How to Prepare Images for Your Web Site – Part 1

You are staring at the your monitor waiting for the image to
download. It finally appears but it has blurry edges. You go to
the next page but can't read the text because of the dark image
in the background. The next page has animated images, that don't
seem to stop. The spinning globes keep spinning. The last page
has a large graphic on it, which is a link. You click on it for
more information but it goes nowhere. You leave the site in
frustration.

Images are an essential ingredient for Web Site design.
You want visitors to have an aesthetically pleasing
experience. Properly preparing your images is necessary to
enhance the appearance of your web site. In Part I of this
article I will explain:

When to use images for your web site.
What image file formats should you use on the Web.

When to use images for your web site - Navigation
Graphical buttons can link to other pages or resources.

Image Maps – this is a graphic that contains several links on
it. It has several "hot spots" or invisible buttons, you can
click on. For example you could have a photograph of your family
and put a hot spot on each person's face that links to that
person's web site.

Logos and Trademarks – your business or organization's trademark
are crucial for name recognition and branding.

Thumbnails – this is a small, "thumbnail-sized version of an
image. When you click on it, you jump to another page with a
larger version of the same image. The visitor can see many
different, small images on the first page without having to wait
for larger files of the larger images to load.

What are the different image file formats?
Web graphics can be categorized into two file formats:
bitmap and vector.
Bitmap – these are composed of individual values for each color
displayed. The larger the dimensions of the image, the larger
the associated file size will be for the same graphic. When
viewed with magnification, a bitmap resembles a series of little
squares, each of which has a color value that contributes to the
overall shape. Bitmaps have a very rough appearance when viewed
closely but form images when viewed from a distance.

Bitmaps are best suited for photos, drop-shadow effects and
soft, glowing or blurry edges.

Vector – these store information about the image in mathematical
instructions that are then interpreted and displayed.

Vector graphics are best suited for line art, shapes and
illustrations.

Image File Formats
Graphic file formats used on the Web are GIF, JPEG and PNG

Graphics Interchange Format (GIF)
GIF is a platform-independent file format that is limited to a
display of 256 colors. GIF has been adopted by most developers
because of its small file size.

GIF is considered a "lossless" format. This means that as the
image is compressed, no information is lost.

Types of GIFs
Animated GIF (89A) This 89a version of GIF allows storage
and playback of a sequence of still images to create the
illusion of animation. Animated GIF files consist of sequential
frames that reload from a browser's cache and replay in an
infinite or predetermined loop to simulate motion.

Transparent GIF
An advantage that a GIF has over a JPEG image is that the
designer can designate a color of the GIF image to be
transparent. For example, you can create a circular logo in a
square image by making the background color transparent. The
image appears circular, when, in fact, it is square with
information to appear transparent.

Interlaced GIF
Graphic interlacing (the progressive rendering of images)
is unique to GIFS and is the preferred method for
display of large graphic files. Many people find the
"fuzzy-to-sharp" animated effect of interlacing visually
appealing, but the most important benefit of interlacing is that
it gives the reader a preview of the full area of the picture,
while the picture downloads into the browser.

When to use a GIF
Buttons, bullets and navigational tools that accent your
Web pages. Interlacing is best for larger GIF images
such as illustrations and photographs.

Joint Photographic Experts Group (JPEG)
Graphics in the JPEG format are capable of much greater color
depth than GIFs, but usually require more time to download.
JPEG can contain up to 24 bits of color information
(16.7 million colors). Remember though, that most users are only
capable of displaying 8-bit color.

When to use a JPEG
JPEG enables you to use brilliant colors and provides support
for complex images and digitized photographs but it is not
designed for use with simple images.

JPEG compression is not as effective as GIF compression and may
distort images with few colors or large areas of the same color.
JPEG compression is therefore not designed for low-resolution
images.

Portable Network Graphics (PNG)
The PNG file format is emerging as the new format for Web graphics.
PNG files are lossless and support transparency like GIFs, yet also
support compression and high bit depth like JPEGs. In addition,
PNG bit depth can be adjusted, unlike GIFs or JPEGs, which must
be 8-bit and 24-bit depth.

When to use a PNG
PNGs behave similarly to GIFs and work best with flat-color,
sharp-edged art. PNGs compress both horizontally and vertically,
so solid blocks of color generally compress best. They also support
better interlacing than interlaced GIFs.

Knowing what types of graphics to use and when to use them for
your web site will help you avoid the many pitfalls of bad web
design.

Part 2 of this article will discuss how to optimize graphics for
your web site and factors that affect optimization.