Android开发 Bitmap图像处理详解

戴斌發表於 2020-8-26 17:43:00

<h1>前言</h1>
　　Bitmap开发涉及到方方面面，比如裁剪图片，压缩图片，镜像图片，旋转图片，各种转存图片等等，是必需掌握Android开发技巧，Android开发提供了2个类来实现这些需求，Bitmap类与BitmapFactory类。此博客会持续更新各种实际需求。
<h1>将Res位图资源转成Bitmap</h1>
请注意，使用这个方法会出现Bitmap为null的问题。这个问题可能是因为资源id异常引起的。特别是你使用了分module形式构建的app
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<pre>Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher);</pre>
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<h1>将指定文件转成Bitmap</h1>
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<pre>Bitmap bitmap = BitmapFactory.decodeFile(getContext().getExternalCacheDir() + File.separator + "demo1.png");</pre>
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<h1>将Drawable矢量图资源转成Bitmap</h1>
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<pre> public static Bitmap getBitmapFromDrawable(Context context, @DrawableRes int drawableId) {
 Drawable drawable = ContextCompat.getDrawable(context, drawableId);
 if (drawable instanceof BitmapDrawable) {
 return ((BitmapDrawable) drawable).getBitmap();
 } else if (drawable instanceof VectorDrawable || drawable instanceof VectorDrawableCompat) {
 Bitmap bitmap = Bitmap.createBitmap(drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight(), Bitmap.Config.ARGB_8888);
 Canvas canvas = new Canvas(bitmap);
 drawable.setBounds(0, 0, canvas.getWidth(), canvas.getHeight());
 drawable.draw(canvas);
 return bitmap;
 } else {
 throw new IllegalArgumentException("unsupported drawable type");
 }
}</pre>
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<h1>将Uri转成Bitmap</h1>
<div class="cnblogs_code">
<pre> @Override
public void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
 super.onActivityResult(requestCode, resultCode, data);
 //相册选择图片
 if (requestCode == GALLERY_RESULT_CODE && resultCode == RESULT_OK) {
 final Uri uri = data.getData();
 try (InputStream inputStream = getActivity().getApplicationContext().getContentResolver().openInputStream(uri)) {
 Bitmap bitmap = BitmapFactory.decodeStream(inputStream);//得到bitmap
 } catch (FileNotFoundException e) {
 e.printStackTrace();
 } catch (IOException e) {
 e.printStackTrace();
 }
 return;
 }
}</pre>
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<h1>将Bitmap输出成文件 </h1>
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<pre>　　　　　　　　 Bitmap bitmap = BitmapFactory.decodeFile(getContext().getExternalCacheDir() + File.separator + "demo1.png");
 File file = new File(getContext().getExternalCacheDir(), "demo.jpg");
 try (FileOutputStream fileOutputStream = new FileOutputStream(file)) {
 //参数1：输出的图片格式参数2：输出图片的压缩质量(范围值为0-100) 参数3：输出流
 bitmap.compress(Bitmap.CompressFormat.JPEG, 90, fileOutputStream);
 } catch (FileNotFoundException e) {
 e.printStackTrace();
 } catch (IOException e) {
 e.printStackTrace();
 }</pre>
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<h1>镜像垂直翻转</h1>
<div class="cnblogs_code">
<pre> Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher);
 Matrix matrix = new Matrix();
 matrix.postScale(1, -1); //镜像垂直翻转
 Bitmap changBitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, false); </pre>
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<h1>镜像水平翻转</h1>
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<pre> Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher);
 Matrix matrix = new Matrix();
 matrix.postScale(-1, 1); //镜像水平翻转
 Bitmap changBitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, false);
 mBinding.weatherIcon.setImageBitmap(changBitmap);</pre>
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<h1>旋转图片</h1>
<div class="cnblogs_code">
<pre> Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher);
 Matrix matrix = new Matrix();
 matrix.postRotate(-90);//旋转-90度
 Bitmap changBitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, false);
 mBinding.weatherIcon.setImageBitmap(changBitmap);</pre>
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<h1>压缩图片质量，降低图片存储大小</h1>
原理其实很简单就是利用compress方法，一点一点的降低图片质量，最后压缩到需要的目标存储大小
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<pre> /**
* 压缩图片
* @param bitmap bitmap图片压缩
* @param targetKB 目标压缩大小
* @return
*/
private Bitmap compressImage(Bitmap bitmap, int targetKB){
 Bitmap outBitmap = null;
 ByteArrayInputStream bais = null;
 ByteArrayOutputStream baos = null;
 try {
 baos = new ByteArrayOutputStream();
 int quality = 80;
 bitmap.compress(Bitmap.CompressFormat.JPEG, quality, baos);
 while ((baos.toByteArray().length/1024) > targetKB){
 quality = quality-10;
 baos.reset();
 bitmap.compress(Bitmap.CompressFormat.JPEG,quality,baos);
 }
 bais = new ByteArrayInputStream(baos.toByteArray());
 outBitmap = BitmapFactory.decodeStream(bais);
 bais.close();
 baos.close();
 } catch (Exception e) {
 e.printStackTrace();
 onError(e);
 } finally {
 try {
 bais.close();
 baos.close();
 } catch (IOException e) {
 e.printStackTrace();
 }

 }
 return outBitmap;

}</pre>
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<h1>压缩图片尺寸</h1>
原理是利用BitmapFactory.decodeStream方法，传入options，以降幂的方式等比例的压缩到目标尺寸，关键是options.inSampleSize = be;这个属性的配置
 
<div class="cnblogs_code">
<pre>/**
* 尺寸压缩
* @param bitmap
*/
private Bitmap sizeCompres(Bitmap bitmap,float targetWidth,float targetHeight){
 Bitmap handleBitmap = null;
 try {
 ByteArrayOutputStream baos = new ByteArrayOutputStream();
 bitmap.compress(Bitmap.CompressFormat.JPEG,100,baos);
 // 判断如果图片大于1M,进行压缩避免在生成图片（BitmapFactory.decodeStream）时溢出
 if (baos.toByteArray().length / 1024 > 1024) {
 baos.reset();// 重置baos即清空baos
 bitmap.compress(Bitmap.CompressFormat.JPEG, 50, baos);// 这里压缩50%，把压缩后的数据存放到baos中
 }
 ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
 BitmapFactory.Options options = new BitmapFactory.Options();
 options.inJustDecodeBounds = true;
 BitmapFactory.decodeStream(bais,null,options);
 options.inJustDecodeBounds = false;
 int imageWidth = options.outWidth;
 int imageHeight = options.outHeight;
 int be = 1;
 if (imageWidth>imageHeight && imageWidth>targetWidth){
 be = Math.round(imageWidth/targetWidth);

 }else if (imageHeight>imageWidth && imageHeight>targetHeight){
 be = Math.round(imageHeight/targetHeight);
 }
 if (be <= 1){
 be =1;//如果小于1等于1就不需要压缩直接返回
 }
 options.inSampleSize = be;
 bais = new ByteArrayInputStream(baos.toByteArray());//bais运行到这里可能已经清空了，所以需要再次添加
 handleBitmap = BitmapFactory.decodeStream(bais,null,options);
 bais.close();
 baos.close();
 } catch (Exception e) {
 e.printStackTrace();
 }
 return handleBitmap;

}</pre>
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<h1>获取图片的角度属性与将图片角度属性设置回去</h1>
获取图片的角度属性很重要，这里说明下，因为我们在压缩或者读取图片成Bitmap后在保存到文件里会丢失图片的角度，这样下次在查看这张图片的时候极有可能是倒的图片
<div class="cnblogs_code">
<pre>try {
 ExifInterface exifInterface = new ExifInterface(inpPath);//获取图片角度
 mDegrees = exifInterface.getAttributeInt(ExifInterface.TAG_ORIENTATION, -1);
 int angle = exifInterface.getAttributeInt(ExifInterface.TAG_ORIENTATION, -1);
 switch (angle){
 case ExifInterface.ORIENTATION_ROTATE_270:
 mDegrees = 270;

 break;
 case ExifInterface.ORIENTATION_ROTATE_180:
 mDegrees = 180;

 break;
 case ExifInterface.ORIENTATION_ROTATE_90:
 mDegrees = 90;

 break;
 default:
 mDegrees = 0;
 break;
 }
 } catch (IOException e) {
 e.printStackTrace();
 }</pre>
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 将图片角度设置回去
<div class="cnblogs_code">
<pre> 　　　　 Matrix matrix = new Matrix();
 matrix.setRotate(mDegrees, bitmap.getWidth(), bitmap.getHeight());
 Bitmap finishBitmap = Bitmap.createBitmap(finishBitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix,true);</pre>
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本文来自博客园，作者：观心静，转载请注明原文链接：https://www.cnblogs.com/guanxinjing/p/13566480.html 
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来源：https://www.cnblogs.com/guanxinjing/p/13566480.html

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Android开发 Bitmap图像处理详解