Typically, DSLR cameras offer two formats, JPEG and RAW. With an iPhone, you have access to two additional formats: HEIF, and ProRAW.
RAW (or True RAW)
First, it’s incredibly important to understand what a RAW image is. RAW indicates the pure data that your sensor captures with no post processing whatsoever. Typically, when you take a photo with your device’s camera, it is post processed by a proprietary set of algorithms that the manufacturer of your device has decided looks nice. This includes an algorithm to debayer or color process the image into a viewable format, as well as a proprietary “magic” to enhance your picture. For more information about debayering and how it is used please see this article. This process produces a JPEG or HEIF file (see below). Sometimes this process loses data that could otherwise be brought out in an image. For instance, it may clip out the information from dark areas that when processed to be lighter reveal interesting or important details in your scene. When you edit a JPEG or HEIF image, much of this information is already missing. RAW preserves this information and allows you some editing tools before the image is “developed” into a JPEG or HEIF format. Think of RAW like a photo negative, you can look at it, but it’s meant to be developed into the final photo. In fact, the RAW file extension is “.dng” which stands for “digital negative”. Many photographers for these reasons prefer to shoot in RAW and develop their photos later, generally on larger screens.
ProRAW
So now you may be wondering, what’s the difference between RAW and ProRAW? Importantly, ProRAW is not RAW, which sounds obvious, but is an important distinction because it’s not the pure data from the camera sensor, it’s been altered with Apple’s “magic” algorithms. However, it is saved without throwing away any of the sensor data, so you can still edit it almost like you would a RAW photo. This means you can still brighten up dark areas without losing detail, but have the added benefit of Apple’s processing. It’s a middle ground, “best of both worlds” approach. It is important to note that with a true RAW photo you can apply your own debayering algorithm, but that is not possible with ProRAW.
One more thing to consider is size. ProRAW is roughly double the size of a regular RAW photo, so if you’re worried about space, it probably isn’t for you.
The RAW Verdict
But which is better? That essentially boils down to two things, personal preference, and application. You may find that RAW produces a better base negative than ProRAW in certain situations and vice versa. Additionally, you may just not like the “magic” that comes with ProRAW. That’s ok! Both formats are perfectly valid choices, however it’s worth noting that ProRAW has much more limited support as far as programs that will allow you to edit it.
The Final Product
So now that you’ve chosen the edits you want to develop your negative with, what do you develop it into? DSLRs tend to offer only JPEG as an option, but with the iPhone, you have the added choice of HEIF. HEIF stands for High Efficiency Image Format, and was introduced into iOS in 2017.
On paper, HEIF looks like a clear winner. Its files are smaller by up to half, it has better color depth and less artifacts. However it has one glaring issue that can’t be ignored: compatibility. Being a relatively new format, HEIF isn’t supported by many popular social media and sharing services. If you share a HEIF photo from your device, it may be converted into a JPEG, which will produce artifacts from being compressed twice, or it may not display at all. So if you frequently post your work, you may want to verify that it supports HEIF before using it. This is compounded exponentially when sharing from a Mac, PC, or on the web, as compatibility on these systems is extremely limited. Otherwise, JPEG is still a very good option.