Patent filings have once again ignited interest in Apple Pencil on iPhone — so what are the odds we're going to get it?

I've wanted Apple Pencil support on iPhone — specifically iPhones with larger than 5-inch displays — for a long time. My background is in art and design and the idea of having a tiny drawing pad delights me. It's my favorite thing about Samsung's Galaxy Note 8 series. It's not my favorite implementation (see below), but the idea of being able to doodle anywhere, any time I have my phone in hand is beyond compelling. Same for markup, notes, all of it.

So far, though, Apple's kept Pencil exclusive to iPad. (And, similarly, 3D Touch to iPhone.) Why?

Tale of two technologies

A while ago I wrote about the different requirements for 3D Touch-based pressure sensitivity and Apple Pencil-based pressure sensitivity:

With 3D Touch on the iPhone, an array of capacitive sensors integrated into the LED backlight system measure microscopic changes in the distance between the array and the cover glass—the kind of changes created by pressure from your finger.

That's combined with data from the accelerometer, which knows how your iPhone is moving through space, and with data from the capacitive multitouch sensor, which knows where your finger is on the horizontal and vertical planes. That way, Apple's algorithm can provide for the precise, linear, and continuous tracking of pressure events.

And because Apple is likely moving away from LCD/LED to OLED in iPhone 8, and will need to implement a different force detection system:

Rumor has it Apple will use a film sensor instead. It's reportedly more expensive but takes up less space, is even more precise, and could theoretically allow for multiple simultaneous points of pressure detection.

Both implementations are different than how Apple Pencil currently works. From my original iPad Pro review:

When the iPad Pro display senses the Apple Pencil, it boosts the scanning rate to 240 Hz. That makes for excellent responsiveness. The multitouch technology in the panel also detects things like the tilt in the Pencil so it can do things like switching from line rendering to shading. What's more, the iPad Pro receives data from the Pencil over Bluetooth, including pressure levels, which lets it dynamically adjust things like opacity and/or size.

Apple has also provided frameworks for coalescing and predicting touch events, allowing apps to fine-tune everything from palm rejection to Pencil tracking. The result is digital input that tracks what you're doing with remarkably little latency and remarkably high accuracy.

Multitouch is actually 3D. It radiates from the display and can sense capacitance even if not in direct contact. Other vendors have used this to add features like hover state or to provide some measure of support with thin gloves. Apple has used it to map the hand, figure out its position, and more accurately register touch events and reject unintentional contact.

With Apple Pencil, that's combined with the pressure and other information coming off the tip and body of the Pencil itself to produce a remarkably real-world feeling from a digital tool. One much better, in my many years of experience, than the kind achieved with previous generation digitizer-layer technologies like those used by Wacom/Samsung and Microsoft.

Putting the two technologies together adds both complexity and cost. It has to be done in such a way that neither interferes with or compromises each other, nor raises the bill of goods higher than Apple's price points (with desired margins) would allow.

Putting Pencil in the palm of your hand

In order to support Apple Pencil on iPhone, a few things would need to happen. First, iPhone would need to be able to ramp up screen refresh to reduce latency. Apple's ProMotion technology, which debuted back in June with the second generation iPads Pro, should be able to handle that.

From my 10.5-inch iPad Pro review:

Apple's brand name for up to 120 Hz adaptive refresh rate, it lets the display ramp up to 120 fps for tasks like drawing with Apple Pencil, so you get ultra-low latency — 20 milliseconds.

ProMotion would also significantly improve the iPhone's display experience, including clearer scrolling and video playback down to "cinematic" 24 fps. When and if Apple adds ProMotion to iPhone, it would have to be compatible with 3D Touch and fit within Apple's cost structure, so that handles that.

Size matters

The only other potential issue when thinking about Apple Pencil on iPhone is size. Apple Pencil was designed to be a full-sized tool. It wasn't shrunk down so it could be stuffed inside a phone. That makes it annoying to cary — where's my Pencil?! — but incredible to use. And since an iPad isn't a pocket device anyway, it's not much more work to pull out a Pencil along with it.

iPhone, though, is often kept in a pocket. That's what makes the shrunk down stylus pens on Galaxy Note so convenient to carry, if less enjoyable to use.

Apple could simply add support for the current or next-generation Apple Pencil to iPhone and require people to either stuff it into a pocket as well, or carry it in a bag. Apple could also come up with something purpose-built for iPhone and the way iPhone is used.

Better on the bigger phone

Yes, Steve Jobs once said "yuck" about stylus pens and claimed the finger was the best input method. And Jobs was correct — at that time. Resistive stylus pens were... yucky. But time marches on and technology improves. Apple Pencil isn't a resistive stylus. It may not be "better" than your finger, but it's an amazing complement and extension to your finger.

Apple has no doubt tested Pencil technology on iPhone. Apple tests everything. Yet, Apple hasn't released an iPhone with Pencil support, nor has the company brought Pencil to iPad mini. That means we have our sketchbook (~13-inch) and notebook (~10-inch), but no field notebook (~6-inches).

Looking at Apple's current product line and projecting forward, it feels like iPad mini's best days are behind it while iPhone's potential is still increasing. Apple Pencil support would only accelerate that.

So, here's hoping Apple starts doing more than just testing Pencil on iPhone — and starts shipping.