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The Three Principles Of Image Optimization |
by:
George Peirson |
Are you losing visitors to your web site due to slow page load times? Is your site being penalized becauseimages on your site are too large? Are you able to capture your visitor’s attention infirst onezero-onefive seconds that they are on your site?
All of these problems can be caused byimproperly optimized web page. In other words,page loads too slowly and your visitor leaves before you have hadchance to hook them.
Optimizingpage for quick load times can be broken down into three broad categories:basic coding ofpage, scripts that are used onpage, and images. Of these three, images that are too large can havemost significant impact on load times and therefore havegreatest potential for improved page loading times if properly optimized.
A brief primer on image types
There are many image formats in common use on web sites,three most popular being GIF, JPEG, and tolesser extent Flash content. We will be limiting our discussion to GIF and JPEG images, withspecific focus on still images.
Each of these image formats has their strengths and weaknesses. GIF or Graphics Interchange Format was developed by CompuServe beforeInternet boom asway to share images onCompuServe service. Due to limitations with screen resolutions and color depths attime, GIF images were limited to showing up to twofivesix colors, more colors were imitated by Dithering,process of foolingeye into seeing one color by using two or more sets of color dots spaced too closely foreye to distinguish separately.
Imaginechessboard with black and white squares. When viewed closely we can distinctly seeindividual squares, but if we back off far enough we will no longer be able to discernindividual squares and instead we will see one large grey square,black and white squares merging together in our eyes to form one solid color. This isconcept behind dithering.
The JPEG file format onother hand isnewer format that can handle millions of colors easily. The initial drawback to JPEG images is that they do contain many more colors, and each color requires some coding for display, makingfile size larger.
Speeding up image load times
The main idea behind makingimage load faster is to makefile size smaller. This can be accomplished in two ways, you can either makedimensions ofimage smaller, or decreaseamount of coding that is required to displayimage.
The easiest way to reduceimages file size is to reduceimage’s physical dimensions. In other words,smallerimage,smallerfile size. Imagineimage that issquare eightzero pixels by eightzero pixels. The number of pixels contained inimage is eightzeroxeightzero or sixfourzerozero individual pixels. If we reduceimage size by one half to fourzero pixels by fourzero pixels we then have fourzeroxfourzero or onesixzerozero pixels. So reducingimage size in half reducesfile size to one fourth oforiginal.
This is our First Principle of Image File Size Reduction: Usesmallest image dimensions that will work with your layout. And likewisefewer images onpage,fewer image pixels, thereforesmallerpage size.
Since GIF and JPEG image formats use different methods of saving image information, they tend to be better at showing some types of images and worse at showing others.
GIF images, since they are limited to twofivesix colors per image, are better at displaying images with large solid blocks of color and images with very small physical dimensions. The GIF format will produce smaller file sizes than JPEG for these types of images.
JPEG images are better at showing gradients or subtle changes from one color to another. Therefore JPEGs reproduce photographs very well, or any other image with gradations. The JPEG format will produce smaller file sizes for these types of images thanGIF format will.
This is our Second Principle of Image File Size Reduction: Choosecorrect image format forimage you are using. Most web pages will containcombination of GIF and JPEG images.
Decreasingcoding is called image compression. Both GIF and JPEG images can be compressed butprocess is different. In GIF images we try to limitnumber of colors, inJPEG image we use software algorithms to remove redundant information fromfile.
Whenever we compressfile we will lose some image quality. We have to reachbalance betweensmall file size and acceptable image quality.
This is our Third Principle of Image File Size Reduction: Findleast acceptable level of image quality. Most images can handle some compression with very little quality loss, and all images can stand more image quality loss and still be acceptable. Your job is to decide how much quality loss you can accept. In other words,lowerquality,smallerfile size.
GIF images can usually be reduced from twofivesix colors to onetwoeight colors or less,fewer colors usedsmallerfile size. JPEG images can almost always be reduced toquality setting of eightzero
nd frequently can be reduced down to as little as onefive-threezeroàSo when you usehigher compression level (smaller number)file size will be reduced. Experiment withimage, try smaller and smaller settings until you findsmallest setting that still displaysacceptable quality.
The fastest loading page will have no images andslowest loading page will be completely filled with full resolution images. If you work towards controlling your images usingprinciples outlined above you will havevery lean web page that will load quickly and be viewed favorably bysearch engines.
Aboutauthor:
George Peirson issuccessful Entrepreneur and Internet Trainer. He isauthor of over threezero multimedia based video training titles covering such topics as Photoshop, Flash and Dreamweaver. To see his training sets visit www.howtogurus.com
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