Android Bitmap 载入与像素操作
一：载入与像素读写
在Android SDK中，图像的像素读写能够通过getPixel与setPixel两个Bitmap的API实现。
Bitmap API读取像素的代码例如以下：
int pixel = bitmap.getPixel(col, row);// ARGB
int red = Color.red(pixel); // same as (pixel >> 16) &0xff
int green = Color.green(pixel); // same as (pixel >> 8) &0xff
int blue = Color.blue(pixel); // same as (pixel & 0xff)
int alpha = Color.alpha(pixel); // same as (pixel >>> 24)得到像素pixel是32位的整数，四个字节分别相应透明通道、红色、绿色、蓝色通道。
Bitmap API 写入像素,代码例如以下：
bm.setPixel(col, row, Color.argb(alpha, red, green, blue));通过Color.argb又一次组装成一个int的像素值。
使用BitmapFactory.decodeFile或者decodeResource等方法实现载入图像的Bitmap对象时。这些方法就会为要构建的Bitmap对象分配合适大小的内存。假设原始的图像文件数据非常大，就会导致DVM不能分配请求的内存大小。从而导致OOM(out of memory)问题。而通过配置BitmapFactory.Option预先读取图像高度与宽带，图像进行适当的下採样，就能够避免OOM问题的发生。预先仅仅获取图像高度与宽带的代码例如以下：
// 获取Bitmap图像大小与类型属性
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(getResources(),
R.drawable.shar_03, options);
int height = options.outHeight;
int width = options.outWidth;
String imageType = options.outMimeType;基于下採样载入超大Bitmap图像的缩小版本号：
// 下採样
int inSampleSize = 1;
if (height > reqHeight || width > reqWidth) {
final int halfHeight = height / 2;
final int halfWidth = width / 2;
// Calculate the largest inSampleSize value
// that is a power of 2 and keeps both
// height and width larger than the requested height and width.
while ((halfHeight / inSampleSize) > reqHeight
&& (halfWidth / inSampleSize) > reqWidth) {
inSampleSize *= 2;
}
}
// 获取採样后的图像显示。避免OOM问题
options.inJustDecodeBounds = false;
srcImage = BitmapFactory.decodeResource(getResources(), R.drawable.shar_03, options);二：像素操作
android彩色图像灰度化的三个简单方法
灰度化方法一：
灰度值GRAY = (max(red, green, blue) + min(red, green, blue))/2
灰度化方法二：
灰度值GRAY = (red + green + blue)/3
灰度化方法三：
灰度值GRAY = red*0.3 + green*0.59 + blue*0.11
代码实现例如以下：
public Bitmap gray(Bitmap bitmap, int schema)
{
Bitmap bm = Bitmap.createBitmap(bitmap.getWidth(),bitmap.getHeight(), bitmap.getConfig());
int width = bitmap.getWidth();
int height = bitmap.getHeight();
for(int row=0; row<height; row++){
for(int col=0; col<width; col++){
int pixel = bitmap.getPixel(col, row);// ARGB
int red = Color.red(pixel); // same as (pixel >> 16) &0xff
int green = Color.green(pixel); // same as (pixel >> 8) &0xff
int blue = Color.blue(pixel); // same as (pixel & 0xff)
int alpha = Color.alpha(pixel); // same as (pixel >>> 24)
int gray = 0;
if(schema == 0)
{
gray = (Math.max(blue, Math.max(red, green)) +
Math.min(blue, Math.min(red, green))) / 2;
}
else if(schema == 1)
{
gray = (red + green + blue) / 3;
}
else if(schema == 2)
{
gray = (int)(0.3 * red + 0.59 * green + 0.11 * blue);
}
bm.setPixel(col, row, Color.argb(alpha, gray, gray, gray));
}
}
return bm;
}Bitmap图像镜像映射与亮度调整的代码实现例如以下：
public Bitmap brightness(Bitmap bitmap, double depth)
{
Bitmap bm = Bitmap.createBitmap(bitmap.getWidth(),bitmap.getHeight(), bitmap.getConfig());
int width = bitmap.getWidth();
int height = bitmap.getHeight();
for(int row=0; row<height; row++){
for(int col=0; col<width; col++){
int pixel = bitmap.getPixel(col, row);// ARGB
int red = Color.red(pixel); // same as (pixel >> 16) &0xff
int green = Color.green(pixel); // same as (pixel >> 8) &0xff
int blue = Color.blue(pixel); // same as (pixel & 0xff)
int alpha = Color.alpha(pixel); // same as (pixel >>> 24)
double gray = (0.3 * red + 0.59 * green + 0.11 * blue);
red += (depth * gray);
if(red > 255) { red = 255; }
green += (depth * gray);
if(green > 255) { green = 255; }
blue += (depth * gray);
if(blue > 255) { blue = 255; }
bm.setPixel(col, row, Color.argb(alpha, red, green, blue));
}
}
return bm;
}
public Bitmap flip(Bitmap bitmap)
{
Bitmap bm = Bitmap.createBitmap(bitmap.getWidth(),bitmap.getHeight(), bitmap.getConfig());
int width = bitmap.getWidth();
int height = bitmap.getHeight();
for(int row=0; row<height; row++){
for(int col=0; col<width; col++){
int pixel = bitmap.getPixel(col, row);// ARGB
int red = Color.red(pixel); // same as (pixel >> 16) &0xff
int green = Color.green(pixel); // same as (pixel >> 8) &0xff
int blue = Color.blue(pixel); // same as (pixel & 0xff)
int alpha = Color.alpha(pixel); // same as (pixel >>> 24)
int ncol = width - col - 1;
bm.setPixel(ncol, row, Color.argb(alpha, red, green, blue));
}
}
return bm;
}执行截图： 
布局XML文件内容例如以下：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.imageprocess1.MainActivity" >
<RelativeLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content">
<Button
android:id="@+id/button_gray_3"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:text="@string/process" />
<Button
android:id="@+id/button_inverse"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_toRightOf="@+id/button_gray_3"
android:layout_alignTop="@+id/button_gray_3"
android:text="@string/inverse" />
<Button
android:id="@+id/button_gray_1"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_toRightOf="@+id/button_inverse"
android:layout_alignTop="@+id/button_gray_3"
android:text="@string/nored" />
<Button
android:id="@+id/button_gray_2"
android:layout_width="100dp"
android:layout_below="@+id/button_gray_3"
android:layout_height="wrap_content"
android:text="@string/noblue" />
<Button
android:id="@+id/button_flip"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_below="@+id/button_inverse"
android:layout_toRightOf="@+id/button_gray_2"
android:text="@string/flip" />
<Button
android:id="@+id/button_save"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_below="@+id/button_gray_3"
android:layout_toRightOf="@+id/button_flip"
android:text="@string/save" />
</RelativeLayout>
<ImageView
android:id="@+id/image_content"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:scaleType="fitCenter"
android:src="@drawable/ic_launcher" />
</LinearLayout>MainActivity中的onCreate方法的代码例如以下：
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ImageView iView = (ImageView) this.findViewById(R.id.image_content);
Bitmap b = Bitmap.createBitmap(400, 400, Bitmap.Config.ARGB_8888);
Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setColor(Color.BLACK);
Canvas c = new Canvas(b);
c.drawText("Load Image from here...", 50, 200, paint);
iView.setImageBitmap(b);
Button saveBtn = (Button) this.findViewById(R.id.button_save);
saveBtn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View view) {
Toast toast = Toast.makeText(getApplicationContext(), "Please load the image firstly...", Toast.LENGTH_SHORT);
toast.show();
loadImage();
ImageView iView = (ImageView) findViewById(R.id.image_content);
iView.setImageBitmap(srcImage);
if(srcImage != null)
{
//saveFile(srcImage);
}
}
});
Button processBtn = (Button) this.findViewById(R.id.button_gray_3);
processBtn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View view) {
if(srcImage == null)
{
loadImage();
}
ImagePixelsProcessor processor = new ImagePixelsProcessor();
Bitmap bm = processor.gray(srcImage, 2); // 有不同的灰度化策略
final ImageView iView = (ImageView) findViewById(R.id.image_content);
iView.setImageBitmap(bm);
}
});
Button inverseBtn = (Button) this.findViewById(R.id.button_inverse);
inverseBtn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View view) {
if(srcImage == null)
{
loadImage();
}
ImagePixelsProcessor processor = new ImagePixelsProcessor();
Bitmap bm = processor.brightness(srcImage, 0.3);
final ImageView iView = (ImageView) findViewById(R.id.image_content);
iView.setImageBitmap(bm);
}
});
Button noRedBtn = (Button) this.findViewById(R.id.button_gray_1);
noRedBtn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View view) {
if(srcImage == null)
{
loadImage();
}
ImagePixelsProcessor processor = new ImagePixelsProcessor();
Bitmap bm = processor.gray(srcImage, 0); // 有不同的灰度化策略
final ImageView iView = (ImageView) findViewById(R.id.image_content);
iView.setImageBitmap(bm);
}
});
Button gray2Btn = (Button) this.findViewById(R.id.button_gray_2);
gray2Btn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View view) {
if(srcImage == null)
{
loadImage();
}
ImagePixelsProcessor processor = new ImagePixelsProcessor();
Bitmap bm = processor.gray(srcImage, 1); // 有不同的灰度化策略
final ImageView iView = (ImageView) findViewById(R.id.image_content);
iView.setImageBitmap(bm);
}
});
Button flipBtn = (Button) this.findViewById(R.id.button_flip);
flipBtn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View view) {
if(srcImage == null)
{
loadImage();
}
ImagePixelsProcessor processor = new ImagePixelsProcessor();
Bitmap bm = processor.flip(srcImage);
final ImageView iView = (ImageView) findViewById(R.id.image_content);
iView.setImageBitmap(bm);
}
});-第一次尝试用CSDN-markdown编辑器写文章。发现这个东西真好用！赞。。！
-gloomyfish@2015-07-02