Android NDK开发-图片的压缩（libjpeg）

动态库的编译

1. 首先要安装ndk的环境，前面的文章里面有提到，这里就不再赘述了。

2. 下载jpeg的源码链接，只需要将jni的部分上传到服务器上面，新建一个文件夹将jni拷贝进去，在jni文件夹中执行ndk build这时候就会生成动态库和一些必要的文件。
   

3. 接下来就是编码的时间。

实现图片的压缩

1.图片的压缩这个项目我用的是eclipse编辑器，同样的需要下载ndk的工具包，这个网上的资源比较多，这里就不再多说了。新建项目后，在项目的根目录下面新建jni文件夹，将我们生成的动态库和头文件拷贝进去，然后与ndk联系起来，右键项目点击Android Tools -》Add Native Support。这样就可以进行NDK开发了。项目的结构如下。

2.接下来就是代码，这里就不在一一讲解了，都比较的简单。
NativeUtil 类

/*
 * Copyright 2014 http://Bither.net
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package net.bither.util;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileOutputStream;

import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Rect;
import android.util.Log;

public class NativeUtil {
     private static int DEFAULT_QUALITY = 95;

        /**
         * @param bit      bitmap对象
         * @param fileName 指定保存目录名
         * @param optimize 是否采用哈弗曼表数据计算 品质相差5-10倍
         * @Description: JNI基本压缩
         */
        public static void compressBitmap(Bitmap bit, String fileName, boolean optimize) {
            saveBitmap(bit, DEFAULT_QUALITY, fileName, optimize);
        }

        /**
         * @param image    bitmap对象
         * @param filePath 要保存的指定目录
         * @Description: 通过JNI图片压缩把Bitmap保存到指定目录
         */
        public static void compressBitmap(Bitmap image, String filePath) {
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            // 质量压缩方法，这里100表示不压缩，把压缩后的数据存放到baos中
            int options = 20;
            // JNI调用保存图片到SD卡 这个关键
            NativeUtil.saveBitmap(image, options, filePath, true);
        }

        /**
         * 计算缩放比
         *
         * @param bitWidth  当前图片宽度
         * @param bitHeight 当前图片高度
         * @return
         * @Description:函数描述
         */
        public static int getRatioSize(int bitWidth, int bitHeight) {
            // 图片最大分辨率
            int imageHeight = 1920;
            int imageWidth = 1080;
            // 缩放比
            int ratio = 1;
            // 缩放比,由于是固定比例缩放，只用高或者宽其中一个数据进行计算即可
            if (bitWidth > bitHeight && bitWidth > imageWidth) {
                // 如果图片宽度比高度大,以宽度为基准
                ratio = bitWidth / imageHeight;
            } else if (bitWidth < bitHeight && bitHeight > imageHeight) {
                // 如果图片高度比宽度大，以高度为基准
                ratio = bitHeight / imageHeight;
            }
            // 最小比率为1
            if (ratio <= 0)
                ratio = 1;
            return ratio;
        }

        /**
         * 调用native方法
         *
         * @param bit
         * @param quality
         * @param fileName
         * @param optimize
         * @Description:函数描述
         */
        public static void saveBitmap(Bitmap bit, int quality, String fileName, boolean optimize) {
            compressBitmap(bit, bit.getWidth(), bit.getHeight(), quality, fileName.getBytes(), optimize);
        }

        /**
         * 调用底层 bitherlibjni.c中的方法
         *
         * @param bit
         * @param w
         * @param h
         * @param quality
         * @param fileNameBytes
         * @param optimize
         * @return
         * @Description:函数描述
         */
        public static native String compressBitmap(Bitmap bit, int w, int h, int quality, byte[] fileNameBytes,
                                                    boolean optimize);

        /**
         * 加载lib下两个so文件
         */
        static {
            System.loadLibrary("jpegbither");
            System.loadLibrary("bitherjni");
        }


        /**
         * 1. 质量压缩
                 设置bitmap options属性，降低图片的质量，像素不会减少
                 第一个参数为需要压缩的bitmap图片对象，第二个参数为压缩后图片保存的位置
                 设置options 属性0-100，来实现压缩
         * @param bmp
         * @param file
         */
        public static void compressImageToFile(Bitmap bmp,File file) {
            // 0-100 100为不压缩
            int options = 20;
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            // 把压缩后的数据存放到baos中
            bmp.compress(Bitmap.CompressFormat.JPEG, options, baos);
            try {
                FileOutputStream fos = new FileOutputStream(file);
                fos.write(baos.toByteArray());
                fos.flush();
                fos.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        /**
         *
         * 2. 尺寸压缩
         通过缩放图片像素来减少图片占用内存大小
         * @param bmp
         * @param file
         */

        public static void compressBitmapToFile(Bitmap bmp, File file){
            // 尺寸压缩倍数,值越大，图片尺寸越小
            int ratio = 8;
            // 压缩Bitmap到对应尺寸
            Bitmap result = Bitmap.createBitmap(bmp.getWidth() / ratio, bmp.getHeight() / ratio, Config.ARGB_8888);
            Canvas canvas = new Canvas(result);
            Rect rect = new Rect(0, 0, bmp.getWidth() / ratio, bmp.getHeight() / ratio);
            canvas.drawBitmap(bmp, null, rect, null);

            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            // 把压缩后的数据存放到baos中
            result.compress(Bitmap.CompressFormat.JPEG, 100 ,baos);
            try {
                FileOutputStream fos = new FileOutputStream(file);
                fos.write(baos.toByteArray());
                fos.flush();
                fos.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }


        /**
         * 设置图片的采样率，降低图片像素
         * @param filePath
         * @param file
         */
        public static void compressBitmap(String filePath, File file){
            // 数值越高，图片像素越低
            int inSampleSize = 8;
            BitmapFactory.Options options = new BitmapFactory.Options();
            options.inJustDecodeBounds = false;
//          options.inJustDecodeBounds = true;//为true的时候不会真正加载图片，而是得到图片的宽高信息。
            //采样率
            options.inSampleSize = inSampleSize;
            Bitmap bitmap = BitmapFactory.decodeFile(filePath, options);

            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            // 把压缩后的数据存放到baos中
            bitmap.compress(Bitmap.CompressFormat.JPEG, 100 ,baos);
            try {
                if(file.exists())
                {
                    file.delete();
                }
                else {
                    file.createNewFile();
                }
                FileOutputStream fos = new FileOutputStream(file);
                fos.write(baos.toByteArray());
                fos.flush();
                fos.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
}

头文件

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class net_bither_util_Test */


#ifdef __cplusplus
extern "C" {
#endif
JNIEXPORT jstring JNICALL Java_net_bither_util_NativeUtil_compressBitmap(JNIEnv*,
        jclass, jobject , int , int , int ,
        jbyteArray , jboolean );

#ifdef __cplusplus
}
#endif

/*
 * Copyright 2014 http://Bither.net
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "bitherlibjni.h"
#include <string.h>
#include <android/bitmap.h>
#include <android/log.h>
#include <stdio.h>
#include <setjmp.h>
#include <math.h>
#include <stdint.h>
#include <time.h>

//统一编译方式
extern "C" {
#include "jpeg/jpeglib.h"
#include "jpeg/cdjpeg.h"        /* Common decls for cjpeg/djpeg applications */
#include "jpeg/jversion.h"      /* for version message */
#include "jpeg/android/config.h"
}


#define LOG_TAG "jni"
#define LOGW(...)  __android_log_write(ANDROID_LOG_WARN,LOG_TAG,__VA_ARGS__)
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO,LOG_TAG,__VA_ARGS__)
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)

#define true 1
#define false 0

typedef uint8_t BYTE;

char *error;
struct my_error_mgr {
  struct jpeg_error_mgr pub;
  jmp_buf setjmp_buffer;
};

typedef struct my_error_mgr * my_error_ptr;

METHODDEF(void)
my_error_exit (j_common_ptr cinfo)
{
  my_error_ptr myerr = (my_error_ptr) cinfo->err;
  (*cinfo->err->output_message) (cinfo);
  error=(char*)myerr->pub.jpeg_message_table[myerr->pub.msg_code];
  LOGE("jpeg_message_table[%d]:%s", myerr->pub.msg_code,myerr->pub.jpeg_message_table[myerr->pub.msg_code]);
 // LOGE("addon_message_table:%s", myerr->pub.addon_message_table);
//  LOGE("SIZEOF:%d",myerr->pub.msg_parm.i[0]);
//  LOGE("sizeof:%d",myerr->pub.msg_parm.i[1]);
  longjmp(myerr->setjmp_buffer, 1);
}

int generateJPEG(BYTE* data, int w, int h, int quality,
        const char* outfilename, jboolean optimize) {

    //jpeg的结构体，保存的比如宽、高、位深、图片格式等信息，相当于java的类
    struct jpeg_compress_struct jcs;

    //当读完整个文件的时候就会回调my_error_exit这个退出方法。setjmp是一个系统级函数，是一个回调。
    struct my_error_mgr jem;
    jcs.err = jpeg_std_error(&jem.pub);
    jem.pub.error_exit = my_error_exit;
    if (setjmp(jem.setjmp_buffer)) {
        return 0;
    }

    //初始化jsc结构体
    jpeg_create_compress(&jcs);
    //打开输出文件 wb:可写byte
    FILE* f = fopen(outfilename, "wb");
    if (f == NULL) {
        return 0;
    }
    //设置结构体的文件路径
    jpeg_stdio_dest(&jcs, f);
    jcs.image_width = w;//设置宽高
    jcs.image_height = h;
//  if (optimize) {
//      LOGI("optimize==ture");
//  } else {
//      LOGI("optimize==false");
//  }

    //看源码注释，设置哈夫曼编码：/* TRUE=arithmetic coding, FALSE=Huffman */
    jcs.arith_code = false;
    int nComponent = 3;
    /* 颜色的组成 rgb，三个 # of color components in input image */
    jcs.input_components = nComponent;
    //设置结构体的颜色空间为rgb
    jcs.in_color_space = JCS_RGB;
//  if (nComponent == 1)
//      jcs.in_color_space = JCS_GRAYSCALE;
//  else
//      jcs.in_color_space = JCS_RGB;

    //全部设置默认参数/* Default parameter setup for compression */
    jpeg_set_defaults(&jcs);
    //是否采用哈弗曼表数据计算 品质相差5-10倍
    jcs.optimize_coding = optimize;
    //设置质量
    jpeg_set_quality(&jcs, quality, true);
    //开始压缩，(是否写入全部像素)
    jpeg_start_compress(&jcs, TRUE);

    JSAMPROW row_pointer[1];
    int row_stride;
    //一行的rgb数量
    row_stride = jcs.image_width * nComponent;
    //一行一行遍历
    while (jcs.next_scanline < jcs.image_height) {
        //得到一行的首地址
        row_pointer[0] = &data[jcs.next_scanline * row_stride];

        //此方法会将jcs.next_scanline加1
        jpeg_write_scanlines(&jcs, row_pointer, 1);//row_pointer就是一行的首地址，1：写入的行数
    }
    jpeg_finish_compress(&jcs);//结束
    jpeg_destroy_compress(&jcs);//销毁 回收内存
    fclose(f);//关闭文件

    return 1;
}

/**
 * byte数组转C的字符串
 */
char* jstrinTostring(JNIEnv* env, jbyteArray barr) {
    char* rtn = NULL;
    jsize alen = env->GetArrayLength( barr);
    jbyte* ba = env->GetByteArrayElements( barr, 0);
    if (alen > 0) {
        rtn = (char*) malloc(alen + 1);
        memcpy(rtn, ba, alen);
        rtn[alen] = 0;
    }
    env->ReleaseByteArrayElements( barr, ba, 0);
    return rtn;
}

jstring Java_net_bither_util_NativeUtil_compressBitmap(JNIEnv* env,
        jclass thiz, jobject bitmapcolor, int w, int h, int quality,
        jbyteArray fileNameStr, jboolean optimize) {
    BYTE *pixelscolor;
    //1.将bitmap里面的所有像素信息读取出来,并转换成RGB数据,保存到二维byte数组里面
    //处理bitmap图形信息方法1 锁定画布
    AndroidBitmap_lockPixels(env,bitmapcolor,(void**)&pixelscolor);

    //2.解析每一个像素点里面的rgb值(去掉alpha值)，保存到一维数组data里面
    BYTE *data;
    BYTE r,g,b;
    data = (BYTE*)malloc(w*h*3);//每一个像素都有三个信息RGB
    BYTE *tmpdata;
    tmpdata = data;//临时保存data的首地址
    int i=0,j=0;
    int color;
    for (i = 0; i < h; ++i) {
        for (j = 0; j < w; ++j) {
            //解决掉alpha
            //获取二维数组的每一个像素信息(四个部分a/r/g/b)的首地址
            color = *((int *)pixelscolor);//通过地址取值
            //0~255：
//          a = ((color & 0xFF000000) >> 24);
            r = ((color & 0x00FF0000) >> 16);
            g = ((color & 0x0000FF00) >> 8);
            b = ((color & 0x000000FF));
            //改值！！！----保存到data数据里面
            *data = b;
            *(data+1) = g;
            *(data+2) = r;
            data = data + 3;
            //一个像素包括argb四个值，每+4就是取下一个像素点
            pixelscolor += 4;
        }
    }
    //处理bitmap图形信息方法2 解锁
    AndroidBitmap_unlockPixels(env,bitmapcolor);
    char* fileName = jstrinTostring(env,fileNameStr);
    //调用libjpeg核心方法实现压缩
    int resultCode = generateJPEG(tmpdata,w,h,quality,fileName,optimize);
    if(resultCode ==0){
        jstring result = env->NewStringUTF("-1");
        return result;
    }
    return env->NewStringUTF("1");
}

Android.mk

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE    :=jpegbither
LOCAL_SRC_FILES :=libjpegbither.so
include $(PREBUILT_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE    :=bitherjni
LOCAL_SRC_FILES :=bitherlibjni.cpp
LOCAL_SHARED_LIBRARIES :=jpegbither
LOCAL_LDLIBS := -ljnigraphics -llog  
include $(BUILD_SHARED_LIBRARY)

Application.mk

APP_ABI := armeabi-v7a armeabi  #表示 编译目标 ABI(应用二进制接口)
APP_PLATFORM := android-9

MainActivity

public class MainActivity extends Activity {
    public static final int REQUEST_PICK_IMAGE = 10011;
    public static final int REQUEST_KITKAT_PICK_IMAGE = 10012;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    public void pickFromGallery(View v) {
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.KITKAT) {
            startActivityForResult(new Intent(Intent.ACTION_GET_CONTENT).setType("image/*"),
                    REQUEST_PICK_IMAGE);
        } else {
            Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT);
            intent.addCategory(Intent.CATEGORY_OPENABLE);
            intent.setType("image/*");
            startActivityForResult(intent, REQUEST_KITKAT_PICK_IMAGE);
        }
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (resultCode == Activity.RESULT_OK) {
            switch (requestCode) {

                case REQUEST_PICK_IMAGE:
                    if (data != null) {
                        Uri uri = data.getData();
                        compressImage(uri);
                    } else {
                        Log.e("======", "========图片为空======");
                    }
                    break;
                case REQUEST_KITKAT_PICK_IMAGE:
                    if (data != null) {
                        Uri uri = ensureUriPermission(this, data);
                        compressImage(uri);
                    } else {
                        Log.e("======", "====-----==图片为空======");
                    }
                    break;
            }
        }
    }

    @SuppressWarnings("ResourceType")
    @TargetApi(Build.VERSION_CODES.KITKAT)
    public static Uri ensureUriPermission(Context context, Intent intent) {
        Uri uri = intent.getData();
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
            final int takeFlags = intent.getFlags() & Intent.FLAG_GRANT_READ_URI_PERMISSION;
            context.getContentResolver().takePersistableUriPermission(uri, takeFlags);
        }
        return uri;
    }


    public void compressImage(Uri uri) {
        Log.e("===compressImage===", "====开始====uri==" + uri.getPath());
        try {
            File saveFile = new File(getExternalCacheDir(), "终极压缩.jpg");
            Bitmap bitmap = MediaStore.Images.Media.getBitmap(getContentResolver(), uri);

            Log.e("===compressImage===", "====开始==压缩==saveFile==" + saveFile.getAbsolutePath());
            NativeUtil.compressBitmap(bitmap, saveFile.getAbsolutePath());
            Log.e("===compressImage===", "====完成==压缩==saveFile==" + saveFile.getAbsolutePath());


            File saveFile1 = new File(getExternalCacheDir(), "质量压缩.jpg");
            NativeUtil.compressImageToFile(bitmap,saveFile1);


            File saveFile2 = new File(getExternalCacheDir(), "尺寸压缩.jpg");
            NativeUtil.compressBitmapToFile(bitmap,saveFile2);

            Log.e("===compressImage===", "====uri==" + uri.toString());

            File saveFile3 = new File(getExternalCacheDir(), "采样率压缩.jpg");

            File f = new File("/storage/sdcard0/DCIM/Camera/IMG_20161130_200251.jpg");
            if(f.exists()){
                NativeUtil.compressBitmap(f.getAbsolutePath(),saveFile3);
            }else{
                Log.e("===compressImage===", "采样率压缩找不到这个代码里面写死的图片哦~~~~");
            }


        } catch (IOException e) {
            e.printStackTrace();
        }

    }

}

当然最后不要忘记权限,6.0以上自己申请哦

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" />

接下来我们来看一下效果。
原图像大小是6.7兆

综合对比 libjpeg有着很大的优势。尺寸压缩虽然小，但是失真严重。质量压缩要比jpeg的压缩大很多。