Android实现图片压缩示例代码

2019-12-12 03:59:42

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来源：转载

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核心思想是通过BitmapFactory.Options来缩放图片，主要是用到了它的inSampleSize参数（采样率）

当inSampleSize为1的时候，采样后的图片大小为图片的原始大小；

当inSampleSize为2的时候，采样后的图片的宽和高是原来的1/2，也就是说，它的像素点是原来的1/4，占的内存自然就是原来的1/4了。以此类推。

当inSampleSize小于1的时候，效果和等于1的时候是一样的。

压缩流程如下：

1.BitmapFactory.Options 的inJustDecodeBounds参数设置为true（这个时候BitmapFactory只是解析图片的原始宽高，并不会去加载图片）。

2.从BitmapFactory.Options 中取出图片的原始宽高，outWidth，outHeight。

3.根据自己的需要设置合适的采样率。

4.BitmapFactory.Options 的inJustDecodeBounds参数设置为false，然后就可以加载图片了。

下面我们看代码：

public Bitmap decodeSampledBitmapFromBytes(byte[] bytes,int reqWidth,int reqHeight){    final BitmapFactory.Options options = new BitmapFactory.Options();    options.inJustDecodeBounds = true;    BitmapFactory.decodeByteArray(bytes,0,bytes.length,options);    options.inSampleSize = calculateInSampleSize(options,reqWidth,reqHeight);    options.inJustDecodeBounds = false;    return BitmapFactory.decodeByteArray(bytes,0,bytes.length,options);  }public int calculateInSampleSize(BitmapFactory.Options options,int reqWidth,int reqHeight){    if(reqWidth == 0 || reqHeight == 0){      return 1;    }    final int width = options.outWidth;    final int height = options.outHeight;    int inSampleSize = 1;    if( width > reqWidth || height > reqHeight){      final int halfWidth = width / 2;      final int halfHeight = height / 2;      while ((halfWidth / inSampleSize) >= reqWidth && (halfHeight / inSampleSize) >= reqHeight){        inSampleSize *=2;      }    }    return inSampleSize;  }

如此一来，就完成了一张图片的压缩。另外，BitmapFactory还有其它的decode方法，我们也可以仿照上面的来写。

public Bitmap decodeSampledBitmapFromResource(Resources res,int resId,int reqWidth,int reqHeight){    final BitmapFactory.Options options = new BitmapFactory.Options();    options.inJustDecodeBounds = true;    BitmapFactory.decodeResource(res,resId,options);    options.inSampleSize = calculateInSampleSize(options,reqWidth,reqHeight);    options.inJustDecodeBounds = false;    return BitmapFactory.decodeResource(res,resId,options);  }

public Bitmap decodeSampledBitmapFromDescrptor(FileDescriptor fd,int reqWidth,int reqHeight){    final BitmapFactory.Options options = new BitmapFactory.Options();    options.inJustDecodeBounds = true;    BitmapFactory.decodeFileDescriptor(fd,null,options);    options.inSampleSize = calculateInSampleSize(options,reqWidth,reqHeight);    options.inJustDecodeBounds = false;    return BitmapFactory.decodeFileDescriptor(fd,null,options);  }

接下来结合一个小demo来实现一个完整的流程

先把图片压缩类封装起来

public class ImageResizer {  private static final String TAG = "ImageResizer";  public ImageResizer(){}  public Bitmap decodeSampledBitmapFromResource(Resources res,int resId,int reqWidth,int reqHeight){    final BitmapFactory.Options options = new BitmapFactory.Options();    options.inJustDecodeBounds = true;    BitmapFactory.decodeResource(res,resId,options);    options.inSampleSize = calculateInSampleSize(options,reqWidth,reqHeight);    options.inJustDecodeBounds = false;    return BitmapFactory.decodeResource(res,resId,options);  }  public Bitmap decodeSampledBitmapFromBytes(byte[] bytes,int reqWidth,int reqHeight){    final BitmapFactory.Options options = new BitmapFactory.Options();    Bitmap a = BitmapFactory.decodeByteArray(bytes,0,bytes.length,options);    Log.d(TAG, "before bitmap : " + a.getRowBytes() * a.getHeight());    options.inJustDecodeBounds = true;    BitmapFactory.decodeByteArray(bytes,0,bytes.length,options);    options.inSampleSize = calculateInSampleSize(options,reqWidth,reqHeight);    options.inJustDecodeBounds = false;    Bitmap b = BitmapFactory.decodeByteArray(bytes,0,bytes.length,options);    Log.d(TAG, "after bitmap : " + b.getRowBytes() * b.getHeight());    return b;  }  public Bitmap decodeSampledBitmapFromDescrptor(FileDescriptor fd,int reqWidth,int reqHeight){    final BitmapFactory.Options options = new BitmapFactory.Options();    options.inJustDecodeBounds = true;    BitmapFactory.decodeFileDescriptor(fd,null,options);    options.inSampleSize = calculateInSampleSize(options,reqWidth,reqHeight);    options.inJustDecodeBounds = false;    return BitmapFactory.decodeFileDescriptor(fd,null,options);  }  public int calculateInSampleSize(BitmapFactory.Options options,int reqWidth,int reqHeight){    if(reqWidth == 0 || reqHeight == 0){      return 1;    }    final int width = options.outWidth;    final int height = options.outHeight;    int inSampleSize = 1;    if( width > reqWidth || height > reqHeight){      final int halfWidth = width / 2;      final int halfHeight = height / 2;      while ((halfWidth / inSampleSize) >= reqWidth && (halfHeight / inSampleSize) >= reqHeight){        inSampleSize *=2;      }    }    return inSampleSize;  }}

然后就可以拿来用了：

activity_main2.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"  xmlns:tools="http://schemas.android.com/tools"  android:id="@+id/activity_main2"  android:layout_width="match_parent"  android:layout_height="match_parent"  android:paddingBottom="@dimen/activity_vertical_margin"  android:paddingLeft="@dimen/activity_horizontal_margin"  android:paddingRight="@dimen/activity_horizontal_margin"  android:paddingTop="@dimen/activity_vertical_margin"  tools:context="com.example.yuan.test.Main2Activity">  <ImageView    android:id="@+id/main2Iv"    android:layout_width="200dp"    android:layout_height="200dp" /></RelativeLayout>

Main2Activity.Java

public class Main2Activity extends AppCompatActivity {  private ImageView iv;  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main2);    initView();    testHttp(iv);  }  private void testHttp(final ImageView iv) {    new Thread(new Runnable() {      @Override      public void run() {        String urlString = "https://static.pexels.com/photos/295818/pexels-photo-295818.jpeg";        HttpURLConnection urlConnection = null;        InputStream in = null;        ByteArrayOutputStream outStream = null;        try {          URL url = new URL(urlString);          urlConnection = (HttpURLConnection) url.openConnection();          in = urlConnection.getInputStream();          byte[] buffer = new byte[1024];          int len;          outStream = new ByteArrayOutputStream();          while ((len = in.read(buffer)) != -1){            outStream.write(buffer,0,len);          }          final byte[] data = outStream.toByteArray();          runOnUiThread(new Runnable() {            @Override            public void run() { //在主线程加载UI              iv.setImageBitmap(new ImageResizer().decodeSampledBitmapFromBytes(data,200,200));            }          });        } catch (IOException e) {          e.printStackTrace();        }finally {          try {            if(urlConnection !=null){              urlConnection.disconnect();            }            if(in != null){              in.close();            }            if(outStream != null){              outStream.close();            }          } catch (IOException e) {            e.printStackTrace();          }        }      }    }).start();  }  private void initView() {    iv = (ImageView) findViewById(R.id.main2Iv);  }}

最后记得获取网络权限

运行的结果：

压缩前后的bitmap大小对比