Android(安卓)compress图片压缩介绍

android的照相功能随着手机硬件的发展，变得越来越强大，能够找出很高分辨率的图片。
有些场景中，需要照相并且上传到服务，但是由于图片的大小太大，那么就上传就会很慢(在有些网络情况下)，而且很耗流量，要想速度快，那么就需要减小图片的大小。减少图片的大小有两种方法，1. 照小图片； 2. 压缩大图片。照相时获取小图片一般不太符合要求，因为，图片的清晰度会很差，但是这种情况有个好处就是应用速度会快些；压缩图片，就是把大图片压缩小，降低图片的质量，在一定范围内，降低图片的大小，并且满足需求（图片仍就清晰）。下面组要是介绍图片的压缩：

1. 照相请查看 http://www.jb51.net/article/37760.htm ->想要保存图片到制定目录，启动Camera应用时，需要指定文件
2. 压缩过程：
2.1 从图片路径中读取图片(图片很大，不能全部加在到内存中处理，要是全部加载到内存中会内存溢出)
[java]

复制代码代码如下:
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(filePath, options);

// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, 480, 800);

// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;

Bitmap bm = BitmapFactory.decodeFile(filePath, options);

final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(filePath, options);

// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, 480, 800);

// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;

Bitmap bm = BitmapFactory.decodeFile(filePath, options);

2.2 处理图片旋转
[java]

复制代码代码如下:
int degree = readPictureDegree(filePath);
bm = rotateBitmap(bm,degree) ;

int degree = readPictureDegree(filePath);
bm = rotateBitmap(bm,degree) ;[java] view plaincopyprint?private static int readPictureDegree(String path) {
int degree = 0;
try {
ExifInterface exifInterface = new ExifInterface(path);
int orientation = exifInterface.getAttributeInt(ExifInterface.TAG_ORIENTATION, ExifInterface.ORIENTATION_NORMAL);
switch (orientation) {
case ExifInterface.ORIENTATION_ROTATE_90:
degree = 90;
break;
case ExifInterface.ORIENTATION_ROTATE_180:
degree = 180;
break;
case ExifInterface.ORIENTATION_ROTATE_270:
degree = 270;
break;
}
} catch (IOException e) {
e.printStackTrace();
}
return degree;
}

private static int readPictureDegree(String path) {
int degree = 0;
try {
ExifInterface exifInterface = new ExifInterface(path);
int orientation = exifInterface.getAttributeInt(ExifInterface.TAG_ORIENTATION, ExifInterface.ORIENTATION_NORMAL);
switch (orientation) {
case ExifInterface.ORIENTATION_ROTATE_90:
degree = 90;
break;
case ExifInterface.ORIENTATION_ROTATE_180:
degree = 180;
break;
case ExifInterface.ORIENTATION_ROTATE_270:
degree = 270;
break;
}
} catch (IOException e) {
e.printStackTrace();
}
return degree;
}

[java]

复制代码代码如下:
view plaincopyprint?private static Bitmap rotateBitmap(Bitmap bitmap, int rotate){
if(bitmap == null)
return null ;

int w = bitmap.getWidth();
int h = bitmap.getHeight();

// Setting post rotate to 90
Matrix mtx = new Matrix();
mtx.postRotate(rotate);
return Bitmap.createBitmap(bitmap, 0, 0, w, h, mtx, true);
}

private static Bitmap rotateBitmap(Bitmap bitmap, int rotate){
if(bitmap == null)
return null ;

int w = bitmap.getWidth();
int h = bitmap.getHeight();

// Setting post rotate to 90
Matrix mtx = new Matrix();
mtx.postRotate(rotate);
return Bitmap.createBitmap(bitmap, 0, 0, w, h, mtx, true);
}

2.3压缩图片
[java]

复制代码代码如下:
bm.compress(Bitmap.CompressFormat.JPEG, 30, baos);//30 是压缩率，表示压缩70%; 如果不压缩是100，表示压缩率为0

bm.compress(Bitmap.CompressFormat.JPEG, 30, baos);//30 是压缩率，表示压缩70%; 如果不压缩是100，表示压缩率为0

完整的方法代码：
[java]

复制代码代码如下:
public static Bitmap getSmallBitmap(String filePath) {

final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(filePath, options);

// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, 480, 800);

// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;

Bitmap bm = BitmapFactory.decodeFile(filePath, options);
if(bm == null){
return null;
}
int degree = readPictureDegree(filePath);
bm = rotateBitmap(bm,degree) ;
ByteArrayOutputStream baos = null ;
try{
baos = new ByteArrayOutputStream();
bm.compress(Bitmap.CompressFormat.JPEG, 30, baos);

}finally{
try {
if(baos != null)
baos.close() ;
} catch (IOException e) {
e.printStackTrace();
}
}
return bm ;

}

public static Bitmap getSmallBitmap(String filePath) {

final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(filePath, options);

// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, 480, 800);

// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;

Bitmap bm = BitmapFactory.decodeFile(filePath, options);
if(bm == null){
return null;
}
int degree = readPictureDegree(filePath);
bm = rotateBitmap(bm,degree) ;
ByteArrayOutputStream baos = null ;
try{
baos = new ByteArrayOutputStream();
bm.compress(Bitmap.CompressFormat.JPEG, 30, baos);

}finally{
try {
if(baos != null)
baos.close() ;
} catch (IOException e) {
e.printStackTrace();
}
}
return bm ;

}

[java]

复制代码代码如下:
view plaincopyprint?private 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) {

// Calculate ratios of height and width to requested height and
// width
final int heightRatio = Math.round((float) height
/ (float) reqHeight);
final int widthRatio = Math.round((float) width / (float) reqWidth);

// Choose the smallest ratio as inSampleSize value, this will
// guarantee
// a final image with both dimensions larger than or equal to the
// requested height and width.
inSampleSize = heightRatio < widthRatio ? widthRatio : heightRatio;
}

return inSampleSize;
}

private 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) {

// Calculate ratios of height and width to requested height and
// width
final int heightRatio = Math.round((float) height
/ (float) reqHeight);
final int widthRatio = Math.round((float) width / (float) reqWidth);

// Choose the smallest ratio as inSampleSize value, this will
// guarantee
// a final image with both dimensions larger than or equal to the
// requested height and width.
inSampleSize = heightRatio < widthRatio ? widthRatio : heightRatio;
}

return inSampleSize;
}

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