Display technologies are rapidly evolving. Improvements in integrated circuit manufacturing, higher levels of transistor integration, general display device improvements, interface advances, etc., place considerable demands on video display control circuitry. Liquid crystal display (LCD) manufacturers conventionally use look-up-tables (LUT) to link index numbers to output values and replace runtime computation with simpler lookup operations. For example, LUTs may quickly provide information to compensate for delays caused in changing liquid crystal (LC) modes. Unfortunately, many factors may change and necessitate additional LUTs. Changes in temperature, in each color, in frame frequency, in display size, and in resolution may all require different LUTs and therefore use a considerable amount of memory.
For instance, temperature variations may affect LC driving response time. A typical LCD operating range is 0 to 55 degrees Celsius. Different LUT values can be used to compensate for these variations, for example, different LUT values at 5 degree increments. In the present example, 12 different LUTs spaced at 5 degree intervals will cover a 55 degree temperature range. Other variations may require different LUTs. As examples, LUTs may differ for each red, green, and blue (RGB) color and for different frame frequencies such as 50 Hz, 60 Hz, 75 Hz, etc.
Active matrix LCDs present additional challenges for LUTs use since optical characteristics are determined by various factors including: the LC material, different LC modes, thin film transistor (TFT) requirements, and manufacturing and driving methods. These variations complicate LUT use and increase LUT requirements.
Furthermore, LUTs may be differentiated by color depth. For example, an 8 bit color depth for RGB data equates to 256 levels of gray scale. Therefore an LUT with 8 bit data can implement 256 levels of gray scale. Color may be compensated with expanded color coordinates, dithering and frame rate control (FRC) to allow 8 bit data to perform like 9 bit data.
To properly implement LUTs with the above constraints, that is, 12 temperature variations, 3 independent color components such as RGB, and 4 frame frequencies, requires 144 independent LUTs. Additionally, a typical LUT may comprise many values, for example 256 source grays, 256 compensated grays, and 8 bits.
For these reasons, LCD manufacturers reduce basic LUT dimensions. An example LUT size reduction uses 16 source grays, 16 compensated grays, and is in 8 bit format, resulting in 2048 bits. Even after LUT size reduction, many LUTs are needed. LCD manufacturers may reduce the number of LUTs by optimizing LCD characteristics. Accordingly, a need remains for improve LUT efficiency.