Android 图片缩放汇总

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。

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
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<?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>

[java] view
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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：

[java] view
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/*

* 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);

}

}

}