Chances are good that you have dealt with a bitmap image. They are the type of images produced by digital cameras and scanners. People also use them when they are editing or enhancing photographs or drawings. These images, though widely used, have various advantages and disadvantages. These include issues with re-sizing a picture, image quality, and file size.
One of the advantages to using a bitmap image is that it can display a picture realistically. Bitmap images are made up out of pixels, which is basically a colored dot. Properly positioning the different colored dots next to each other will perform the illusion of one color blending into another. Thus, it is easier to get a more real-looking image using this format.
The ease at which people can share and edit pictures is another advantage of these images. Computer programs ranging from oekaki drawing forums to professional image editing software are available for viewing, creating, and editing these pictures. With all the options available, it is possible for virtually anyone with access to a computer to share and manipulate some formats of these images. And many people do. Different formats of bitmap images are used on website graphics as well as in online art galleries.
One of the disadvantages associated with a bitmap image is that it does not tend to re-size very well. While it may be easy to scale down an image without loss of clarity, it is not easy to enlarge the image without the image becoming pix elated. Another disadvantage associated with a bitmap is the large file size. An uncompressed image can be quite large because of the amount of information needed to display all the pixels in the various colors. Such a file can take a long time to load, send, or receive.
To combat this, different compressed file formats can be used. The disadvantage with this is that many times compressing a bitmap file can result in artifacts, areas of blurry or incorrect color that can ruin the detail and overall look of an image. JPEG (.jpg or .jpeg) and CompuServe Graphics Interface (.gif) are both compressed bitmap file types. Depending on the image you have, you may choose to use one of these file types. The JPEG file type may work on a very large and detailed file, such as a photograph, but a GIF may be best suited for graphics, text, or animations.
Source: WiseGeek