说明：网上找到一个图片处理的jni方法，试着自己调用一下，然后处理图片，效果还是非常不错的，参考网址在MainActivity里面可以找到，自己创建一个c++的android项目，然后写代码，怎么创建，请先安装ndk
效果图：
（1）CMakeLists.txt
# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html
# Sets the minimum version of CMake required to build the native library.
cmake_minimum_required(VERSION 3.10.2)
# Declares and names the project.
project("imagecolor")
# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.
add_library( # Sets the name of the library.
native-lib
# Sets the library as a shared library.
SHARED
# Provides a relative path to your source file(s).
native-lib.cpp)
# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.
find_library( # Sets the name of the path variable.
log-lib
# Specifies the name of the NDK library that
# you want CMake to locate.
log)
# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.
target_link_libraries( # Specifies the target library.
native-lib
jnigraphics
# Links the target library to the log library
#android提供的图像处理库
# included in the NDK.
${log-lib})（2）native-lib.cpp
#include <jni.h>
#include <string>
#include <jni.h>
#include <string>
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <android/bitmap.h>
#define MAKE_RGB565(r,g,b) ((((r) >> 3) << 11) | (((g) >> 2) << 5) | ((b) >> 3))
#define MAKE_ARGB(a,r,g,b) ((a&0xff)<<24) | ((r&0xff)<<16) | ((g&0xff)<<8) | (b&0xff)
#define RGB565_R(p) ((((p) & 0xF800) >> 11) << 3)
#define RGB565_G(p) ((((p) & 0x7E0 ) >> 5) << 2)
#define RGB565_B(p) ( ((p) & 0x1F ) << 3)
#define RGB8888_A(p) (p & (0xff<<24) >> 24 )
#define RGB8888_R(p) (p & (0xff<<16) >> 16 )
#define RGB8888_G(p) (p & (0xff<<8) >> 8 )
#define RGB8888_B(p) (p & (0xff) )
#define RGBA_A(p) (((p) & 0xFF000000) >> 24)
#define RGBA_R(p) (((p) & 0x00FF0000) >> 16)
#define RGBA_G(p) (((p) & 0x0000FF00) >> 8)
#define RGBA_B(p) ((p) & 0x000000FF)
#define MAKE_RGBA(r,g,b,a) (((a) << 24) | ((r) << 16) | ((g) << 8) | (b))
extern "C" JNIEXPORT void JNICALL
Java_com_example_imagecolor_MainActivity_nativeProcessBitmap(JNIEnv *env,
jobject instance,
jobject bitmap) {
if (bitmap == NULL) {
return;
}
AndroidBitmapInfo bitmapInfo;
memset(&bitmapInfo , 0 , sizeof(bitmapInfo));
// Need add "jnigraphics" into target_link_libraries in CMakeLists.txt
AndroidBitmap_getInfo(env , bitmap , &bitmapInfo);
// Lock the bitmap to get the buffer
void * pixels = NULL;
int res = AndroidBitmap_lockPixels(env, bitmap, &pixels);
// From top to bottom
int x = 0, y = 0;
for (y = 0; y < bitmapInfo.height; ++y) {
// From left to right
for (x = 0; x < bitmapInfo.width; ++x) {
int a = 0, r = 0, g = 0, b = 0;
void *pixel = NULL;
// Get each pixel by format
if(bitmapInfo.format == ANDROID_BITMAP_FORMAT_RGBA_8888)
{
pixel = ((uint32_t *)pixels) + y * bitmapInfo.width + x;
int r,g,b;
uint32_t v = *((uint32_t *)pixel);
r = RGB8888_R(v);
g = RGB8888_G(v);
b = RGB8888_B(v);
int sum = r+g+b;
*((uint32_t *)pixel) = MAKE_ARGB(0xff , sum/3, sum/3, sum/3);
}
else if (bitmapInfo.format == ANDROID_BITMAP_FORMAT_RGB_565) {
pixel = ((uint16_t *)pixels) + y * bitmapInfo.width + x;
int r,g,b;
uint16_t v = *((uint16_t *)pixel);
r = RGB565_R(v);
g = RGB565_G(v);
b = RGB565_B(v);
int sum = r+g+b;
*((uint16_t *)pixel) = MAKE_RGB565(sum/3, sum/3, sum/3); }
}
}
AndroidBitmap_unlockPixels(env, bitmap);
}
extern "C" JNIEXPORT jstring JNICALL
Java_com_example_imagecolor_MainActivity_stringFromJNI(
JNIEnv* env,
jobject /* this */) {
std::string hello = "this is C++ camke code";
return env->NewStringUTF(hello.c_str());
}（3）MainActivity
package com.example.imagecolor;
import androidx.appcompat.app.AppCompatActivity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.widget.ImageView;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
// Used to load the 'native-lib' library on application startup.
static {
System.loadLibrary("native-lib");
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Example of a call to a native method
TextView tv = findViewById(R.id.sample_text);
tv.setText(stringFromJNI());
initView();
}
private void initView(){
ImageView source_img = (ImageView)findViewById(R.id.source_img);
ImageView operation_img = (ImageView)findViewById(R.id.operation_img);
Bitmap bitmap = BitmapFactory.decodeResource(getResources(),R.drawable.scape);
source_img.setImageBitmap(bitmap);
operation_img.setImageBitmap(handleBitmap(bitmap));
}
/**
* 处理图片，此方法中会调用nativeProcessBitmap
* @param bitmap
* @return
*/
private Bitmap handleBitmap(Bitmap bitmap) {
Bitmap bmp = bitmap.copy(Bitmap.Config.ARGB_8888, true);
nativeProcessBitmap(bmp);
return bmp;
}
public native void nativeProcessBitmap(Bitmap bitmap);
/**
* A native method that is implemented by the 'native-lib' native library,
* which is packaged with this application.
*/
public native String stringFromJNI();
}（4）activity_main
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".MainActivity">
<TextView
android:id="@+id/sample_text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!"
android:textColor="@android:color/holo_red_dark"
android:textSize="38sp"/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal">
<ImageView
android:id="@+id/source_img"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:scaleType="fitXY" />
<ImageView
android:id="@+id/operation_img"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:scaleType="fitXY" />
</LinearLayout>
</LinearLayout>end
