Images that can be Used on the Web

 

Introduction

There are two main types of images that can be viewed by other people on the Net. They are GIFs and JPEGs. To understand the differences between these types of pictures, you must first have a bit of background as to how pictures are stored electronically.

A picture can be divided up into a very fine grid of pixels. A pixel is the smallest dot that you can see on your computer. Typical computer screens have 800 x 600 or 640 x 480 pixels. Each pixel in the grid is given a location and a color. Because the picture is going to be stored electronically, the color is represented as a number. Then all these numbers are compressed in size. The pictures can be compressed in size easily because for most pictures there are large areas that are the same color (like the sky for instance). When you view this electronic picture on your computer, it is decompressed and then the computer simply rebuilds the grid of pixels.

There are many ways of ordering the grid and different methods for compressing the pictures. The methods to store pictures on the Internet are called GIFs or JPEGs. (JPEGs are also referred to as JPGs. This is the same type of file, just a slightly different name.). It is possible to tell what sort of image you are using by the extension.

For Example

 

Filename

Can be viewed by browsers?

*.gif

Yes

*.jpg, *.jpeg

Yes

*.bmp

No

*.tiff

No

*.psd

No

*.shg

No

*.png

Some

There is shareware software available that will convert from any graphics format to any other format. Do a Web search on Paint Shop Pro™.

Where can these Images be Found?

The easiest way to find images is on the Net. There are repositories of pictures and many institutions publish their own pictures for general use (like NASA). If you find a picture that you want on the Net but are not sure as to whether you can copy it, e-mail the person who made the site. Usually they will be happy for you to put it on your own Website, along with a credit and a link back to their own site. (This is how Websites get famous!)

What do you need to create your own Images?

To create your own pictures from scratch you will need access to a scanner. A scanner is a machine (a lot like a fax machine) that copies ordinary photos, pictures or paintings electronically to digital files (such as GIF or JPEG files). You will also need software to manipulate these images. For example, you may wish to add special effects to a picture or to change the contrast. A very well written tool is called Paint Shop Pro. See if you can get hold of a copy (it’s shareware).