关于android 图片加载压缩处理
android应用对图片处理算是比较频繁的了，尤其是在程序加载大量图片和高分辨率图片时，最容易产生oom异常，下面是个人平时一些省内存加载方法
resoursce加载
public Bitmap ReadBitMap(Context context, int resId){
BitmapFactory.Options opt = new BitmapFactory.Options();
opt.inPreferredConfig = Bitmap.Config.RGB_565; //小于ARGB_8888 样式大小
opt.inPurgeable = true;
opt.inInputShareable = true;
//获取资源图片
InputStream is = context.getResources().openRawResource(resId);
return BitmapFactory.decodeStream(is,null,opt);
}
计算bitmap内存大小：
int calculateBitmapSize(Bitmap candidate,Resources res, int resId){
BitmapFactory.Options targetOptions=new BitmapFactory.Options();
targetOptions.inJustDecodeBounds = true;
BitmapFactory.decodeResource(res, resId, targetOptions);
int width = targetOptions.outWidth / targetOptions.inSampleSize;
int height = targetOptions.outHeight / targetOptions.inSampleSize;
int byteCount = width * height * getBytesPerPixel(candidate.getConfig());
return byteCount;
}
/**
* A helper function to return the byte usage per pixel of a bitmap based on its configuration.
*/
static int getBytesPerPixel(Config config) {
if (config == Config.ARGB_8888) {
return 4;
} else if (config == Config.RGB_565) {
return 2;
} else if (config == Config.ARGB_4444) {
return 2;
} else if (config == Config.ALPHA_8) {
return 1;
}
return 1;
}
指定尺寸压缩：
public static int calculateInSampleSize(
BitmapFactory.Options options, int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;
if (height > reqHeight || width > reqWidth) {
final int halfHeight = height / 2;
final int halfWidth = width / 2;
// Calculate the largest inSampleSize value that is a power of 2 and keeps both
// height and width larger than the requested height and width.
while ((halfHeight / inSampleSize) > reqHeight
&& (halfWidth / inSampleSize) > reqWidth) {
inSampleSize *= 2;
}
}
return inSampleSize;
}
public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId,
int reqWidth, int reqHeight) {
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(res, resId, options);
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
return BitmapFactory.decodeResource(res, resId, options);
}
如果你的控件大小小于原始图片大小，那么就需要对图片进行压缩处理，来减少内存使用。
现在知道了原图片的尺寸，根据实际情况决定你要加载它缩小多少倍后的图片。例如你用一个128x96的ImageView显示一张1024x768的原图，根本没有必要把原图读加载到内存。
加载一张缩小后的图片到内存，只需要把BitmapFactory.Options对象的inSampleSize设为true，
然后给inSampleSize设一个值就行了（可以理解inSampleSize为n，图片就缩小到1/n大小）。
public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId,
int reqWidth, int reqHeight) {
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(res, resId, options);
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
return BitmapFactory.decodeResource(res, resId, options);
}
public static int calculateInSampleSize(
BitmapFactory.Options options, int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;
if (height > reqHeight || width > reqWidth) {
if (width > height) {
inSampleSize = Math.round((float)height / (float)reqHeight);
} else {
inSampleSize = Math.round((float)width / (float)reqWidth);
}
}
return inSampleSize;
}
官方压缩计算：更新2016-07-16
public static int calculateInSampleSize(
BitmapFactory.Options options, int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;
if (height > reqHeight || width > reqWidth) {
final int halfHeight = height / 2;
final int halfWidth = width / 2;
// Calculate the largest inSampleSize value that is a power of 2 and keeps both
// height and width larger than the requested height and width.
while ((halfHeight / inSampleSize) >= reqHeight
&& (halfWidth / inSampleSize) >= reqWidth) {
inSampleSize *= 2;
}
}
return inSampleSize;
}
public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId,
int reqWidth, int reqHeight) {
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(res, resId, options);
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
return BitmapFactory.decodeResource(res, resId, options);
}
2017-5-26更新参考picasso计算图形拉伸处理
static void calculateInSampleSize(int reqWidth, int reqHeight, BitmapFactory.Options options,
boolean centerInside) {
calculateInSampleSize(reqWidth, reqHeight, options.outWidth, options.outHeight, options,
centerInside);
}
static void calculateInSampleSize(int reqWidth, int reqHeight, int width, int height,
BitmapFactory.Options options, boolean centerInside) {
int sampleSize = 1;
if (height > reqHeight || width > reqWidth) {
final int heightRatio;
final int widthRatio;
if (reqHeight == 0) {
sampleSize = (int) Math.floor((float) width / (float) reqWidth);
} else if (reqWidth == 0) {
sampleSize = (int) Math.floor((float) height / (float) reqHeight);
} else {
heightRatio = (int) Math.floor((float) height / (float) reqHeight);
widthRatio = (int) Math.floor((float) width / (float) reqWidth);
sampleSize = centerInside
? Math.max(heightRatio, widthRatio)
: Math.min(heightRatio, widthRatio);
}
}
options.inSampleSize = sampleSize;
options.inJustDecodeBounds = false;
}
use:
void useCalucateBitmapCompress(){
if (calculateSize) {
BitmapFactory.decodeStream(stream, null, options);
calculateInSampleSize(request.targetWidth, request.targetHeight, options,
true);
}
Bitmap bitmap = BitmapFactory.decodeStream(stream, null, options);
if (bitmap == null) {
// Treat null as an IO exception, we will eventually retry.
throw new IOException("Failed to decode stream.");
}
return bitmap;
}
使用内存缓存
对于缓存，没有大小或者规则适用于所有应用，它依赖于你分析自己应用的内存使用确定自己的方案。
缓存太小可能只会增加额外的内存使用，缓存太大可能会导致内存溢出或者应用其它模块可使用内存太小
private LruCache<String, Bitmap> mMemoryCache;
@Override
protected void onCreate(Bundle savedInstanceState) {
...
// Get max available VM memory, exceeding this amount will throw an
// OutOfMemory exception. Stored in kilobytes as LruCache takes an
// int in its constructor.
final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
// Use 1/8th of the available memory for this memory cache.
final int cacheSize = maxMemory / 8;
mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {
@Override
protected int sizeOf(String key, Bitmap bitmap) {
// The cache size will be measured in kilobytes rather than
// number of items.
return bitmap.getByteCount() / 1024;
}
};
...
}
public void addBitmapToMemoryCache(String key, Bitmap bitmap) {
if (getBitmapFromMemCache(key) == null) {
mMemoryCache.put(key, bitmap);
}
}
public Bitmap getBitmapFromMemCache(String key) {
return mMemoryCache.get(key);
}
使用磁盘缓存
你的应用也有可能被其他任务打断，如电话呼入，应用在后台有可能会被结束，这样缓存的数据也会丢失。
当用户回到应用时，所有的图片还需要重新获取一遍。
磁盘缓存可应用到这种场景中，它可以减少你获取图片的次数，当然，从磁盘获取图片比从内存中获取要慢的多，所以它需要在非UI线程中完成。
示例代码中是磁盘缓存的一个实现，在Android4.0源码中（libcore/luni/src/main/java/libcore/io/DiskLruCache.java），
有更加强大和推荐的一个实现，它的向后兼容使在已发布过的库中很方便使用它
private DiskLruCache mDiskCache;
private static final int DISK_CACHE_SIZE = 1024 * 1024 * 10; // 10MB
private static final String DISK_CACHE_SUBDIR = "thumbnails";
@Override
protected void onCreate(Bundle savedInstanceState) {
...
// Initialize memory cache
...
File cacheDir = getCacheDir(this, DISK_CACHE_SUBDIR);
mDiskCache = DiskLruCache.openCache(this, cacheDir, DISK_CACHE_SIZE);
...
}
class BitmapWorkerTask extends AsyncTask {
...
// Decode image in background.
@Override
protected Bitmap doInBackground(Integer... params) {
final String imageKey = String.valueOf(params[0]);
// Check disk cache in background thread
Bitmap bitmap = getBitmapFromDiskCache(imageKey);
if (bitmap == null) { // Not found in disk cache
// Process as normal
final Bitmap bitmap = decodeSampledBitmapFromResource(
getResources(), params[0], 100, 100));
}
// Add final bitmap to caches
addBitmapToCache(String.valueOf(imageKey, bitmap);
return bitmap;
}
...
}
public void addBitmapToCache(String key, Bitmap bitmap) {
// Add to memory cache as before
if (getBitmapFromMemCache(key) == null) {
mMemoryCache.put(key, bitmap);
}
// Also add to disk cache
if (!mDiskCache.containsKey(key)) {
mDiskCache.put(key, bitmap);
}
}
public Bitmap getBitmapFromDiskCache(String key) {
return mDiskCache.get(key);
}
// Creates a unique subdirectory of the designated app cache directory. Tries to use external
// but if not mounted, falls back on internal storage.
public static File getCacheDir(Context context, String uniqueName) {
// Check if media is mounted or storage is built-in, if so, try and use external cache dir
// otherwise use internal cache dir
final String cachePath = Environment.getExternalStorageState() == Environment.MEDIA_MOUNTED
|| !Environment.isExternalStorageRemovable() ?
context.getExternalCacheDir().getPath() : context.getCacheDir().getPath();
return new File(cachePath + File.separator + uniqueName);
}
2019-10-14，相机图片压缩并旋转
private fun getBitmap(uri: Uri): Bitmap? {
var ism: InputStream? = null
var returnedBitmap: Bitmap? = null
try {
// ism = mContentResolver!!.openInputStream(uri)
val f = File(uri.path)
if(false==f.exists()){
return null
}
ism = FileInputStream(f)
//Decode image size
val o = BitmapFactory.Options()
o.inJustDecodeBounds = true
BitmapFactory.decodeStream(ism, null, o)
ism!!.close()
// BitmapFactory.decodeFile(f.path, o)
var scale = 1
if (o.outHeight > IMAGE_MAX_SIZE || o.outWidth > IMAGE_MAX_SIZE) {
scale = Math.pow(2.0, Math.round(Math.log(IMAGE_MAX_SIZE / Math.max(o.outHeight, o.outWidth).toDouble()) / Math.log(0.5)).toInt().toDouble()).toInt()
}
o.inSampleSize = scale
o.inJustDecodeBounds = false
// val o2 = BitmapFactory.Options()
// o2.inSampleSize = scale
// o2.inJustDecodeBounds = false
// ism = mContentResolver!!.openInputStream(uri)
// val inputStream = FileInputStream(f)
// val bytes = readStream(inputStream)
// val bitmap = BitmapFactory.decodeByteArray(bytes, 0, bytes.size,o2)
// val bitmap = BitmapFactory.decodeStream(inputStream, null, o2)
val loadBitmap = BitmapFactory.decodeFile(f.path, o)
// ism!!.close()
returnedBitmap = fixOrientationBugOfProcessedBitmap(bitmap)
return returnedBitmap
// return loadBitmap
} catch (e: FileNotFoundException) {
Log.d(TAG, "FileNotFoundException")
} catch (e: IOException) {
Log.d(TAG, "IOException")
}
return null
}
private fun fixOrientationBugOfProcessedBitmap(bitmap: Bitmap?): Bitmap? {
try {
if (getCameraPhotoOrientation(this, Uri.parse(mFileTemp!!.path)) == 0) {
return bitmap
} else {
val matrix = Matrix()
matrix.postRotate(getCameraPhotoOrientation(this, Uri.parse(mFileTemp!!.path)).toFloat())
// recreate the new Bitmap and set it back
return Bitmap.createBitmap(bitmap!!, 0, 0, bitmap.width, bitmap.height, matrix, true)
}
} catch (ex: Exception) {
ex.printStackTrace()
return null
}
}
