Android 圖片特效

在Android上使用JAVA實現彩圖轉換為灰度圖，跟J2ME上的實現類似，不過遇到頻繁地轉換或者是大圖轉換時，就必須使用NDK來提高速度了。本文主要通過JAVA和NDK這兩種方式來分別實現彩圖轉換為灰度圖，并給出速度的對比。

從轉換灰度圖的耗時來說，NDK的確比JAVA所用的時間短不少。

<?xml version="1.0" encoding="utf-8" ?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android&quot; 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轉換灰度圖" /> 
<Button 
android:layout_height="wrap_content"
android:layout_width="fill_parent" 
android:id="@+id/btnNDK" 
android:text="使用NDK轉換灰度圖" /> 
<ImageView 
android:id="@+id/ImageView01" 
android:layout_width="fill_parent"
android:layout_height="fill_parent" /> 
</LinearLayout> </pre> 
  
 主程序demo.java的源碼如下： 
  
package eoe.demo;

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轉換灰度圖---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; 
//顯示灰度圖 
imgView.setImageBitmap(img); 
testToGray.this.setTitle("w:"+String.valueOf(img.getWidth())+",h:"+String.valueOf(img.getHeight()) 
+" JAVA耗時 "+String.valueOf(performance)+" 毫秒"); 
} 
else if(v==btnNDK) 
{ 
long current=System.currentTimeMillis();
//先打開圖像并讀取像素 
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); 
//通過ImgToGray.so把彩色像素轉為灰度像素 
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; 
//顯示灰度圖 
imgView.setImageBitmap(resultImg); 
testToGray.this.setTitle("w:"+String.valueOf(img1.getWidth())+",h:"+String.valueOf(img1.getHeight()) 
+" NDK耗時 "+String.valueOf(performance)+" 毫秒"); 
} 
} 
}
/**

把資源圖片轉為灰度圖 
@param resID 資源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++) { 
// 獲得像素的顏色 
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; 
} 
} </pre> 
  
 封裝NDK函數的JAVA類LibFuns.java的源碼如下 
  
package eoe.demo; 
public class LibFuns { 
static { 
System.loadLibrary("Imgdemo"); 
} 
/**


@param寬度當前視圖的寬度
@param高度當前視圖的高度
*/ 
public static native int[] ImgToGray(int[] buf, int w, int h); 
} </pre> 
 彩圖轉換為灰度圖的Imgdemo.cpp源碼: 
#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++) { 
// 獲得像素的顏色 
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; 
} </pre> 
  
 Android.mk的源碼： 
  
LOCAL_PATH:= $(call my-dir) 
include $(CLEAR_VARS) 
LOCAL_MODULE := ImgToGray 
LOCAL_SRC_FILES := ImgToGray.cpp 
include $(BUILD_SHARED_LIBRARY)