压缩bitmap算法

public static Bitmap decodeFile(File f) {
try {
// decode image size
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
//			BitmapFactory.decodeStream(new FileInputStream(f), null, options);
int inSampleSize = computeSampleSize(options, -1, 128 * 128);
// decode with inSampleSize
options.inSampleSize = inSampleSize;
options.inJustDecodeBounds = false;
return BitmapFactory.decodeStream(new FileInputStream(f), null, options);
} catch (Exception e) {
}
return null;
}

public static void copyStream(InputStream is, OutputStream os) {
final int buffer_size = 1024;
try {
byte[] bytes = new byte[buffer_size];
for (;;) {
int count = is.read(bytes, 0, buffer_size);
if (count == -1)
break;
os.write(bytes, 0, count);
}
} catch (Exception ex) {
ex.printStackTrace();
}
}

/**
* 根据实际需要，计算出合适的inSampleSize，以减少内存的开销
*
* @param options
* @param minSideLength 最小长度，不限制则为-1
* @param maxNumOfPixels 最大像素点，128 * 128
* @return
*/
public static int computeSampleSize(BitmapFactory.Options options,
int minSideLength, int maxNumOfPixels) {
int initialSize = computeInitialSampleSize(options, minSideLength,
maxNumOfPixels);

int roundedSize;
if (initialSize <= 8) {
roundedSize = 1;
while (roundedSize < initialSize) {
roundedSize <<= 1;
}
} else {
roundedSize = (initialSize + 7) / 8 * 8;
}

return roundedSize;
}

private static int computeInitialSampleSize(BitmapFactory.Options options,
int minSideLength, int maxNumOfPixels) {
double w = options.outWidth;
double h = options.outHeight;
//ceil   get the integer number >parameter
int lowerBound = (maxNumOfPixels == -1) ? 1 : (int) Math.ceil(Math
.sqrt(w * h / maxNumOfPixels));
int upperBound = (minSideLength == -1) ? 128 : (int) Math.min(
Math.floor(w / minSideLength), Math.floor(h / minSideLength));

if (upperBound < lowerBound) {
// return the larger one when there is no overlapping zone.
return lowerBound;
}

if ((maxNumOfPixels == -1) && (minSideLength == -1)) {
return 1;
} else if (minSideLength == -1) {
return lowerBound;
} else {
return upperBound;
}
}