Why does saving a loaded Bitmap increase it's size?

Question

I load a png file from the sdcard. I alter it in someway and then save it again. I have noticed that the saved file is much larger than the original.

At first I thought it was because of modifying the file. Then I tested with the code below and still happens.

I just load a png file and then save it with another name.

The Original file is 32Kb and the Saved file is 300Kb. Any ideas?

     try
     {  Bitmap bm = BitmapFactory.decodeFile(Environment.getExternalStorageDirectory() + "/Original.png");
        FileOutputStream out = new FileOutputStream(Environment.getExternalStorageDirectory() + "/Saved.png"); 
        bm.compress(Bitmap.CompressFormat.PNG, 100, out);
     } 
     catch (Exception e)
     {  //Never gets here
     }

Answer 1

You can control the size of your Bitmap by the compress factor (quality):

Bitmap.compress(Bitmap.CompressFormat format, int quality, FileOutputStream out);

100 = maximum quality, 0 = low quality.

Try like "10" or something to keep your image smaller. It could also be that you are loading a Bitmap that is in 16-Bit color and than later save it in 32-Bit color, increasing its size.

Check BitmapConfig.RGB_565, BitmapConfig.ARGB_4444 and BitmapConfig.ARGB_8888 respectively.

EDIT:

Here is how to load Bitmaps correctly:

public abstract class BitmapResLoader {

    public static Bitmap decodeBitmapFromResource(Bitmap.Config config, Resources res, int resId, int reqWidth, int reqHeight) {

        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeResource(res, resId, options);

        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

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

        return BitmapFactory.decodeResource(res, resId, options);
    }

    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 ? heightRatio : widthRatio;
        }

        return inSampleSize;
    }
}

In code:

// Bitmap.Config.RGB_565 = 16 Bit
Bitmap b = BitmapResLoader.decodeBitmapFromResource(Bitmap.Config.RGB_565, getResources(), width, height);

That way, you can control how your Bitmap is loaded into Memory (see Bitmap.Config).