Take a journey through the creation of an educational game that brings together Core ML, ARKit, and other app frameworks. Discover opportunities for magical interactions in your app through the power of machine learning. Gain a deeper understanding of approaches to solving challenging computer vision problems. See it all come to life in an interactive coding session.
Good morning, and thank you
for coming to our session.
At Apple, we build technologies.
We build technologies so that
you can make great apps with
And my favorite apps are the
ones that seamlessly blend those
technologies and really immerse
us in the experience.
Today we'd like to talk to you
about two of these technologies:
Core ML and ARKit.
Both of these help our devices
gain a level of understanding
about the world around us.
They help us blend the physical
and virtual worlds.
Today we're going to take you on
a journey of building an app
that does just that.
Along the way, we're going to
look at some challenges that we
faced and how we overcame them,
and we're going to look at some
themes that arose from facing
The first, being the question,
can machine learning help?
Well, okay, if I said no, then
this would be a pretty short
But I can't just say a blanket
yes, because the answer really
depends on the type of problem
you're trying to solve and the
data you have to solve it,
because machine learning is
about understanding data.
It's about understanding
patterns in data, patterns in
data that may be difficult to
write down programmatically.
And this data exists in your
Your users enter it every day.
They use the keyboard and they
They use the microphone and they
They use the camera and they
capture video and pictures.
So when facing a problem, asking
yourself, can machine learning
help, is a good question to ask.
Now, you need to take a close
look at the problem you're
trying to solve and the data you
have available to solve it.
The second theme that we're
going to look at today is
understanding the behavior of
These models are trained to
expect certain inputs in certain
formats and to provide outputs
in certain formats.
And so if your input is not in
the format that's expected for
the model, then the output is
going to be unexpected as well.
And speaking of outputs, if you
don't understand what's being
output from your model, it's
going to be difficult to use it
to make that magical experience
in your app.
We're going to look at a couple
ways that you can visualize the
inputs and the outputs of some
But for now, on with our
We said that we're going to
combine technologies to blend
the physical and virtual worlds,
and what better context to do
this in than an app?
We thought that it would be fun
to build an educational game app
for children to practice their
math skills, like counting, or
addition, or multiplication.
And we know that children
sometimes use dice to practice
Now, we could've just put
virtual dice in the app and let
those roll around on the screen,
but we thought, wouldn't it be a
lot more fun if the children
could play with physical dice
and roll those on the table and
then interact with our app?
So that's what we did.
And the first challenge that we
ran into was, how do you get an
app to recognize dice?
Well, there's a couple
Let's start programmatically.
But this is going to be a little
If we constrain our problem to
only six-sided dice, we can
start to look at the properties
of a die.
For instance, the die behind me,
its color is gray.
But not all dice are gray, so
that's not necessarily helpful.
If you look at it in a 2D plane,
it's a hexagon shape and it has
three skewed squares for sides.
But those move and change as the
die rolls around on the table.
If we take a closer look at each
side, there's a number of dots
on them; but again, that's
different depending on the side
you're looking at and depending
on your perspective of the die.
So with all of these properties
changing, it's going to be
pretty difficult to write a
program to recognize dice.
So let's take a look at the
machine learning approach.
We could train an image
classification model to
recognize dice in an image.
But we want to know how many
dice are in an image -- not just
the existence of dice in an
So instead, we looked at using
an object detection model.
An object detection model will
tell us if there's dice in an
image, but it will also tell us
where it is in the image; and if
we know where the dice are in
the image, then we can count
To do this, we needed to get
data, so we took a bunch of
pictures of dice rolling around
on the table.
Next, we took those pictures and
we annotated them with bounding
boxes, indicating where the dice
are in the images.
After that, we used the new
Create ML to train our custom
object detection model.
If you'd like to learn more
about this training, please see
the Create ML for Object
Detection and Sound
Now I'd like to invite Scott up
to show you this in action.
Good morning, everyone.
As Brent discussed, we're
going to be exploring adding the
ability for our app to count
dice using a machine learning
technique called object
And I'm sure you're all eager to
see it in action, so let's get
right to it.
So here, we have a very simple
app that's wired with a live
camera view, and we've added our
object detector trained to
detect dice so that we can count
So let's see what happens when
we add dice to the frame.
One, two, three, and four.
We can even take a roll for more
So this is great.
Our app is able to count dice
using object detection.
But one of the themes that we
want to discuss with you today
is understanding your model's
So let's actually take a look at
a debug visualization of what
the model is seeing.
As you can see, we're drawing
bounding boxes around each of
the detected objects -- in this
case, dice -- on the board.
And if we move them around,
those boxes will move as well.
This is important to you because
if you are training an object
detector and you start playing
around with it, and you don't
notice certain boxes around
objects that aren't what you're
trying to detect, or you're not
seeing boxes around the objects
that you are trying to detect,
this is probably the opportunity
for you to go and collect more
data in this kind of lighting.
You may want to collect more
data with different kinds of
backgrounds, different lighting,
with a different number of
objects -- in this case, we have
four, but you may want to
collect with five, six, up to
ten dice, or less, or even
images without them to train it
to not recognize other objects.
Let's take a look at some code
to do this.
When you use your object
detector that you've trained
with Create ML, in the Vision
framework, what you get back as
a result is a list of VN
recognized object observations.
So here we have a function that
handles those observations and
does a couple things for us.
The first one is the easiest:
we're just counting dice.
And this just is as simple as
counting the number of
observations because we have one
Next, we have a couple helper
functions that help us draw
these bounding boxes on screen
based on these recognized object
We have a first function that
matched the bounds you get from
each recognized object
observation, which come in
normalized coordinates based on
the input image you provide to
Vision, so that function maps
those back to our view
controller's views coordinate
system so that we can
appropriately draw them on
screen, overlaying them on top
of the actual objects.
Next we have a helper function
that creates our beautiful
rounded rectangles that we
display on screen, which is a
CALayer, and we add that CALayer
to an overlay layer to be
rendered on screen.
All this code is available in
the sample app associated with
this session, which I encourage
you to check out.
So this is really promising: our
app is able to count dice using
But you may have already
realized or thought about the
fact that games typically don't
rely on the count of dice; they
typically rely on the values
displayed on them.
So we need to take this one step
further and figure out how to
recognize the values displayed
on these dice.
This is ultimately the goal that
we want our app to have: we want
it to be able to tell that the
die on the right side is a 5 and
the one on the left is a 1.
Luckily for us, as Brent
mentioned, object detectors can
not only detect but classify
objects, because they're built
to be able to recognize all
sorts of different objects and
So we went ahead and updated all
our training data to actually
consider dice with different
values to be of a different
class, just like you can see on
So this sounded really
promising, and so we gave it a
try in our app.
Let's take a look at some of the
examples that we ran into.
In most cases, it worked
As you can see in the picture
behind me, our object detector
is able to correctly and
accurately detect and classify
the dice on the left of the
screen; but if we focus in on
the other side, we can see that
our object detector is actually
detecting the 6 and the 4 as one
And if we think a little bit
about what's happening, it's
clear that the model isn't able
to tell those apart as two
separate dice, and it really
comes down to the fact that the
4 is being occluded by the one
So after thinking about this a
little bit, what we realized was
that we really care about the
tops of these dice, and those
are always visible in our frame.
So we went ahead and we helped
our model a little bit.
We updated all our training data
to actually focus in on the tops
of these dice.
So now we're actually training
an object detector, not to
detect dice, but to detect tops
So let's take a look at what
happened when we did that.
As you can see, our model was
still able to correctly predict
and classify the same dice as
before, but now it's also able
to correctly detect and identify
the dice on the right.
We wanted to share with you
another anecdote today.
At some point along our journey,
we noticed this behavior, where
our model was actually detecting
the left side of the dice,
This was very confusing at
first, but if we actually rotate
this image, we can understand
how the model thought these were
This was super easy to realize
as soon as we looked at the
input of our model.
We were simply not handling the
image orientation according to
our device's orientation, which
is a very common problem for
So the key lesson here is, if
you notice odd behavior in your
model's output, it doesn't hurt
to take a look at the input.
It may be as simple as rotating
your image based on the
orientation of the device.
So let's see this new model in
So here we have the same app,
but we updated it to have our
model that's able to detect and
classify diced as well.
For simplicity, I'm going to
focus on three dice.
We can see that our model is
predicting 6, 5 and 2.
So let's take a roll.
Four, 6 and 5.
Awesome. This is really
So I want to bring your
attention to a detail here that
I think is very important.
If I move the dice around, you
can see that the list updates.
We're actually displaying the
list of values according to the
order in which the dice are laid
out on the table.
This is a minor design detail,
but it really brings consistency
to the experience, because the
user is seeing these dice laid
out in that fashion on the
So since we're blending the
physical and virtual worlds,
we're actually giving the user a
very consistent display of the
There's another thing we need to
figure out: when does a roll
Again, games typically don't
rely on transient states of a
roll; they rely on the result of
When you play a game, you roll
some dice, and based on the
result of that, your pawn either
moves or you make some decision.
In this case, we may want to
animate something or provide
feedback to the user.
And you may have noticed in the
demos that I just showed, I
didn't show the numbers until
the roll had ended.
So how do we do this?
Well, first we need to ask our
self, what do we observe?
In this case, we notice that the
dice stop moving and the values
are stable between different
So can machine learning help us
Perhaps we could build a
sequential model that takes in
frames and decides when the roll
has ended, but we already have a
model that has a really good
understanding of dice on the
So what we really need to do is
interpret the output of our
So let's take a look at how to
do this in code.
Here we have a function that
takes in two lists of object
observations: one from the
current camera frame and one
from the previous camera frame.
So there's a few things we need
to check in order to decide that
the roll has ended.
The first is, do we have as many
dice now as we had before?
If not, maybe one die has
entered the camera frame, so we
now have more than before.
If we have less than before,
maybe one of them is bouncing
around so the detector isn't
picking that up.
So if we don't have as many now
as before, the roll is still
Next we're going to compare each
of the observations in the
previous prediction and in the
If the values represented on top
of the dice aren't the same, our
roll has not ended yet.
And we also check that the
bounding boxes overlap between
these predictions by more than
If the bounding boxes between
the prediction we're looking at
and the one we're comparing it
with don't overlap, either we're
looking at two completely
different dice, or it's the same
one that has moved by a
Finally, if we have as many
matches now as we have dice on
the table, the roll has ended.
So now that our app can find,
count, recognize dice on a table
and figuring out the end of a
roll, we have a foundation for
building something more.
And it's time to talk about the
next steps of our journey.
To do that, I'd like to welcome
Brent back up to the stage.
Thank you, Scott.
As Scott said, our app can now
recognize dice on the table.
The next thing we need to look
at is, how do we handle user
We know that our users are going
to be entering numbers into our
app, because we're practicing
And we could've just put a large
number pad up on the screen and
have them tap in the numbers,
but we wanted to facilitate a
more natural interaction with
And remember: we're working with
children here, and children are
also practicing writing their
So we thought, why not just let
them draw directly on the
Well, to do this, we're going to
need our app to be able to
recognize handwritten digits.
Fortunately, machine learning is
already doing a very good job at
solving this problem; in fact,
there's an entire dataset
available to let you train your
own models to recognize
It's called MNIST.
Well, we did that, and we put
that model on our new Core ML
So let's take a look in code at
how we'd use this model.
We're going to use Vision and
We set up Vision to use our Core
ML model; in this case,
Next, we get our image from the
PencilKit canvas view.
After that, we set up our Vision
request handler to use that
Then, we perform the request and
we get the results.
It's as easy as that.
So we integrated this into our
model, and it started working
We were recognizing quite a few
But as we started drawing some
larger digits, we noticed
something interesting: our model
was sometimes getting the
So what's happening?
Well, to understand, we need to
see what image is being input to
And we can do that in Xcode.
So we set a break point where we
get the image from PencilKit,
and we use Xcode's quick view to
actually look at what that image
And when we did, we saw
something interesting: our 7s
from the example are not looking
like 7s to the model.
They're looking a lot more like
So what's happening here?
We need to think about what the
model's expecting for an input.
This model is expecting a 28 by
28 pixel image, but the image
that we get drawn on the screen
is much bigger than that.
So to get the image in the right
format, we have to downscale it.
But as we downscaled it, we lost
information about the strokes
that were being drawn on the
screen, and our 7s started
looking a lot more like 1s.
Once we knew that, the fix was
pretty easy: we just needed to
have a thicker stroke on the
And when we did that, after we
downscaled, our images going to
the model looked a lot more like
what was being drawn on the
screen, and the model started
getting the predictions correct.
PencilKit makes this really
Here we have allowsFingerDrawing
set to true, since we're drawing
on the screen with our fingers;
and then, we set the tool to be
something like a marker with a
Our model is now predicting
single digits really well, but
we have another couple
Some digits are written with
Our model takes a static image
of a digit, not stroke
information about that digit.
So how do we know when to take
what's being drawn on the screen
and pass it to our model to get
Additionally, since we're adding
dice or possibly multiplying
dice, we may be working with
numbers that have multiple
digits, and our model is only
trained to recognize single
digits, not multiple digits.
So how do we handle that?
We could've used machine
learning to solve these
We could've trained a model to
recognize stroke information
about digits, or we could've
trained a model to recognize
numbers with multiple digits,
but we already know a lot of
information about what's being
drawn on the screen.
So instead, we decided to solve
this problem programmatically,
and I'll show you how.
Let's take this example.
Someone draws the first stroke
of a 1 on the screen.
We take that, we pass it as an
image to our model, and we get a
prediction, and it's a 1.
Next, they draw the second
stroke of a 1, the base.
We look to see if any of that
stroke is overlapping any of the
Since it is, we know that it's
the same number, so we get rid
of the first prediction, we
combine the first stroke with
the second stroke into one
image, and we pass that entire
image to the model.
And that gets predicted to be a
Next, the user draws another
stroke on the screen.
We look at that third stroke and
see if any of it overlaps either
of the first two strokes.
Since it doesn't, we know that
it's a separate number, so we
pass it separately to the model,
and it gets predicted to be a 2.
Now I'd like to invite Scott
back up to show you this in the
We now have an updated app that
still has our object detector
that's able to detect and
classify dice and their values,
but we've also added the ability
to draw input just like Brent
discussed with you.
So I think it's time to do some
Here, the user has the option to
either add the values displayed
on the dice or multiply them.
And so to keep things simple,
I'm going to start with
So let's see how input handling
So if we multiply these values,
I'm pretty sure we get 24.
Now, that's an interesting
I want you to pay close
attention to what happens when I
draw the 4 on screen.
If you think about a 4 that's
drawn with two strokes, our
model's going to have a pretty
hard time figuring out that's a
4 when it only sees the first
stroke, so it may predict some
other digit until I draw the
Let's have a look.
Did you notice that the first
stroke of my 4 was predicted as
a 1, but as soon as I had the
second stroke, that was a 4?
There's one other answer that is
always correct, and I just want
to show you more 4s, so let's
Cool. So our app can recognize
dice on the table, understand a
roll, it can check our math, we
can input that using drawing to
draw the digits on screen, but
we're talking about blending the
physical and virtual worlds
together, so we thought it would
be a lot of fun and also very
interactive if the kids playing
with our game could input their
answers in the form of voice.
So let's take a look at that.
Again, I'm going to add or
multiply these two together and
And let's do that using speech.
This is super easy to do using
the speech framework.
And new this year in speech, we
have offline speech recognition.
This means that speech
recognition can work in your app
even when your device is not
connected to the internet.
And if you really want your
user's data to remain on their
device, you can actually require
speech recognition to happen on
device by setting
true on your speech recognizer.
So now our app can understand a
dice roll and handle input in
various different ways, but we
need to move on with our journey
and finish this up.
So I'd like to welcome Brent
back up to the stage.
Thank you, Scott.
As Scott mentioned, we have our
app recognizing dice, and we
know how to handle user input.
But we said this was going to be
a game, right?
So let's make it that.
Next we're going to integrate in
ARKit and really finalize the
Of course, any game needs rules,
so let's go over those first.
Our game is played on a circular
board with nine sections.
Each player starts on section
one, and the goal is to move
clockwise around the board and
land directly on section nine.
A roll that's too small, and you
don't go far enough.
A roll that's too large, and
you're going to overshoot your
During each player's turn, they
roll the dice, and they have two
options: they can take the sum
of that dice and move that
number in a clockwise direction,
or they can take the difference
of the dice and move that number
in a clockwise direction.
So Scott, you up for a game?
So we've now integrated our
virtual board into our ARKit
game that's also using Core ML
to recognize dice.
How about you start off, Brent?
The 5 -- I've got a 5 and a 2.
I think I'm going to add those.
Ooh, you got really close.
So we got 6 and 1; I can
either subtract these and get 5
or add them and join Brent on
the 8 slot, so let's add these.
I don't think I'm going to be
able to get a 1.
I think I'll subtract this time.
Let me do a 2.
Okay. So I got 6 and 1 again.
This time I'm going to change it
up and do a 5.
And Brent really thinks -- yeah.
Brent thinks I draw funny 5s.
You know, this game could
probably go on pretty long, but
I think Scott might've mentioned
something about a number always
being correct, so let's see if
this works in our game.
Ah, you found the secret,
Today we looked at combining
multiple technologies together
to blend our physical and
We built an experience that goes
beyond any single technology and
it let us play this fun game in
this enhanced new world.
We used object detection to
recognize dice on the table.
We used image classification to
recognize handwritten digits on
We used speech recognition as
another way to interact with our
And we brought in ARKit to
really finalize the whole
If you'd like more information,
please see our session 228 on
the developer website or come
talk to us in the labs tomorrow.
Thank you, and have a great rest
of the show.
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