A picture or graphic representation
What is an Image File?
The physical means by which an image is implemented on a computer
What is a Web Image Format?
A type of image file that can be viewed by web browsers, the programs people use to look at websites.
Why Do We Need Web Formats?
Images can do a lot to spruce up a website. However the files that images are in tend to be far larger in size than the text on the webpage. Many website visitors are on slow speed dial-up connections and the time it takes for a webpage to become visible is usually limited by the size of the image files. To help solve this problem web browser program e.g. Internet Explorer, Netscape, Opera support two types of compressed image files – GIF’s and JPEG’s (or JPG’s). These web image formats are compressed so that the information can be represented in smaller size files and get presented to the person visiting the website more quickly.
What is Compression?
Compression is a means to make a computer file smaller through some kind of encoding algorithm; a technical way of saying that the information is manipulated by a computer program so that it’s smaller when transmitted, and then can be decompressed by the receiving program into its full necessary size.
What are GIFs?
GIF stands for Compuserve’s Graphic Image Format. It is a non-lossy compression which means that the compressed image will be reconstituted into the original image with no loss of detail. It works by noting sections of the image which are the same color and works quite well for images that has large areas of solid color with little to no texture. The GIF format is an excellent choice for images that are cartoonlike in appearance such as banner ads, logos, and text on a solid background. It is a poor choice for real-life depictions such as photographs of nature or people which tend to have lots of detailed variations.
What are JPEGs – or JPGs?
JPEG stands for the Joint Photographic Experts Group which is the committee that developed the format. It is a lossy compression meaning the compressed image will not render in as much detail as the original from which it was created. The JPEG format is an excellent choice for photograpic images which depict the real world such as nature or people and also for complex backgrounds with lots of texture and detailed variation.
What are PNGs?
PNGs are a newer format which aims to replace the GIF format as a lossless form of bitmap compression. However PNGs do not require a license to use.
Which To Use
Use GIF’s for graphics that have large areas of solid colors and few if any areas of fine detail. GIF’s are very well suited to images such as logos, banner ads, and text rendered on solid backgrounds. Use JPG’s for graphics that have lots of texture and variation with few areas of solid colors. JPEG’s are very well suited to photographic images such as people and nature scenes. The two most widely accepted graphics formats for the web, GIF’s and JPEG’s are designed to each excel at the types of images they were designed to handle well. They do poor jobs of representing other types of images, e.g. a picture of a waterfall will generally make a terrible gif, while text on a solid background will generally make a poor jpeg.