Android图片缩放

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();
}
}
}

转自：/article/1516584.html