<span style="font-family: Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);">用了很久图片压缩，之前人们一直使用google的官方图片压缩方法</span>
final BitmapFactory.Options options = new BitmapFactory.Options(); options.inJustDecodeBounds = true; BitmapFactory.decodeResource(res, resId, options); options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight); options.inJustDecodeBounds = false; return BitmapFactory.decodeResource(res, resId, options);
public static int calculateInSampleSize(
BitmapFactory.Options options, int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
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;
}
}
return inSampleSize;
}http://developer.android.com/training/displaying-bitmaps/load-bitmap.html
仔细看calucelateInSamplesize方法，该算法返回的是一种压缩比例，仔细一看他的计算过程，你会发现，inSampleSize的变化过程是2-4-8,，而真正进入wile循环时，宽高就已经被看成是小了一半来计算的了，所以，上面那个网站说12M能压缩到0.75M,就是因为差距太大，如果安卓手机内部压缩自己的图片(大概是2M压缩到100K)，所以此时，这个方法就适用于android编码压缩了。
所以鄙人针对于android编码时压缩，在此对它进行了优化，优化后代码如下：
运行: culculateInSampleSize(bm,200,300)效果:
<pre name="code" class="java"><span style="font-family: Arial, Helvetica, sans-serif;">/**</span>* 计算压缩比例值(改进版 by touch_ping)
文件大小从1.12M变成81.75k
最终附上完整压缩工具类:
package com.example.mqtest;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Log;
/**
* 图片压缩工具类
* @author touch_ping
* 2015-1-5 下午1:29:59
*/
public class BitmapCompressor {
/**
* 质量压缩
* @author ping 2015-1-5 下午1:29:58
* @param image
* @param maxkb
* @return
*/
public static Bitmap compressBitmap(Bitmap image,int maxkb) {
//L.showlog("压缩图片");
ByteArrayOutputStream baos = new ByteArrayOutputStream();
image.compress(Bitmap.CompressFormat.JPEG, 50, baos);// 质量压缩方法，这里100表示不压缩，把压缩后的数据存放到baos中
int options = 100;
// Log.i("test","原始大小" + baos.toByteArray().length);
while (baos.toByteArray().length / 1024 > maxkb) { // 循环判断如果压缩后图片是否大于(maxkb)50kb,大于继续压缩
// Log.i("test","压缩一次!");
baos.reset();// 重置baos即清空baos
options -= 10;// 每次都减少10
image.compress(Bitmap.CompressFormat.JPEG, options, baos);// 这里压缩options%，把压缩后的数据存放到baos中
}
// Log.i("test","压缩后大小" + baos.toByteArray().length);
ByteArrayInputStream isBm = new ByteArrayInputStream(baos.toByteArray());// 把压缩后的数据baos存放到ByteArrayInputStream中
Bitmap bitmap = BitmapFactory.decodeStream(isBm, null, null);// 把ByteArrayInputStream数据生成图片
return bitmap;
}
/**
* http://developer.android.com/training/displaying-bitmaps/load-bitmap.html
* 官网：获取压缩后的图片
*
* @param res
* @param resId
* @param reqWidth
* 所需图片压缩尺寸最小宽度
* @param reqHeight
* 所需图片压缩尺寸最小高度
* @return
*/
public static Bitmap decodeSampledBitmapFromResource(Resources res,
int resId, int reqWidth, int reqHeight) {
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(res, resId, options);
options.inSampleSize = calculateInSampleSize(options, reqWidth,
reqHeight);
options.inJustDecodeBounds = false;
return BitmapFactory.decodeResource(res, resId, options);
}
/**
* 官网：获取压缩后的图片
*
* @param res
* @param resId
* @param reqWidth
* 所需图片压缩尺寸最小宽度
* @param reqHeight
* 所需图片压缩尺寸最小高度
* @return
*/
public static Bitmap decodeSampledBitmapFromFile(String filepath,
int reqWidth, int reqHeight) {
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(filepath, options);
options.inSampleSize = calculateInSampleSize(options, reqWidth,
reqHeight);
options.inJustDecodeBounds = false;
return BitmapFactory.decodeFile(filepath, options);
}
public static Bitmap decodeSampledBitmapFromBitmap(Bitmap bitmap,
int reqWidth, int reqHeight) {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
bitmap.compress(Bitmap.CompressFormat.PNG, 90, baos);
byte[] data = baos.toByteArray();
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeByteArray(data, 0, data.length, options);
options.inSampleSize = calculateInSampleSize(options, reqWidth,
reqHeight);
options.inJustDecodeBounds = false;
return BitmapFactory.decodeByteArray(data, 0, data.length, options);
}
/**
* 计算压缩比例值(改进版 by touch_ping)
*
* 原版2>4>8...倍压缩
* 当前2>3>4...倍压缩
*
* @param options
* 解析图片的配置信息
* @param reqWidth
* 所需图片压缩尺寸最小宽度O
* @param reqHeight
* 所需图片压缩尺寸最小高度
* @return
*/
public static int calculateInSampleSize(BitmapFactory.Options options,
int reqWidth, int reqHeight) {
final int picheight = options.outHeight;
final int picwidth = options.outWidth;
Log.i("test", "原尺寸:" + picwidth + "*" +picheight);
int targetheight = picheight;
int targetwidth = picwidth;
int inSampleSize = 1;
if (targetheight > reqHeight || targetwidth > reqWidth) {
while (targetheight >= reqHeight
&& targetwidth>= reqWidth) {
Log.i("test","压缩:" +inSampleSize + "倍");
inSampleSize += 1;
targetheight = picheight/inSampleSize;
targetwidth = picwidth/inSampleSize;
}
}
Log.i("test","最终压缩比例:" +inSampleSize + "倍");
Log.i("test", "新尺寸:" + targetwidth + "*" +targetheight);
return inSampleSize;
}
}
public static int calculateInSampleSize(
BitmapFactory.Options options, int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
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;
}
}
return inSampleSize;
}原文地址：http://blog.csdn.net/u010499721/article/details/42421459
