图片的二次采样

public class BitmapUtil {

/**
* 灵活的方法:获取期望的宽和高.
* 图片实际的宽与高，根据默认最大大小值，得到图片实际的缩放比例
* @param maxPrimary
* @param maxSecondary
* @param actualPrimary
* @param actualSecondary
* @return
*/
private static int getResizedDimension(int maxPrimary, int maxSecondary,
int actualPrimary, int actualSecondary) {
// If no dominant value at all, just return the actual.
if (maxPrimary == 0 && maxSecondary == 0) {
return actualPrimary;
}

// If primary is unspecified, scale primary to match secondary's scaling
// ratio.
if (maxPrimary == 0) {
double ratio = (double) maxSecondary / (double) actualSecondary;
return (int) (actualPrimary * ratio);
}

if (maxSecondary == 0) {
return maxPrimary;
}

double ratio = (double) actualSecondary / (double) actualPrimary;
int resized = maxPrimary;
if (resized * ratio > maxSecondary) {
resized = (int) (maxSecondary / ratio);
}
return resized;
}

//计算最佳采样率的方法.actualWidth=120,actualHeight=120,desiredWidth=100,desiredHeight=100
public static int findBestSampleSize(int actualWidth, int actualHeight,
int desiredWidth, int desiredHeight) {
//1.73
double wr = (double) actualWidth / desiredWidth;
//1.73
double hr = (double) actualHeight / desiredHeight;
//1.73
double ratio = Math.min(wr, hr);
float n = 1.0f;
while ((n * 2) <= ratio) {
n *= 2;
}

return (int) n;
}

/**
* 图片二次采样的方法   图片的像素压缩 修改图片的宽度/高度  图片按照比例大小进行压缩
* @param maxWidth
* @param maxHeight
* @param data
* @param config
* @return
*/
public static Bitmap ParserBitmap(int maxWidth,int maxHeight,
byte[] data,Bitmap.Config config){
Bitmap bm=null;
//第一次采样
BitmapFactory.Options options=new BitmapFactory.Options();
if(maxWidth==0 && maxHeight==0){
//设置图片的位数  rgb_565 rgb_4444 rgb_8888
options.inPreferredConfig=config;
bm=BitmapFactory.decodeByteArray(data,0,data.length,options);
}else{
//该属性设置为true表示只加载图片的边框 不会加载图片的具体像素点  测量边界
options.inJustDecodeBounds=true;
//第一次加载图片 只加载图片的边框 并不加载像素点
BitmapFactory.decodeByteArray(data,0,data.length,options);
//图片的真实的宽度和高度 原图
int trueWidth=options.outWidth;
int trueHeight=options.outHeight;

Log.i("tag","原图的宽度:"+trueWidth+",原图的高度:"+trueHeight);

//期望的宽度和高度
int desWidth=getResizedDimension(maxWidth,maxHeight,trueWidth,trueHeight);
int desHeight=getResizedDimension(maxHeight,maxWidth,trueHeight,trueWidth);

//            int desWidth=300;
//            int desHeight=500;

Log.i("tag","期望的宽度:"+desWidth+",期望的高度:"+desHeight);

//至此第一次采样结束   开始第二次采样
//第二次采样不仅只是加载图片的边缘
options.inJustDecodeBounds=false;
//inSampleSize 设置图片的采样率  获取压缩比例
options.inSampleSize=findBestSampleSize(trueWidth,trueHeight,desWidth,desHeight);
Log.i("tag","----options.inSampleSize-----"+ options.inSampleSize);
//生成临时的bitmap对象
Bitmap tempBitmap=BitmapFactory.decodeByteArray(data,0,data.length,options);
if(tempBitmap!=null || tempBitmap.getWidth()>desWidth
|| tempBitmap.getHeight()>desHeight){
//创建压缩后的bitmap对象
bm=tempBitmap.createScaledBitmap(tempBitmap,desWidth,desHeight,true);
tempBitmap.recycle();
}else{
bm=tempBitmap;
}
}
return bm;
}