELS_MICRO_THUMBNAIL=128*128;
privatestaticfinalintUNCONSTRAINED=-1;
/*Optionsusedinternally.*/
privatestaticfinalintOPTIONS_NONE=0x0;
privatestaticfinalintOPTIONS_SCALE_UP=0x1;
/**
*Constantusedtoindicateweshouldrecycletheinputin
*{@link#extractThumbnail(Bitmap,int,int,int)}unlesstheoutputistheinput.
*/
publicstaticfinalintOPTIONS_RECYCLE_INPUT=0x2;
/**
*Constantusedtoindicatethedimensionofminithumbnail.
*@hideOnlyusedbymediaframeworkandmediaproviderinternally.
*/
publicstaticfinalintTARGET_SIZE_MINI_THUMBNAIL=320;
/**
*Constantusedtoindicatethedimensionofmicrothumbnail.
*@hideOnlyusedbymediaframeworkandmediaproviderinternally.
*/
publicstaticfinalintTARGET_SIZE_MICRO_THUMBNAIL=96;
/**
*ThismethodfirstexaminesifthethumbnailembeddedinEXIFisbiggerthanourtarget
*size.Ifnot,thenit'llcreateathumbnailfromoriginalimage.Duetoefficiency
*consideration,wewanttoletMediaThumbRequestavoidcallingthismethodtwicefor
*bothkinds,soitonlyrequestsforMICRO_KINDandsetsaveImagetotrue.
*
*Thismethodalwaysreturnsa"squarethumbnail"forMICRO_KINDthumbnail.
*
*@paramfilePaththepathofimagefile
*@paramkindcouldbeMINI_KINDorMICRO_KIND
*@returnBitmap
*
*@hideThismethodisonlyusedbymediaframeworkandmediaproviderinternally.
*/
publicstaticBitmapcreateImageThumbnail(StringfilePath,intkind){
booleanwantMini=(kind==Images.Thumbnails.MINI_KIND);
inttargetSize=wantMini
?TARGET_SIZE_MINI_THUMBNAIL
:TARGET_SIZE_MICRO_THUMBNAIL;
intmaxPixels=wantMini
?MAX_NUM_PIXELS_THUMBNAIL
:MAX_NUM_PIXELS_MICRO_THUMBNAIL;
SizedThumbnailBitmapsizedThumbnailBitmap=newSizedThumbnailBitmap();
Bitmapbitmap=null;
MediaFileTypefileType=MediaFile.getFileType(filePath);
if(fileType!=null&&fileType.fileType==MediaFile.FILE_TYPE_JPEG){
createThumbnailFromEXIF(filePath,targetSize,maxPixels,sizedThumbnailBitmap);
bitmap=sizedThumbnailBitmap.mBitmap;
}
if(bitmap==null){
try{
FileDescriptorfd=newFileInputStream(filePath).getFD();
BitmapFactory.Optionsoptions=newBitmapFactory.Options();
options.inSampleSize=1;
options.inJustDecodeBounds=true;
BitmapFactory.decodeFileDescriptor(fd,null,options);
if(options.mCancel||options.outWidth==-1
||options.outHeight==-1){
returnnull;
}
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(IOExceptionex){
Log.e(TAG,"",ex);
}
}
if(kind==Images.Thumbnails.MICRO_KIND){
//nowwemakeita"squarethumbnail"forMICRO_KINDthumbnail
bitmap=extractThumbnail(bitmap,
TARGET_SIZE_MICRO_THUMBNAIL,
TARGET_SIZE_MICRO_THUMBNAIL,OPTIONS_RECYCLE_INPUT);
}
returnbitmap;
}
/**
*Createavideothumbnailforavideo.Mayreturnnullifthevideois
*corruptortheformatisnotsupported.
*
*@paramfilePaththepathofvideofile
*@paramkindcouldbeMINI_KINDorMICRO_KIND
*/
publicstaticBitmapcreateVideoThumbnail(StringfilePath,intkind){
Bitmapbitmap=null;
MediaMetadataRetrieverretriever=newMediaMetadataRetriever();
try{
retriever.setMode(MediaMetadataRetriever.MODE_CAPTURE_FRAME_ONLY);
retriever.setDataSource(filePath);
bitmap=retriever.captureFrame();
}catch(IllegalArgumentExceptionex){
//Assumethisisacorruptvideofile
}catch(RuntimeExceptionex){
//Assumethisisacorruptvideofile.
}finally{
try{
retriever.release();
}catch(RuntimeExceptionex){
//Ignorefailureswhilecleaningup.
}
}
if(kind==Images.Thumbnails.MICRO_KIND&&bitmap!=null){
bitmap=extractThumbnail(bitmap,
TARGET_SIZE_MICRO_THUMBNAIL,
TARGET_SIZE_MICRO_THUMBNAIL,
OPTIONS_RECYCLE_INPUT);
}
returnbitmap;
}
/**
*Createsacenteredbitmapofthedesiredsize.
*
*@paramsourceoriginalbitmapsource
*@paramwidthtargetedwidth
*@paramheighttargetedheight
*/
publicstaticBitmapextractThumbnail(
Bitmapsource,intwidth,intheight){
returnextractThumbnail(source,width,height,OPTIONS_NONE);
}
/**
*Createsacenteredbitmapofthedesiredsize.
*
*@paramsourceoriginalbitmapsource
*@paramwidthtargetedwidth
*@paramheighttargetedheight
*@paramoptionsoptionsusedduringthumbnailextraction
*/
publicstaticBitmapextractThumbnail(
Bitmapsource,intwidth,intheight,intoptions){
if(source==null){
returnnull;
}
floatscale;
if(source.getWidth()<source.getHeight()){
scale=width/(float)source.getWidth();
}else{
scale=height/(float)source.getHeight();
}
Matrixmatrix=newMatrix();
matrix.setScale(scale,scale);
Bitmapthumbnail=transform(matrix,source,width,height,
OPTIONS_SCALE_UP|options);
returnthumbnail;
}
/*
*ComputethesamplesizeasafunctionofminSideLength
*andmaxNumOfPixels.
*minSideLengthisusedtospecifythatminimalwidthorheightofa
*bitmap.
*maxNumOfPixelsisusedtospecifythemaximalsizeinpixelsthatis
*tolerableintermsofmemoryusage.
*
*Thefunctionreturnsasamplesizebasedontheconstraints.
*BothsizeandminSideLengthcanbepassedinasIImage.UNCONSTRAINED,
*whichindicatesnocareofthecorrespondingconstraint.
*Thefunctionsprefersreturningasamplesizethat
*generatesasmallerbitmap,unlessminSideLength=IImage.UNCONSTRAINED.
*
*Also,thefunctionroundsupthesamplesizetoapowerof2ormultiple
*of8becauseBitmapFactoryonlyhonorssamplesizethisway.
*Forexample,BitmapFactorydownsamplesanimageby2eventhoughthe
*requestis3.SoweroundupthesamplesizetoavoidOOM.
*/
privatestaticintcomputeSampleSize(BitmapFactory.Optionsoptions,
intminSideLength,intmaxNumOfPixels){
intinitialSize=computeInitialSampleSize(options,minSideLength,
maxNumOfPixels);
introundedSize;
if(initialSize<=8){
roundedSize=1;
while(roundedSize<initialSize){
roundedSize<<=1;
}
}else{
roundedSize=(initialSize+7)/8*8;
}
returnroundedSize;
}
privatestaticintcomputeInitialSampleSize(BitmapFactory.Optionsoptions,
intminSideLength,intmaxNumOfPixels){
doublew=options.outWidth;
doubleh=options.outHeight;
intlowerBound=(maxNumOfPixels==UNCONSTRAINED)?1:
(int)Math.ceil(Math.sqrt(w*h/maxNumOfPixels));
intupperBound=(minSideLength==UNCONSTRAINED)?128:
(int)Math.min(Math.floor(w/minSideLength),
Math.floor(h/minSideLength));
if(upperBound<lowerBound){
//returnthelargeronewhenthereisnooverlappingzone.
returnlowerBound;
}
if((maxNumOfPixels==UNCONSTRAINED)&&
(minSideLength==UNCONSTRAINED)){
return1;
}elseif(minSideLength==UNCONSTRAINED){
returnlowerBound;
}else{
returnupperBound;
}
}
/**
*MakeabitmapfromagivenUri,minimalsidelength,andmaximumnumberofpixels.
*Theimagedatawillbereadfromspecifiedpfdifit'snotnull,otherwise
*anewinputstreamwillbecreatedusingspecifiedContentResolver.
*
*ClientsareallowedtopasstheirownBitmapFactory.Optionsusedforbitmapdecoding.A
*newBitmapFactory.Optionswillbecreatedifoptionsisnull.
*/
privatestaticBitmapmakeBitmap(intminSideLength,intmaxNumOfPixels,
Uriuri,ContentResolvercr,ParcelFileDescriptorpfd,
BitmapFactory.Optionsoptions){
Bitmapb=null;
try{
if(pfd==null)pfd=makeInputStream(uri,cr);
if(pfd==null)returnnull;
if(options==null)options=newBitmapFactory.Options();
FileDescriptorfd=pfd.getFileDescriptor();
options.inSampleSize=1;
options.inJustDecodeBounds=true;
BitmapFactory.decodeFileDescriptor(fd,null,options);
if(options.mCancel||options.outWidth==-1
||options.outHeight==-1){
returnnull;
}
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(OutOfMemoryErrorex){
Log.e(TAG,"Gotoomexception",ex);
returnnull;
}finally{
closeSilently(pfd);
}
returnb;
}
privatestaticvoidcloseSilently(ParcelFileDescriptorc){
if(c==null)return;
try{
c.close();
}catch(Throwablet){
//donothing
}
}
privatestaticParcelFileDescriptormakeInputStream(
Uriuri,ContentResolvercr){
try{
returncr.openFileDescriptor(uri,"r");
}catch(IOExceptionex){
returnnull;
}
}
/**
*TransformsourceBitmaptotargetedwidthandheight.
*/
privatestaticBitmaptransform(Matrixscaler,
Bitmapsource,
inttargetWidth,
inttargetHeight,
intoptions){
booleanscaleUp=(options&OPTIONS_SCALE_UP)!=0;
booleanrecycle=(options&OPTIONS_RECYCLE_INPUT)!=0;
intdeltaX=source.getWidth()-targetWidth;
intdeltaY=source.getHeight()-targetHeight;
if(!scaleUp&&(deltaX<0||deltaY<0)){
/*
*Inthiscasethebitmapissmaller,atleastinonedimension,
*thanthetarget.Transformitbyplacingasmuchoftheimage
*aspossibleintothetargetandleavingthetop/bottomor
*left/right(orboth)black.
*/
Bitmapb2=Bitmap.createBitmap(targetWidth,targetHeight,
Bitmap.Config.ARGB_8888);
Canvasc=newCanvas(b2);
intdeltaXHalf=Math.max(0,deltaX/2);
intdeltaYHalf=Math.max(0,deltaY/2);
Rectsrc=newRect(
deltaXHalf,
deltaYHalf,
deltaXHalf+Math.min(targetWidth,source.getWidth()),
deltaYHalf+Math.min(targetHeight,source.getHeight()));
intdstX=(targetWidth-src.width())/2;
intdstY=(targetHeight-src.height())/2;
Rectdst=newRect(
dstX,
dstY,
targetWidth-dstX,
targetHeight-dstY);
c.drawBitmap(source,src,dst,null);
if(recycle){
source.recycle();
}
returnb2;
}
floatbitmapWidthF=source.getWidth();
floatbitmapHeightF=source.getHeight();
floatbitmapAspect=bitmapWidthF/bitmapHeightF;
floatviewAspect=(float)targetWidth/targetHeight;
if(bitmapAspect>viewAspect){
floatscale=targetHeight/bitmapHeightF;
if(scale<.9F||scale>1F){
scaler.setScale(scale,scale);
}else{
scaler=null;
}
}else{
floatscale=targetWidth/bitmapWidthF;
if(scale<.9F||scale>1F){
scaler.setScale(scale,scale);
}else{
scaler=null;
}
}
Bitmapb1;
if(scaler!=null){
//thisisusedforminithumbandcrop,sowewanttofilterhere.
b1=Bitmap.createBitmap(source,0,0,
source.getWidth(),source.getHeight(),scaler,true);
}else{
b1=source;
}
if(recycle&&b1!=source){
source.recycle();
}
intdx1=Math.max(0,b1.getWidth()-targetWidth);
intdy1=Math.max(0,b1.getHeight()-targetHeight);
Bitmapb2=Bitmap.createBitmap(
b1,
dx1/2,
dy1/2,
targetWidth,
targetHeight);
if(b2!=b1){
if(recycle||b1!=source){
b1.recycle();
}
}
returnb2;
}
/**
*SizedThumbnailBitmapcontainsthebitmap,whichisdownsampledeitherfrom
*thethumbnailinexiforthefullimage.
*mThumbnailData,mThumbnailWidthandmThumbnailHeightaresettogetheronlyifmThumbnail
*isnotnull.
*
*Thewidth/heightofthesizedbitmapmaybedifferentfrommThumbnailWidth/mThumbnailHeight.
*/
privatestaticclassSizedThumbnailBitmap{
publicbyte[]mThumbnailData;
publicBitmapmBitmap;
publicintmThumbnailWidth;
publicintmThumbnailHeight;
}
/**
*CreatesabitmapbyeitherdownsamplingfromthethumbnailinEXIForthefullimage.
*ThefunctionsreturnsaSizedThumbnailBitmap,
*whichcontainsadownsampledbitmapandthethumbnaildatainEXIFifexists.
*/
privatestaticvoidcreateThumbnailFromEXIF(StringfilePath,inttargetSize,
intmaxPixels,SizedThumbnailBitmapsizedThumbBitmap){
if(filePath==null)return;
ExifInterfaceexif=null;
byte[]thumbData=null;
try{
exif=newExifInterface(filePath);
if(exif!=null){
thumbData=exif.getThumbnail();
}
}catch(IOExceptionex){
Log.w(TAG,ex);
}
BitmapFactory.OptionsfullOptions=newBitmapFactory.Options();
BitmapFactory.OptionsexifOptions=newBitmapFactory.Options();
intexifThumbWidth=0;
intfullThumbWidth=0;
//ComputeexifThumbWidth.
if(thumbData!=null){
exifOptions.inJustDecodeBounds=true;
BitmapFactory.decodeByteArray(thumbData,0,thumbData.length,exifOptions);
exifOptions.inSampleSize=computeSampleSize(exifOptions,targetSize,maxPixels);
exifThumbWidth=exifOptions.outWidth/exifOptions.inSampleSize;
}
//ComputefullThumbWidth.
fullOptions.inJustDecodeBounds=true;
BitmapFactory.decodeFile(filePath,fullOptions);
fullOptions.inSampleSize=computeSampleSize(fullOptions,targetSize,maxPixels);
fullThumbWidth=fullOptions.outWidth/fullOptions.inSampleSize;
//ChoosethelargerthumbnailasthereturningsizedThumbBitmap.
if(thumbData!=null&&exifThumbWidth>=fullThumbWidth){
intwidth=exifOptions.outWidth;
intheight=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);
}
}
}

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