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
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
压缩前后的bitmap大小对比
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。
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