"Complexity of the real world is frightening"

The original graphics devices were printers. [You can still find ASCII art around today]

Display tubes (CRT) were developed in the 1920's and produced an image by scanning across the tube one line at a time. The TV signal is analog and drove the electron gun intensity, but the beam deflectors were on autopilot tracing out their path.

Vector graphics was the first real effort at computer graphics. It operates on the same principle as pen plotting requiring only two basic commands: MOVETO(X,Y) and DRAWTO(X,Y). Think of these as being pen up and pen down.

Along came Raster graphics, aka bitmapped graphics, where the screen was divided into little dots (or pixels) which in color displays requires 3 separate phosphors. These are RGB (red green blue) which are each driven by their own electron gun. The problem with this scheme is that it requires memory for each pixel. Modern graphics can require one byte per color or more and the screen image is refreshed 60 times a second, yielding about 3*1280*1024 = 3.9MB memory and 3.9M*60 = 235M operations/second!

Frame buffers. The amount of memory designed into the frame buffer determines the image resolution and number of available colors. Old graphics processors used .5MB VideoRAM and could display 4-bit (16) color at high resolution. Today we can assign 1 byte to each of the three primary color pixels to generate 24-bit (16.7M) color at very high resolutions using only 3MB VideoRAM.

The mobile computing user has driven a branch of the video display technology to produce designs that are lightweight and small enough to be portable. These fall into two basic camps: gas plasma and liquid crystal display (LCD).

"ultra-sophisticated neon sign"

The gas plasma display used two sets of parallel wires offset from each other and filled the intervening volume with a gas that would glow when a charge potential built up. This produces a good picture, but at greater expense and less durability than the LCD technology.

"ultra-sophisticated Oakley sunglasses"

LCDs work on the principle of polarized light. One set of slits are fixed and another set is adjustable at the pixel level, thus allowing the appropriate pixels to shine through to composed the image.

Both technologies suffer from refresh rates, gas plasma due to the time required to make the gas glow and the LCDs from the time it takes to rotate the moveable slits.

We next explored the wonderful world of hardcopy technology. We start with the venerable dot-matrix printer, which was good enough for rough drafts and computer printouts, but the spacing between dots was too coarse to produce nice looking documents. Letter Quality (LQ) printers used impact technology (remember the good old Remington typewriters?) to form high quality letters, but they were good for nothing else. At least the dot-matrix could be used to generate images using the grid of dots. These progressed through IBM's Selectric (using a ball) and the daisy-wheel impact printers that could change fonts by changing balls/wheels.

The dot-matrix technology was refined through the introduction of the inkjet printer and the laser printer, which could create images because of the smaller dot sizes and gaps. The inkjet printer uses valves and nozzles to spray miniscule drops of ink in the desired patterns. The laser printer uses an electrostatic drum that has the negative of the images discharged through the use of a laser to apply ink toner to the paper where it is fused using heat.

Both devices broke the printing task into two processes. The image is actually printed by the print engine, which is fed by the output from the image processor. This allows for instructions on how to construct the image (eg postscript) to be communicated over the slow wire and internally processed within the printer into an image pixelmap stored in the frame buffer.

Color printing is a subtractive process since the starting background is white (the sum of all colors) and the primary complementary colors (Cyan Magenta Yellow) are used as filters, whereas on the display tube we start out with a black background (the absence of all color) and the primary colors (Red Green Blue) are used to build images.

The memory scheme for implementing frame buffers will directly influence overall system performance. The old scheme used part of the system RAM for frame buffers. This created a lot of traffic on the main system bus (60 images/sec) contending with the normal bus activities (like program loading, reading and writing to memory, shuttling info from the various input/output devices...). A better scheme separated the VideoRAM and Graphics Processor into a separate standalone peripheral-like unit. This reduced system bus traffic at the expense of making every graphic operation a system call, even if only a simple memory write (to change a field's color from red to yellow, for example) could do the task. This led to the development of the local bus architecture, where the VideoRAM is logically connected to the end of system RAM so the CPU or other devices can write directly to it while maintaining pathways from the graphics processor.

Locater Devices. Mouse, Track Ball, Touch Screen & Pad, Light Pen, etc.

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