Android提高十六篇之使用NDK把彩图转换灰度图

  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：

<?
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：

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：

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:

#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：

LOCAL_PATH:
= $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    :
= 
ImgToGray
LOCAL_SRC_FILES :
= 
ImgToGray
.cpp

include $(BUILD_SHARED_LIBRARY)