WO2006038186A2

WO2006038186A2 - Method and apparatus for updating look-up tables of a display apparatus

Info

Publication number: WO2006038186A2
Application number: PCT/IB2005/053260
Authority: WO
Inventors: John Edward Dean; Lucian Remus Albu
Original assignee: Koninklijke Philips Electronics, N.V.
Priority date: 2004-10-06
Filing date: 2005-10-04
Publication date: 2006-04-13
Also published as: WO2006038186A3

Abstract

A display apparatus including a plurality active look-up tables and a substitute look-up table. Each of the active look-up tables stores parameters of a waveform that drives a scanning line of the display apparatus. The substitute look-up table is able to replace any one of the plurality of active look-up tables to change the parameters of the waveform associated with the replaced active look-up table. When the substitute look-up table replaces one of the plurality of active look-up tables, the other active look-up table may be unchanged. The display apparatus may a liquid crystal display (LCD), a liquid crystal on silicon (LCOS), a plasma display, or a digital light processing (DLP) display.

Description

METHOD AND APPARATUS FOR UPDATING LOOK-UP TABLES OF A DISPLAY

APPARATUS

Display devices continue to evolve and are used in disparate applications. Examples of devices that include displays are televisions, computers, cell phones and personal digital assistants, to name only a few. Moreover, displays can be based on widely varying technologies, including, but not limited to liquid crystal display (LCD) technology, plasma display technology, digital light processing (DLP) display technology, and liquid crystal on silicon (LCOS) display technology.

Displays have electrical circuitry useful in forming images on a display surface and the quality of the image, collectively referred to as image processing. The circuitry may include logic and memory (e.g. read only memory (ROM) or random access memory (RAM)). The circuitry may control qualitative aspects of the display (e.g. brightness or contrast). Frequently the RAM memories are configured as look-up tables (LUTs). In video processing, LUTs often used to implement functions such as gamma. In this case they are used to process pixels at the video rate. They may also be used for arithmetic operations such as multiplication by a coefficient. In addition, they may be used to drive a digital-to-analog converter to produce arbitrary waveforms.

In many known displays, the image processing circuitry requires significant real estate. Ultimately, this impacts the cost of the display, and can impact the size of the display device.

What is needed, therefore, is display apparatus and method of use that addresses at least the shortcomings of known structures described above.

In accordance with an example embodiment, a display apparatus includes a plurality of active look up tables. Illustratively, each of the plurality of active look up tables stores parameters of an analog "ramp" waveform which is used as the gamma reference for a display apparatus. The display apparatus also includes a substitute look up table, which is adapted to replace any one of the plurality of active look up tables to change the parameters of the waveform associated with the replaced active look up table. In accordance with another example embodiment, a method of driving a display apparatus includes driving a scanning line of the display apparatus according to a plurality of active look up tables. Illustratively, each of the plurality of look up tables stores parameters of an analog "ramp" waveform which is used as the gamma reference for a display apparatus. The method also includes replacing any of the plurality of active look up tables with a substitute look up table to change the parameters of the waveform that that drives the scanning line of the display apparatus.

The invention is best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, the dimensions may be arbitrarily increased or decreased for clarity of discussion.

Fig. 1 is a schematic diagram showing a plurality of active look-up tables with corresponding 2-to-l multiplexers and a substitute look-up table with a 2-to-l substitute multiplexer, in accordance with an example embodiment. Fig. 2 is a schematic diagram of a plurality of active look-up tables with corresponding 4-to-l active multiplexers and a substitute look-up table with a corresponding 4-to-l substitutes multiplexer, in accordance with an example embodiment.

Fig. 3 is a schematic diagram of a plurality of active look-up tables with corresponding 2-to-l active multiplexers and a substitute multiplexer with a 4-to-l substitute multiplexer, in accordance with an example embodiment.

In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth in order to provide a thorough understanding of the example embodiments. However, it will be apparent to one having ordinary skill in the art having had the benefit of the present disclosure that other embodiments that depart from the specific details disclosed herein. Moreover, descriptions of well-known devices, methods, systems and protocols may be omitted so as to not obscure the description of the present invention. Nonetheless, such devices, methods, systems and protocols that are within the purview of one of ordinary skill in the art may be used in accordance with the example embodiments. Finally, wherever practical, like reference numerals refer to like features.

Briefly, in accordance with illustrated embodiments, methods and apparati are described that reduce the circuitry necessary to drive a display apparatus. In accordance with certain example embodiments, a single substitute look-up table and corresponding substitute multiplexer are used to substitute for a plurality of active look-up tables. Because only one substitute look-up table and substitute multiplexer is necessary, the amount of logic and memory resources needed are reduced, which beneficially simplifies manufacturing processes circuit complexity reducing costs.

Figure 1 is a schematic diagram showing a plurality of active look-up tables (e.g. LUTA 101, LUTB 102, LUTC 103 and substitute look up table LUTSWP 108) each with a corresponding 2-to-l active multiplexers (e.g. active multiplexers 104, 105, and 106) and a single substitute look-up table (e.g. LUTSWP) with corresponding 2-to-l substitute multiplexer 107. During normal operation of a display apparatus, display data (din), address control data (ctl addr) are input into multiplexers 104, 105, 106, and 107. In embodiments, the display data (din) and the address control data (ctl addr) are digital data. Each of the multiplexers 104, 105, 106, and 107 output either in the display data (din) or the address control (ctl addr) to the corresponding look-up tables (LUTA 101, LUTB 102, LUTC 103 and LUTSWP 108), according to the corresponding selection signals (sel_ai, sel_bi, sel_ci, or sel_swp). To perform a write operation to a LUT; i.e., in order to change the LUTs function, the LUT addr input must be connected to signal ctl addr and the LUT data input is loaded via the ctl dat input. To perform a read operation from the LUT; i.e., operational mode, the addr input must be connected to the din input. When din is driving a LUT, then, based on the data stored in the look-up tables LUTA 101, LUTB 102, LUTC 103, or LUTSWP 108, adjusted display data (do_a, do_b, do_c, or do_swp) are output to multiplexer 109. Multiplexer 109 outputs adjusted display data (dout) 110, according to the selection signal (SCL_OUT) to a display driving unit.

The LUTs of the example embodiment may be used for functions other than storing a waveform. For example, a common use of LUTs is to store a gamma correction of digital video. In this case, a function, y=f(x), is applied to each pixel, where f(x) is the gamma correction function. In general, the LUTs store parameters of a digital video processing chain of a display apparatus. The waveform and gamma correction functions are merely illustrations of such parameters. The adjusted display output data (dout) 110 contains parameters for a waveform to drive a particular of a display apparatus. This waveform may represent, for example, the reference analog ramp for a distributed digital-to-analog converter within the display device. This ramp signal, which represents the voltage-to-light transfer charateristic of the pixels at various wavelengths, is represented in digital form within the LUT. For example, each of the LUTs (LUTA, LUTB, and LUTC) may be pre-loaded with ramp waveforms that correspond to the colors red, green, and blue respectively. The din input, a simple 8- bit counter which represents all 256 possible pixel values and is the same for all 3 LUTs, is input into multiplexer 104, is processed by look-up table LUTA 101 and produces a red digital ramp waveform at signal do_a. This is then output from multiplexer 109 as dout. The selected ramp signal (dout 110) can be used to drive a DAC which will in turn create a red ramp waveform into the display. The adjustment according to the data stored in look-up table LUTA 101 may affect the brightness and/or contrast of the illumination of the red pixels. In the present example, a similar protocol is used to drive other colors associated with look-up table LUTB 102 with corresponding multiplexer 105 and look-up table LUTC 103 with corresponding look-up table 106.

During operation or calibration of the display apparatus, it may be useful to change the values of the look-up tables LUTA 101, LUTB 102, or LUTC 103 or a combination thereof. For example, look-up table LUTA 101 may correspond to the color red and it may be useful to increase the contrast of the illumination of corresponding red pixels in the display apparatus. Accordingly, the contents of look-table LUTA 101 need to be changed. Substitute look-up table LUTSWP 108 may be updated with new look-up table information and replace look-up LUTA according to data signal (ctl dat) 111, address signal (ctl addr) 112 and address selection signal (sel_swp) which correspond to the substitute look-up table LUTSWP 108. Likewise, according to the various control signals, substitute look-up tables LUTSWP (e.g. 108) may be substituted for any of the other active look-up tables (e.g. LUTA 101, LUTB 102, and LUTC 103). In accordance with example embodiments, after substitute look-up table LUTSWP

108 replaces one of the active look-up tables (e.g. LUTA, LUTB, or LUTC), the substitute look-up table 108 becomes the active look-up table and the replaced look-up table (e.g. LUTA 101) becomes the substitute look-up table that can be used for future replacement of any of the other active look-up tables. Accordingly, based on control signals, only one look-up table is replaced at a time. However, as will be readily appreciated, because there is only one substitute look-up table LUTSWP and corresponding multiplexer, the amount of circuitry required for updating active look-up tables is substantially reduced. Stated differently, redundancy of look-up tables is reduced; thereby reducing display circuit complexity. Accordingly, costs of manufacturing a display apparatus may be reduced. Alternatively, because only one substitute look-up table is necessary, the display apparatus may be able offer more features via circuitry, as there is more room on the semiconductor device for circuitry accommodating such additional features.

One of ordinary skill in the art would appreciate that using a single substitute look¬ up table may be implemented in a variety of display devices. For instance, embodiments of the present invention may be implemented in a liquid crystal display (LCD), a liquid crystal on silicon (LCOS) display, a plasma display, or a digital light processing (DLP) display. For a LCOS display, there may be a single active look-up table for each combination of color and polarity (liquid crystal displays require polarity inversion to prevent DC build-up in the cells) that the display supports. For example, in a three color two polarity LCOS display, there will be two look-up tables for each of the colors red, blue, and green. In other words, there will be a look-up table red with a positive polarity, a look-up table for red with a negative polarity, a look-up table for green with a positive polarity, a look-up table for green with a negative polarity, a look-up table for blue with a positive polarity, and a look¬ up table for blue with a negative polarity. Likewise, in a five color two polarity LCOS display, there will additionally be a look-up table for yellow with a positive polarity, a look-up table for yellow with a negative polarity, a look-up table for cyan with a positive polarity and a look-up table for cyan with a negative polarity. However, in order to avoid obscuring the description of the example embodiment, only three look-up tables (LUTA, LUTB, and LUTC) are illustrated in Figs 1, 2 and 3.

Fig. 2 illustrates a plurality of active look-up tables LUTA 201, LUTB 202, and LUTC 203, with corresponding 4-to-l multiplexers 204, 205 and 206, respectively, and a single substitute look-up table LUTSWP with corresponding 4-to-l multiplexer 26. In the embodiments illustrated in Fig. 2, instead of a single data input (din) as in the embodiments in Fig. 1, there are data inputs (din_a 207, din_b 208, and din_c 209) corresponding to each active look-up tables LUTA 201, LUTB 202, and LUTC203, respectively. Accordingly, since there is a possibility that each of the active look-up tables LUTA 201, LUTB 202, and LUTC 203) can be replaced with a substitute look-up table LUTSWP 210 with corresponding multiplexers (204, 205, 206, and 26), each of the multiplexers (204-206, 211) must have four input ports and a single output port. Likewise, look-tables LUTA 201, LUTB 202, LUTC 203, and LUTSWP 207 have corresponding 4-to-l multiplexers (212, 213, and 214) as shown. Because the substitute look-up table LUTSWP 207 with corresponding multiplexer 16 can be replaced with any of the active look-up tables LUTA 101, LUTB 102, and LUTC 103) with corresponding active multiplexers (104, 105, and 106), each of the look-up tables LUTA 201, LUTB 202, LUTC 203, and LUTSWP 204) and corresponding multiplexers (204, 205, 206, and 211) must have the same structure.

Figure 3 is a schematic diagram of a circuit in accordance with an example embodiment. In the present example embodiment, active look-tables LUTA 301, LUTB 302, and LUTC 303 with corresponding multiplexers (305, 306, and 307) have different structures than a substitute look-up table LUTSWP 308 with corresponding multiplexer 309. Specifically, multiplexer 309 is a 4-to-l multiplexer, while the active multiplexers 305, 306, and 307 are 2-to-l multiplexers. The different data input (din_a309, din_b310, and din_c311) are input according to the corresponding colors associated with look-up tables LUTA 301, LUTB 302, and LUTC 303. However, unlike the embodiments illustrated in Fig. 2, look-up table LUTA 301 with corresponding active multiplexer 305 can only be used for a single color because only the data input for a single color (din_a309) is input into 2-to-l multiplexer 305. This is also true for look-up table LUTB 302 with corresponding multiplexer 306 and look-up table LUTC 303 with corresponding active multiplexer 307 with data input (din_b) and (din_c311), respectively. Accordingly, fox example when the data stored in active look-up table LUTA 301 are updated, the substitute look-up table LUTSWP 308 is swapped with active look-up table LUTA 301. Then, active look-up table LUTA 301 is updated with the same information that is stored in the substitute look-up table LUTSWP 308 and then swapped back. Substitute look-up table LUTSWP 308 is different from the active look-up tables LUTA 301, LUTB 302, and LUTC 303 with corresponding multiplexers, as a multiplexer associated with the substitute look-up table LUTSWP is a 4-to-l multiplexer, which is able to receive all of the data input types (din_a309 din_b310, and din__c311). Likewise, output multiplexers 312, 313, and 314 are also only 2-to-l multiplexers. As one of ordinary skill in the art would appreciate, the circuitry required for 2-to-l multiplexers is less complicated than the circuitry required for 4-to-l multiplexers. Accordingly, the embodiments illustrated in Figure 3 conserves circuitry in a display apparatus, as it requires more simple multiplexers. However, embodiments illustrated in Figure 3 require that when a look-up table is substituted, a look-up table needs to be replaced twice, while the embodiments illustrated in Figure 2 the data are only replaced once.

When the substitute look-up table LUTSWP of Figure 3 replaces one of the active look-up tables (e.g. LUTA, LUTB, or LUTC), each active look-up table is only compatible with one color/polarity. Conversely, in the embodiments illustrated in Figure 2, a swapped out active look-up table will be compatible with any of the other colors. In other words, embodiments illustrated in Figure 2 require fewer logical operations when updating a look¬ up table, but require more circuitry; while embodiments illustrated in Figure 3 require more logical operations for updating look-up tables, but consume less circuitry. One of ordinary skill in the art will appreciate that either one of the embodiments illustrated in Figure 2 or the embodiments illustrated in Figure 3 may be implemented, if there are multiple data input signals (din_a, din_b, or din_c).

In view of this disclosure it is noted that the various methods and devices described herein can be implemented in hardware and software in a variety of display applications. Further, the various methods, devices and parameters are included by way of example only and not in any limiting sense. In view of this disclosure, those skilled in the art can implement the various example devices and methods in determining their own techniques and needed equipment to effect these techniques, while remaining within the scope of the appended claims.

Claims

CLAIMS:

1. A display apparatus comprising: a plurality of active look up tables (101, 102, 103), wherein each of the active look up tables stores parameters of a digital video processing chain of the display apparatus; and a substitute look up table (108), wherein the substitute look up table is adapted to replace any one of the plurality of active look up tables to change the parameters associated with the replaced active look up table.

2. The display apparatus of claim 1, wherein when the substitute look up table replaces one of the plurality of active look up tables, the other active look up tables are unchanged.

3. The display apparatus of claim 1, wherein the display apparatus is selected from a group consisting of: a liquid crystal display; a liquid crystal on silicon display; a plasma display; and a digital light processing display.

4. The display apparatus of claim 1, wherein the plurality of active look up tables comprises at least one of: a look up table for red with a positive polarity; a look up table for red with a negative polarity; a look up table for green with a positive polarity; a look up table for green with a negative polarity; a look up table for blue with a positive polarity; a look up table for blue with a negative polarity, a look up table for yellow with a positive polarity; a look up table for yellow with a negative polarity; a look up table for cyan with a positive polarity; and a look up table for cyan with a negative polarity.

5. The display apparatus of claim 1, wherein: each of the plurality of look up tables has a corresponding active multiplexer

(104,105,106,107); the substitute look up table has a corresponding substitute multiplexer (107); and when one of the active look up tables is replaced with the substitute look up table, the corresponding active multiplexer is replaced with the substitute multiplexer.

6. The display apparatus of claim 5, wherein: the active multiplexers and the substitute multiplexer receive display data and address data and output either the display data or the address data based on a selection signal input into the corresponding active multiplexer or substitute multiplexer; each of the plurality of look up tables receives the output of the corresponding active multiplexer and a data control signal; and each of the plurality of look up tables outputs a data output signal based on the output from the corresponding active multiplexer, the data control signal, and the contents of the look up table.

7. The display apparatus of claim 5, wherein the each of the corresponding active multiplexers and the substitute multiplexer have the same number of input ports.

8. The display apparatus of claim 7, wherein the substitute look up table and the substitute multiplexer are adapted to replace any one of the plurality of active look up tables and the corresponding active multiplexer, respectively, whereby the substitute look up table becomes an active look up table and the substitute multiplexer becomes an active multiplexer.

9. The display apparatus of claim 5, wherein the substitute multiplexer has more input ports than each of the corresponding active multiplexers.

10. The display apparatus of claim 9, wherein after one of the plurality of active look up tables is replaced with the substitute look up table, the one of the active look up tables is updated with the same information stored in the substitute look up table and then the one of the active look up tables replaces the substitute look up table.

11. The display apparatus as recited in claim 1 , wherein the parameters are an analog ramp waveform, which is used as a gamma waveform for the display device.

12. The display apparatus as recited in claim 1, wherein the parameters are gamma correction digital video.

13. A method of driving a display apparatus comprising: providing a plurality of active look up tables (101, 102, 103), wherein each of the active look up tables stores parameters of a digital video processing chain of the display apparatus; and replacing any one of the plurality of active look up tables with a substitute look up table (108) to change the parameters the display apparatus.

14. The method of claim 13, wherein when the substitute look up table replaces one of the plurality of active look up tables, the other active look up tables are unchanged.

15. The method of claim 13, wherein the display apparatus is one of: a liquid crystal display; a liquid crystal on silicon display; a plasma display; and a digital light processing display.

16. The method of claim 13, wherein the plurality of active look up tables comprises at least one of: a look up table for red with a positive polarity; a look up table for red with a negative polarity; a look up table for green with a positive polarity; a look up table for green with a negative polarity; a look up table for blue with a positive polarity; a look up table for blue with a negative polarity, a look up table for yellow with a positive polarity; a look up table for yellow with a negative polarity; a look up table for cyan with a positive polarity; and a look up table for cyan with a negative polarity.

17. The method of claim 13, wherein: each of the plurality of look up tables has a corresponding active multiplexer (104,

105, 106); the substitute look up table has a corresponding substitute multiplexer (108); and when one of the active look up tables is replaced with the substitute look up table, the corresponding active multiplexer is also replaced with the substitute multiplexer.

18. The method of claim 13, wherein: both the active multiplexers and the substitute multiplexer receive display data and address data and output either the display data or the address data based on a selection signal input into the corresponding active multiplexer or substitute multiplexer; each of the plurality of look up tables receives the output of the corresponding active multiplexer and a data control signal; and each of the plurality of look up tables outputs a data output signal based on the output from the corresponding active multiplexer, the data control signal, and the contents of the look up table.

19. The method of claim 17, wherein the corresponding active multiplexers and the substitute multiplexer have the same number of input ports.

20. The method of claim 19, wherein when one of the plurality of active look up tables and the corresponding active multiplexer is replaced with the substitute look up table and the substitute multiplexer, the substitute look up table becomes an active look up table and the substitute multiplexer becomes an active multiplexer.

21. The method of claim 17, wherein the substitute multiplexer has more input ports than each of the corresponding active multiplexers.

22. The method of claim 21 , wherein after one of the plurality of active look up tables is replaced with the substitute look up table, the one active look up table is updated with information stored in the substitute look up table and then the one of the active look up tables replaces the substitute look up table.

23. A method as recited in claim 13, wherein the parameters are analog ramp waveform, which is used as a gamma waveform for the display device.

24. A method as recited in claim 13, wherein the parameters are gamma correction digital video.