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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…)

Hey Apple, Fix This: The Future of the Finder

This is the last installment of this column, and as such, I wanted to cover one of the most important features on the Mac: the Finder. This file manager, browser, and user interface layer is the tool that people use to launch applications, work with and manage files and folders, and control pretty much everything their computer does.

The early Mac was revolutionary, bringing the desktop metaphor to everyday computers. It wasn’t the first computer to use this type of interface, but it was the first one that was widely adopted. Instead of controlling a computer by typing lines of text commands, it used the WIMP interface: windows, icons, menus, and pointer. (And even before text commands, computers were controlled by punch cards, tapes, and other ways of inputting commands and data.)

One thing the desktop metaphor does is allow us to organize files any way we want. Unlike tags, where you set keywords for your files—that you may or may not recall later—folders let you sort items in the way that best fits your style of organizing items. They’re flexible and extensible, through sub-folders, and sub-sub-folders. You could dump all your files in a single folder and use Spotlight to find the ones you want, but you’d quickly find that it’s more time consuming to use this type of interface than to keep your files sorted.

While the desktop metaphor is practical and useful, maybe it’s time to move on.

Read the rest of the article on Macworld.

As the article says above, this is the last installment of my Hey Apple, Fix This column. I’m looking for freelance writing work, notably about iTunes, but also about Apple hardware and software, third-party apps, and more.

Use Smart Albums in Apple’s Photos

I posted an article yesterday about using smart albums in Apple Photos to find which lens or camera you use most. I discovered that many people don’t know about smart albums in Photos, so here’s an overview of how you can use them.

If you’re familiar with smart playlists in iTunes, then you’ll understand smart albums. Each one is made up of one or more conditions that the app uses to filter your content, and display only those items that match your choices. In iTunes, it’s a great way to find tracks with ratings, that you have or haven’t played recently, by certain artists, and much more.

In Photos, you have a number of interesting choices you can use as conditions. Start by choosing File > New Smart Album, and you’ll see a dialog offering you a number of options.

Smart album

Select the first menu after Match the following condition to see a number of types of metadata – data about your photos – that you can use.

Smart album menu 1You can choose any of these types of metadata, such an existing album, the date you took a photo, a keyword or description, and more. You can choose technical information, such as the camera model, lens, focal length, aperture, shutter speed, and whether you’ve used a flash.

The second menu lets you select operator such as is or is not, numerical operators such as greater than or less than, ranges (from x to y), and more.

For each of the bits of metadata in the first menu, you have a number of options in the third menu. They are contextual; they depend on what you’ve chosen in the first menu. For example, the default option you see is Photo is favorite, but you can, from the third menu, choose things like Photo is edited, movie, HDR, tagged with GPS, and more. For all the technical metadata in the bottom part of the first menu, Photos presents a list that you can choose from with the existing metadata in your photos. For example, if you chose Lens, you can select a specific lens that you have used from a list. Camera model will show all the cameras you have used, and so on.

You may want to make a smart album with, say, all the photos you’ve shot with an iPhone; any model, among those you’ve used over the years. In this case, you can make a smart playlist with the condition Camera model includes iPhone, and Photos will find all the pictures that were taken with any iPhone.

You can also add conditions; click the + button, and you can have another condition, and you can continue adding conditions until your smart album shows exactly those photos you want.

Smart albumsTo the left you can see the smart albums I have in my Photos library. As you can see, most of them sort by camera or lens, but I also have a Recent Photos album (Date is in the last 1 months), and a Panoramas album (Keyword is Panorama; I’ve entered this manually, because the default Panoramas album doesn’t find all of mine).

If you want to sort your photos by any of these conditions, to easily scan photos you’ve tagged with a certain keyword, such as “vacation,” photos of a specific person (as long as you’ve tagged them), or, as I do, photos taken with specific equipment, smart albums are versatile and easy to set up.

Note that smart albums do not sync to iCloud Photos Library, so you cannot view them on your iPad or iPhone. That’s a shame; it would be useful to be able to sort photos like that to view on a mobile device.

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Kirkville

Writings about Macs, music, and more by Kirk McElhearn