Lecture Notes

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• monitor, display
• CRT
• Picture element, pixel
• Resolution
• Refresh rate
• XY coordinate system

• Raster
• VRAM
• Graphics accelerator
• Video bus
• Bitmap
• Bitmap file formats

• There are two types of displays:
• Cathode Ray Tube (crt)
• The inside of the screen is coat with a layer of phosphorus.
• In the rear of the screen is the "Gun".
• The gun emits cathode rays (electrons), and is aimed by magnets located in the rear of the screen.
• The gun fires from left to right, starting at the top left, and works its way down to the bottom right.
• When the cathode rays hit the phosphorus, various colors of light are emitted.
• There is a metal screen on the other side of the phosphorus that results in a more exact region for the cathode ray to hit.
• Flat screen
• Wire grids are sandwiched between thin layers of glass.
• The wires act as pathways for electric current to pass.
• When current is passed along these wires, when current is sent along intersecting wires, at the point where they intersect, the pixel is activated.
• Pixel- contraction between picture element. (The dots on the screen).
• When screen dimensions are given, they refer to the diagonal screen measurement.
• Note: be aware of dimension given; viewable area, or actual area.
• Resolution-number of pixels across by number of pixels down.
• The size of the pixel itself can vary.
• Smaller value is better.
• Refresh rate-number of times the gun make one complete pass per second.
• Measured in Hz
• Today’s screen have refresh rates around 85 Hz, well above the rage in which "screen flicker" is noticeable. (While this value varies, it is somewhere in the rage of 60-65 Hz).
• Note: flat screens do not have refresh rates.
• Black and white screens
• Each pixel has two options: light emitting or non-light emitting.
• This, like everything in binary, is represented by 1’s and 0’s: yes and no respectively.
• If you recall, a 1 is communicated to the computer with the presence of an electrical impulse; and a 0 with the absence of an electrical impulse.
• So with black and white screens, a 0 translates to off (the gun is not fired at that pixel) or a 1, (the gun is fired at that pixel).
• Color screens
• All colors on the screen are created by the use of three colors: red, green, and blue. (RGB)
• So with color screens, each pixel is composed of a three smaller pixels, one of each of the above mentioned colors.
• Now that each pixel’s color is created by the use of three colors, three separate guns are needed.
• To produce the colors the eye perceives, the RGB colors are used in various intensities.
• So now three bits are needed to represent one pixel.
• With color screens, there is a huge jump in the amount of data needed to represent an image to be displayed, as compared with a black and white screens. To help the computer handle this increased data:
• Video bus (so the system bus will not be bogged down).
• VRAM (video RAM)
• Some computers even have a second chip just for processing video.