Android(安卓)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    := ImgToGrayLOCAL_SRC_FILES := ImgToGray.cppinclude $(BUILD_SHARED_LIBRARY)

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