Image
Format Comparisons: GIF, JPEG, PNG
SolveYourProblem.com Article Series: Web Site Design
When you want to put graphics on your website,
you'll face an unexpected problem: what format should they
be in? On their own computers, many people save pictures in
Windows' default BMP (bitmap) format, but the files it creates
are simply much too large to put on a website – they'd take
about a minute for visitors to download and use up all your
bandwidth in the process.
When
you put pictures on the web, you need to consider the
trade-off you want between image quality and speed: the smaller
the file, the worse it's going to look. To help you out, here's
a comparison.
GIF
GIF stands for Graphics
Interchange Format, and was the first
image format used on the web. It was invented by CompuServe
in 1987, updated in 1989, and hasn't changed since – and it
shows. Images stored in GIF format can only use a maximum of
256 colors, which makes things like photographs and logos look
terrible. GIFs popularity is mainly due to it being first and
producing very small files, although it is also notable for
being the only image format that allows you to create small
animations.
Really, the only things you should use GIFs for now are files
that have a limited number of colors, and are technical in
nature – diagrams, for example, work well in GIF format. Things
like photographs that use many colours will come out looking
very strange.
JPEG
JPEG was designed by the Joint
Photographic Experts Group,
who gave it its name. It was designed as a format suitable
for storing high-quality photographs at low file sizes – file
sizes small enough to put on the web. Today, the format is
supported in almost all web browsers, and is also the format
that you'll get photos in if you take them with a digital camera.
The most important feature of JPEG is both the best and worst
thing about it: lossy compression. The word 'lossy' means that
data is lost from the picture when it is saved at smaller file
sizes. Image-editing programs will generally let you choose
how much compression you want, from none (highest quality,
large file size) to 100% (very small files, but terrible quality).
Unfortunately, JPEGs that have been compressed too much come
out looking worse than useless, but many people still use high
compression settings out of a misguided desire to have the
very smallest files possible. If you've ever seen images on
the web that look very 'blocky', you've been a victim of JPEG
compression.
If you do use JPEG, then, it's really recommended that you
turn compression off altogether, or use a maximum of about
25% – the files are quite small already, without going overboard
with the compression.
PNG
PNG stands for Portable
Network Graphics, and is the newest
web image format in widespread use. It was designed as a replacement
for the outdated GIF format, allowing files to use millions
of colours instead of only 256. PNG files have smaller file
sizes than GIFs, although they are often larger than JPEGs,
since PNG compression is lossless (never loses any image quality).
The most useful feature of PNG is that it supports something
known as 'alpha transparency': basically, images with transparent
backgrounds that blend in perfectly. The only thing stopping
widespread adoption of this feature is that it isn't currently
supported by Internet Explorer, but there is a workaround for
this problem: search for ‘AlphaImageLoader’ for more information.
Converting Between Formats
For most purposes on the web, all the graphics you want to
use should either be in JPEG format (for photos) or PNG format
(for less complicated graphics). That's a problem if you've
got a collection of images in all sorts of other formats.
Luckily, a good image editor should be able to convert from
any format to any other very easily. In Paint Shop Pro, for
example, you simply open your images and save them again using
whatever format you want – you can even run the 'Batch Converter',
which will convert a whole folder full of files all at once.
If you don't have an image editing program, there are plenty
of free image viewers that will do the same job for you.
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SolveYourProblem.com : 2007
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