Photo Optimization is necessary to allow
a web page to load in the shortest amount of time possible.
Fast loading time require small files. This article
discusses the methods used for photo optimization.
In an ideal world, a web designer could use the highest
quality photos and have the webpage download lightening
fast. Fast loading requires small file sizes for pictures.
Unfortunately, there is a trade off between picture
quality and file size.
Web surfers are a notoriously impatient bunch. If
a website takes too long to load, they will just click
away and never come back.
Computer monitors can only display images at 72dpi
(dots per inch). So the first step in photo optimization
is to reduce the resolution to 72 dpi. Large picture
can be sliced up into smaller ones and the put back
together on the web page. Each piece will be a very
small file and together will load in a fraction of
the time a single image file would load.
Most graphic files contain information about the
color palette of the image. This information is usually
unnecessary for displaying on the web. Many graphic
programs included the ability to “Save for the
web”. This option discards all of the unnecessary
information in the file without any loss of picture
quality.
Another method that appears to speed up load time
is to use either the GIF or PNG interlaced or the
JPEG progressive property. Both of these properties
allow the picture to load gradually as first a blurry
image that becomes sharper and clearer. In reality
the picture actually loads a fraction of a second
slower than the regular formats do but it appears
to load faster the site visitor.
Width and Height IMG Attributes
The HTML <IMG> tag tells the web browser to
create a specific sized box to hold the graphic. That
way the browser can continue loading the rest of the
web page while the graphic file is downloading. If
you don’t put the width and height attributes,
the web browser must pause until the images is downloaded
before it can load the rest of the page.
How Many Images should you use?
Some web designers use images for everything. While
it may look good, it will definitely slow down the
speed of the page loading. Page loading speed in the
sum of the HTML file plus the size of all of the embedded
files. Images constitute more than 50% of the download
time.
Using fewer images will speed download time and just
may keep a visitor from bailing through impatience.
Photo Quality
Photo quality is determined by the clarity, color
purity and detail of a photo. Use a graphic editor
to remove noise and other unwanted features. Most
editors allow you to correct red-eye and sharpen edges
to improve clarity.
Professional editors like Fireworks or Photoshop
will let you change the background, adjust the color
levels and do almost anything else you want to do
to the photo.
You can also use a thumbnail on the webpage that
links to a larger and higher resolution version of
the image so that people who want to can view it.
Photo Optimization Guidelines
The following suggestions will allow you to optimize
your photos for fast download times without sacrificing
picture quality: