Graphics Device Principles B.Sc. (Hons) Multimedia Computing Media Technologies
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Graphics Device Principles
B.Sc. (Hons) Multimedia Computing
Media Technologies
Agenda
Basic CRT Principles Vector Graphic Displays Raster Graphics Displays Aliasing
B.Sc. (Hons) Multimedia Computing
Media Technologies
Cathode Ray Tube (CRT)
Basic Principle of the CRT
Electrons emitted here
Focused here
x axis deflection plate
y axis deflection plate
Phosphor coatingPhosphor coating emits light from energy provided by electron beam but only lasts for short period and must be ‘refreshed’ to remove flicker of screen image. Typical refresh rates are 60Hz - 80 Hz the higher the more stable is the resultant display.
Cheaper CRTs would not always support higher refresh rates.
Display Devices
B.Sc. (Hons) Multimedia Computing
Media Technologies
Vector Displays (Random Scan) Raster Displays (Raster Scan)
Vector Scan Displays
Vector Displays
Vector Displays
Vector Displays Often referred to as Random Scan Devices, stroke-
writing or calligraphic displays Picture definition stored as a set of line drawing
commands Draws each component line in turn Originally designed for architectural and engineering
layouts High resolutions with smooth point-to-point line
drawing functions Not able to display photo-realistic images
Raster Scan Displays
Raster Scan Displays Based on TV Technology Electron beam sweeps scan lines row by row down
the phosphor screen based on information stored in the Frame Buffer ‘painting’ one line at a time
Frame buffer holds total screen area Screen area comprised of picture elements (pixels, or
pel) Often characterised by their resolution, aspect ratio,
and colour depth.
Raster Scan
Raster Scan
Raster Scan Properties Resolution = number of pixels available on display,
640 x 480 ( VGA ), 800 x 600, 1024 x 768 ( SVGA ) Aspect ratio = number of horizontal pixels / vertical
pixels so 800 / 600 = 1.3. or 4 / 3 = 1024 / 768 etc 4/3 artistically (visually) pleasing? Try wide-screen! Bit depth determined by Frame Buffer - colours
available for each pixel - determined by number of bits stored for each pixel - hence bits per pixel.
1 bit per pixel = monochrome (black and white) Typically 24 or 32 bits per pixel gives ‘true colour’
Raster Scan Aliasing
Raster Scan
Raster Scan
Raster Scan
Raster Scan
Aliasing
B.Sc. (Hons) Multimedia Computing
Media Technologies
Bitmap images will exhibit aliasing of lines due to the underlying method of their storage and display.
Algorithms applied to final image to smooth jagged edges and give more gradation between edge colours to provide antialising
Aliasing
B.Sc. (Hons) Multimedia Computing
Media Technologies
Antialiasing Lines
B.Sc. (Hons) Multimedia Computing
Media Technologies
Aliased
Anitaliased
Aliased
Antialiased
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