Camera specs never tell the full story when it comes to the iPhone, and this year’s iPhone 15 and iPhone 15 Pro announcements reinforce how extensively Apple melds hardware and software to capture and create photos. All models get bumped to 48 megapixels of resolution, but Apple’s Photonic Engine and Deep Fusion technologies are working overtime - with the help of a new processor in the pro models - to boost image quality and add new camera features.

48MP on all iPhone 15 models

Apple knows people are conditioned to respond to increased megapixel numbers, and even those of us who have been taking photos with iPhones since the beginning were happy last year when the camera system finally broke out of the 12MP box. But getting that resolution involved tradeoffs: it was only on the iPhone 14 Pro, the Camera app has to be in Raw capture mode and there’s a perceptible lag between shots as the camera captures, processes and saves the file.

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As usual, when we see '48MP' on smartphone camera, it's a strong hint that the sensor has a quad bayer color filter array, which is designed so that groups of four pixels can be combined to give 12MP images. It's also possible to read the pixels individually, but some additional processing needs to be done to try to re-interpret the data as something approximating what a 48MP sensor with a conventional color layout would have captured. This process is imperfect, so images output at full resolution may be a little less detailed than the pixel count suggests.

Now, the main camera on each iPhone 15 model has a 48MP Quad Bayer sensor, enabling high-resolution captures. The iPhone 15 Pro and iPhone 15 Pro Max appear to share the same lens and sensor as the iPhone 14 Pro (even though during Apple’s event it was billed as being “even more advanced,” the specs the company shared match the previous year’s model). That would be a 24mm equivalent focal length lens at f/1.78, and a 48MP Type 1/1.28 (9.8x7.3mm) sensor with 1.22µm (Which effectively act as 2.44µm 'quad pixels' when combined at 12MP mode).

Look familiar? These are the same specs as the iPhone 14 Pro main camera. Image: Apple

The iPhone 15 and iPhone 15 Plus use a different, smaller 48MP sensor that features 2.0 µm 'quad pixels' and a 26mm equivalent lens at f/1.6. Again these are actually 1.0µm individual pixels, on an 8x6mm sensor: a third smaller than the main camera.

The main camera in the iPhone 15 and iPhone 15 Plus now sports 48MP in a slightly smaller overall size. Image: Apple

More pixels, more compression options

Capturing higher dynamic range 48MP Raw images is still a premium feature reserved for the Pro models, but now every iPhone 15 device can also record 48MP HEIF (or JPEG if you opt for "Most Compatibility" in the Camera Capture settings) files. In an odd choice of terminology crossover, Apple calls the 48 MP option ‘HEIF Max’ or ‘RAW Max’ - so you can shoot in RAW Max on your iPhone 15 Pro Max or in HEIF Max on your iPhone 15 Plus. Too many superlatives!

There’s good news here for iPhone 14 Pro owners who upgrade to iOS 17: with the 48MP sensor onboard, you can also choose to capture 48MP HEIF images, which average around 5MB in size compared to the 75MB size for ProRAW files at the maximum resolution.

48 megapixels is no longer limited to Raw files. The main camera sensor's full resolution can be captured as HEIF or JPEG files (left). Quickly switch between modes by pressing the format button (right); the 'RAW 12' refers to Raw format at 12MP on the iPhone 14 Pro.

The iPhone 15 Pro models are powered by Apple’s A17 Pro processor, which delivers performance gains throughout the iPhone experience. Relevant to this discussion, based on some reports from people who attended the Apple event and got brief hands-on time with actual units, the shutter lag when capturing Raw 48MP (sorry, 'RAW Max') images is far shorter with the new phones than the iPhone 14 Pro.

24 MP default mode

Although the sensors are capable of creating 48MP images, the default shooting mode takes advantage of pixel-binning to create lower-resolution images with better dynamic range and sharpening, aided by the iPhone’s image processing pipeline. (The camera will also switch to the lower resolution, even if 48MP is specified, when Night mode, Live Photo, macro, and flash photos are active.) In the prior iPhone 14 Pro, the main camera's default resolution is 12MP, but in the iPhone 15 and iPhone 15 Pro models, the new default is 24MP.

But if the sensors are mostly unchanged from the iPhone 14 Pro, how does that work? As before, the phones are grouping quartets of photosites as 'quad pixels' to effectively act as 12M larger, less noisy pixels. However, did we mention that the term “computational photography” comes up a lot in the keynote and on Apple’s web pages?

The quad-pixel 48MP sensor groups photosites (left) that are combined to capture the default image size for better light gathering ability (right). Images: Apple

Using Apple’s Photonic Engine technology, the camera captures multiple versions of a scene that are optimized for different things, such as light capture, noise removal, color fidelity, subject awareness and so on. It then compresses those images into a single layer. What the iPhone 15 series adds is another computational step, combining that optimized result with a 48MP image to add detail, resulting in the default 24MP image.

An optimized 12MP image is combined with a 48MP capture to create the default 24MP version. Image: Apple

The iPhone 15 Pro Max 5x Telephoto camera

There’s one sensor that didn’t gain more megapixels: the new telephoto camera found only on the iPhone 15 Pro Max is a 12MP sensor with 1.12µm pixels. This is a 4.5x3.4mm sensor, 25% larger than the 4x3mm one found in the iPhone 14 Pro's telephoto camera, which helps when receiving the light that’s been bounced and focused through the four angles of an internal tetraprism, creating a 120mm equivalent focal range. The lens doesn’t offer an actual zoom mechanism.

With the variety of the small sensors used in smartphones it can be hard to visualize what it takes to deliver a 120mm equiv lens. We calculate that the prism design in the iPhone 15 Pro Max has an effective focal length of 15.5mm to deliver that 120mm equiv reach, which makes you appreciate how its internal reflective design helps keep the size of the camera down, to fit in a phone.

Incoming light is focused by a series of prisms and stabilized by a 3D OIS. Image: Apple

Contributing to the quality of the image is a new 3D optical image stabilizer (OIS) making 10,000 microadjustments per second. With any standard long lens or telephoto lens, small camera movements are exaggerated, making it more difficult to get a clean image. Whereas the OIS in the other iPhone 15 models accounts for horizontal and vertical movement, the OIS in the iPhone 15 Pro Max also compensates for front-to-back movement.

New 'faux-cal' lengths

The iPhone 15 and iPhone 15 Plus, which both sport two physical cameras on the back, now include a 2x “zoom” option to add a little more perceived reach. This 52mm equivalent focal length is another holdover from the iPhone 14 Pro and a benefit of working with 48MP of resolution. The mode captures 12MP from the middle of the sensor, cropping out the surrounding area (though again, the Quad Bayer design means this area has a 3MP Bayer pattern spread across those twelve million pixels, so some re-interpretation is needed to deliver a 12MP image).

To achieve the '2x' zoom on all of the iPhone 15 and iPhone 15 Pro models, only a 12MP area is captured. Image: Apple

On the Pro models, Apple has implemented a similar scheme for three other increments of the main camera. Tapping the ‘1x’ button cycles among three zoom levels, which Apple has also marked as photographer-friendly millimeter equivalents: 24mm (1x), 28mm (1.2x) and 35mm (1.5x).

Three fixed focal lengths can be generated from the main camera. Apple is likening the feature to having multiple cameras, but they're actually computationally processed crops of the 48MP sensor. Image: Apple

It’s tempting to think these increments are additional crops to the 48MP sensor, the way the 2x zoom is, but on Apple’s iPhone 15 Pro product page, it specifically says, “That’s the power of computational photography.” The camera system appears to be capturing a specific range of the sensor, and then processing with Photonic Engine and other ML technologies in its pipeline.

Still, it’s nice to see the millimeter equivalents noted on the zoom dial and when you tap the 1x button. (The focal lengths are also added in the Camera app under iOS 17 for other iPhone models.) Most people won’t pay attention to those markings, but for photographers who like particular focal length comfort zones, it’s a nice frame of reference. And you can choose a default for the main camera.

The iPhone engine keeps humming

There's no getting away from the physics inherent in small sensors and small lenses, even when the hardware is highly advanced and incorporates mechanisms like the tetraprism telephoto camera. This year's iPhone is a big upgrade for the entry-level cameras for those who want more resolution and the software to make those images look good. On the pro side, except for the iPhone 15 Pro Max telephoto camera, the story has flagged a bit, but Apple's ongoing flexing of its computational photography muscles keeps things interesting (even for owners of the iPhone 14 Pro who may be content to wait for next year).