編輯:關於Android編程
核心思想是通過BitmapFactory.Options來縮放圖片,主要是用到了它的inSampleSize參數(采樣率)
當inSampleSize為1的時候,采樣後的圖片大小為圖片的原始大小;
當inSampleSize為2的時候,采樣後的圖片的寬和高是原來的1/2,也就是說,它的像素點是原來的1/4,占的內存自然就是原來的1/4了。以此類推。
當inSampleSize小於1的時候,效果和等於1的時候是一樣的。
壓縮流程如下:
1.BitmapFactory.Options 的inJustDecodeBounds參數設置為true(這個時候BitmapFactory只是解析圖片的原始寬高,並不會去加載圖片)。
2.從BitmapFactory.Options 中取出圖片的原始寬高,outWidth,outHeight。
3.根據自己的需要設置合適的采樣率。
4.BitmapFactory.Options 的inJustDecodeBounds參數設置為false,然後就可以加載圖片了。
下面我們看代碼:
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; }
如此一來,就完成了一張圖片的壓縮。另外,BitmapFactory還有其它的decode方法,我們也可以仿照上面的來寫。
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); }
接下來結合一個小demo來實現一個完整的流程
先把圖片壓縮類封裝起來
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; } }
然後就可以拿來用了:
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() { //在主線程加載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); } }
最後記得獲取網絡權限
運行的結果:
壓縮前後的bitmap大小對比
壓縮前後的bitmap大小對比
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