If you take photos with an iPhone, you don’t really pay attention to the format of the digital files it saves. They are JPEGs, the standard compressed format that has been in use for for about 25 years. They’re commonly used on digital cameras because they save a lot of space. They’re like the MP3s of image files.
With most digital cameras – other than a smartphone – you can choose the level of compression you use for your JPEGs. My Fuji X100F has two options: normal and fine. As an example, the manual explains that on an 8 GB memory card, you can store 800 photos at normal compression, but only 540 at fine compression. My Olympus Pen-F has four options: basic, normal, fine, and super-fine, which, at full-size allows you to store from 510 to 2347 photos on the same 8 GB. (Note that the Pen-F has 20 Mp while the X100F has 24 Mp, so the largest files of the former are smaller.)
But you can also choose to shoot in RAW format. This stores uncompressed files that contain the raw data that the camera’s sensor records. They are much larger – you can only store 150 or 340 of these on the same memory card with each camera – but if I retain the music comparison, they’re like the original music on a CD that hasn’t been compressed.
Apple’s Photos app supports most RAW formats. (Here is a list of the cameras that are supported.) One notable exception is my Fuji’s compressed RAW format; not only does Photos not support this, but many other photo apps can’t handle this type of file.
If you shoot in RAW, you can import your photos into Apple’s Photos app just as you would do with JPEGs. And if you shoot in both RAW and JPEG – any camera that can shoot in RAW allows you to do this – Photos detects that the two photos go together, and imports them as a pair, and displays the photos with a small icon on the top right corner of a thumbnail. Photos picks the JPEG as the main photo, and this icon shows the letter J.
However, you can edit the RAW photo, and use it as the main photo. To do this, select a photo and press Return to enter edit mode. As part of the information that Photos shows about this picture, it says which format it’s in. Here, Photos tells me that the photo above is being edited in JPEG mode.
To switch to the RAW file, choose Image > Use RAW as Original, or right-click on the photo and choose Use RAW as Original. When you do this, you may notice that the photo changes a bit; it may become lighter, or have more contrast. This is because RAW files have greater dynamic range; they cover more gradations of light. You can then edit the photo the same as you would any other.
When you export the photo by dragging it from Photos to the Desktop or to a folder, it will be a JPEG, since RAW files aren’t intended to be viewed or shared. If you export it by using the File > Export command, you can choose JPEG, PNG, or TIFF format. And if you want to export the RAW file to use in another app, choose File > Export Unmodified Original for 1 Photo. This will export the RAW file, if that’s all you have, or both files, if you have a JPEG/RAW pair. But these files won’t contain any of your edits.