1. Information Processes and Technology Multimedia: Graphics

2. Types of Graphics Bit mapped graphics: (also known as Raster Graphics) Every pixel that makes up an image occupies its own piece of computer memory. Each pixel can display from 2 colours (black and white) up to 2 32 colours (true colour) or more.

3. Example of a Bitmap graphic Magnified view of selected area Note how each pixel has its own colour that contributes in producing the whole

4. Pixel A pixel is the smallest controllable unit of a bitmap graphic. There are two items of data stored for each pixel in a graphic: –Its position (X-Y coordinates) –Its colour.

5. Colour Depth The term colour depth refers to the amount of data required to determine the number of colours in a graphic Colour Depth (N0. Of bits)No, of colours I bit2 colours 4 bits16 colours 8 bits256 colours 16 bits65 536 colours 24 bitsOver 24 000 000 colours

6. Advantages of bitmap graphics. Can be used to store a variety of different images including highly irregular images and photographs. Suitable for images that are highly detailed. Resolution of images only restricted by hardware( video card and display). High compression ratios can be achieved using certain algorithms.

7. Disadvantages of bitmap graphics. File sizes can be very large. Some file formats are unsuitable for use on the internet due to demands on bandwidth. Some compression methods are very “lossy”. Resizing images can cause aliasing effects. Cannot group elements together to form an object.

8. Vector Graphics Also known as object oriented graphics Images are stored in memory as a collection of objects such as lines, rectangles, circles, …etc. Mathematical equations can also be used to describe and store graphics.

9. Advantages of vector graphics. File sizes are comparatively small compared to bitmap graphics. Images can be resized without aliasing effects. More effective for producing architectural and engineering diagrams.

10. Disadvantages of vector based graphics There are a limited number of objects(shapes) that are available to create images. Vary from application to application. Very fine detail normally not possible with vectors as there no pixel level control. Compression ratios are not as high as bitmap graphics as the file sizes are quite small to begin with. There are a variety of file formats that are native to different applications that can only be manipulated from within that application.

11. Comparison of different file formats and compression methods Bitmap file – 32 Kbytes (original) JPG file – 5 Kbytes lossy GIF file – 10 Kbytes lossy PNG file – 19 Kbytes Non-lossy

12. File Formats File Type: bitmap File extension: bmp Format: Raster Description: The native format for the Microsoft Windows environment. Following the header is information including the image width and height, number of planes, bits-per- pixel, compression type, image size, horizontal and vertical resolution, and number of colors in the image. Bitmap files currently support color images at 1, 4, 8, and 24 bits. The popularity of Windows has made the bitmap format very popular and a de facto standard for multimedia applications.

13. File Formats File Type: Graphics Interchange Format File extension: gif Format: Raster Description: GIF from CompuServe has been developed for graphic interchange between various platforms and operating system environments The raster data is compressed according to the LZW algorithm GIF files can hold multiple images, so that several definitions (and raster data) follow one another in the file creating animation effects.

14. File Formats File Type: Joint Photographic Experts Group File extension: jpg Format: Raster Description: JPEG files are used for compression of monochrome, full-color (24 bit), and grayscale digital still images. JPEG uses the lossy, sequential DCT compression algorithm. JPG files are commonly used on the internet especially in web page design.

15. File Formats File Type: Metafile File extension: wmf Format: Vector Description: Image data is stored as a series of Windows Graphic Device Interface functions. The functions, stored as records, which are executed to display the image. Image drawing commands have the advantage of be scalable. Metafiles can contain bitmap images. Metafiles can contain other metafiles.

16. File Formats File Type: Portable Network Graphics File extension: png Format: Raster Description: PNG is for lossless, portable, well-compressed storage of raster images. It provides a patent-free replacement for the GIF format PNG features include: Streamability: files can be read and written serially, thus allowing the file format to be used as a communications protocol for on-the-fly generation and display of images. Transparency: portions of the image can be marked as transparent, creating the effect of a nonrectangular image.

17. File Formats File Type: Encapsulated PostScript File extension: eps Format: Vector Description: EPS files are lists of commands written in the PostScript page description language. EPS files contain strings in ASCII that define the image. A printer or application program interprets the commands in the EPS file. EPS is intended as a device independent language.