Transcript N-bit plane Frame buffer

Input & Output Devices
Display Devices
Kocaeli University
Computer Engineering
Advanced Computer Graphics
Spring 2012
Input Devices
• Alphanumeric Input
– Keyboards
• 2D Inputs
– (Joystick, Mouse, etc)
• 3D Inputs
– Glove, Space, ball
• Image Inputs
– Camera, Scanner
Output Graphic Devices
• Color Raster CRT
• Calligraphic (vector) CRT
• Flat-panel displays:
– Color LCD (Liquid Crystal)
– Plasma Display
• Hardcopy Devices
– Printers
CRT
• Cathode Ray Tube
• Enclosed vacuum tube; electron beam is focused toward front
surface of the tube, which is coated in phosphor
• Single gun for monochrome and three guns for color
• High voltage reduces the electron density and thus brightness
Vertical and
horizantal
reflection plates
CRT -Cont
• Technology relatively old; has disadvantages
– Physical size and weight
– Power consumption
• Random scan display (Vector Display) & Rater scan display
Vector Displays
• Random scan display
• Also called
– vector,
– stroke-writing,
– or calligraphic displays.
• The electron beam directly
draws the picture in any
specified order.
• A pen plotter is an
example of such a system
Raster Displays
• The image is stored in a frame buffer
containing the total screen area and where
each memory location corresponds to a pixel.
• In a monochrome system, each bit is 1 or 0 for
the corresponding pixel to be on or off
(bitmap).
• Image is represented as a bitmap (1 bit/pixel)
or as a pixmap (8 or 24 bits/pixel)
(a)
(b)
(c)
(d)
A raster-scan system displays an object as a set of points across each screen scan line
Raster Displays
Buffers in Raster Display
• Image description is stored in a memory area
called refresh buffer or frame buffer
• The video controller sweeps the beam across the
screen, one row at a time, from top to bottom
and back to the top again.
• Three beams are controlled (red, green, blue) and
the intensity of each color is stored in the frame
buffer
• To give an idea: refreshing is carried out at the
rate of 60 to 80 frames/second
Buffers in Raster Display
Buffers in Raster Display
N-bit plane Frame buffer
• Choice of the number of gray scales and colors
depend on the value of N (bit plane size)
–N=1
• two colors (B&W)
–N=3
• 8 gray scales or colors
–N=8
• 256 gray scales or colors
– N = 24
• 16 million colours
A single bit-plane frame Buffer
• For colored displays (raster-scan), three separate color guns
must be used.
• Each bit plane drives a color gun
An N-bit plane gray level frame
buffer
Simple color frame buffer
N-bit plane gray level Frame
buffer
• In case of one-bit for each color frame buffer, we get 8 colors
LCD
• Contains matrix of liquid crystals sandwiched between
two polarizing filter panels
• Active and passive matrix displays
• Manufactured with thin film transistor (TFT)
technology
• Compared with CRTs
–
–
–
–
Less contrast
Reduced size, weight, and power consumption
Higher cost
energy-efficient, have sharp picture
– Contrast: how big the difference between "white" and
"black"
Plasma Display
• Combine elements of CRT and LCD technology
• Flat panel, active matrix devices
• Actively generate colored light near surface of
the display; good brightness and viewing
• Require more power than LCDs, less than CRTs
• Shortcomings
– Limited operational lifetime
– Larger pixel size reduces comparative image
quality when viewed from short distances
How Plasma Display Works
• Plasma displays have no backlight and no color filters; each pixel
contains a gas that emits ultraviolet light when electricity is applied.
Plasma
• Plasma technology consists of hundreds of thousands of
individual pixel cells, which allow electric pulses to excite
rare natural gases-usually xenon and neon-causing them to
glow and produce light.
• This light illuminates the proper balance of red, green, or
blue phosphors contained in each cell to display the proper
color sequence from the light.
• Each pixel cell is essentially an individual microscopic
florescent light bulb, receiving instruction from software
contained on the rear electrostatic silicon board. Look very
closely at a plasma TV and you can actually see the
individual pixel cell coloration of red, green, and blue bars.
You can also see the black ribs which separate each.
LED TV
• LED (light emitting diode)
• LED TVs are a new form of LCD Television. The
panel on an LED TV is still an LCD TV panel and
operates with the same twisting crystals
matrix.
• The backlight is the difference - changing from
fluorescent to LED based backlighting
• Have better contrast and more accurate colors
than LCD
Digital Images from Scanners and Cameras
• The color and brightness of each tiny area seen by a sensor is
"sampled", meaning the color value of each area is measured and
recorded as a numeric value which represents the color there
• Each one of these sampled numeric color data values is called a
pixel
• A 6 inch photograph scanned at 100 dpi will produce 600 pixels
across that dimension of the image.
• The scanner scanning resolution (pixels per inch) and the size of the
area being scanned (inches) determine the image size (pixels)
created from the inches scanned.
– If we scan 8x10 inch paper at 300 dpi, we will create (8 inches x 300
ppi) x (10 inches x 300 ppi) = 2400x3000 pixels