问题
Background
I need to rotate images taken by the camera so that they will always have a normal orientation.
for this, I use the next code (used this post to get the image orientation)
//<= get the angle of the image , and decode the image from the file
final Matrix matrix = new Matrix();
//<= prepare the matrix based on the EXIF data (based on https://gist.github.com/9re/1990019 )
final Bitmap rotatedBitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(),matrix,false);
bitmap.recycle();
fileOutputStream = new FileOutputStream(tempFilePath);
rotatedBitmap.compress(CompressFormat.JPEG, 100, fileOutputStream);
rotatedBitmap.recycle();
here the compression rate (AKA "quality" parameter) is 100.
The problem
The code works fine, but the result is larger than the original, much much larger.
The original file is around 600-700 KB, while the resulting file is around 3MB ...
This is even though both the input file and the output file are of the same format (JPEG).
The camera settings are at "super fine" quality. not sure what it means, but I think it has something to do with the compression ratio.
What I've tried
I've tried to set the "filter" parameter to either false or true. both resulted in large files.
Even without the rotation itself (just decode and encode), I get much larger files sizes...
Only when I've set compression ratio to around 85, I get similar files sizes, but I wonder how the quality is affected compared to the original files.
The question
Why does it occur?
Is there a way to get the exact same size and quality of the input file ?
Will using the same compression rate as the original file make it happen? Is it even possible to get the compression rate of the original file?
What does it mean to have a 100% compression rate ?
EDIT: I've found this link talking about rotation of JPEG files without losing the quality and file size , but is there a solution for it on Android ?
Here's another link that says it's possible, but I couldn't find any library that allows rotation of jpeg files without losing their quality
回答1:
I tried two methods but I found out those methods take too long in my case. I still share what I used.
Method 1: LLJTran for Android
Get the LLJTran from here: https://github.com/bkhall/AndroidMediaUtil
The code:
public static boolean rotateJpegFileBaseOnExifWithLLJTran(File imageFile, File outFile){
try {
int operation = 0;
int degree = getExifRotateDegree(imageFile.getAbsolutePath());
//int degree = 90;
switch(degree){
case 90:operation = LLJTran.ROT_90;break;
case 180:operation = LLJTran.ROT_180;break;
case 270:operation = LLJTran.ROT_270;break;
}
if (operation == 0){
Log.d(TAG, "Image orientation is already correct");
return false;
}
OutputStream output = null;
LLJTran llj = null;
try {
// Transform image
llj = new LLJTran(imageFile);
llj.read(LLJTran.READ_ALL, false); //don't know why setting second param to true will throw exception...
llj.transform(operation, LLJTran.OPT_DEFAULTS
| LLJTran.OPT_XFORM_ORIENTATION);
// write out file
output = new BufferedOutputStream(new FileOutputStream(outFile));
llj.save(output, LLJTran.OPT_WRITE_ALL);
return true;
} catch(Exception e){
e.printStackTrace();
return false;
}finally {
if(output != null)output.close();
if(llj != null)llj.freeMemory();
}
} catch (Exception e) {
// Unable to rotate image based on EXIF data
e.printStackTrace();
return false;
}
}
public static int getExifRotateDegree(String imagePath){
try {
ExifInterface exif;
exif = new ExifInterface(imagePath);
String orientstring = exif.getAttribute(ExifInterface.TAG_ORIENTATION);
int orientation = orientstring != null ? Integer.parseInt(orientstring) : ExifInterface.ORIENTATION_NORMAL;
if(orientation == ExifInterface.ORIENTATION_ROTATE_90)
return 90;
if(orientation == ExifInterface.ORIENTATION_ROTATE_180)
return 180;
if(orientation == ExifInterface.ORIENTATION_ROTATE_270)
return 270;
} catch (IOException e) {
e.printStackTrace();
}
return 0;
}
Method 2: Using libjepg-turbo's jpegtran executable
1 Follow the step describe here: https://stackoverflow.com/a/12296343/1099884
Except that you don't need obj/local/armeabi/libjpeg.a on ndk-build because I only want the jpegtran executable but not mess with JNI with libjepg.a .
2 Place the jpegtran executable on asset folder. The code:
public static boolean rotateJpegFileBaseOnExifWithJpegTran(Context context, File imageFile, File outFile){
try {
int operation = 0;
int degree = getExifRotateDegree(imageFile.getAbsolutePath());
//int degree = 90;
String exe = prepareJpegTranExe(context);
//chmod ,otherwise premission denied
boolean ret = runCommand("chmod 777 "+exe);
if(ret == false){
Log.d(TAG, "chmod jpegTran failed");
return false;
}
//rotate the jpeg with jpegtran
ret = runCommand(exe+
" -rotate "+degree+" -outfile "+outFile.getAbsolutePath()+" "+imageFile.getAbsolutePath());
return ret;
} catch (Exception e) {
// Unable to rotate image based on EXIF data
e.printStackTrace();
return false;
}
}
public static String prepareJpegTranExe(Context context){
File exeDir = context.getDir("JpegTran", 0);
File exe = new File(exeDir, "jpegtran");
if(!exe.exists()){
try {
InputStream is = context.getAssets().open("jpegtran");
FileOutputStream os = new FileOutputStream(exe);
int bufferSize = 16384;
byte[] buffer = new byte[bufferSize];
int count;
while ((count=is.read(buffer, 0, bufferSize))!=-1) {
os.write(buffer, 0, count);
}
is.close();
os.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return exe.getAbsolutePath();
}
public static boolean runCommand(String cmd){
try{
Process process = Runtime.getRuntime().exec(cmd);
BufferedReader reader = new BufferedReader(
new InputStreamReader(process.getInputStream()));
int read;
char[] buffer = new char[4096];
StringBuffer output = new StringBuffer();
while ((read = reader.read(buffer)) > 0) {
output.append(buffer, 0, read);
}
reader.close();
// Waits for the command to finish.
process.waitFor();
return true;
} catch (Exception e) {
e.printStackTrace();
return false;
}
}
Unfortunately, both take too long. It is 16 seconds on my Samsung Galaxy S1!!!! But I found out this app (https://play.google.com/store/apps/details?id=com.lunohod.jpegtool) only take 3-4 seconds. There must be some way to do.
回答2:
Once you are done setting you bestPreviewSize You have to now set for bestPictureSize every phone supports different picture sizes so to get Best Picture quality you have to check supported picture sizes and then set best size to camera parameter. You have to set those parameters in surface changed to get the width and height. surfaceChanged will be called in start and thus your new parameters will be set.
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
Camera.Parameters myParameters = camera.getParameters();
myPicSize = getBestPictureSize(width, height);
if (myBestSize != null && myPicSize != null) {
myParameters.setPictureSize(myPicSize.width, myPicSize.height);
myParameters.setJpegQuality(100);
camera.setParameters(myParameters);
Toast.makeText(getApplicationContext(),
"CHANGED:Best PICTURE SIZE:\n" +
String.valueOf(myPicSize.width) + " ::: " + String.valueOf(myPicSize.height),
Toast.LENGTH_LONG).show();
}
}
Now the getBestPictureSize ..
private Camera.Size getBestPictureSize(int width, int height)
{
Camera.Size result=null;
Camera.Parameters p = camera.getParameters();
for (Camera.Size size : p.getSupportedPictureSizes()) {
if (size.width>width || size.height>height) {
if (result==null) {
result=size;
} else {
int resultArea=result.width*result.height;
int newArea=size.width*size.height;
if (newArea>resultArea) {
result=size;
}
}
}
}
return result;
}
回答3:
For rotation, try this..
final Matrix matrix = new Matrix();
matrix.setRotate(90):
final Bitmap rotatedBitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(),matrix,false);
I am using PNG images and it is working fine.... for JPEG images, please check the above code.
回答4:
100% quality rate probably is a higher quality setting than the setting the files are originally saved with. This results in higher size but (almost) the same image.
I'm not sure how to get exactly the same size, maybe just setting the quality to 85% will do (Quick and Dirty).
However if you just want to rotate the pic in 90°-steps, you could edit just the JPEG-metadata without touching the pixel data itself.
Not sure how it's done in android, but this is how it works.
来源：https://stackoverflow.com/questions/21572023/how-to-rotate-a-jpeg-file-on-android-without-losing-quality-and-gaining-file-siz