WO2009138965A1

WO2009138965A1 - Ultra black bars in lcd tv

Info

Publication number: WO2009138965A1
Application number: PCT/IB2009/052026
Authority: WO
Inventors: Han Joosten
Original assignee: Nxp B.V.
Priority date: 2008-05-16
Filing date: 2009-05-15
Publication date: 2009-11-19

Abstract

A liquid crystal display (LCD) system to improve image quality of video content. The LCD system includes a backlight, which includes sections of upper, lower, and intermediate backlights, and an image controller, which includes a content detector and a sealer de-interlacer. The image controller receives an input video signal from a video source and generates a processed video signal for display on a display device. The image controller also designates upper, lower, and intermediate display sections of the display device. The content detector detects video content in the input video signal from the video source. The sealer de-interlacer controls a backlight inverter to adjust illumination levels of the upper and lower backlights in response to detection of an absence of video content in the corresponding upper and lower display sections of the display device to adjust an image quality in the intermediate display section of the display device.

Description

ULTRA BLACK BARS IN LCD TV

Black bars appear on the upper and lower viewing sections of a television (TV) screen when the aspect ratio of an input video signal does not match the inherent aspect ratio of the TV screen. After the introduction of high-definition TV, the aspect ratio mismatch problem worsened. The aspect ratio of a standard definition TV is 4:3, the aspect ratio of a high-definition TV is 16:9, and the typical movie cinema aspect ratio is 22:9. A standard definition 4:3 source may be displayed on a high- definition 16:9 TV by transforming the source to 14:9, and so forth. However, transforming the source aspect ratio to better fit the inherent aspect ratio of a TV screen often still leaves black bars on the top and bottom of the TV screen.

Fig. IA depicts a conventional standard-definition LCD TV 102. Fig. IB depicts a conventional high-definition LCD TV 104. As illustrated, the standard- definition and high-definition LCD TVs 102 and 104 include viewing areas 110 and 116, respectively, to display video content. As depicted, the viewing area 110 of the standard-definition LCD TV 102 includes upper and lower black bars 106 and 108. Likewise, the viewing area 116 of the high-definition LCD TV 104 includes upper and lower black bars 112 and 114. However, instead of displaying "black" bars, the standard- definition and high-definition LCD TVs 102 and 104 display "grey" bars because of the use of backlight illumination. In a typical LCD panel, the backlighting includes multiple illumination devices. Currently, many LCD panels use multiple cold-cathode fluorescent lamps (CCFLs) for illumination of the liquid crystals. Due to costs and heat distribution, the CCFLs are typically mounted horizontally behind the display. The number of individual CCFLs implemented increases as the size of the LCD panel increases. An average LCD panel contains between 8 and 10 individual CCFLs, mounted horizontally behind the display.

The use of backlights in LCD TVs prevents the black bar areas from appearing to be black because of light leakage through the liquid crystals. The liquid crystals of the display operate to control the transparency depending on the video content. If an image is black, then the optimum situation is no light throughput, and if white, then full transparency with maximum light output. This is controlled on a per pixel basis in the LCD panel for the 3 primary colors, red, green and blue. In the black bar areas, the transmission of light is not typically zero, and so the perceived color is grey rather than black. Thus, in typical TV room conditions, the black bars appear as grey instead of black. Grey bars on the upper and lower viewing sections of an LCD screen reduce the perception of picture quality for LCD TV's.

Embodiments of a system are described. In one embodiment, the system is a liquid crystal display (LCD) system to improve an image quality of video content displayed on an LCD TV. The LCD system includes a backlight, a content detector, and an image controller. The backlight includes a section of upper backlights, a section of lower backlights, and a section of intermediate backlights. The content detector detects video content in an input signal from a video source. The image controller receives an input video signal from the video source and processes the input video signal to generate a processed video signal for display on the display device. The image controller also designates upper, lower, and intermediate display sections of the display device. The image controller also includes a sealer de-interlacer. The sealer de-interlacer controls a backlight inverter to adjust illumination levels of the upper and lower backlights in response to detection of an absence of video content in the corresponding upper and lower display sections of the display device to adjust an image quality in the intermediate display section of the display device. Other embodiments of the system are also described.

Embodiments of an apparatus are also described. In one embodiment, the apparatus is an image controller to receive an input video signal from a video source. The image controller includes a digital processor, a content detector, and a sealer de-interlacer. The digital processor processes the input video signal to generate a processed video signal for display on the display device. The content detector detects video content in the input video signal. The sealer de-interlacer controls a backlight inverter to adjust illumination levels of upper and lower backlights in response to detection of an absence of video content in corresponding upper and lower display sections of the display device to adjust an image quality in an intermediate display section of the display device. Other embodiments of the apparatus are also described. Embodiments of a method are also described. In one embodiment, the method is a method for controlling backlights in an LCD panel. The method includes generating a processed video signal from an input video signal for display on a display device. The display device includes upper, lower, and intermediate display sections. The method also includes displaying video content for the processed video signal on the intermediate display section of the display device. The method also includes adjusting backlight illumination levels of the upper and lower display sections of the display device in response to an absence of video content in the upper and lower display sections of the display device to adjust an image quality of the processed video content on the intermediate display section of the display device. Other embodiments of the method are also described.

Other aspects and advantages of embodiments of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrated by way of example of the principles of the invention.

Fig. IA depicts a conventional standard-definition television.

Fig. IB depicts a conventional high-definition television.

Fig. 2 depicts a schematic block diagram of one embodiment of a video display system.

Fig. 3 depicts a schematic block diagram of one embodiment of the image controller and the display device of the video display system of Fig. 2.

Fig. 4 depicts a schematic flow chart diagram of one embodiment of a backlight control method for controlling upper and lower backlights of the display device of Fig. 3.

Fig. 5 depicts a schematic flow chart diagram of one embodiment of a backlight dimming method for dimming the upper and lower backlights of the display device of Fig. 3.

Throughout the description, similar reference numbers may be used to identify similar elements.

While many embodiments are described herein, at least some of the described embodiments facilitate displaying an improved picture quality on an LCD TV while displaying black bars in the upper and lower viewing areas, or display sections, of the LCD screen. In some embodiments, the upper and lower backlights are turned off to display darker black bars in the upper and lower viewing areas of the LCD screen. In some embodiments, the upper and/or lower backlights are dimmed to display a subtitle in the upper and/or lower viewing areas of the LCD screen, while improving the image quality of video content displayed on the LCD viewing area. In other words, by disabling and/or dimming the upper and lower backlights of an LCD panel, the perceived picture quality of the video content displayed between the black bars can be improved even when subtitles are displayed on the LCD panel. Fig. 2 depicts a schematic block diagram of one embodiment of a video display system 150. The illustrated video display system 150 includes a video source 152, an image controller 154, and a display device 156. Although the depicted video display system 150 includes several functional blocks described herein, other embodiments of the video display system 150 may include fewer or more functional blocks to implement more or less functionality.

In general, the video source 152 generates a video signal. In one embodiment, the video signal generated by the video source 152 includes video content that is processed by the image controller 154 and displayed on the display device 156. As used herein, video content includes images and moving images. Additionally, the video signal generated by the video source 152 may supply other content that is not video content. One example of content supplied by the video source 152 that is not video content is a subtitle. The video source 152 may include digital video from a digital video disk (DVD) playing on a DVD player, digital video from a camcorder, digital video from a digital camera, a digital video file stored on a media player, and so on. The video source 152 may also include analog video such as a video home system (VHS) cassette playing on a VHS player or an analog video from an analog camcorder.

The image controller 154 receives the video from the video source 152 and processes the video for display on the display device 156. One example of the image controller 154 is shown in Fig. 3 and described in more detail below. The display device 156 includes an LCD panel or another type of display device used to display a video source 152. The display device 156 may include a television LCD panel, a computer monitor LCD panel, an LCD panel of a mobile multimedia device, and so on. One example of the display device 156 is shown in Fig.3 and described in more detail below.

Fig. 3 depicts a schematic block diagram of one embodiment of the image controller 154 and the display device 156 of the video display system of Fig. 2. The illustrated image controller 154 includes a content detector 160, a sealer de- interlacer 162, a processor 164, a memory device 166, and at least one bus interface 158. Additionally, the memory device 166 includes a lookup table 168. The illustrated display device 156 includes a backlight inverter 170 and a backlight 172. In one embodiment, the display device 156 is subdivided into upper, intermediate, and lower viewing areas 174, 176, and 178, respectively. Other embodiment may use fewer or more areas. The illustrated backlight 172 includes upper, intermediate, and lower backlights 180, 182, and 184, respectively. Other embodiments of the backlight 172 may include fewer or more sections of backlights. In some embodiments, the backlight sections 180, 182, and 184 correspond to the viewing areas 172, 176, and 178 of the display device 156. Although the depicted image controller 154 includes several functional blocks described herein, other embodiments of the image controller 154 may include fewer or more functional blocks to implement more or less functionality. In one embodiment, the image controller 154 processes an input video signal supplied by the video source 152. The image controller 154 then sends the processed video signal for viewing on the display device 156. In some embodiments, the image controller 154 designates boundaries for the upper, intermediate, and lower viewing areas 174, 176, and 178, respectively, of the display device 156. In general, the content detector 160 detects video content for display in one or more of the upper, intermediate, and lower viewing areas 174, 176, and 178, respectively, of the display device 156. In some embodiments, the content detector 160 detects the type of video content supplied by the video source 152. Examples of types of video content include a TV broadcast video source, a DVD video source, and so on. In some embodiments, the content detector 160 detects the aspect ratio associated with the video content supplied by the video source 152. In some embodiments, the content detector 160 detects a subtitle in the upper viewing area 174 and/or the lower viewing area 178 of the display device 156. The content detector 160 also may detect an absence of content in one or more of the viewing areas 174, 176, and 178.

In general, the sealer de-interlacer 162 scales a video signal from the video source 152 according to the native resolution of the display device 156. The sealer de-interlacer 162 may also de-interlace an interlaced video signal from the video source 152 according to the progressive scanning of the display device 156. In some embodiments, the resolution of the video signal from the video source 152 matches the native resolution of the display device 156 and the scaling function of the sealer de-interlacer 162 may be bypassed. Similarly, in some embodiments, the video signal from the video source 152 is a progressive scanned video signal and the de-interlacing function of the sealer de-interlacer 162 may be bypassed.

In one embodiment, the sealer de-interlacer 162 adjusts illumination levels of the upper and lower backlights 180 and 184 in response to detection of an absence of video content in the corresponding upper and lower display sections of the display device 156 by the content detector 160. In some embodiments, the sealer de-interlacer 162 controls the backlight inverter 170 to disable the upper and/or lower backlights 180 and 184. In one embodiment, the sealer de-interlacer 162 controls the backlight inverter 170 to dim the upper and/or lower backlights 180 and 184. In some embodiments, the sealer de-interlacer 162 dims the upper and/or lower backlights 180 and 184 in response to the detection of a subtitle in the corresponding upper and/or lower viewing areas 174 and 178.

In some embodiments, the sealer de-interlacer 162 controls the backlight inverter 170 in conjunction with the processor 164. In some embodiments, the processor 164 processes a backlight disable command. In some embodiments, the processor 164 processes a backlight dim command.

In one embodiment, the memory device 166 stores a lookup table 168. In some embodiments, a lookup table 168 stores backlight illumination levels associated with video content detected by the content detector 160. In some embodiments, the sealer de-interlacer 162 is further configured to dim the upper and lower backlights 180 and 184 according to a backlight illumination levels associated with a detected subtitle and stored in the lookup table 168. In one embodiment, the display device 156 displays the video content processed by the image controller 154. In some embodiments, the display device 156 displays relatively darker black bars in the upper and lower viewing areas 174 and 178 in response to the sealer de-interlacer 162 dimming or disabling the upper and/or lower backlights 180 and 184, compared to when the upper and lower backlights 180 and 184 are fully enabled. In some embodiments, the display device 156 displays an improved image quality (i.e., the perceived image quality) in the intermediate viewing area 176 of the display device 156, relative to the image quality of the intermediate viewing area 176 when the upper and lower backlights 180 and 184 are enabled.

In one embodiment, the display device 156 displays subtitles in the upper and lower viewing areas 174 and 178 in response to the content detector 160 detecting a subtitle in the upper viewing area 174 and/or the lower viewing area 178 of the display device 172. In some embodiments, the display device 156 displays relatively darker black bars in the upper and lower viewing areas 174 and 178 while displaying a subtitle in the upper viewing area 174 when the sealer de- interlacer 162 dims the upper backlight 180 and disables the lower backlight 184 in response to the content detector 160 detecting subtitles in the upper viewing area 174 of the display device 172. Likewise, in some embodiments, the display device 156 displays relatively darker black bars in the upper and lower viewing areas 174 and 178 while displaying a subtitle in the lower viewing area 178 when the sealer de-interlacer 162 dims the lower backlight 184 and disables the upper backlight 180 in response to the content detector 160 detecting subtitles in the lower viewing area 178 of the display device 172. In some embodiments, the backlight 172 includes cold-cathode fluorescent lamps (CCFLs). Alternatively, the backlight 172 includes light emitting diodes (LEDs). Other embodiments include other similar backlighting devices. In one embodiment, the bus interface 158 facilitates communications between the image controller 154 and the display device 156. Some examples of these communications include backlight control operations, including operations to disable one or more backlight sections, operations to dim backlight sections, as well as operations to store, send, and receive data packets and illumination levels associated with the backlight control operations of the image controller 154. Fig. 4 depicts a schematic flow chart diagram of one embodiment of a backlight control method 200 for controlling upper and lower backlights 180 and 184 of the display device 156 of Fig. 3. Although the backlight control method 200 is described in conjunction with the video display system 150 of Fig. 2 and components thereof, other embodiments of the backlight control method 200 may be implemented with other video display systems and/or other video display system components.

In the depicted backlight control method 200, at block 202, the image controller 154 receives an input video signal from the video source 152. At block 204, the content detector 160 determines whether the input video signal supplied by the video source 152 includes video content in the upper and lower viewing areas 174 and 178 of the display device 156. When the content detector 160 determines that the input video signal does not include video content in the upper and/or lower viewing areas 174 and 178 of the display device 156, at block 206, the sealer de-interlacer 162 disables the upper and/or lower backlights 180 and

184, accordingly. Otherwise, at block 208 the sealer de-interlacer 162 enables the upper and/or lower backlights 180 and 184. The depicted backlight control method 200 continues while video content is received from the video source 152. Fig. 5 depicts a schematic flow chart diagram of one embodiment of a backlight dimming method 300 for dimming the upper and lower backlights 180 and 184 of the display device 156 of Fig. 3. Although the backlight dimming method 300 is described in conjunction with the video display system 150 of Fig. 2 and components thereof, other embodiments of the backlight dimming method 300 may be implemented with other video display systems and/or other video display system components. As depicted, some of the operations of the backlight dimming method 300 are substantially similar to the operations of the backlight control method 200, except as described below.

In the depicted backlight dimming method 300, after determining the input video signal supplied by the video source 152 does not include video content in the upper and/or lower viewing areas 174 and 178 of the display device 156, at block 302, the content detector 160 determines whether the input video signal supplied by the video source 152 includes subtitles in the upper and/or lower viewing areas 174 and 178 of the display device 156. When the content detector 160 determines that the input video signal does not include subtitles in the upper and/or lower viewing areas 174 and 178 of the display device 156, at block 206 the sealer de-interlacer 162 disables the upper and/or lower backlights 180 and 184 accordingly. Otherwise, at block 304 the sealer de-interlacer 162 disables and dims the upper and/or lower backlights 180 and 184 accordingly. In other words, in an example embodiment, when the content detector 160 detects a subtitle in the lower viewing area 178 of the display device 156, the sealer de-interlacer 162 dims the lower backlight 184 and disables the upper backlight 180, accordingly. Thus, the image quality of the video content displayed on the intermediate viewing area 176 of the display device 156 is improved while still displaying a subtitle in the lower viewing area 178.

Other embodiments of the backlight control method 200 and the backlight dimming method 300 may implement fewer or more operations. In particular, some embodiments of the backlight control method 200 and the backlight dimming method 300 facilitate implementation of any of the functions described in relation to the video display system 150 or any of the components thereof. Some embodiments of the backlight disabling schemes of the sealer de-interlacer 162 substantially improve the image quality of the video content displayed on the display device 156, relative to the same video content displayed on the display device 156 with all of the backlights enabled. Moreover, when the video content includes subtitles, embodiments described herein improve the image quality of the video content through the backlight dimming scheme of the sealer de-interlacer 162, compared to displaying subtitles with the upper and lower backlights 180 and 184 enabled without any dimming. Thus, embodiments of the backlight disabling and dimming schemes improve the image quality of video content displayed on the display device 156 with and without subtitles in the video content.

At least some of the operations for the backlight control method 200, the backlight dimming method 300, and the video display system 150 may be implemented using software instructions stored on a computer useable storage medium for execution by a computer. As an example, an embodiment of a computer program product includes a computer useable storage medium to store a computer readable program that, when executed on a computer, causes the computer to perform operations, as described above. Embodiments of the invention can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment containing both hardware and software elements. In one embodiment, the invention is implemented in software, which includes but is not limited to firmware, resident software, microcode, etc.

Furthermore, embodiments of the invention can take the form of a computer program product accessible from a computer-usable or computer- readable storage medium providing program code for use by or in connection with a computer or any instruction execution system. For the purposes of this description, a computer-usable or computer readable storage medium can be any apparatus that can store the program for use by or in connection with the instruction execution system, apparatus, or device.

The computer-useable or computer-readable storage medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device), or a propagation medium. Examples of a computer- readable storage medium include a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk, and an optical disk. Current examples of optical disks include a compact disk with read only memory (CD- ROM), a compact disk with read/write (CD-RTW), a digital video disk (DVD), and high-definition (HD) disks such as Blu-Ray and HD-DVD.

An embodiment of a data processing system suitable for storing and/or executing program code includes at least one processor coupled directly or indirectly to memory elements through a system bus such as a data, address, and/or control bus. The memory elements can include local memory employed during actual execution of the program code, bulk storage, and cache memories which provide temporary storage of at least some program code in order to reduce the number of times code must be retrieved from bulk storage during execution. Although the operations of the method(s) herein are shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may be performed in an inverse order or so that certain operations may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub-operations of distinct operations may be implemented in an intermittent and/or alternating manner.

Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The scope of the invention is to be defined by the claims appended hereto and their equivalents.

Claims

What is claimed is:

1. A liquid crystal display (LCD) system comprising: a backlight coupled to a display device, the backlight comprising a section of upper backlights, a section of lower backlights, and a section of intermediate backlights; and an image controller coupled to the display device and a video source, the image controller to process an input video signal from the video source and to generate a processed video signal for display on the display device, wherein the image controller designates upper, lower, and intermediate display sections of the display device, and wherein the image controller comprises: a content detector coupled to the video source, the content detector to detect video content in the input video signal from the video source; and a sealer de-interlacer to control a backlight inverter coupled to the backlight, the sealer de-interlacer to adjust illumination levels of the upper and lower backlights in response to detection of an absence of video content in the corresponding upper and lower display sections of the display device to adjust an image quality in the intermediate display section of the display device.

2. The LCD system of claim 1, wherein the content detector is further configured to detect a subtitle in the lower display section of the display device, wherein the sealer de-interlacer is further configured to dim the lower backlights in response to the subtitle detected in the lower display section of the display device.

3. The LCD system of claim 1, wherein the content detector is further configured to detect a subtitle in the upper display section of the display device, wherein the sealer de-interlacer is further configured to dim the upper backlights in response to the subtitle detected in the upper display section of the display device.

4. The LCD system of claim 1, wherein the content detector is further configured to detect the absence of the video content from the upper and lower display sections of the display device, wherein the sealer de-interlacer is further configured to turn off the upper and lower backlights in response to the absence of the video content in the upper and lower display sections of the display device.

5. The LCD system of claim 1, wherein the image controller further comprises a lookup table stored on a memory device, the lookup table to store a plurality of backlight illumination levels associated with the detected video content.

6. The LCD system of claim 1, wherein the sealer de-interlacer is further configured to turn off one section of the upper and lower backlights and to dim the other section of the upper and lower backlights according to a backlight illumination level associated with detection of a subtitle in the other section of the upper and lower backlights.

7. The LCD system of claim 1, wherein the upper, lower, and intermediate backlights comprise cold cathode fluorescent lamps (CCFLs).

8. The LCD system of claim 1, wherein the upper, lower, and intermediate backlights comprise light emitting diodes (LEDs).

9. An image controller to receive an input video signal from a video source, the image controller comprising: a digital processor to process the input video signal to generate a processed video signal for display on a display device; a content detector coupled to the video source, the content detector to detect video content in the input video signal; and a sealer de-interlacer coupled to the digital processor and the content detector, the sealer de-interlacer to control a backlight inverter coupled to the display device, the sealer de-interlacer to adjust illumination levels of upper and lower backlights of the display device in response to detection of an absence of video content in corresponding upper and lower display sections of the display device to adjust an image quality in an intermediate display section of the display device.

10. The image controller of claim 8, wherein the content detector is further configured to detect a subtitle in the lower display section of the display device, wherein the sealer de-interlacer is further configured to dim the lower backlights in response to the subtitle detected in the lower display section of the display device.

1 1. The image controller of claim 8, wherein the content detector is further configured to detect a subtitle in the upper display section of the display device, wherein the sealer de-interlacer is further configured to dim the upper backlights in response to the subtitle detected in the upper display section of the display device.

12. The image controller of claim 8, wherein the content detector is further configured to detect the absence of the video content from the upper and lower display sections of the display device, wherein the sealer de-interlacer is further configured to turn off the upper and lower backlights in response to the absence of the video content in the upper and lower display sections of the display device.

13. The image controller of claim 8, wherein the image controller further comprises a lookup table stored on a memory device, the lookup table to store a plurality of backlight illumination levels associated with the detected video content.

14. The image controller of claimδ, wherein the sealer de-interlacer is further configured to dim one section of the upper and lower sections of backlights to a stored backlight illumination level associated with detection of a subtitle.

15. A method for controlling backlights in a liquid crystal display panel, the method comprising: generating a processed video signal from an input video signal for display on a display device, wherein the display device comprises, upper, lower, and intermediate display sections; displaying video content for the processed video signal on the intermediate display section of the display device; and adjusting backlight illumination levels of the upper and lower display sections of the display device in response to an absence of video content in the upper and lower display sections of the display device to adjust an image quality of the processed video on the intermediate display section of the display device.

16. The method of claim 15, further comprising: detecting a subtitle in the lower display section of the display device; and dimming lower backlights corresponding to the lower display section of the display device in response to the detection of the subtitle in the lower display section of the display device.

17. The method of claim 15, further comprising: detecting a subtitle in the upper display section of the display device; and dimming upper backlights corresponding to the upper display section of the display device in response to the detection of the subtitle in the upper display section of the display device.

18. The method of claim 15, further comprising: detecting the absence of the video content from the upper and lower display sections of the display device; and turning off upper and lower backlights corresponding to the upper and lower display sections of the display device in response to the absence of the video content in the upper and lower display sections of the display device.

19. The method of claim 15, further comprising storing in a lookup table a plurality of backlight illumination levels associated with the processed video content in the lookup table.

20. The method of claim 19, further comprising dimming one section of the upper and lower backlights to a stored backlight illumination level associated with detection of a subtitle.