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
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:
Change the resolution of all images to 72dpi.
Convert graphic text into stylized text.
Crop the images to the actual size needed.
Minimize color depth when it’s not necessary for quality.
Specify the actual width and height of all images.
Use thumbnails where appropriate.
Bottom Line – Graphics should enhance the content of a web page except in that rare occurrence where the images are the content. In either case, you need to optimize photos and other graphic files to allow for the fastest downloading time possible for the web page otherwise you risk losing the visitor forever.
Source : http://articles.webdesigners123.com/photo_optimization.php
