Understanding photography-related file formats

The lowdown on file formats used by cameras.

photofileformat hero
Credit: AdobeStock.com/#91558084 Felix Jork

The previous Creaticity column covered basic image file formats such as JPEG, PNG, PDF, etc. However, once you pick up a camera, terms such as raw and file formats such as DNG, XMP, along with a plethora of proprietary formats, can creep into your life. In this column, you’ll learn what all that means. As a result, you can make sense of the files you encounter and make an informed choice about which format to capture in-camera.

Raw isn’t really a file format so you won’t see it as a file extension. Instead, it’s a way to describe the unprocessed sensor data that some cameras—and even some Android smart phones—can record (it’s not an acronym either, so there’s no need to write it in all caps). You may not realize it, but when you shoot in JPEG format, your camera processes the image by applying the settings buried deep within your camera’s menu such as noise reduction, sharpening, color and contrast boosting, color space, and some compression to save space on the memory card. While you can certainly edit a JPEG, the changes your camera made when converting the sensor data into the JPEG are baked into the file and cannot be undone. (The same thing happens with a TIFF and since it can produce dramatically larger file sizes than raw, it’s now rarely used as a capture format.)

photofileformat 1 Lesa Snider

Here’s a raw file (top) compared with a JPEG (bottom). A raw file’s wider range of colors is especially noticeable when photographing saturated colors (flowers, sunsets, etc.), and when trying to maintain shadow and highlight detail (say, clouds or interiors)

None of that permanent in-camera processing happens with raw files, which is one reason why a JPEG and a raw file of the exact same image probably won’t look the same when you view them on your computer. Another reason is that raw files contain a wider range of colors and tones than JPEGs (tones refers to luminosity info, which you can think of as brightness values). For the mathematically curious, there are potentially four trillion colors and tones that can theoretically be saved into a 14-bit per channel raw file versus a maximum of 16 million colors that can be saved into a standard 8-bit per channel JPEG.

Using raw data in applications that can interpret it—Apple Photos, Pixelmator, Affinity Photo, Adobe Camera Raw, Adobe Photoshop Lightroom, PhaseOne Capture One Pro, Alien Skin Exposure X, Nikon Capture NX-D, etc.—gives you far more editing flexibility because you have more data to work with and you can process it however you want. Raw files also let you change the color of light, called white balance, captured in the scene. With a JPEG, the white balance is baked into the file, so all you can really do is shift the colors by fiddling with your image editor’s temperature and tint sliders.

photofileformat 2

The white balance menu for a raw image (top) contains far more options than it does for a JPEG (bottom). In fact, this is one way to tell if the file you’re editing is really a raw file or not.

Because of the sheer amount of data in them, raw files can be gigantic and many apps don’t understand them, so unless you’re a photo journalist handing memory cards off to the editing department, you won’t pass raw files around. Instead, edit the raw file in the image editor of your choice and then export it as a JPEG for sharing with others. (If the image is headed to the web, be sure to change its color space to sRGB.) By the way, asking a photographer for his or her raw files is like asking a film photographer for his or her negatives. Why? Because how the photographer processes the files/film is an essential part of their art.

CR2, NEF, ORF, ERF, ARW, SRF, SR2 are actual raw file formats (this is not a complete list). Most camera manufacturers have their own proprietary format for saving raw files—the formats above (respectively) belong to Canon, Nikon, Olympus, Epson, and the last three are Sony. These proprietary formats are closed, so unless you’re using a raw processor made by the camera manufacturer, the edits you make and the metadata you add (copyright info, keywords, etc.) in third-party processors (say, Adobe Camera Raw) get stored as a separate XMP file, which is also referred to as a sidecar file that’s saved alongside the original raw file. If the third-party processor is also a database (say, Adobe Photoshop Lightroom, Alien Skin Exposure X) then the edits and metadata are stored inside the database for the sake of speed, though you can use the application’s preferences to store the data in a separate XMP file, too.

photofileformat 3

Here’s what your file structure looks like if you edit a proprietary raw format such as CR2 in a third-party application.

DNG stands for digital negative and it’s Adobe’s attempt at standardizing an open format for raw files (Samsung uses it as the factory-setting for their cameras, too.) As such, one benefit to this format over a proprietary raw format is that your edits and metadata can be stored inside the original file, instead of in a separate XMP file. Another benefit of DNG is that Lightroom uses it for Smart Previews, which let you sync your desktop catalog onto your mobile device for editing in Lightroom Mobile.

photofileformat 4

Click Save Image in Adobe Camera Raw and the resulting dialog box lets you convert to DNG and reduce file size.

Converting proprietary raw formats, or JPEGs for that matter, into DNG is optional, though it’s great for archival purposes since it stores all your edits and metadata, too. It takes a while so if you’re going to do it, wait until you’ve culled your image collection! Many applications will do the conversion, though you can download the free Adobe DNG Converter to convert files yourself en masse.

That’s the scoop on the photography-related file formats you’re likely to run into. As you can see, this is fairly heady stuff though it’s well worth the effort to understand. Until next time, may the creative force be with you all!

Shop ▾
arrow up Amazon Shop buttons are programmatically attached to all reviews, regardless of products' final review scores. Our parent company, IDG, receives advertisement revenue for shopping activity generated by the links. Because the buttons are attached programmatically, they should not be interpreted as editorial endorsements.

Subscribe to the Best of Macworld Newsletter

Comments