File formats 101: What do
they all mean?
.jpg .gif .png .pdf .tif .bmp
.psd .psp .raw
By Yetta Blair
Anyone working on a
computer, which basically means nearly everyone, has a basic working knowledge
of file formats. If you are like most
however, this knowledge means you sort of kind of have a feeling of which file
format you should use, but are not exactly sure how it works and why it should
be your choice.
With this in mind, I
created a cheat sheet, so to speak, of the most highly used file formats and
hints of when to use them.
.jpg – Great to use for web sites and email. This file format is optimized
for photographs and compresses continuous-tone images that contain many colors down
to a size that can be downloaded quickly on the internet. This is the format of
choice for nearly all photographs on the web. You can achieve excellent quality
even at rather high compression settings.
However, the downside to this format is that compressing the image too
much will cause it to look jagged. The JPG
file extension is used interchangeably with JPEG. JPEG stands for “Joint Photographic Experts
Group” who created the standard. JPG
files can be opened by most image editing software from Microsoft Paint to
Adobe Photoshop.
.gif – Another good file type for
the Internet and emailing. GIF’s do a great job of compressing images and
making them suitable for fast downloads. If your image has fewer than 256
colors and contains large areas of uniform color, GIF is your choice. The files
will be small yet perfect and is well suited for some cartoons or clip art. Do
NOT use GIF for photographic images, since it can contain only 256 colors per
image. An added bonus is that GIF images can be placed on a web page with a
clear background, so you can layer them. However, the downside is that sometimes
the artwork has a sharp, unattractive border when the image's background is
invisible. When this happens, try the PNG format. GIF stands for “Graphics
Interchange Format”.
.png – “Portable Network Graphics”. If you want to display a photograph
exactly without loss on the web, PNG is your choice. Its strategy is similar to
that of GIF, but it supports 16 million colors, not just 256. PNG is the only lossless format that web browsers support. (A lossless
compression algorithm discards no information. All image information is
restored when the file is decompressed during viewing. In contrast, lossy
algorithms accept some degradation in the image in order to achieve smaller
file size.)PNG’s are usually larger in file size than jpg and gif files but they
allow people to save artwork to be layered on web pages or other artwork
without any sharp or disruptive border. PNG’s are extremely versatile, but they
usually result in larger files and longer download times.
.eps – "encapsulated post Script". EPS is used in vector-based
images in Adobe Illustrator. An EPS file can contain text as well as graphics. Professional
printers and printable advertising media, like a magazine, will typically ask
that the artwork be saved as an EPS file but a TIF or PDF are also good
choices.
.tif – The TIF is an image format file for high-quality graphics. TIF files are also
called TIFF, which stands for “Tagged Image Format File .TIF files originally
only supported black and white. However, the update in 1988 added a color
palette. Now owned by Adobe, the .TIF format is used for high color-depth
images. TIF files can be converted to JPEG, GIF or PDF format. Printers and advertisers will often
permit final artwork to be designed in a TIF. TIF is not widely supported by web
browsers, and should be avoided for web use.
.pdf – "portable document format", Adobe's native file format
that is read by a program called Adobe Acrobat. Most computer users have
Acrobat on their system, if they don't, they can download Acrobat Reader for
free. The PDF has a wide range of uses, including a lot of usage on web, and
they can even be used for printing when saved as a high resolution PDF.
.bmp – is an uncompressed proprietary format and there is really no reason to
ever use this format. BMP stands for
“Bitmap”.
.psd, .psp – are proprietary formats used by graphics programs. Photoshop's files
have the PSD extension, (PSD stands for Photoshop Document) while Paint Shop
Pro files use PSP (PSP stands for Paint shop pro). These are the preferred
working formats as you edit images in the software, because only the
proprietary formats retain all the editing power of the programs. These
packages use layers, for example, to build complex images, and layer
information may be lost in the nonproprietary formats such as TIF and JPG.
However, be sure to save your end result as a standard TIF or JPG, or you may
not be able to view it in a few years when your software has changed.
.raw – The RAW file format is digital photograhpy’s equivalent of a negative in
film photography: it contains untouched “raw” pixel information straight from
the digital cameras sensor. Use RAW only for in-camera storage.
Copy or convert to TIFF, PNG, or JPG as soon as you transfer to your PC.
You do not want your image archives to be in a proprietary format since you
can’t be sure you will be able to read that format in 5, 10 or 20 years. Most believe that JPG is the format most
likely to be readable in 50 years. Thus, it is appropriate to use RAW to store
images in the camera but be sure to create a TIFF, PNG or JPG, for archival
storage.