Android NDK Bitmap to gray

Source:http://blog.csdn.net/hellogv/archive/2010/12/23/6094127.aspx

 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。

　　　　　　

从转换灰度图的耗时来说，NDK的确比JAVA所用的时间短不少。

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;
    }
}

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);
}

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;
}

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)