Digital imaging

Two types of graphic Bitmap Vector

Bitmap Image itself is stored as a map showing the position of each pixel. Details of the colour of each pixel are stored. This is a huge amount of data. Files to store bitmap images are large.

Vector Information about how to draw the image is stored rather than the image itself. Stored as a series of equations. The equations tell the computer how to draw the parts of the image. Only instructions/equations are stored, so file size is small.

Impact of large file size for bitmap Large file size means large upload time (i.e., time to transfer file to a website is large). Large file size means download time is large (i.e., the time taken for a user to view the image on a website). Files are compressed to reduce file size.

Other problems of bitmap graphics Harder to edit than a vector. Image loses sharpness when re-sized. This bitmap image has been re-sized. The jaggedness of the pixels can be seen.

Impact of small file size for vector graphics Quick upload time. Quick download time. Can store lots more images in the same storage space compared to bitmaps.

Advantages of vector graphics compared to bitmap graphics Small upload/download time. Easier to edit as you can edit parts of the image. Can re-size image without loss in quality.

Disadvantages of vector graphics Only suitable for images with a limited number of colours. No good for images with continuous colours like a photograph.

Optimising Graphics This means changing a graphic file so that it is stored as the best file type possible. Usually this will be the smallest file size, so in other words you will be compressing the graphic. When you made your powerpoint last year you ortimised your graphic files…..you changed them from .png files to either .jpeg or .gif files as they were smaller, so they would load up more quickly. .jpeg and .gif files are both bitmap graphics