Image brightness control system

A brightness control system enhances a displayed image. The system selectively alters the brightness of a portion of the image to improve the clarity, noticeability, and intelligibility of information provided on the display. When used with a vehicle navigation system, the brightness adjustment system may emphasize vehicle or destination location display, driving directions, route planning information, or other information provided to the driver.

PRIORITY CLAIM

This application claims the benefit of priority from European Patent Application No. 05002975.0, filed Feb. 11, 2005, which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates to a brightness controller for adjusting the brightness of an image on a display. In particular, the invention relates to a brightness control system for modifying the brightness of specific portions of an image.

2. Related Art

Both analog displays such as Cathode Ray Tubes (CRTs) and digital displays such as Liquid Crystal Displays (LCDs) create images from individual closely spaced points. Each point in the image is referred to as a picture element or pixel. The image data in the video data stream sent to the display conveys information which controls the brightness of each pixel.

In the past, dynamic changes to image brightness often required time consuming and computationally expensive brightness recalculations. This was particularly true when the recalculation of image data was done on a pixel-by-pixel basis. With the introduction and widespread use of high resolution displays, processing demands for dynamic brightness changes were often quite significant.

Displays are common components of vehicle navigation systems, entertainment systems, and game systems. A navigation system, for example, provides core functionality including the display of map location and route information to the driver. In addition to these core functions, the navigation system often provides extensive additional functionality for the driver. Thus, the processing demands on the navigation system (and other systems) are already significant, even without the added burden of dynamic image brightness control.

Therefore, a need exists for an improved brightness control system.

SUMMARY

A brightness control system adjusts the brightness of a portion of an image, without time consuming or computationally expensive pixel-by-pixel image recalculation. When used with a vehicle navigation system, the brightness control system may emphasize vehicle or destination location display, driving directions, route planning information, or other information provided to the driver. The brightness control system may be used with any other system which displays images, including entertainment systems, game systems, communication systems, or other systems.

The brightness control system includes a video signal input and a brightness control signal input. A video signal including pixel image data is provided on the video signal input, while a brightness control signal is provided on the brightness control signal input. The brightness control signal is synchronized with the video signal (e.g., with horizontal synchronization information) to specify enhancement for a selected pixel subset of the pixel image data. Modification logic in the brightness control system enhances the brightness of the selected pixel subset. To that end, the modification logic may determine a brightness adjustment responsive to the brightness control signal and apply the brightness adjustment to the selected pixel subset of the pixel image data.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

InFIG. 1, an image brightness control system100includes a video signal input102, a brightness controller104, a brightness control signal input106, and a video signal output108. A control signal generator108provides a brightness control signal on the brightness control signal input106. A reference voltage input110provides a reference voltage112to the brightness controller104. In response to the brightness control signal, the brightness controller104selectively alters the brightness of the image or portion of the image represented by the output video signal114, compared to the original image represented in the input video signal116.

The image may include, for example, navigation information118received from a navigation system120. The brightness control system100may receive and enhance input video signals from many other sources, however, including entertainment systems, video game systems, car phone systems, or other systems. The navigation system120may include a receiver for navigation signals, including radio signals from a Global Positioning System (GPS), radio signals from a LOng RAnge Navigation (LORAN) system, or other navigation signals. The navigation information118may include map data, such as street, road, intersection, bridge, viaduct, ferry, building, traffic regulation and street closure information; point of interest (POI) information; road and weather conditions; directory and address range information; destination information; route information; or other navigation information The navigation information118may also include position and motion data, such as relative position, altitude, bearing, average velocity, instantaneous velocity, acceleration, expected position and/or expected arrival time information. Any of the navigation information118may be rendered in the image, and may be selectively enhanced for clarity and intelligibility through brightness adjustment of the pixels which represent the navigation information118in the display, or through brightness attenuation of surrounding pixels.

The input video signal116may convey a sequence of individual images to the brightness controller104. The input video signal116may also include timing and synchronization information such as horizontal and vertical blanking period information, horizontal and vertical synchronization information, luminance and color information, and other video signal information. The input video signal116may include or may be encoded as a luminance/chrominance signal (e.g., a YUV signal), red-blue-green (RGB) signal, or as another type of signal. Thus, input video signal116may define the brightness and color for each pixel in the image, as well as the horizontal (e.g., line), vertical (e.g., frame), and pixel timing and synchronization information for displaying the image on an analog or digital display.

The control signal generator108may include synchronization logic responsive to the synchronization information included in or accompanying the input video signal116. The control signal generator108generates a brightness control signal synchronized to the position of pixels to be brightened (or to be attenuated) in one or more frames of an image sequence. The brightness control signal may be synchronized with respect to any combination of horizontal synchronization information, vertical synchronization information, pixel timing information, or other information in or accompanying the input video signal116. The synchronized brightness control signal may specify a brightness adjustment or attenuation for any selected pixel subset in the pixel image data represented in the input video signal116.

The control signal generator108may also receive the navigation information118from the navigation system120. The brightness control signal may then be synchronized to the presence and/or location in the image of any desired navigation information118, or to the presence and/or location of any other desired information provided by an entertainment system, game system, or other system. For example, the brightness control signal may be asserted for those pixels at which the navigation information118(e.g., a vehicle location or destination location) is rendered in the image, for the pixels at which the navigation information118is absent, or for image areas (e.g., a bounding box or circle) around those pixels.

The reference voltage112may specify a brightness adjustment for the brightness controller104. Alternatively, the brightness controller104may derive a brightness adjustment using the reference voltage112. For example, when the brightness control signal is asserted, the brightness controller104may use pulse width modulation and a resistor-capacitor (RC) filter to derive a brightness adjustment responsive to the reference voltage112.

The brightness controller104receives the input video signal116and the brightness control signal. In response to the brightness control signal, the brightness controller104determines a brightness adjustment and enhances the brightness of the pixel subset to which the brightness control signal is synchronized. The brightness controller104avoids time consuming and computationally expensive recalculation of image data on a pixel-by-pixel basis. Instead, the brightness controller responds to the synchronized brightness control signal which specifies the pixel subset for which to enhance brightness.

FIG. 2shows an example of brightness control for a subset of image pixel data in a navigation map200on a display. In the example shown inFIG. 2, the navigation map200shows a section of a larger map around the area in which the vehicle currently is located. The current position of the vehicle is indicated by an icon210(e.g., an arrow pointing in the direction of vehicle movement) on the map200. The brightness controller104provides a brightness enhanced region220around the icon210. While the region220is shown as a rectangle, the region220may take other shapes, including a circle shape, oval shape, polygonal shape, sector shape, or other shape.

The driver may select the shape (e.g., square or circular), size (e.g., 100×100 pixels or 50 pixel radius), and position (e.g., centered on the vehicle location, destination, or a point of interest) of the region220using any available operator input. The operator input may include a voice recognition system, keyboard including cursor keys, or other input. The brightness controller104may enhance the brightness of the region220by increasing the overall brightness of a subset of image pixel data corresponding to the region220. Alternatively or additionally, the brightness controller104may enhance the brightness of the region220by attenuating the brightness of the pixels surrounding the region220. The selective enhancement is particularly effective at night, when the overall illumination of a vehicle cabin is low. The brightness controller104thereby helps to increase the clarity, intelligibility, and speed of recognition of the information provided on the display.

FIG. 3illustrates a navigation map300including an additional brightness enhanced subset of image pixel data in the form of a directional arrow302. The navigation system120may generate the directional arrow302to indicate the next direction to take on the route to a destination. The brightness control signal may then be asserted for each pixel which makes up the directional arrow302and/or the region220, or for each pixel which makes up the surrounding regions.

FIG. 4illustrates a navigation map400including a brightness enhanced subset of image pixel data in the form of a target circle402. The target circle402highlights a vehicle destination404. Alternatively, the target circle402may highlight an area of interest, location of traffic congestion, a locus of points of pre-defined distance from a position, or other location of interest. Multiple target circles or other shapes may be generated for multiple locations of interest.FIG. 5illustrates another example brightness control for a subset of image pixel data. InFIG. 5, a brightness enhanced hazard symbol502is rendered on the map500. The hazard symbol502may represent a serious traffic, road, or weather condition at any given location. Furthermore, the hazard symbol502may be displayed to provide a warning about a particular vehicle condition, such as an engine malfunction, low tire pressure, fuel, oil, or other fluid level warning, an electronics error, GPS signal error, or a collision avoidance warning. The brightness control system106may flash or otherwise draw attention to the warning symbol502(or any other brightness enhanced region on the display) by altering the brightness enhancement between different levels, e.g., on a periodic basis.

FIG. 6illustrates another example of brightness enhancement in a navigation map600. InFIG. 6, the navigation map600includes a brightness enhanced road information symbol602. The road information symbol602may indicate a road or traffic condition, such as a limited access road, construction site, parade route, or any other time or space-restricted road condition. As another example, the road information symbol602illustrated inFIG. 6may depict a one-way road, with the direction of the arrow pointing in the direction of allowed traffic flow.

FIG. 7illustrates voltage-time diagrams which show brightness control selectively activated during a horizontal line of a displayed image.FIG. 7shows a portion of the input video signal116, a modulated reference voltage702, and a brightness enhanced output video signal114. Several points in time, t1, t2, t3, and t4are labeled on the horizontal axis. The points in time t1and t4correspond to the beginning and end of a horizontal line of the input video signal116. The input video signal116includes an active video portion704which includes brightness and color information and also includes horizontal blanking intervals706. The black-level708represents the brightness of the darkest portion of the image.

The modulated reference voltage702assumes a maximum value, Uref,max during the time interval between t2and t3. In the time periods before t2and after t3, the modulated reference voltage702may be reduced. In the example shown inFIG. 7, the modulated reference voltage is reduced by V, resulting in a nominal level Uref,max−V. The brightness control signal may be asserted between t2and t3(or before t2and after t3) to coordinate brightness enhancement with the brightness controller104.

Specifically, the brightness control signal may be asserted between t2and t3to prevent the brightness controller104from applying an attenuation to the active video portion704of the input video signal. The assertion of the brightness control signal may cause the modulated reference voltage to rise (e.g., to the value Uref,max) to a value which prevents attenuation of the input video signal between t2and t3. The assertion of the brightness control signal may also cause the modulated voltage to rise to an intermediate level which causes the brightness controller104to apply less attenuation between t2and t3than before t2or after t3. Alternatively, the brightness control signal may be asserted before t2and after t3to instruct the brightness controller104to apply an attenuation to the active video portion704of the input video signal outside of the range t2to t3. The brightness control signal may specify the amount of attenuation (e.g., the brightness adjustment), the brightness controller104may determine the amount of attenuation using pulse width modulation techniques, or the brightness controller may determine the brightness adjustment in other manners.

The brightness controller104modifies the input video signal116to enhance the brightness of the pixel subset selected through synchronization of the brightness control signal with the input video signal. The resulting output video signal114conveys a brightness enhanced pixel subset to the display. In particular,FIG. 7shows the original level710of the input video signal116superimposed on the enhanced level712of the output video signal114.

The brightness controller104responds to the brightness control signal and the modulated reference voltage702to hold the voltage level of the input video signal unchanged between t2and t3. In addition, the brightness controller104attenuates the voltage level of the input video signal before t2and after t3. Thus, the image area around the selected pixel subset is lowered in brightness, thereby enhancing the perceived brightness of the selected pixel subset. Brightness enhanced pixel data714results between t2and t3. Depending on the sampling rate of the active portion of the output video signal114, there many be one or more pixels defined in the pixel data714. The brightness control signal and modulated reference voltage702may change line-by-line and pixel-by-pixel to specify the shape or shapes to be brightness enhanced.

The attenuation applied to the input video signal116may be set as a configurable gain factor (e.g., an operator settable gain factor) for brightness enhancement. Alternatively, the brightness control signal may specify the gain factor. The gain factor may also be based on, and vary according to, the value of V. In other implementations, the brightness controller104may enhance the selected pixel subset by applying a configurable amplification factor to the input video signal116between t2and t3, while holding constant, attenuating, or applying a smaller gain to the input video signal before t2and after t3.

FIG. 8shows a more detailed implementation of the brightness control system100. The control signal generator may include a control signal source802and synchronization logic804. The control signal source802supplies a control signal to the synchronization logic804. The control signal source802may include a DC voltage source, a pulse generator, waveform generator, look-up-table, mathematical function generator, square-wave generator, an external source of control signal input, a pulse width modulated signal source, or other source.

The synchronization logic804determines when to assert the brightness control signal to the brightness controller104. The brightness control signal is synchronized to horizontal, vertical, and/or pixel synchronization information in or accompanying the input video signal116and/or to other sources of information, such as the navigation information118. The control signal generator108may specify in the brightness control signal (or with separate signals) the brightness adjustment associated with selected subsets of image pixel data. The synchronization logic804may be implemented with counters, timers, and/or other timing logic using integrated or discrete circuits, including a microprocessor, microcontroller, digital signal processor (DSP), ASIC, FPGA, custom IC, or other circuitry. Alternatively or additionally, the synchronization logic804may include programs or firmware encoded or stored in a memory to count lines, frames, pixel clock transitions or any other synchronization data to locate any specific pixel or pixels in an image, and responsively assert the brightness control signal.

In the brightness controller104, a modulator806may establish the brightness adjustment for the selected pixel subset (e.g., by varying the modulated reference voltage702or the voltage V). To that end, the modulator may switch a reference voltage ‘on’ and ‘off’ at a specified duty ratio. The reference voltage112may provide the DC voltage, while the control signal generator108may specify the duty ratio (i.e., the fraction of a period during which the voltage is switched ‘on’). However, the duty ratio and reference voltage may be set according to an operator preference setting for brightness enhancement, may be a pre-configured parameter, or the duty ratio may be established in other manners.

FIG. 9illustrates a filtering operation which the modulator806may employ to convert a pulse width modulated control signal into a DC brightness adjustment level. The left hand portion ofFIG. 9depicts a sequence of voltage pulses1405having a period T, a duty ratio d and a maximum voltage Vm. The duty cycle, d, may be determined by dividing the period during which the pulse has a high value, here dT, by the total period of the waveform, here T. This yields dT/T=d for the duty cycle. The right hand part ofFIG. 8indicates the DC brightness adjustment1410resulting from filtering the pulse width modulated control signal using an RC integrator. The brightness adjustment1410may correspond to the duty ratio d. Thus, by adjusting the duty ratio d, every voltage value between 0 and Vm may be generated as a brightness adjustment. The brightness adjustment may be determined in other manners, however, including using a digital to analog converter (DAC), or other circuitry.

The brightness control signal may cause the modulator806to generate or change the brightness adjustment. For example, the brightness control signal may itself be a pulse width modulated signal, converted to the brightness adjustment. Alternatively, the brightness control signal may trigger the application, generation, or modification to another source of a pulse width modulated signal (e.g., by gating ‘on’ and ‘off’ the reference voltage input112) to obtain the brightness adjustment. Using an RC filter, the duty ratio, d, over the cycle period T, may set the brightness adjustment according to the following equation:

where the voltage function U(t) is given by

The result is

Thus, by varying the duty ratio, d, between 0 and 100%, voltage values in the range between 0 and U0may be obtained.

FIGS. 10,11, and12illustrate a sequence of brightness enhanced images controlled by pulse width modulation. During the sequence, the brightness controller104changes the degree of enhancement of a selected pixel subset corresponding to a turn arrow1002. The turn arrow1002becomes darker during the sequence to slowly fade the turn arrow1002from the image.

InFIG. 10, a pulse width modulated control signal1004determines the brightness adjustment applied to the turn arrow1002. With the duty ratio set at 90%, a relatively large brightness enhancement is selected. Thus, the pixels corresponding to the turn arrow1002may be amplified in brightness, or the surrounding pixels may be attenuated in brightness according to the relatively large brightness enhancement. InFIG. 11, the pulse width modulated control signal1102has a duty ratio of 50%. The turn arrow1002is therefore less enhanced than the turn arrow1002shown inFIG. 10. InFIG. 12, the pulse width modulated control signal1202has a duty ratio of 10%. Accordingly, the turn arrow1002is less enhanced than that shown inFIG. 11. As a result, the brightness controller104initially enhances the turn arrow1002then fades out the enhancement.

InFIG. 8, the enhancement logic808modifies the input video signal116to apply the desired brightness adjustment to any selected pixel subset of the image. For example, the enhancement logic808may include an analog multiplier, attenuator, or level shifter which applies a gain or attenuation based on the brightness adjustment to a selected part of the active portion704of the input video signal116. Alternatively, the enhancement logic808may include an analog to digital converter, a digital adder or multiplier, and a digital to analog converter to apply the brightness adjustment and output the enhanced video signal. As another example, the enhancement logic808may include a digital adder or multiplier which modifies digital RGB, YCbCr, or other digital values, according to the brightness adjustment, in a digital video signal for a digital display to change the perceived brightness of the image. The brightness adjustment may be expressed in terms of a ratio (e.g., 50% brighter or dimmer than the original signal), and absolute measure (e.g., 2V signal level or a specific brightness determined by R, G, and B values), or in other manners.

FIG. 13provides an additional example of pulse width modulated brightness control. The enhancement logic808receives a digital input video signal1302, which includes RGB image data. The enhancement logic808enhances selected pixels of the input video signal by modifying the levels of the RGB data in response to a synchronized brightness control signal and according to the brightness adjustment to generate the output video signal1304.

The brightness adjustment is represented inFIG. 13by the Uref signal1312. The brightness adjustment signal1312may vary in accordance with a pulse width modulated control signal1306output by the pulse width modulator1308. An integrating stage1310(e.g., an RC filter) converts the pulse width modulated control signal1306to the brightness adjustment signal1312. As the duty cycle of the modulated control signal1306varies, the brightness adjustment signal1312changes to specify a new level of enhancement for the selected pixel subset.

The brightness control system100may be incorporated into stand alone devices (e.g., portable game systems or personal data assistants) as well as any vehicle component.FIG. 14shows a vehicle component system1400in which the components interface and communicate on a vehicle bus1402. The vehicle component system1400includes electronic modules which display information for the driver and passengers. Examples of the electronic modules include vehicle entertainment systems1404(e.g., a DVD player, CD player, portable music player, or other entertainment system), video game systems1406, and a navigation system1408.

The electronic modules1404-1408may accept input from the operator inputs1410, including a voice recognition system, keyboard, function switches, or other inputs. The operator inputs1410may communicate operator selections over the vehicle bus1402to any of the electronic modules1404-1408. Alternatively, one or more of the electronic module1404-1408may include local operator inputs. Sensors1412may measure and communicate levels of ambient light, noise, vehicle performance, or other data to a bus interface (e.g., the bus interface1416in the navigation system1408) of any of the electronic modules1404-1408.

Each electronic module1404-1408may include a brightness control system100and a display. Thus, for example, the navigation system1408may enhance the clarity, intelligibility, or visibility of any portion of navigation information provided on the navigation display1414. In the navigation system1408, the processor1418executes, from a memory1420, a navigation program1422. The navigation program1422may provide route guidance data1424, location information1426, or any other navigation data to the driver on the navigation display1414. A navigation database1428may provide a source of map data, route data, points of interest data, or any other navigation data for the navigation program1422. In addition, the memory1420may store shape data. The shape data may define the shapes for image enhancement regions. For example, the vehicle position region shape data1432may define the shape and/or size of the enhancement region220, while the point-of-interest region shape data1434may define the shape and/or size of the enhancement region402.

In response to the data provided by the sensors1412, any of the electronic modules1404-1408may initiate brightness control over displayed images. As one example, a light level sensor may detect and report ambient light levels. The navigation system1408, for instance, may respond to low ambient light levels (e.g., below a low-light threshold) to enhance the brightness of navigation information on the navigation display1414. Such light levels may be present at night, when the vehicle is underground, or when the vehicle travels through a tunnel. Similarly, when the ambient light levels are significant (e.g., above a high-light threshold), the navigation system1408may also enhance brightness to make selected navigation information more visible on the navigation display1414.

FIG. 15illustrates acts which the brightness control system100may take to enhance brightness of an image or selected pixels in the image, particularly in the context of a vehicle navigation system. The navigation system120supplies the navigation information to the brightness control system100. In addition, the brightness controller104receives an input video signal116(Act1504). The input video signal116may be an analog or digital video signal which defines a sequence of images.

The brightness control system100may determine whether to buffer the input video signal116(Act1506). The video buffer may store image data for later processing (including brightness enhancement), frame synchronization, error checking, or other processing. When the brightness control system100determines to buffer the input video signal116, the brightness control system100stores the image data in a memory (Act1508).

The control signal generator108synchronizes to horizontal, vertical, and/or pixel synchronization information in or accompanying the input video signal116(Act1510). The control signal generator outputs a brightness control signal which specifies a selected pixel subset in the image pixel data for brightness enhancement (Act1512). The brightness control signal may directly specify a brightness adjustment, may specify the duty ratio of am modulated control signal which determines a brightness adjustment, or the brightness control system100may determine the brightness adjustment in other manners (e.g., by retrieving a configurable operator preference setting from a memory).

In one implementation, the brightness control system100modulates a reference voltage to determine the brightness adjustment. To that end, the brightness control system100receives the reference voltage input112(Act1514). The modulator806may apply a pulse width modulated control signal to switch the reference voltage ‘on’ and ‘off’ through an RC filter. A DC brightness adjustment results, at a level which is set according to the duty ratio of the modulated control signal.

The brightness control system100may enhance image brightness in many different ways. Accordingly, the brightness control system100determines which enhancement technique to apply (Act1518) using preset preferences or settings, by accepting operator input, or in other manners. As examples, the brightness control system100may select between black level adjustment, contrast adjustment, direct manipulation of an active portion of the input video signal116, direct manipulation of RGB or other pixel data, or other techniques. The brightness control system100may also determine whether to amplify brightness of a selected pixel subset, attenuate brightness of surrounding pixels, or perform the enhancement in another manner. The brightness controller104applies the brightness adjustment to the selected pixel subset (Act1520). The brightness control system may then provide the output video signal114to the display (Act1522).

FIG. 16illustrates the acts which the modulator806may take to establish a modulated reference voltage for use as a brightness adjustment. The modulator806obtains an input reference voltage112(Act1602). The reference voltage may establish a voltage level which the modulator will pulse width modulate to obtain the modulated reference voltage.

To that end, the modulator806determines a duty ratio, d, for the pulse width modulation (Act1604). The reference voltage is switched ‘on’ and ‘off’ at the duty ratio. (Act1606). The modulator806integrates the switched reference voltage (e.g., using an RC filter) to obtain the modulated reference voltage (Act1608). The modulated reference voltage may take any value between 0 and the value of the reference voltage, and may be set as the brightness adjustment applied to image data through black level adjustment, contrast adjustment, direct manipulation of the active portion of the input video signal116, or through other techniques (Act1610).

FIG. 17illustrates the acts which the brightness control system100may take to enhance brightness in response to bus messages on the vehicle bus1402. A bus interface1416receives bus messages transmitted on the vehicle bus1402(Act1702). Any of the electronic modules1404-1408may prepare and send the bus messages. In addition, the bus messages may be sent by any of the sensors1412or operator inputs1410.

For example, the operator inputs1410may send bus messages which convey operator commands to move, resize, reshape, or change the brightness adjustment to brightness enhanced regions on the display, such as those shown inFIGS. 2-6. As another example, the sensors1412may transmit bus messages conveying the ambient light level, vehicle status and warnings, noise levels, speed, proximity to other objects, or any other information. The brightness control system100extracts the data from the bus message (Act1706). Based on the data, the brightness control system100may determine whether to enhance the brightness of a selected pixel subset of an image (Act1706).

For example, when the brightness control system100receives a bus message that ambient light is relatively low, the brightness control system100may enhance the brightness of selected navigational information in the image. The navigational information is thereby made more noticeable and intelligible for the driver. As another example, when the brightness control system100receives warning information about speed, proximity to other objects, engine (or other vehicle system) operation, the brightness control system100may respond by enhancing the brightness of a portion (e.g., a warning message) of an image.

The enhancement logic808may enhance image brightness in other manners than that described above. As additional examples, the enhancement logic808may enhance image brightness through black level adjustment or contrast adjustment using level shifters, analog or digital adders or multipliers, or other circuitry.FIG. 18illustrates a black level adjustment for a selected pixel subset of an image. The enhancement logic808may apply a modulated reference voltage as an additive component to the selected pixel subset or as a subtractive component to pixels around the selected pixel subset to enhanced the brightness of the selected pixel subset in the output video signal114.

InFIG. 18, a segment of an active portion1802of an input video signal conveys pixel image data for a portion of a line in the image. The active portion1802varies in voltage between the black level1804and the maximum brightness voltage1806. The brightness controller104level shifts the active portion1802to enhance brightness of a portion of the image.

In particular, the brightness controller104level shifts the active portion1802of the input video signal by the reference voltage1808. The reference voltage1808may be provided by the reference voltage input112, by modulating a reference voltage (e.g., using an RC filter), by the control signal generator108, or by other sources of a brightness adjustment. After level shifting, the segment of the active portion1802is lowered in voltage.

FIG. 18shows the corresponding segment of the active portion1810of the output signal. The black level1812has been reduced by the reference voltage1808. In addition, there is a corresponding decrease in the maximum brightness voltage1814in the output video signal. A decrease in brightness for the segment of the active portion1810results, thereby enhancing the brightness of surrounding pixels in the image.

The brightness controller104may also enhance brightness through a contrast adjustment. The contrast adjustment may be implemented as the application of a gain to a selected pixel subset of an image.FIG. 19provides an example of a gain adjustment for a portion of an image. The brightness controller104applies an attenuation factor ‘g’ to a segment of an active portion1902of an input video signal which defines one or more pixels of the image. The attenuation factor may be defined as the ratio of a voltage value U′ after attenuation (or amplification) to the corresponding voltage value U before attenuation (or amplification):

The attenuation factor ‘g’ may be constant or may vary over the segment of the active portion1902. Holding the attenuation factor constant may mitigate signal distortion.

InFIG. 19the segment of the active portion1902of the input video signal varies between the black level1904and the maximum brightness voltage1906. The segment of the active portion1906of the output video signal results from the application of the attenuation factor by the brightness controller104. After attenuation, the segment of the active portion1906has a decreased modulation depth. In other words, the difference between the upper limit of the maximum brightness voltage1908and the black level1904has been decreased compared with the corresponding values of the maximum brightness voltage1906and the black level1904prior to attenuation.

Both the black level adjustment illustrated inFIG. 18and the gain adjustment illustrated inFIG. 19may be performed on a selected subset of image pixel data. The brightness control signal may be synchronized vertically, horizontally, and by individual pixel to select a pixel subset for enhancement on a line-by-line basis. In response to the brightness control signal, the brightness controller104adjusts the contrast and/or black level of the input video signal116to generate an output video signal114with brightness adjustments made to the selected subset of pixel image data. The brightness control system100thereby avoids individual pixel-by-pixel recalculation of image data.

Although selected aspects, features, or components of the implementations are depicted as being stored in hardware memories, all or part of systems and methods consistent with the brightness control system100may be stored on, distributed across, or read from other machine-readable media, for example, secondary storage devices such as hard disks, floppy disks, and CD-ROMs; other forms of ROM or RAM; transmitted signals; or other machine readable media. Furthermore, the brightness control system100may include additional or different components than described above. For example, a processor may be implemented as a microprocessor, microcontroller, application specific integrated circuit (ASIC), discrete logic, or a combination of other types of circuits or logic. Level shifting, multiplication, modulation, and other logic may be implemented in hardware, software, or a combination of hardware and software.

While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. For example, the brightness control system may additionally or alternatively modify red, green, and/or blue color information to enhance an image by color, rather than overall brightness. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.