Android: Loading images Super-Fast like WhatsApp – Part 2

We discussed earlier in Part 1 of this tutorial how Zingoo team wants to deliver the best UX possible to the users, & because WhatsApp is doing a great job with images, so we watched what they are doing, like:

  • Photos are cached, so no need to load them every time you open the app.
  • They first show a very small thumbnail (about 10KB or less) until the real image is loaded, & this is the real pro-tip for their better UX.
  • Photos sizes range around 100KB, which loads the images pretty fast on most common mobile-network speeds.

First 2 points are already discussed in part 1, so question here in part 2 is how could we compress images to be about 100KB to be sent easily over common mobile-networks.

How is it done?
After taking the picture and saving it to a file with path imagePath, we start compressing it to be ready for sending over network:

ImageCompressionAsyncTask imageCompression = new ImageCompressionAsyncTask() {
    @Override
    protected void onPostExecute(byte[] imageBytes) {
        // image here is compressed & ready to be sent to the server
    }
};
imageCompression.execute(imagePath);// imagePath as a string

& here is what we do in ImageCompressionAsyncTask:

public abstract class ImageCompressionAsyncTask extends AsyncTask<String, Void, byte[]> {

    @Override
    protected byte[] doInBackground(String... strings) {
        if(strings.length == 0 || strings[0] == null)
            return null;
        return ImageUtils.compressImage(strings[0]);
    }

    protected abstract void onPostExecute(byte[] imageBytes) ;
}

It is clear that the real juice exists in ImageUtils.compressImage(). Thanks to Ambalika Saha & her brilliant post that enabled me from using this solution in Zingoo, and even writing this post right here 🙂 . And here is my version of doing it:

public class ImageUtils {
    private static final float maxHeight = 1280.0f;
    private static final float maxWidth = 1280.0f;

    public static byte[] compressImage(String imagePath) {
        Bitmap scaledBitmap = null;

        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        Bitmap bmp = BitmapFactory.decodeFile(imagePath, options);

        int actualHeight = options.outHeight;
        int actualWidth = options.outWidth;
        float imgRatio = (float) actualWidth / (float) actualHeight;
        float maxRatio = maxWidth / maxHeight;

        if (actualHeight > maxHeight || actualWidth > maxWidth) {
            if (imgRatio < maxRatio) {
                imgRatio = maxHeight / actualHeight;
                actualWidth = (int) (imgRatio * actualWidth);
                actualHeight = (int) maxHeight;
            } else if (imgRatio > maxRatio) {
                imgRatio = maxWidth / actualWidth;
                actualHeight = (int) (imgRatio * actualHeight);
                actualWidth = (int) maxWidth;
            } else {
                actualHeight = (int) maxHeight;
                actualWidth = (int) maxWidth;

            }
        }

        options.inSampleSize = ImageUtils.calculateInSampleSize(options, actualWidth, actualHeight);
        options.inJustDecodeBounds = false;
        options.inDither = false;
        options.inPurgeable = true;
        options.inInputShareable = true;
        options.inTempStorage = new byte[16 * 1024];

        try {
            bmp = BitmapFactory.decodeFile(imagePath, options);
        } catch (OutOfMemoryError exception) {
            exception.printStackTrace();

        }
        try {
            scaledBitmap = Bitmap.createBitmap(actualWidth, actualHeight, Bitmap.Config.ARGB_8888);
        } catch (OutOfMemoryError exception) {
            exception.printStackTrace();
        }

        float ratioX = actualWidth / (float) options.outWidth;
        float ratioY = actualHeight / (float) options.outHeight;
        float middleX = actualWidth / 2.0f;
        float middleY = actualHeight / 2.0f;

        Matrix scaleMatrix = new Matrix();
        scaleMatrix.setScale(ratioX, ratioY, middleX, middleY);

        Canvas canvas = new Canvas(scaledBitmap);
        canvas.setMatrix(scaleMatrix);
        canvas.drawBitmap(bmp, middleX - bmp.getWidth() / 2, middleY - bmp.getHeight() / 2, new Paint(Paint.FILTER_BITMAP_FLAG));

        ExifInterface exif;
        try {
            exif = new ExifInterface(imagePath);
            int orientation = exif.getAttributeInt(ExifInterface.TAG_ORIENTATION, 0);
            Matrix matrix = new Matrix();
            if (orientation == 6) {
                matrix.postRotate(90);
            } else if (orientation == 3) {
                matrix.postRotate(180);
            } else if (orientation == 8) {
                matrix.postRotate(270);
            }
            scaledBitmap = Bitmap.createBitmap(scaledBitmap, 0, 0, scaledBitmap.getWidth(), scaledBitmap.getHeight(), matrix, true);
        } catch (IOException e) {
            e.printStackTrace();
        }
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        scaledBitmap.compress(Bitmap.CompressFormat.JPEG, 85, out);
        return out.toByteArray();
    }

    public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;

        if (height > reqHeight || width > reqWidth) {
            final int heightRatio = Math.round((float) height / (float) reqHeight);
            final int widthRatio = Math.round((float) width / (float) reqWidth);
            inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;
        }
        final float totalPixels = width * height;
        final float totalReqPixelsCap = reqWidth * reqHeight * 2;

        while (totalPixels / (inSampleSize * inSampleSize) > totalReqPixelsCap) {
            inSampleSize++;
        }

        return inSampleSize;
    }
}

I hope you like it.

Advertisements