android bitmap compress（图片压缩）

android bitmap compress

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://blog.csdn.net/luhuajcdd/article/details/8826587 ->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] view
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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] view
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int degree = readPictureDegree(filePath);

bm = rotateBitmap(bm,degree) ;

[java] view
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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] view
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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] view
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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] view
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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] view
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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;

}