Internet, it’s easy to feel as though you’re swimming for your life in a
giant bowl of alphabet soup, surrounded by shouting acronyms: GIF!
JPEG! PNG! TIFF! What do those names mean? Why does your camera spit out
JPEGs? What’s the best format for a Web graphic? Grab onto a capital O
and let’s get some answers.
First off, don’t worry about the
acronyms, because expanding them doesn’t explain much. For example, JPEG
stands for Joint Photographic Experts Group, which is the standards
body that invented the JPEG format. Helpful? Not really. So think of
them just as names, like Gabriela or Jayden. That said, it can be
helpful to know how they’re pronounced:
- GIF: Either “jif,” as in jiffy, or “gif” as in “gift” — it’s an interesting story.
- JPEG: “jay-peg”
- PNG: “ping”
- TIFF: “tiff”
Here’s the lowdown on each.
GIF
The oldest of these formats, GIF was
long the standard for computer-generated images. It worked well for
graphics and logos with large areas of solid color, but less so for
photos. Due in part to a patent licensing kerfuffle, GIF has been
superseded by PNG in all ways but one.
GIF’s remaining use lies in
flipbook-style animations, where each frame is a separate GIF image.
Animated GIFs that run in short loops have become wildly popular on the
Internet because they’re small and easy to embed in a Facebook or
Twitter post, email message, or Web page. Numerous utilities exist for
turning a short movie clip into an animated GIF; check out GIF Brewery on the Mac or Giphy Cam for an iPad or iPhone.
JPEG
The most common graphics format on
the Internet, JPEG owes its popularity to being the default format for
photos created by all digital cameras, including (until iOS 11) those in
iPhones and iPads. JPEG works well for photos because it can compress
file sizes significantly while barely affecting the image quality.
For instance, a 20 MB photo saved in
JPEG format might end up as only 4 MB, with reductions in image quality
that most people would never notice. Most graphics software lets you
adjust a slider to specify different quality levels, and while the
results vary by the photo, saving at a 75% quality level is usually a
good compromise between quality and file size.
The downside of JPEG is that it
achieves these minuscule file sizes by throwing away data in the file,
which limits how it can be edited in the future. That’s why professional
photographers generally shoot in what are called “raw” formats (which
contain all the image data the camera sensor recorded when the shutter
was opened). Raw files are huge but can be edited in ways that aren’t
possible with a JPEG file. Once edits have been made, photographers save
a copy as a JPEG for sharing or posting online.
PNG
Conceived as an improved, patent-free
alternative to GIF, PNG is now the go-to format for online graphics
that have large areas of solid color, such as buttons, logos, and
screenshots That’s because PNG can compress such images well without
introducing fuzziness, as can happen with JPEG. Similarly, you can edit
PNG images repeatedly without hurting image quality.
In another contrast with JPEG, PNG
supports transparency, which means you can define one color in an image
as “transparent” rather than an actual color. When the image is
displayed on a Web page, the transparent pixels are rendered in whatever
the background color is. That’s tremendously handy for creating images
that seem to float over the background.
Don’t use PNG for photos, since a photographic image saved in PNG format will be much larger than the corresponding JPEG.
TIFF
Like PNG, TIFF files can be
compressed without losing any data. Because of this, TIFF is used
extensively for archiving original photos instead of JPEG; TIFF files
may be much larger, but that’s acceptable when it comes to preserving
originals from which you could later make edited copies.
TIFF also boasts some additional
color-related features that PNG lacks, making TIFF useful in the print
world—if you were to write a book that was going to be printed
professionally, the publisher might ask for any photos or other
illustrations in TIFF format. Useful as TIFF can be, for most people,
most of the time, JPEG and PNG are all you need.
Back and Forth
Nearly any graphics program can open
images in these formats and convert to the other formats, but look no
further than the Preview app from Apple on your Mac for basic image
conversion features. For more info about using Preview, check out Take Control of Preview, by Adam Engst and Josh Centers.
Now that you know the basics of the
Mac’s most important graphics formats, you’re ready to put your best
foot forward whenever you need to pick a file format for your images.
One last thing! You might start
hearing about a new format that iOS 11 and macOS 10.13 High Sierra
introduced this year: HEIF, or High Efficiency Image File Format (we
don’t know what happened to the extra F either). HEIF provides tight
compression, transparency support, animations, and much more. But you
probably won’t interact with HEIF files, since Apple plans to use HEIF
only behind the scenes. Instead, when you save or share an image, the
operating system will automatically convert it to one of the more
standard formats.
