Full Color System

Color CRTs in graphics systems are designed as RGB monitors. These monitors use shadow mask method and take the intensity level for each gun. A RGB color system with 34 bits of storage per pixel is known as full color system or true color system.

Look Up Tables !

An array or matrix of data that contains items that are searched. Lookup tables may be arranged as key-value pairs, where the keys are the data items being searched (looked up) and the values are either the actual data or pointers to where the data are located. Sometimes, lookup tables contain only data items (just values, not key-value pairs). For example, in a 256-color palette, the location in the table and the key are synonymous (item 0, item 1, item 2, etc.)

A lookup table is a data structure, usually an array or associative array, often used to replace a runtime computation with a simpler array indexing operation. The savings in terms of processing time can be significant, since retrieving a value from memory is often faster than undergoing an 'expensive' computation. Lookup tables are also used extensively to validate input values by matching against a list of valid (or invalid) items in an array and, in some programming languages, may include pointer functions (or offsets to labels) to process the matching input.

In data analysis applications, such as image processing, a lookup table is used to transform the input data into a more desirable output format. For example, a grayscale picture of the planet Saturn will be transformed into a color image to emphasize the differences in its rings.

A classic example of reducing run-time computations using lookup tables is to obtain the result of a trigonometry calculation, such as the sine of a value. Calculating trigonometric functions can substantially slow a computing application. The same application can finish much sooner when it first precalculates the sine of a number of values, for example for each whole number of degrees. Then, when the program requires the sine of a value, it can use the lookup table to retrieve the closest sine value from a memory address, and may also take the step of interpolating to the sine of the desired value, rather than work out the unique value every time using the mathematical formula. Lookup tables are thus used by mathematics co-processors in computer systems. An error in a lookup table was responsible for Intel's infamous floating-point divide bug.

Before the advent of computers, printed lookup tables of values were used by people to speed up hand calculations of complex functions, such as in trigonometry, logarithms, and statistical density functions.

Functions of a single variable (such as sine and cosine) may be implemented by a simple array. Functions involving two or more variables require multidimensional array indexing techniques. The latter case may thus employ a two-dimensional array of power[x][y] to replace a function to calculate xy for a limited range of x and y values. Functions that have more than one result may be implemented with lookup tables that are arrays of structures.

As mentioned, there are intermediate solutions that use tables in combination with a small amount of computation, often using interpolation. Pre-calculation combined with interpolation can produce higher accuracy for values that fall between two precomputed values. This technique requires slightly more time to be performed but can greatly enhance accuracy in applications that require the higher accuracy. Depending on the values being precomputed, pre-computation with interpolation can also be used to shrink the lookup table size while maintaining accuracy.

In image processing, lookup tables are often called LUTs and give an output value for each of a range of index values. One common LUT, called the colormap or palette, is used to determine the colors and intensity values with which a particular image will be displayed. Windowing in computed tomography refers to a related concept.

While often effective, employing a lookup table may nevertheless result in a severe penalty if the computation that the LUT replaces is relatively simple. Memory retrieval time and the complexity of memory requirements can increase application operation time and system complexity relative to what would be required by straight formula computation. The possibility of polluting the cache may also become a problem. Table accesses for large tables will almost certainly cause a cache miss. This phenomenon is increasingly becoming an issue as processors outpace memory. A similar issue appears in rematerialization, a compiler optimization. In some environments, such as the Java programming language, table lookups can be even more expensive due to mandatory bounds-checking involving an additional comparison and branch for each lookup.

There are two fundamental limitations on when it is possible to construct a lookup table for a required operation. One is the amount of memory that is available: one cannot construct a lookup table larger than the space available for the table, although it is possible to construct disk-based lookup tables at the expense of lookup time. The other is the time required to compute the table values in the first instance; although this usually needs to be done only once, if it takes a prohibitively long time, it may make the use of a lookup table an inappropriate solution. Tables can however be statically defined in many cases, avoiding any additional processing once compiled.

Plasma Panels !

The plasma panel is composed of two sheets of glass with a series of ribs ( like corrugated cardboard ) filled with color phosphors in between. The top glass with embedded electrodes seals and forms a pixel where the junctions of the channels and the plate come together. Inside the sealed pixel, is a mixture of rare gases- typically argon and neon, although xenon has also been used.

Actually a small electric capacitor has been created, with one electrode on the rear and a pair on the front. These 3 electrodes control the capacitor charge, sustain and discharge functions intrinsic to the plasma imaging process.

The plasma imaging cycle can be broken into following steps. initially, the pixel is at its resting ( ie. Off ) state. while a voltage is applied to the addressing electrodes ( pixel ). When the applied voltage reaches a certain level- say 200+ volts - the resistance in the pixel is overcome, and an electrical discharge is made across the electrodes. Once this discharge occurrs, the mixture of rare gases is ionized into a plasma state, which means the gas mixture can now conduct electricity, an intense burst of ultraviolet ( UV ) light is emitted. This burst of UV energy stimulates the color phosphors, in turn makes them glow brightly.

Once the pixel is switched On, a much lower voltage sustains the UV emissions and keeps the phosphors glowing. This sustain voltage is typically in the 50 volts range. Eventually, the pixel will need to be turned off to rest the phosphors. This is done by removing the sustain voltage first, then reversing the charge in the pixel through the addressing electrodes. At this point, the pixel is back to its resting