如何在不改变文件大小的情况下旋转位图？

Question

I try do this:

Bitmap bitmapOrg = BitmapFactory.decodeFile("/sdcard/"+ photoName + ".jpg");

        int width = bitmapOrg.getWidth();
        int height = bitmapOrg.getHeight();

        Matrix matrix = new Matrix();

        matrix.postRotate(90);

        Bitmap resizedBitmap = Bitmap.createBitmap(bitmapOrg, 0, 0, width,
                height, matrix, true);

        FileOutputStream os;
        try {
            os = new FileOutputStream(String.format(
                "/sdcard/" + photoName + "-rotate.jpg",
                    System.currentTimeMillis()));

        resizedBitmap.compress(Bitmap.CompressFormat.JPEG, 100, os);

rotated file size > original file size, because rotated file resolution = 96 dpi, but original file = 72 dpi. Why is this happening and how to fix it?

Answer 1

You could add in the following line right before FileOutputStream os; :

resizedBitmap.setDensity(bitmapOrig.getDensity());

Answer 2

It seems to me that another possible solution is to change the first line:

Bitmap bitmapOrg = BitmapFactory.decodeFile("/sdcard/"+ photoName + ".jpg");

With the code:

Bitmap bitmapOrg = BitmapFactory.decodeFile("/sdcard/"+ photoName + ".jpg", (new BitmapFactory.Options()).inDensity=0);

But I did not check this solution.

Moreover, it seems to me that your solution should also work. I think there is somewhere an error in the AOSP, because:

1. Function createBitmap(Bitmap source, int x, int y, int width, int height, Matrix m, boolean filter) does not change the density of the file ( bitmap.mDensity = source.mDensity; ) . New density is equal to density of the source. Thus, it seems that the density is changed before this call.
2. BitmapFactory.decodeFile calls BitmapFactory.decodeFile with the parameters (pathName, null)
3. BitmapFactory.decodeFile(pathName, null) transforms file into the stream and calls BitmapFactory.decodeStream(stream, null, opts) where opts = null
4. BitmapFactory.decodeStream(stream, null, opts) call native function bm = nativeDecodeStream(is, tempStorage, outPadding, opts); and then calls finishDecode(bm, outPadding, opts); Remember that in our case opts are equal to null.

5. In the finishDecode(bm, outPadding, opts) there is the first check that should return bitmap unchanged (opts in our case should be null):

   if (bm == null || opts == null) { return bm; }

6. Thus, it seems that something bad has happened with opts in the native function: nativeDecodeStream(is, tempStorage, outPadding, opts)

It needs a lot of time to check further where the problem is. Also, I'm not sure that I'm right in my findings.