[Android advanced] detailed explanation of Android image compression algorithm,

[Android advanced] detailed explanation of Android image compression algorithm,


For more information about image compression (size and quality), see.


1. Quality Compression Method
Private Bitmap compressImage (Bitmap image ){

ByteArrayOutputStream baos = new ByteArrayOutputStream ();
Image. compress (Bitmap. CompressFormat. JPEG, 100, baos); // quality compression method. Here, 100 indicates no compression. Store the compressed data in baos.
Int options = 100;
While (baos. toByteArray (). length/1024> 100) {// cyclically determine if the image is larger than kb after compression and greater than Continue compression
Baos. reset (); // reset baos to clear baos
Image. compress (Bitmap. CompressFormat. JPEG, options, baos); // compress options % to save the compressed data to baos.
Options-= 10; // reduce each time by 10
}
ByteArrayInputStream isBm = new ByteArrayInputStream (baos. toByteArray (); // store the compressed data baos in ByteArrayInputStream
Bitmap bitmap = BitmapFactory. decodeStream (isBm, null, null); // generates an image from ByteArrayInputStream
Return bitmap;
}
2. Proportional compression: first the image size and then the image quality compression (obtain and compress the Image Based on the path)
Private Bitmap getimage (String srcPath ){
BitmapFactory. Options newOpts = new BitmapFactory. Options ();
// Start reading the image, and set options. inJustDecodeBounds back to true.
NewOpts. inJustDecodeBounds = true;
Bitmap bitmap = BitmapFactory. decodeFile (srcPath, newOpts); // at this time, the returned bm is empty.


NewOpts. inJustDecodeBounds = false;
Int w = newOpts. outWidth;
Int h = newOpts. outHeight;
// Currently, most mainstream mobile phones have a resolution of 800*480, so we set the height and width
Float hh = 800f; // set the height to 800f.
Float ww = 480f; // set the width to 480f.
// Scale ratio. Because it is a fixed proportional scaling, only one of the data in the height or width can be calculated.
Int be = 1; // be = 1 indicates no Scaling
If (w> h & w> ww) {// if the width is large, scale it according to the fixed width.
Be = (int) (newOpts. outWidth/ww );
} Else if (w

Be = (int) (newOpts. outHeight/hh );
}
If (be <= 0)
Be = 1;
NewOpts. inSampleSize = be; // set the scaling ratio.
// Read the image again. Note that options. inJustDecodeBounds has been set back to false.
Bitmap = BitmapFactory. decodeFile (srcPath, newOpts );
Return compressImage (bitmap); // compress the proportion before performing quality compression.
}
3. Proportional compression: first the image size and then the image quality compression (obtain and compress the Image Based on the path)
Private Bitmap comp (Bitmap image ){


ByteArrayOutputStream baos = new ByteArrayOutputStream ();
Image. compress (Bitmap. CompressFormat. JPEG, 100, baos );
If (baos. toByteArray (). length/1024> 1024) {// determine if the image is larger than 1 MB, compress the image to avoid overflow when generating the image (BitmapFactory. decodeStream ).
Baos. reset (); // reset baos to clear baos
Image. compress (Bitmap. CompressFormat. JPEG, 50, baos); // compress 50% to save the compressed data to baos.
}
ByteArrayInputStream isBm = new ByteArrayInputStream (baos. toByteArray ());
BitmapFactory. Options newOpts = new BitmapFactory. Options ();
// Start reading the image, and set options. inJustDecodeBounds back to true.
NewOpts. inJustDecodeBounds = true;
Bitmap bitmap = BitmapFactory. decodeStream (isBm, null, newOpts );
NewOpts. inJustDecodeBounds = false;
Int w = newOpts. outWidth;
Int h = newOpts. outHeight;
// Currently, most mainstream mobile phones have a resolution of 800*480, so we set the height and width
Float hh = 800f; // set the height to 800f.
Float ww = 480f; // set the width to 480f.
// Scale ratio. Because it is a fixed proportional scaling, only one of the data in the height or width can be calculated.
Int be = 1; // be = 1 indicates no Scaling
If (w> h & w> ww) {// if the width is large, scale it according to the fixed width.
Be = (int) (newOpts. outWidth/ww );
} Else if (w

Be = (int) (newOpts. outHeight/hh );
}
If (be <= 0)
Be = 1;
NewOpts. inSampleSize = be; // set the scaling ratio.
// Read the image again. Note that options. inJustDecodeBounds has been set back to false.
IsBm = new ByteArrayInputStream (baos. toByteArray ());
Bitmap = BitmapFactory. decodeStream (isBm, null, newOpts );
Return compressImage (bitmap); // compress the proportion before performing quality compression.
}