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AS Computing

AS Computing. Data transmission and Network. Display a picture. Visual Display Unit (VDU) resolution is measured by the number of dots, or pixels that make up a screen. For example, many VDU s are set to a resolution of 800 x 600 pixels = 480 000 pixels

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AS Computing

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  1. AS Computing Data transmission and Network

  2. Display a picture Visual Display Unit (VDU) resolution is measured by the number of dots, or pixels that make up a screen. For example, many VDU s are set to a resolution of 800 x 600 pixels = 480 000 pixels The number of bits used to represent each pixel determines how many colours or shades of grey can be displayed.

  3. Pixels • The number of bits used to represent each pixel determines how many colours or shades of grey can be displayed. • A Black & White picture: each pixel that makes up the picture will need 1 bit to store whether that pixel is black or white • A colour picture using up to 256 colours: each pixel needs 1 byte to record the shade of colour of each pixel. • A colour picture using about 65000 colours: each pixel needs 2 bytes to record the shade of colour of each pixel. • A colour picture using about 16.7 million colours: each pixel needs 3 bytes to record the shade of colour of each pixel.

  4. Bitmap • BMP - Windows Bitmap • Windows bitmaps store a single raster image in any colour depth, from black and white to 24-bit colour. • The Windows bitmap file format is compatible with other Microsoft Windows programs. • BMP files are suitable for wallpaper in Windows.

  5. Bitmap • Advantages • 1-bit through 24-bit colour depth • Widely compatible with existing Windows programs, especially older programs • Disadvantages • No compression, which results in very large files • Not supported by Web browsers

  6. JPG(JPEG) • Joint Photographic Experts Group (JPEG) pictures store a single raster image in 24-bit colour. JPEG is a platform-independent format that supports the highest levels of compression. • The level of JPEG file compression can be increased or decreased, sacrificing image quality for file size. The compression ratio can be as high as 100:1. (The JPEG format comfortably compresses files at a 10:1 to 20:1 ratio with little picture degradation.)

  7. JPG • Advantages • Superior compression for photographic or realistic artwork • Variable compression allows file size control • Interlacing (for Progressive JPEG files) • Widely supported Internet standard • Disadvantages • When you edit and resave JPEG files, JPEG compounds the degradation of the original picture data; this degradation is cumulative. • JPEG is not suitable for simpler pictures that contain few colours, broad areas of similar colour, or stark differences in brightness.

  8. GIF GIF (Graphics Interchange Format) pictures store single or multiple raster image data in 8-bit, or 256 colours. GIF pictures support transparency, compression, interlacing, and multiple-image pictures (animated GIFs).GIF compression is LZW compression, at a roughly 3:1 ratio.

  9. GIF • Advantages • Widely supported Internet standard • Lossless compression and transparency supported • Disadvantages • 256-colour palette; detailed pictures and photo-realistic images lose colour information • Limited transparency; no semi-transparent or faded effects like those provided by alpha channel transparency

  10. Other Format MPEGs AVI MP3

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