How to Use Jni Bitmap Operations for Helping to Avoid Oom When Using Large Images

How to use JNI bitmap operations for helping to avoid OOM when using large images?

NOTE: this is a bit old code. for the most updated one, check out the project page on github.

jni/Android.mk

LOCAL_PATH := $(call my-dir)

#bitmap operations module
include $(CLEAR_VARS)

LOCAL_MODULE    := JniBitmapOperations
LOCAL_SRC_FILES := JniBitmapOperations.cpp
LOCAL_LDLIBS := -llog
LOCAL_LDFLAGS += -ljnigraphics

include $(BUILD_SHARED_LIBRARY)
APP_OPTIM := debug
LOCAL_CFLAGS := -g

#if you need to add more module, do the same as the one we started with (the one with the CLEAR_VARS)

jni/JniBitmapOperations.cpp

#include <jni.h>
#include <jni.h>
#include <android/log.h>
#include <stdio.h>
#include <android/bitmap.h>
#include <cstring>
#include <unistd.h>

#define  LOG_TAG    "DEBUG"
#define  LOGD(...)  __android_log_print(ANDROID_LOG_DEBUG,LOG_TAG,__VA_ARGS__)
#define  LOGE(...)  __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)

extern "C"
  {
  JNIEXPORT jobject JNICALL Java_com_jni_bitmap_1operations_JniBitmapHolder_jniStoreBitmapData(JNIEnv * env, jobject obj, jobject bitmap);
  JNIEXPORT jobject JNICALL Java_com_jni_bitmap_1operations_JniBitmapHolder_jniGetBitmapFromStoredBitmapData(JNIEnv * env, jobject obj, jobject handle);
  JNIEXPORT void JNICALL Java_com_jni_bitmap_1operations_JniBitmapHolder_jniFreeBitmapData(JNIEnv * env, jobject obj, jobject handle);
  JNIEXPORT void JNICALL Java_com_jni_bitmap_1operations_JniBitmapHolder_jniRotateBitmapCcw90(JNIEnv * env, jobject obj, jobject handle);
  JNIEXPORT void JNICALL Java_com_jni_bitmap_1operations_JniBitmapHolder_jniCropBitmap(JNIEnv * env, jobject obj, jobject handle, uint32_t left, uint32_t top, uint32_t right, uint32_t bottom);
  }

class JniBitmap
  {
  public:
    uint32_t* _storedBitmapPixels;
    AndroidBitmapInfo _bitmapInfo;
    JniBitmap()
      {
      _storedBitmapPixels = NULL;
      }
  };

/**crops the bitmap within to be smaller. note that no validations are done*/ //
JNIEXPORT void JNICALL Java_com_jni_bitmap_1operations_JniBitmapHolder_jniCropBitmap(JNIEnv * env, jobject obj, jobject handle, uint32_t left, uint32_t top, uint32_t right, uint32_t bottom)
  {
  JniBitmap* jniBitmap = (JniBitmap*) env->GetDirectBufferAddress(handle);
  if (jniBitmap->_storedBitmapPixels == NULL)
    return;
  uint32_t* previousData = jniBitmap->_storedBitmapPixels;
  uint32_t oldWidth = jniBitmap->_bitmapInfo.width;
  uint32_t newWidth = right - left, newHeight = bottom - top;
  uint32_t* newBitmapPixels = new uint32_t[newWidth * newHeight];
  uint32_t* whereToGet = previousData + left + top * oldWidth;
  uint32_t* whereToPut = newBitmapPixels;
  for (int y = top; y < bottom; ++y)
    {
    memcpy(whereToPut, whereToGet, sizeof(uint32_t) * newWidth);
    whereToGet += oldWidth;
    whereToPut += newWidth;
    }
  //done copying , so replace old data with new one
  delete[] previousData;
  jniBitmap->_storedBitmapPixels = newBitmapPixels;
  jniBitmap->_bitmapInfo.width = newWidth;
  jniBitmap->_bitmapInfo.height = newHeight;
  }

/**rotates the inner bitmap data by 90 degress counter clock wise*/ //
JNIEXPORT void JNICALL Java_com_jni_bitmap_1operations_JniBitmapHolder_jniRotateBitmapCcw90(JNIEnv * env, jobject obj, jobject handle)
  {
  JniBitmap* jniBitmap = (JniBitmap*) env->GetDirectBufferAddress(handle);
  if (jniBitmap->_storedBitmapPixels == NULL)
    return;
  uint32_t* previousData = jniBitmap->_storedBitmapPixels;
  AndroidBitmapInfo bitmapInfo = jniBitmap->_bitmapInfo;
  uint32_t* newBitmapPixels = new uint32_t[bitmapInfo.height * bitmapInfo.width];
  int whereToPut = 0;
  // A.D D.C
  // ...>...
  // B.C A.B
  for (int x = bitmapInfo.width - 1; x >= 0; --x)
    for (int y = 0; y < bitmapInfo.height; ++y)
      {
      uint32_t pixel = previousData[bitmapInfo.width * y + x];
      newBitmapPixels[whereToPut++] = pixel;
      }
  delete[] previousData;
  jniBitmap->_storedBitmapPixels = newBitmapPixels;
  uint32_t temp = bitmapInfo.width;
  bitmapInfo.width = bitmapInfo.height;
  bitmapInfo.height = temp;
  }

/**free bitmap*/  //
JNIEXPORT void JNICALL Java_com_jni_bitmap_1operations_JniBitmapHolder_jniFreeBitmapData(JNIEnv * env, jobject obj, jobject handle)
  {
  JniBitmap* jniBitmap = (JniBitmap*) env->GetDirectBufferAddress(handle);
  if (jniBitmap->_storedBitmapPixels == NULL)
    return;
  delete[] jniBitmap->_storedBitmapPixels;
  jniBitmap->_storedBitmapPixels = NULL;
  delete jniBitmap;
  }

/**restore java bitmap (from JNI data)*/  //
JNIEXPORT jobject JNICALL Java_com_jni_bitmap_1operations_JniBitmapHolder_jniGetBitmapFromStoredBitmapData(JNIEnv * env, jobject obj, jobject handle)
  {
  JniBitmap* jniBitmap = (JniBitmap*) env->GetDirectBufferAddress(handle);
  if (jniBitmap->_storedBitmapPixels == NULL)
    {
    LOGD("no bitmap data was stored. returning null...");
    return NULL;
    }
  //
  //creating a new bitmap to put the pixels into it - using Bitmap Bitmap.createBitmap (int width, int height, Bitmap.Config config) :
  //
  //LOGD("creating new bitmap...");
  jclass bitmapCls = env->FindClass("android/graphics/Bitmap");
  jmethodID createBitmapFunction = env->GetStaticMethodID(bitmapCls, "createBitmap", "(IILandroid/graphics/Bitmap$Config;)Landroid/graphics/Bitmap;");
  jstring configName = env->NewStringUTF("ARGB_8888");
  jclass bitmapConfigClass = env->FindClass("android/graphics/Bitmap$Config");
  jmethodID valueOfBitmapConfigFunction = env->GetStaticMethodID(bitmapConfigClass, "valueOf", "(Ljava/lang/String;)Landroid/graphics/Bitmap$Config;");
  jobject bitmapConfig = env->CallStaticObjectMethod(bitmapConfigClass, valueOfBitmapConfigFunction, configName);
  jobject newBitmap = env->CallStaticObjectMethod(bitmapCls, createBitmapFunction, jniBitmap->_bitmapInfo.width, jniBitmap->_bitmapInfo.height, bitmapConfig);
  //
  // putting the pixels into the new bitmap:
  //
  int ret;
  void* bitmapPixels;
  if ((ret = AndroidBitmap_lockPixels(env, newBitmap, &bitmapPixels)) < 0)
    {
    LOGE("AndroidBitmap_lockPixels() failed ! error=%d", ret);
    return NULL;
    }
  uint32_t* newBitmapPixels = (uint32_t*) bitmapPixels;
  int pixelsCount = jniBitmap->_bitmapInfo.height * jniBitmap->_bitmapInfo.width;
  memcpy(newBitmapPixels, jniBitmap->_storedBitmapPixels, sizeof(uint32_t) * pixelsCount);
  AndroidBitmap_unlockPixels(env, newBitmap);
  //LOGD("returning the new bitmap");
  return newBitmap;
  }

/**store java bitmap as JNI data*/  //
JNIEXPORT jobject JNICALL Java_com_jni_bitmap_1operations_JniBitmapHolder_jniStoreBitmapData(JNIEnv * env, jobject obj, jobject bitmap)
  {
  AndroidBitmapInfo bitmapInfo;
  uint32_t* storedBitmapPixels = NULL;
  //LOGD("reading bitmap info...");
  int ret;
  if ((ret = AndroidBitmap_getInfo(env, bitmap, &bitmapInfo)) < 0)
    {
    LOGE("AndroidBitmap_getInfo() failed ! error=%d", ret);
    return NULL;
    }
  LOGD("width:%d height:%d stride:%d", bitmapInfo.width, bitmapInfo.height, bitmapInfo.stride);
  if (bitmapInfo.format != ANDROID_BITMAP_FORMAT_RGBA_8888)
    {
    LOGE("Bitmap format is not RGBA_8888!");
    return NULL;
    }
  //
  //read pixels of bitmap into native memory :
  //
  //LOGD("reading bitmap pixels...");
  void* bitmapPixels;
  if ((ret = AndroidBitmap_lockPixels(env, bitmap, &bitmapPixels)) < 0)
    {
    LOGE("AndroidBitmap_lockPixels() failed ! error=%d", ret);
    return NULL;
    }
  uint32_t* src = (uint32_t*) bitmapPixels;
  storedBitmapPixels = new uint32_t[bitmapInfo.height * bitmapInfo.width];
  int pixelsCount = bitmapInfo.height * bitmapInfo.width;
  memcpy(storedBitmapPixels, src, sizeof(uint32_t) * pixelsCount);
  AndroidBitmap_unlockPixels(env, bitmap);
  JniBitmap *jniBitmap = new JniBitmap();
  jniBitmap->_bitmapInfo = bitmapInfo;
  jniBitmap->_storedBitmapPixels = storedBitmapPixels;
  return env->NewDirectByteBuffer(jniBitmap, 0);
  }

src/com/jni/bitmap_operations/JniBitmapHolder.java

package com.jni.bitmap_operations;
import java.nio.ByteBuffer;
import android.graphics.Bitmap;
import android.util.Log;

public class JniBitmapHolder
  {
  ByteBuffer _handler =null;
  static
    {
    System.loadLibrary("JniBitmapOperations");
    }

  private native ByteBuffer jniStoreBitmapData(Bitmap bitmap);

  private native Bitmap jniGetBitmapFromStoredBitmapData(ByteBuffer handler);

  private native void jniFreeBitmapData(ByteBuffer handler);

  private native void jniRotateBitmapCcw90(ByteBuffer handler);

  private native void jniCropBitmap(ByteBuffer handler,final int left,final int top,final int right,final int bottom);

  public JniBitmapHolder()
    {}

  public JniBitmapHolder(final Bitmap bitmap)
    {
    storeBitmap(bitmap);
    }

  public void storeBitmap(final Bitmap bitmap)
    {
    if(_handler!=null)
      freeBitmap();
    _handler=jniStoreBitmapData(bitmap);
    }

  public void rotateBitmapCcw90()
    {
    if(_handler==null)
      return;
    jniRotateBitmapCcw90(_handler);
    }

  public void cropBitmap(final int left,final int top,final int right,final int bottom)
    {
    if(_handler==null)
      return;
    jniCropBitmap(_handler,left,top,right,bottom);
    }

  public Bitmap getBitmap()
    {
    if(_handler==null)
      return null;
    return jniGetBitmapFromStoredBitmapData(_handler);
    }

  public Bitmap getBitmapAndFree()
    {
    final Bitmap bitmap=getBitmap();
    freeBitmap();
    return bitmap;
    }

  public void freeBitmap()
    {
    if(_handler==null)
      return;
    jniFreeBitmapData(_handler);
    _handler=null;
    }

  @Override
  protected void finalize() throws Throwable
    {
    super.finalize();
    if(_handler==null)
      return;
    Log.w("DEBUG","JNI bitmap wasn't freed nicely.please rememeber to free the bitmap as soon as you can");
    freeBitmap();
    }
  }

Rotating a bitmap using JNI & NDK

Since you're using ARGB_8888 format every pixel is an uint32_t not uint16_t. Try changing your rotated Bitmap creation to use uint32_t for source and destination arrays and it should work better.

How to avoid OutOfMemory ex while rotating the image?

Since there was no answer I assume there is no answer or maybe I just had asked the question a bit incorrectly. It looks like the only option here is to increase the app's heap size

UPDATE:

There is also another option - to work with bitmaps via NDK/JNI like here or to use Android Image-Magic lib. The Image Magic lib is pretty cool, to rotate an image all you need is:

ImageInfo imageInfo = new ImageInfo(imageFile.getAbsolutePath());
MagickImage magickImage = new MagickImage(imageInfo);
magickImage.setCompression(100); // to minimize loss
magickImage.rotateImage(90.0f).writeImage(imageInfo);

MagickImage has many other image manipulating options as well. Blur, matte, scale, charcoal and many more. However its libraries size is noticable. Authors made a great job and they covered all possible plaforms: arm64-v8a, armeabi, armeabi-v7a, mips, mips64, x86, x86_64 and final size of all these libs is over 36Mb. So you should think before adding all the libs into one apk, maybe packaging 6 different versions using manifest to filter by chipset/platform is the right way.

UPDATE

Another option is to convert Immutable Bitmap into Mutable (wrap bitmaps into MappedByteBuffer)

How to cache bitmaps into native memory

explanation

the sample code shows how to store 2 different bitmaps (small ones, but it's just a demo), recycle the original java ones, and later restore them to java instances and use them.

as you might guess, the layout has 2 imageViews. i didn't include it in the code since it's quite obvious.

do remember to change the code to your own package if you need, otherwise things won't work.

MainActivity.java - how to use:

package com.example.jnibitmapstoragetest;
...
public class MainActivity extends Activity
  {
  @Override
  protected void onCreate(final Bundle savedInstanceState)
    {
    super.onCreate(savedInstanceState);
    //
    Bitmap bitmap=BitmapFactory.decodeResource(getResources(),R.drawable.ic_launcher);
    final JniBitmapHolder bitmapHolder=new JniBitmapHolder(bitmap);
    bitmap.recycle();
    //
    Bitmap bitmap2=BitmapFactory.decodeResource(getResources(),android.R.drawable.sym_action_call);
    final JniBitmapHolder bitmapHolder2=new JniBitmapHolder(bitmap2);
    bitmap2.recycle();
    //
    setContentView(R.layout.activity_main);
      {
      bitmap=bitmapHolder.getBitmapAndFree();
      final ImageView imageView=(ImageView)findViewById(R.id.imageView1);
      imageView.setImageBitmap(bitmap);
      }
      {
      bitmap2=bitmapHolder2.getBitmapAndFree();
      final ImageView imageView=(ImageView)findViewById(R.id.imageView2);
      imageView.setImageBitmap(bitmap2);
      }
    }
  }

JniBitmapHolder.java - the "bridge" between JNI and JAVA :

package com.example.jnibitmapstoragetest;
...
public class JniBitmapHolder
  {
  ByteBuffer _handler =null;
  static
    {
    System.loadLibrary("JniBitmapStorageTest");
    }

  private native ByteBuffer jniStoreBitmapData(Bitmap bitmap);

  private native Bitmap jniGetBitmapFromStoredBitmapData(ByteBuffer handler);

  private native void jniFreeBitmapData(ByteBuffer handler);

  public JniBitmapHolder()
    {}

  public JniBitmapHolder(final Bitmap bitmap)
    {
    storeBitmap(bitmap);
    }

  public void storeBitmap(final Bitmap bitmap)
    {
    if(_handler!=null)
      freeBitmap();
    _handler=jniStoreBitmapData(bitmap);
    }

  public Bitmap getBitmap()
    {
    if(_handler==null)
      return null;
    return jniGetBitmapFromStoredBitmapData(_handler);
    }

  public Bitmap getBitmapAndFree()
    {
    final Bitmap bitmap=getBitmap();
    freeBitmap();
    return bitmap;
    }

  public void freeBitmap()
    {
    if(_handler==null)
      return;
    jniFreeBitmapData(_handler);
    _handler=null;
    }

  @Override
  protected void finalize() throws Throwable
    {
    super.finalize();
    if(_handler==null)
      return;
    Log.w("DEBUG","JNI bitmap wasn't freed nicely.please rememeber to free the bitmap as soon as you can");
    freeBitmap();
    }
  }

Android.mk - the properties file of JNI:

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := JniBitmapStorageTest
LOCAL_SRC_FILES := JniBitmapStorageTest.cpp
LOCAL_LDLIBS := -llog
LOCAL_LDFLAGS += -ljnigraphics

include $(BUILD_SHARED_LIBRARY)
APP_OPTIM := debug
LOCAL_CFLAGS := -g

JniBitmapStorageTest.cpp - the "magical" stuff goes here :

#include <jni.h>
#include <jni.h>
#include <android/log.h>
#include <stdio.h>
#include <android/bitmap.h>
#include <cstring>
#include <unistd.h>

#define  LOG_TAG    "DEBUG"
#define  LOGD(...)  __android_log_print(ANDROID_LOG_DEBUG,LOG_TAG,__VA_ARGS__)
#define  LOGE(...)  __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)

extern "C"
  {
  JNIEXPORT jobject JNICALL Java_com_example_jnibitmapstoragetest_JniBitmapHolder_jniStoreBitmapData(JNIEnv * env, jobject obj, jobject bitmap);
  JNIEXPORT jobject JNICALL Java_com_example_jnibitmapstoragetest_JniBitmapHolder_jniGetBitmapFromStoredBitmapData(JNIEnv * env, jobject obj, jobject handle);
  JNIEXPORT void JNICALL Java_com_example_jnibitmapstoragetest_JniBitmapHolder_jniFreeBitmapData(JNIEnv * env, jobject obj, jobject handle);
  }

class JniBitmap
  {
  public:
    uint32_t* _storedBitmapPixels;
    AndroidBitmapInfo _bitmapInfo;
    JniBitmap()
      {
      _storedBitmapPixels = NULL;
      }
  };

JNIEXPORT void JNICALL Java_com_example_jnibitmapstoragetest_JniBitmapHolder_jniFreeBitmapData(JNIEnv * env, jobject obj, jobject handle)
  {
  JniBitmap* jniBitmap = (JniBitmap*) env->GetDirectBufferAddress(handle);
  if (jniBitmap->_storedBitmapPixels == NULL)
    return;
  delete[] jniBitmap->_storedBitmapPixels;
  jniBitmap->_storedBitmapPixels = NULL;
  delete jniBitmap;
  }

JNIEXPORT jobject JNICALL Java_com_example_jnibitmapstoragetest_JniBitmapHolder_jniGetBitmapFromStoredBitmapData(JNIEnv * env, jobject obj, jobject handle)
  {
  JniBitmap* jniBitmap = (JniBitmap*) env->GetDirectBufferAddress(handle);
  if (jniBitmap->_storedBitmapPixels == NULL)
    {
    LOGD("no bitmap data was stored. returning null...");
    return NULL;
    }
  //
  //creating a new bitmap to put the pixels into it - using Bitmap Bitmap.createBitmap (int width, int height, Bitmap.Config config) :
  //
  //LOGD("creating new bitmap...");
  jclass bitmapCls = env->FindClass("android/graphics/Bitmap");
  jmethodID createBitmapFunction = env->GetStaticMethodID(bitmapCls, "createBitmap", "(IILandroid/graphics/Bitmap$Config;)Landroid/graphics/Bitmap;");
  jstring configName = env->NewStringUTF("ARGB_8888");
  jclass bitmapConfigClass = env->FindClass("android/graphics/Bitmap$Config");
  jmethodID valueOfBitmapConfigFunction = env->GetStaticMethodID(bitmapConfigClass, "valueOf", "(Ljava/lang/String;)Landroid/graphics/Bitmap$Config;");
  jobject bitmapConfig = env->CallStaticObjectMethod(bitmapConfigClass, valueOfBitmapConfigFunction, configName);
  jobject newBitmap = env->CallStaticObjectMethod(bitmapCls, createBitmapFunction, jniBitmap->_bitmapInfo.height, jniBitmap->_bitmapInfo.width, bitmapConfig);
  //
  // putting the pixels into the new bitmap:
  //
  int ret;
  void* bitmapPixels;
  if ((ret = AndroidBitmap_lockPixels(env, newBitmap, &bitmapPixels)) < 0)
    {
    LOGE("AndroidBitmap_lockPixels() failed ! error=%d", ret);
    return NULL;
    }
  uint32_t* newBitmapPixels = (uint32_t*) bitmapPixels;
  int pixelsCount = jniBitmap->_bitmapInfo.height * jniBitmap->_bitmapInfo.width;
  memcpy(newBitmapPixels, jniBitmap->_storedBitmapPixels, sizeof(uint32_t) * pixelsCount);
  AndroidBitmap_unlockPixels(env, newBitmap);
  //LOGD("returning the new bitmap");
  return newBitmap;
  }

JNIEXPORT jobject JNICALL Java_com_example_jnibitmapstoragetest_JniBitmapHolder_jniStoreBitmapData(JNIEnv * env, jobject obj, jobject bitmap)
  {
  AndroidBitmapInfo bitmapInfo;
  uint32_t* storedBitmapPixels = NULL;
  //LOGD("reading bitmap info...");
  int ret;
  if ((ret = AndroidBitmap_getInfo(env, bitmap, &bitmapInfo)) < 0)
    {
    LOGE("AndroidBitmap_getInfo() failed ! error=%d", ret);
    return NULL;
    }
  LOGD("width:%d height:%d stride:%d", bitmapInfo.width, bitmapInfo.height, bitmapInfo.stride);
  if (bitmapInfo.format != ANDROID_BITMAP_FORMAT_RGBA_8888)
    {
    LOGE("Bitmap format is not RGBA_8888!");
    return NULL;
    }
  //
  //read pixels of bitmap into native memory :
  //
  //LOGD("reading bitmap pixels...");
  void* bitmapPixels;
  if ((ret = AndroidBitmap_lockPixels(env, bitmap, &bitmapPixels)) < 0)
    {
    LOGE("AndroidBitmap_lockPixels() failed ! error=%d", ret);
    return NULL;
    }
  uint32_t* src = (uint32_t*) bitmapPixels;
  storedBitmapPixels = new uint32_t[bitmapInfo.height * bitmapInfo.width];
  int pixelsCount = bitmapInfo.height * bitmapInfo.width;
  memcpy(storedBitmapPixels, src, sizeof(uint32_t) * pixelsCount);
  AndroidBitmap_unlockPixels(env, bitmap);
  JniBitmap *jniBitmap = new JniBitmap();
  jniBitmap->_bitmapInfo = bitmapInfo;
  jniBitmap->_storedBitmapPixels = storedBitmapPixels;
  return env->NewDirectByteBuffer(jniBitmap, 0);
  }

JniBitmapOperations rotation causes image corruption

ok, the bug was with setting the wrong width and height for the rotation functions.

i've now updated the code. now it should work.

I am very sorry for this bug. was sure that i've fixed it before. i've now added the ability to also rotate by 180 degrees, so that you won't need to rotate twice (a little more efficient).

and just to say that the sample code wasn't for nothing, here's a nicer sample code.

it will go over all of your camera images, and rotate them in any of the 3 ways, and put the result files into Android/data/PACKAGE_NAME .

here's the code:

public class MainActivity extends Activity
  {
  @Override
  protected void onCreate(final Bundle savedInstanceState)
    {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    final File picFolder=Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DCIM);
    final int screenWidth=getResources().getDisplayMetrics().widthPixels;
    final int screenHeight=getResources().getDisplayMetrics().heightPixels;
    final File outputDir=getExternalFilesDir(null);
    final ProgressDialog progressDialog=ProgressDialog.show(this,"please wait","processing");
    new AsyncTask<Void,Void,Void>()
      {
        @Override
        protected Void doInBackground(final Void... params)
          {
          final File[] listFiles=outputDir.listFiles((FileFilter)null);
          for(final File file : listFiles)
            file.delete();
          final List<String> imageFilesPaths=new ArrayList<String>();
          getPicturesPaths(picFolder.getAbsolutePath(),imageFilesPaths);
          final JniBitmapHolder bitmapHolder=new JniBitmapHolder();
          int i=0;
          final Options options=new Options();
          for(final String filePath : imageFilesPaths)
            {
            options.inJustDecodeBounds=true;
            options.inPreferredConfig=Config.ARGB_8888;
            prepareForDownsampling(options,screenWidth,screenHeight);
            Bitmap b=BitmapFactory.decodeFile(filePath,options);
            bitmapHolder.storeBitmap(b);
            b.recycle();
            switch(i++%3)
              {
              case 0:
                bitmapHolder.rotateBitmapCw90();
                break;
              case 1:
                bitmapHolder.rotateBitmap180();
                break;
              case 2:
                bitmapHolder.rotateBitmapCcw90();
                break;
              }
            b=bitmapHolder.getBitmapAndFree();
            final File imageFile=new File(outputDir.getAbsoluteFile()+File.separator+System.currentTimeMillis()+".jpg");
            imageFile.getParentFile().mkdirs();
            FileOutputStream stream=null;
            try
              {
              stream=new FileOutputStream(imageFile);
              b.compress(CompressFormat.JPEG,80,stream);
              stream.flush();
              stream.close();
              }
            catch(final Exception e)
              {
              e.printStackTrace();
              }
            finally
              {
              if(stream!=null)
                try
                  {
                  stream.close();
                  }
                catch(final IOException e)
                  {
                  e.printStackTrace();
                  }
              }
            }
          return null;
          }

        @Override
        protected void onPostExecute(final Void result)
          {
          super.onPostExecute(result);
          progressDialog.dismiss();
          finish();
          }
      }.execute();
    }

  private static void prepareForDownsampling(final Options bitmapOptions,final int reqWidth,final int reqHeight)
    {
    final int inSampleSize=calculateInSampleSize(bitmapOptions,reqWidth,reqHeight);
    // as much as possible, use google's way to downsample:
    bitmapOptions.inSampleSize=1;
    bitmapOptions.inDensity=1;
    bitmapOptions.inTargetDensity=1;
    bitmapOptions.inJustDecodeBounds=false;
    while(bitmapOptions.inSampleSize*2<=inSampleSize)
      bitmapOptions.inSampleSize*=2;
    // if google's way to downsample isn't enough, do some more :
    if(bitmapOptions.inSampleSize!=inSampleSize)
      {
      // downsample by bitmapOptions.inSampleSize/originalSampleSize .
      bitmapOptions.inTargetDensity=bitmapOptions.inSampleSize;
      bitmapOptions.inDensity=inSampleSize;
      }
    }

  public static int calculateInSampleSize(final BitmapFactory.Options options,final int reqWidth,final int reqHeight)
    {
    final int height=options.outHeight;
    final int width=options.outWidth;
    int inSampleSize=1;
    if(height>reqHeight||width>reqWidth)
      {
      final int heightRatio=Math.round((float)height/(float)reqHeight);
      final int widthRatio=Math.round((float)width/(float)reqWidth);
      inSampleSize=heightRatio<widthRatio ? heightRatio : widthRatio;
      }
    return Math.max(inSampleSize,1);
    }

  private static void getPicturesPaths(final String path,final List<String> filesPaths)
    {
    final Options options=new Options();
    options.inJustDecodeBounds=true;
    File f=new File(path);
    if(f.isFile())
      {
      BitmapFactory.decodeFile(path,options);
      if(options.outHeight>=0&&options.outWidth>=0)
        filesPaths.add(path);
      return;
      }
    if(!f.isDirectory())
      return;
    final String[] childrenPaths=f.list();
    for(final String fileName : childrenPaths)
      {
      if(fileName.startsWith("."))
        continue;
      f=new File(path+File.separator+fileName);
      final String fullFilePath=f.getAbsolutePath();
      if(f.isFile())
        {
        BitmapFactory.decodeFile(fullFilePath,options);
        if(options.outHeight>=0&&options.outWidth>=0)
          filesPaths.add(fullFilePath);
        continue;
        }
      getPicturesPaths(fullFilePath,filesPaths);
      }
    }
  }

Rotate the image as per the passed orientation to the functions using Native Code

The code I've made already supports rotation. just look at the sample project to see how to call it.

Also, gray scaling shouldn't be a too hard operation to implement on the C++ code I've made. I'm sure there are examples of it on the Internet.

About downsampling, I didn't make it as it's a lot of work, but I have added scaling of images that are already decoded (meaning they are stored as bitmap objects).
However, you can always downscale using the normal Google's way , or my way (the bottom code).

How to solve java.lang.OutOfMemoryError trouble in Android

You can't increase the heap size dynamically but you can request to use more by using.

android:largeHeap="true"

in the manifest.xml,you can add in your manifest these lines it is working for some situations.

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:largeHeap="true"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">

Whether your application's processes should be created with a large Dalvik heap. This applies to all processes created for the application. It only applies to the first application loaded into a process; if you're using a shared user ID to allow multiple applications to use a process, they all must use this option consistently or they will have unpredictable results.
Most apps should not need this and should instead focus on reducing their overall memory usage for improved performance. Enabling this also does not guarantee a fixed increase in available memory, because some devices are constrained by their total available memory.

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To query the available memory size at runtime, use the methods getMemoryClass() or getLargeMemoryClass().

If still facing problem then this should also work

 BitmapFactory.Options options = new BitmapFactory.Options();
 options.inSampleSize = 8;
 mBitmapInsurance = BitmapFactory.decodeFile(mCurrentPhotoPath,options);

If set to a value > 1, requests the decoder to subsample the original image, returning a smaller image to save memory.

This is the optimal use of BitmapFactory.Options.inSampleSize with regards to speed of displaying the image.
The documentation mentions using values that are a power of 2, so I am working with 2, 4, 8, 16 etc.

Lets get more deeper to Image Sampling:

For example, it’s not worth loading a 1024x768 pixel image into memory if it will eventually be displayed in a 128x128 pixel thumbnail in an ImageView.

To tell the decoder to subsample the image, loading a smaller version into memory, set inSampleSize to true in your BitmapFactory.Options object. For example, an image with resolution 2100 x 1500 pixels that is decoded with an inSampleSize of 4 produces a bitmap of approximately 512x384. Loading this into memory uses 0.75MB rather than 12MB for the full image (assuming a bitmap configuration of ARGB_8888). Here’s a method to calculate a sample size value that is a power of two based on a target width and height:

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;
}

Note: A power of two value is calculated because the decoder uses a
final value by rounding down to the nearest power of two, as per the
inSampleSize documentation.

To use this method, first decode with inJustDecodeBounds set to true, pass the options through and then decode again using the new.

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