Apple’s Photos App and Lens Correction

When you take a digital photo, the camera you use receives light through its lens, but the light information it gets can be slightly distorted. Because of this, cameras often use lens correction to create JPEGs from the original light information, or when converting RAW files into JPEGs.

If you shoot RAW files, many apps that process these files can also apply lens correction, using metadata stored with the files, to create better images. In some cases, this can even be using a huge database of information about lenses and cameras.

It’s interesting to know that Apple’s Photos app also applies lens correction, yet doesn’t tell you anything about it. This lens correction is not only applied in the Photos app, but also within macOS; if you have a RAW file and view it using Quick Look (select the file and press the space bar), lens correction is applied.

I haven’t been able to find a database of which lenses Apple is aware of, but there is a document showing which cameras are supported for RAW files. It’s likely that Apple supports those lenses that add metadata to the RAW files, which covers most lenses people are likely to use. This said, if you’re using a non-digital lens on a camera with an adapter, you won’t get any such information; it’s possible that some third-party software may be able to apply correction for this type of lens.

So what is lens correction? Let me quote an explanation from an Adobe document about its Camera Raw app:

  • Vignetting causes the edges, especially the corners, of an image to be darker than the center.
  • Barrel distortion causes straight lines to appear to bow outward.
  • Pincushion distortion causes straight lines to appear to bend inward.
  • Chromatic aberration is caused by the failure of the lens to focus different colors to the same spot.

Here is a good explanation of these types of distortion, with a number of images showing how each one presents in photos.

Not all of these types of distortion will be obvious with all lenses; you have more pincushion distortion in a wide angle lens than a telephoto, and chromatic aberration may be very visible, or may be hard to spot, and it may depend on your subject and lighting. But have a look at an example to see how different a RAW file can look without and with lens correction.

The first screenshot below shows a file opened in Affinity Photos with the lens correction setting turned off; this makes the app display the RAW file with no alteration. The second version is from a screenshot taken when viewing the same file with Quick Look in the macOS Finder. I then scaled both screenshots to the same size.

The correction is most obvious if you look at the top corners. In correcting the distortion, the photo cuts off the corners a bit to make them straighter. You can also see an overall difference in lighting; this is a bit surprising, but both Apple Photos and Affinity Photo show the corrected photo like this. If you look very closely, you can also see the curves are a bit different, correcting the distortion.

My camera also made the same corrections to this photo in creating a JPEG. Since the information about lens distortion is included in the metadata in the RAW file, either the camera can correct when creating a JPEG or software can correct later, if you only shoot in RAW. (I generally shoot RAW + JPEG.)

Some cameras offer a setting to enable or disable lens correction, but mine don’t. And some software also has its own database of lens and camera information to correct distortion. However, “Olympus says it does not disclose its RAW file format to third-party software providers,” according to DPReview, but I see lens correction in photos shot with my Olypmus lenses in Photos and other apps. (The photo above was show with a Panasonic Lumix 20mm f 1.7 lens on an Olympus Pen-F.) It may be that software developers reverse engineer some lenses to be able to apply correction.

So why don’t camera manufacturers make better lenses? I would expect that the more expensive the lens, the less correction needed, but since this correction is possible via software, as Olympus says, quoted in this article, “[this] enables us to greatly reduce the length and volume of a lens, and gives manufacturers flexibility of small and light weight designs.”

So it’s good to know that, if you shoot RAW, Apple’s Photos applies lens correction to some or all of your images. This can save you from having to use third-party software to process your RAW files, if this distortion is problematic. It’s also interesting to know that Apple does this and doesn’t mention it; I think it would be a useful point to make to get users to stick with Apple’s simpler photo management and editing tool rather than buying a third-party app to get this feature.

(It’s interesting that DxO makes an app called DxO OpticsPro for Photos, which claims to apply optical corrections as an editing extension to Photos. However, unless it supports a much broader range of lenses and cameras than Photos itself, this optical correction is useless. It’s worth pointing out that it doesn’t support RAW files from my Fuji X100F, something that Photos does support. Go figure…)