Android提高十六篇之使用NDK把彩图转换灰度图-优快云博客

本文链接：https://blog.youkuaiyun.com/iteye_20755/article/details/81994139

在Android上使用JAVA实现彩图转换为灰度图，跟J2ME上的实现类似，不过遇到频繁地转换或者是大图转换时，就必须使用NDK来提高速度了。本文主要通过JAVA和NDK这两种方式来分别实现彩图转换为灰度图，并给出速度的对比。

先来简单地介绍一下Android的NDK使用步骤：

以NDK r4为例，或许以后新版的NDK的使用方法略有不同。
1、下载支持C++的android-ndk-r4-crystax，支持C++的话可玩性更强......
2、下载cygwin，选择 ftp://mirrors.kernel.org 这个镜像，搜索 Devel Install 安装 gcc 和 make 等工具；

在搜索框里分别搜索gcc和make，必须是 Devel Install 栏的。

3、Cygwin安装目录下，找到home/username的目录下的.bash_profile文件，打开文件在最后加上：
NDK=/cygdrive/d/android-ndk-r4-windows/android-ndk-r4
export NDK
PS：假设安装在d:\android-ndk-r4-windows\android-ndk-r4。
4、运行cygwin，通过cd命令去到NDK\samples\例子目录\，运行$NDK/ndk-build来编译该目录下的Android.mk

以下是个人习惯.......
5、安装Eclipse的CDT，官方下载cdt安装包，解压缩后把plugins和feagures 复制覆盖到eclipse文件夹下即可
6、去到系统属性->环境变量->Path添加"D:\cygwin\bin"（假设cygwin安装在D:下），重启计算机，然后就可以在 Eclipse里面建立基于cygwin的C/C++工程了，先通过这一步来验证NDK的程序能够编译成功，然后再通过第4步来生成SO文件。

接下来看看本文程序运行的效果：

从转换灰度图的耗时来说，NDK的确比JAVA所用的时间短不少。

main.xml源码如下：

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<? xml version = "1.0" encoding = "utf-8" ?>
- < LinearLayout xmlns:android = "http://schemas.android.com/apk/res/android" android:orientation = "vertical" android:layout_width = "fill_parent" android:layout_height = "fill_parent" >
< Button android:layout_height = "wrap_content" android:layout_width = "fill_parent" android:id = "@+id/btnJAVA" android:text = "使用JAVA转换灰度图" />
< Button android:layout_height = "wrap_content" android:layout_width = "fill_parent" android:id = "@+id/btnNDK" android:text = "使用NDK转换灰度图" />
< ImageView android:id = "@+id/ImageView01" android:layout_width = "fill_parent" android:layout_height = "fill_parent" />
</ LinearLayout >

<?xml version="1.0" encoding="utf-8" ?> - <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent"> <Button android:layout_height="wrap_content" android:layout_width="fill_parent" android:id="@+id/btnJAVA" android:text="使用JAVA转换灰度图" /> <Button android:layout_height="wrap_content" android:layout_width="fill_parent" android:id="@+id/btnNDK" android:text="使用NDK转换灰度图" /> <ImageView android:id="@+id/ImageView01" android:layout_width="fill_parent" android:layout_height="fill_parent" /> </LinearLayout>

主程序testToGray.java的源码如下：

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package com.testToGray;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.drawable.BitmapDrawable;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
public class testToGray extends Activity {
/** Called when the activity is first created. */
Button btnJAVA,btnNDK;
ImageView imgView;
@Override
public void onCreate(Bundle savedInstanceState) {
super .onCreate(savedInstanceState);
setContentView(R.layout.main);
this .setTitle( "使用NDK转换灰度图---hellogv" );
btnJAVA=(Button)this .findViewById(R.id.btnJAVA);
btnJAVA.setOnClickListener(new ClickEvent());
btnNDK=(Button)this .findViewById(R.id.btnNDK);
btnNDK.setOnClickListener(new ClickEvent());
imgView=(ImageView)this .findViewById(R.id.ImageView01);
}
class ClickEvent implements View.OnClickListener{
@Override
public void onClick(View v) {
if (v==btnJAVA)
{
long current=System.currentTimeMillis();
Bitmap img=ConvertGrayImg(R.drawable.cat);
long performance=System.currentTimeMillis()-current;
//显示灰度图
imgView.setImageBitmap(img);
testToGray.this .setTitle( "w:" +String.valueOf(img.getWidth())+ ",h:" +String.valueOf(img.getHeight())
+" JAVA耗时 " +String.valueOf(performance)+ " 毫秒" );
}
else if (v==btnNDK)
{
long current=System.currentTimeMillis();
//先打开图像并读取像素
Bitmap img1=((BitmapDrawable) getResources().getDrawable(R.drawable.cat)).getBitmap();
int w=img1.getWidth(),h=img1.getHeight();
int [] pix = new int [w * h];
img1.getPixels(pix, 0 , w, 0 , 0 , w, h);
//通过ImgToGray.so把彩色像素转为灰度像素
int [] resultInt=LibFuns.ImgToGray(pix, w, h);
Bitmap resultImg=Bitmap.createBitmap(w, h, Config.RGB_565);
resultImg.setPixels(resultInt, 0 , w, 0 , 0 ,w, h);
long performance=System.currentTimeMillis()-current;
//显示灰度图
imgView.setImageBitmap(resultImg);
testToGray.this .setTitle( "w:" +String.valueOf(img1.getWidth())+ ",h:" +String.valueOf(img1.getHeight())
+" NDK耗时 " +String.valueOf(performance)+ " 毫秒" );
}
}
}
/**
* 把资源图片转为灰度图
* @param resID 资源ID
* @return
*/
public Bitmap ConvertGrayImg( int resID)
{
Bitmap img1=((BitmapDrawable) getResources().getDrawable(resID)).getBitmap();
int w=img1.getWidth(),h=img1.getHeight();
int [] pix = new int [w * h];
img1.getPixels(pix, 0 , w, 0 , 0 , w, h);
int alpha= 0xFF << 24 ;
for ( int i = 0 ; i < h; i++) {
for ( int j = 0 ; j < w; j++) {
// 获得像素的颜色
int color = pix[w * i + j];
int red = ((color & 0x00FF0000 ) >> 16 );
int green = ((color & 0x0000FF00 ) >> 8 );
int blue = color & 0x000000FF ;
color = (red + green + blue)/3 ;
color = alpha | (color << 16 ) | (color << 8 ) | color;
pix[w * i + j] = color;
}
}
Bitmap result=Bitmap.createBitmap(w, h, Config.RGB_565);
result.setPixels(pix, 0 , w, 0 , 0 ,w, h);
return result;
}
}

package com.testToGray; import android.app.Activity; import android.graphics.Bitmap; import android.graphics.Bitmap.Config; import android.graphics.drawable.BitmapDrawable; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.ImageView; public class testToGray extends Activity { /** Called when the activity is first created. */ Button btnJAVA,btnNDK; ImageView imgView; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); this.setTitle("使用NDK转换灰度图---hellogv"); btnJAVA=(Button)this.findViewById(R.id.btnJAVA); btnJAVA.setOnClickListener(new ClickEvent()); btnNDK=(Button)this.findViewById(R.id.btnNDK); btnNDK.setOnClickListener(new ClickEvent()); imgView=(ImageView)this.findViewById(R.id.ImageView01); } class ClickEvent implements View.OnClickListener{ @Override public void onClick(View v) { if(v==btnJAVA) { long current=System.currentTimeMillis(); Bitmap img=ConvertGrayImg(R.drawable.cat); long performance=System.currentTimeMillis()-current; //显示灰度图 imgView.setImageBitmap(img); testToGray.this.setTitle("w:"+String.valueOf(img.getWidth())+",h:"+String.valueOf(img.getHeight()) +" JAVA耗时 "+String.valueOf(performance)+" 毫秒"); } else if(v==btnNDK) { long current=System.currentTimeMillis(); //先打开图像并读取像素 Bitmap img1=((BitmapDrawable) getResources().getDrawable(R.drawable.cat)).getBitmap(); int w=img1.getWidth(),h=img1.getHeight(); int[] pix = new int[w * h]; img1.getPixels(pix, 0, w, 0, 0, w, h); //通过ImgToGray.so把彩色像素转为灰度像素 int[] resultInt=LibFuns.ImgToGray(pix, w, h); Bitmap resultImg=Bitmap.createBitmap(w, h, Config.RGB_565); resultImg.setPixels(resultInt, 0, w, 0, 0,w, h); long performance=System.currentTimeMillis()-current; //显示灰度图 imgView.setImageBitmap(resultImg); testToGray.this.setTitle("w:"+String.valueOf(img1.getWidth())+",h:"+String.valueOf(img1.getHeight()) +" NDK耗时 "+String.valueOf(performance)+" 毫秒"); } } } /** * 把资源图片转为灰度图 * @param resID 资源ID * @return */ public Bitmap ConvertGrayImg(int resID) { Bitmap img1=((BitmapDrawable) getResources().getDrawable(resID)).getBitmap(); int w=img1.getWidth(),h=img1.getHeight(); int[] pix = new int[w * h]; img1.getPixels(pix, 0, w, 0, 0, w, h); int alpha=0xFF<<24; for (int i = 0; i < h; i++) { for (int j = 0; j < w; j++) { // 获得像素的颜色 int color = pix[w * i + j]; int red = ((color & 0x00FF0000) >> 16); int green = ((color & 0x0000FF00) >> 8); int blue = color & 0x000000FF; color = (red + green + blue)/3; color = alpha | (color << 16) | (color << 8) | color; pix[w * i + j] = color; } } Bitmap result=Bitmap.createBitmap(w, h, Config.RGB_565); result.setPixels(pix, 0, w, 0, 0,w, h); return result; } }

封装NDK函数的JAVA类LibFuns.java的源码如下：

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package com.testToGray;
public class LibFuns {
static {
System.loadLibrary("ImgToGray" );
}
/**
* @param width the current view width
* @param height the current view height
*/
public static native int [] ImgToGray( int [] buf, int w, int h);
}

package com.testToGray; public class LibFuns { static { System.loadLibrary("ImgToGray"); } /** * @param width the current view width * @param height the current view height */ public static native int[] ImgToGray(int[] buf, int w, int h); }

彩图转换为灰度图的ImgToGray.cpp源码:

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#include <jni.h>
#include <stdio.h>
#include <stdlib.h>
extern "C" {
JNIEXPORT jintArray JNICALL Java_com_testToGray_LibFuns_ImgToGray(
JNIEnv* env, jobject obj, jintArray buf, int w, int h);
}
;
JNIEXPORT jintArray JNICALL Java_com_testToGray_LibFuns_ImgToGray(
JNIEnv* env, jobject obj, jintArray buf, int w, int h) {
jint *cbuf;
cbuf = env->GetIntArrayElements(buf, false );
if (cbuf == NULL) {
return 0; /* exception occurred */
}
int alpha = 0xFF << 24;
for ( int i = 0; i < h; i++) {
for ( int j = 0; j < w; j++) {
// 获得像素的颜色
int color = cbuf[w * i + j];
int red = ((color & 0x00FF0000) >> 16);
int green = ((color & 0x0000FF00) >> 8);
int blue = color & 0x000000FF;
color = (red + green + blue) / 3;
color = alpha | (color << 16) | (color << 8) | color;
cbuf[w * i + j] = color;
}
}
int size=w * h;
jintArray result = env->NewIntArray(size);
env->SetIntArrayRegion(result, 0, size, cbuf);
env->ReleaseIntArrayElements(buf, cbuf, 0);
return result;
}

#include <jni.h> #include <stdio.h> #include <stdlib.h> extern "C" { JNIEXPORT jintArray JNICALL Java_com_testToGray_LibFuns_ImgToGray( JNIEnv* env, jobject obj, jintArray buf, int w, int h); } ; JNIEXPORT jintArray JNICALL Java_com_testToGray_LibFuns_ImgToGray( JNIEnv* env, jobject obj, jintArray buf, int w, int h) { jint *cbuf; cbuf = env->GetIntArrayElements(buf, false); if (cbuf == NULL) { return 0; /* exception occurred */ } int alpha = 0xFF << 24; for (int i = 0; i < h; i++) { for (int j = 0; j < w; j++) { // 获得像素的颜色 int color = cbuf[w * i + j]; int red = ((color & 0x00FF0000) >> 16); int green = ((color & 0x0000FF00) >> 8); int blue = color & 0x000000FF; color = (red + green + blue) / 3; color = alpha | (color << 16) | (color << 8) | color; cbuf[w * i + j] = color; } } int size=w * h; jintArray result = env->NewIntArray(size); env->SetIntArrayRegion(result, 0, size, cbuf); env->ReleaseIntArrayElements(buf, cbuf, 0); return result; }

Android.mk的源码：