WO1995035561A1

WO1995035561A1 - Method and apparatus for optimizing the presentation of information on a display

Info

Publication number: WO1995035561A1
Application number: PCT/US1995/007099
Authority: WO
Inventors: James B. Armstrong; Robert B. Burdoin; Steven D. Martinez; John E. Rasinski; Teddy J. Wood
Original assignee: Honeywell Inc.
Priority date: 1994-06-17
Filing date: 1995-06-05
Publication date: 1995-12-28
Also published as: IL114117A0

Abstract

A method and apparatus are provided for optimizing the optical characteristics of information presented on a display. First a display signal, characterizing an image to be displayed, is received. Next, a modified display signal, capable of driving a display, is generated from said display signal and a user selected or generated transfer function.

Description

METHOD AND APPARATUS FOR OPTIMIZING THE PRESENTATION OF INFORMATION ON A DISPLAY

BACKGROUND OF THE INVENTION

1. Field of the Invention The present invention relates to electronic displays. More particularly, a method and apparatus are provided for optimally presenting information on a display.

2. Description of the Related Art

Several methods exist for presenting information on a monochrome display capable of producing different luminance levels. Most methods use either a digital or analog display signal to represent the image or information to be presented on the display. Generally, the display signal is comprised of intensity and positional information. This information can be contained in a single signal or multiple synchronized signals, each carrying a different type of information. The intensity information is comprised of a magnitude or level indicative of a display luminance level. The display driver uses the positional information to determine the location where the intensity information should be presented on the display.

In many cases, a sensor generates the display signal, either directly or indirectly, such that when a larger condition is sensed, the intensity level increases. A transfer function, sometimes called a gray scale transfer function, typically converts the intensity level into a discrete display luminance level, often called a gray level, or gray shade. The term "gamma ratio," or simply "gamma," is often used to refer to the luminance transfer function defining the relationship between the display signal intensity level and the resulting luminance level. An infinite number of luminance transfer functions can be defined. Figure 1 graphically depicts two transfer functions, Cl and C2. It should be noted that other transfer functions can be defined having a profile more complex than those shown. The horizontal axis represents the display signal intensity level, while the vertical axis represents the display's luminance level. The magnitude represented by each axis increases with the distance from the origin.

The shape of the transfer function determines the luminance level that will be assigned to a given display signal intensity level. When transfer function Cl is utilized, a display signal having an intensity level in range A- A' produces a corresponding luminance level in range Zl-Zl'. When transfer function C2 is utilized, an intensity level in range A- A' produces a luminance level in range Z2-Z2'. Likewise a display signal intensity level in range B-B' using transfer function Cl produces a luminance level in range XI -XI' while transfer function C2 produces a luminance level in range X2-X2'.

One common way of defining a transfer function specification for a monochrome self-luminous display is to first define N equally spaced display signal intensity levels, often called the reference signal intensity levels. A unique reference luminance level is specified for each reference signal intensity level. The relationship between the specified reference luminance level and the reference signal intensity level defines a specific point on the desired transfer function. A given display signal intensity level falling between two reference signal intensity levels, is often assigned to the same reference luminance level as the closest reference signal intensity level.

Each reference luminance level may be defined so that a relationship exists between the specific luminance level and the next lower or higher luminance level. For displays having a wide luminance range, this relationship is commonly chosen to be a ratio approximately equal to the square root of 2. This ratio essentially complements the human eye's logarithmic response to varying luminance levels.

Other assignment schemes are also used, including, for example, linearly assigning each reference luminance level such that each is related to the next lower or higher luminance level by a constant difference. This assignment scheme is often used in flat panel displays.

It should be noted that some display's luminance characteristics are affected by environmental conditions. In these displays, the displayed luminance, for a given display signal intensity level, may change as the temperature of the display changes.

Some displays have temperature compensation functions which automatically adjust the transfer function to ensure a specific display signal intensity level always maps to a specific display luminance level.

In all of these assignment schemes, the mapping of intensity levels to luminance levels is kept constant for a given transfer function. In other words, a specific display signal intensity level always results in the display of a specific luminance level. Unfortunately, having an immutable mapping can cause information loss. More specifically, information can become confusing or non-intelligible any time the image detail of interest lies within a relatively narrow range of display signal intensity levels. This can occur in many different circumstances. For example, information can be lost when a video image consists principally of sun-lit clouds and an aircraft's contrail. In this case, almost all of the information of interest consists of small variations in an essentially all-bright image. Traditionally, the information of interest is assigned only to the display's brightest luminance levels, while most of the display's lower luminance range is unused. This makes it extremely difficult for a user viewing the display to distinguish one brightly lit object from another.

Similarly, a forward-looking infrared radar (FLIR) detector produces variations in the display signal intensity level depending on the sensed object's temperature. In some circumstances, the perceived object and its surroundings are very close to the same temperature; a downed flier in the ocean, for instance. Typically, the information of interest is assigned to a narrow band of low luminance levels, while the rest of the display's luminance range is unused. The user's task of distinguishing between objects close to the same temperature is difficult because the display's full luminance range has not been utilized.

In some situations, it might be desirable to use a monochrome display to display information which was originally generated for presentation on a color display. This situation might arise, in a transitory stage of system development, when color displays are not available. Alternately, a monochrome display may be used instead of a color display in order to reduce the cost of a system.

Three signals are often used to provide a display with color information, each representing one of the primary additive colors: red, green and blue. In subtractive color systems, like certain liquid crystal displays, the signals would correspond to the complements of the primary colors: yellow, cyan, and magenta. In these devices, there is a fixed, independent luminance transfer function for each of the primary colors. At any instant in time, a given desired color is created by providing signals in the three primary color channels such that the resulting primary color components combine additively to provide the desired color. Unfortunately, feeding these signals singly, or in fixed ratios, into a monochrome display causes information loss. If a single color's signal is used to feed a monochrome display, all of the information contained in the other color signals is lost. On the other hand, if the three signals are simply averaged, the information previously obtained only by color differentiation would be lost. For example, blue or green information displayed at the same intensity would be indistinguishable in a monochrome display.

This information loss can be particularly dangerous. For example, many aircraft utilize a computer database to generate color images depicting a map of both the terrain and cultural features the aircraft is currently flying over. Some cultural features that might be displayed include: roads, bridges, towers, power lines and cities. The stored information can have several different formats. Some systems store the information as a bitmapped image. Other, more sophisticated, systems have database identifiers which categorize and distinguish each type of cultural and terrain data. This enables a user to selectively display only those cultural features of interest. Different colors are often used, not only to discriminate between the different cultural features, but also to distinguish between different terrain elevations.

Unfortunately, different colors are occasionally mapped to the same gray shade. This could cause a pilot to miss information that otherwise would have been noticed had the information been displayed on a color monitor. Sometimes, in an attempt to distinguish between colors on a monochrome display, many pilots will increase the brightness of the display to accentuate small luminance differences. Unfortunately, if this is done at night while wearing night-vision goggles, the increased brightness could accidentally shut the goggles off. SUMMARY OF THE INVENTION

A method and apparatus are provided for optimizing the optical characteristics of information presented on a display. First, a display signal, characterizing an image to be displayed is received. Next, a modified display signal, capable of driving a display, is generated from the display signal and a user selected, or generated, transfer function. Each embodiment allows a user to adjust a display's luminance transfer function, by selecting or generating different transfer functions which map each particular display signal intensity level to a specific display luminance level. More specifically, controls are provided which allow the user to assign a relatively narrow range of intensity levels to a large portion of the display's luminance range. This essentially increases the contrast of features present in the narrow range of intensity levels. Thus, the user is able to see more detail than would have been possible had the display's full luminance range been equally distributed across the entire range of display signal intensity levels.

For example, the user could elect to assign only a selected band of the highest display signal intensity levels to the display's full luminance range. This would increase the contrast among high intensity features, while sacrificing the contrast of low intensity features. In another instance, the user could elect to assign the lowest intensity levels to the display's full luminance range. This allows low display signal intensity levels to drive the display to full luminance, thus increasing contrast among low intensity features.

Other embodiments allow a user to selectively alter the luminance transfer function which maps a particular display signal containing color information to a specific monochromatic luminance level. A particular feature of this embodiment allows a user to selectively determine which color's intensity information will drive the display through its entire luminance range. The user may also decrease the contribution a specific color makes to the resulting monochromatic luminance level, by selectively altering the luminance transfer function. Another embodiment allows a user to select a transfer function that maps a particular display signal to a specific luminance level based on criteria other then intensity level.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates two prior art transfer functions. Figure 2 is a block diagram illustrating one preferred embodiment of a device utilizing a method for converting display signals into a modified display signal having information indicative of monochromatic luminance levels.

Figure 3 is a block diagram depicting an alternate preferred embodiment of the claimed invention. Figure 4 is a block diagram depicting an alternate preferred embodiment of the claimed invention. DESCRIPTION OF THE PREFERRED EMBODIMENT

Figure 2 depicts a block diagram illustrating the use of a user controlled translator 15 constructed and operated in accordance with this invention. An image generator 50 produces a display signal having intensity level information. Translator 15 receives the display signal produced by generator 50 through connection 10. Translator

15 contains a plurality of transfer functions. A user interface 60 is connected to translator 15 by a connection 25. Translator 15 receives user commands from user interface 60 to select one or more transfer functions. Translator 15 generates a monochromatic modified display signal, containing information indicative of a display luminance level, from the display signal intensity information and the user selected transfer function. A display driver 100 receives said modified display signal from translator 15 through a connection 20. In the preferred embodiment, translator 15, display driver 100, and user interface 60, are located in a monitor 200.

As described, generator 50 produces a display signal having intensity information. An increase in the magnitude of the intensity information is representative of a desired increase in display luminance level. It should be noted that other mapping schemes, known to those skilled in the art, can be used consistent with this invention. The display signal can also carry additional information, such as positional, color, or other identifying information. The display signal can have several different formats, and still be consistent with the teachings of this invention. The display signal can be an analog or digital signal. It could also consist of three digital or three analog signals, each one containing information for a different color. The display signal could also consist of separate synchronized signals. For example, one signal could carry intensity information, while another carries positional information. Because translator 15 can be configured to convert display signals having a broad range of different formats, generator 50 can take the form of many different devices, including, but not limited to, a sensor, a camera, or even computer memory.

Translator 15 generates a modified display signal from a display signal and a user selected transfer function. Translator 15 contains a plurality of transfer functions which assign a specific modified display signal to each received display signal. Translator 15 can use an infinite number of transfer functions. Each transfer function can be defined as a simple linear function, or can be more complex, such as a polynomial, trigonometric or logarithmic function. Each transfer function does not have to be continuous.

In one preferred embodiment, a modified display signal, having a distinct monochromatic luminance level, is assigned based on the display signal's intensity level information. Transfer functions, however, can be defined so that a modified display signal is assigned to a given display signal based on other information contained in the display signal. For example, a transfer function can be defined so that it maps a set of display signals based on the display signal's positional information to one luminance level, while another set of display signals having different positional information is mapped to a different luminance level.

In some situations, transfer functions can be implemented that take advantage of a prior knowledge of the relationship between types of information and the colors assigned to them to restore some of the information otherwise subject to loss if displayed on a monochrome display.

For example, many aircraft utilize a computer data base to generate color images depicting a map of both the terrain and cultural features the aircraft is currently flying over. Different colors are often used not only to discriminate between the different cultural features, but also to distinguish between different terrain elevations. These color associations with types of data provide a potential means for operating on the signals generated for a color display to create a transformed signal for use on a monochrome display which achieves luminance discrimination of certain information previously discriminated by color.

If, for example, the features of interest are associated with a specific primary color (e.g., blue for water features), then the displayed elements of that particular primary color may be made more visible in a monochrome display by simply amplifying the signals for that primary color only relative to the other primary colors prior to summing the three signals to obtain a single monochrome signal. This amounts to multiplying the luminance transfer function by a constant, but other distortions of the transfer function may be made as necessary to achieve the desired luminance-derived discrimination. A more likely implementation is an attenuation of the other two primary signals so that the blue signal does not overdrive the display. In this example, the information previously conveyed by differentiation of the blue information is to some extent, at least for the highest intensity portion of the blue information, restored by increasing the luminance of that information relative to that of the other primary colors. This concept may be extended to the other primary colors, or to combinations of colors and/or luminance levels, by using comparators and intensity gating to detect the desired combinations, followed by alteration of the signals through modification of the transfer function. Further, because such comparators, gating, and modifications to the transfer function may be programmed, the selection of information to be highlighted from the color signals may also be programmed.

In the preferred embodiment, the plurality of transfer functions are stored in a pre-defined look-up table. Translator 15 receives user commands, from user interface 60 through connection 25, to select a single transfer function from the plurality of transfer functions. The transfer function produces a modified display signal based on the received display signal.

Generally, each transfer function requires a specific amount of memory. As the number of transfer functions increase, the amount of required memory increases as well. Several methods, consistent with the teachings of this invention, can be utilized to decrease the amount of required memory. For example, translator 15 could be designed to generate a transfer function based on information provided from user interface 60. Thus, instead of containing several closely related transfer functions, one embodiment of translator 15 could generate a transfer function from a polynomial equation based on coefficients provided via user interface 60. Similarly, mathematical functions other than polynomial equations, such as trigonometric, exponential or logarithmic equations can also be utilized. For example, translator 15 could be designed to generate a transfer function based on an inverse tangent function. This might be of particular use in liquid crystal displays. The specific shape of the inverse tangent transfer function would be determined by the information provided from user interface 60. Other tecliniques, consistent with the teachings of this invention, can be used to generate the transfer function. For example, the look-up table can be replaced with an electronic circuit. Generally, an electronic circuit is capable of generating a large number of transfer functions with a small number of components. Electronic circuits, however, tend to be more complex, especially when a discontinuous transfer function is needed.

The user can define an infinite number of transfer functions that map a modified display signal to each display signal received by translator 15. For example, transfer functions can map several different intensity levels to the same display luminance level. Transfer functions can be designed to spread a narrow range of display signal intensity levels across a broad range of display luminance levels. Conversely, transfer functions can be designed to converge a broad range of display signal intensity levels into a narrow range of display luminance levels. It should be noted that the transfer functions can map two or more ranges of intensity levels to different ranges of display luminance levels.

It has been discovered that logarithmic or exponential transfer functions generally produce better results than linear transfer functions. It is not required, however, that the transfer functions be continuous. Thus, translator 15 can generate modified display signals having a large difference in luminance level, from display signals having very little difference in intensity level.

It should be noted that the transfer functions do not have to be time invariant. This allows a single transfer function to map specific display signal information, such as intensity level or position, to different intensity levels at different times. This allows translator 15, in effect, to generate a modulated modified display signal. In fact, different transfer functions can be defined to modulate at different spatial or temporal frequencies. When portions of the modified display signal are modulated, those portions will appear textured or scintillate when displayed. Allowing the user to select different transfer functions alters the display's luminance transfer function. This permits the user to optimize the display of information which is most important at any time. For instance, a pilot wearing night- vision goggles is able to select a transfer function which will inverse a normally bright display, and highlight or turn on only those specific features the pilot wants to see. An inverse luminance transfer function maps high display signal levels to low luminance levels, and low display signal levels to high luminance levels. This reduces the amount of background illumination present in the cockpit, thus increasing night- vision goggle performance.

Although not required, it is preferred that the modified display signal have a format similar to the display signal (i.e., digital input-digital output, or analog input- analog output). It is also preferred that other information contained in the display signal be synchronously contained in the modified display signal, such as positional information. However, in some situations, the modified display signal need not contain information that was present in the display signal, such as color information.

It should be apparent to one skilled in the art that in some embodiments, translator 15 need only receive the intensity signal, while any other signal can be sent directly to display driver 100. In this configuration, steps must be taken to ensure that the modified display signal remains synchronized with the other signals. This can be accomplished by using delay lines or other methods widely known to those skilled in the art. User interface 60 can have several different embodiments. For example, user interface 60 could comprise a variable potentiometer which is capable of altering electrical circuitry, which in turn, changes the transfer function. Bezel buttons could be provided to activate transfer functions which selectively causes display signals having a specific characteristic to be displayed differently than those display signals not having the specific characteristic. Similarly, bezel buttons could be used to select transfer functions which eliminate the display of those display signals having a specific characteristic. A single knob or switch could also be provided for allowing the user to select a transfer function which provides inverse video. Finally, a digital interface, such as a digital increment/decrement switch, could be used consistent with this invention. Figure 3 depicts a block diagram illustrating another embodiment of translator

15. It should be noted that like elements have maintained like reference numbers. Translator 15 receives a digital display signal, having intensity information, from generator 50 through input 10. An intensity word substitution table 35 contains a plurality of transfer functions, or gray scale transfer functions, for assigning a digital modified display signal to a given digital display signal. A data terminal 30 connects translator 15 to substitution table 35. Translator 15 receives user commands from user interface 60 through connection 25. These commands cause translator 15 to select one or more transfer functions from substitution table 35. Display driver 100 receives the digital modified display signal, generated by translator 15, through connection 20.

In this embodiment, translator 15 uses the user selected transfer function to convert the digital display signal's intensity information, representing a pixel intensity level, to a different intensity level. Each transfer function, located in look-up table 35, comprises a digital look-up table, which maps each possible magnitude of the display signal to a specific modified display signal.

Figure 4 depicts another embodiment of translator 15. Again, like elements have maintained like reference numbers. In this embodiment, translator 15 receives color display signals from generator 50 through color inputs 11a, l ib and l ie. Translator 15 contains a plurality of transfer functions. Translator 15 receives user commands from user interface 60 through connection 25 to select one or more transfer functions. Translator 15 generates a modified display signal, containing information indicative of a monochromatic display luminance level, from said color display signals and said user selected transfer function. Display driver 100 receives said modified display signal from translator 15 through connection 20.

In this embodiment, each color display signal is indicative of an image or information to be displayed for a specific color. Each color display signal has a magnitude indicative of the luminance level for that particular color. In the preferred embodiment, an increase in the magnitude of each color display signal is representative of a desired increase in luminance level for that particular color. Color inputs 11a, l ib and l ie receive red, green and blue color display signals respectively. Those skilled in the art should note that other color assignment schemes can also be used.

In this embodiment, the user selected transfer function selectively translates the three color display signals into a single modified display signal having information indicative of a monochromatic display luminance level. The plurality of transfer functions allows a user to optimize the monochromatic display of color information. For example, a transfer function could reduce or exclude the effect one or two of the color display signals has on the modified display signal. Conversely, the modified display signal intensity information could be increased in the presence of a selected color signal. This allows the user to increase the luminance level displayed for a specific color, or reduce the luminance level displayed for other colors. As in other embodiments the selected transfer function can cause selected portions of the modified display signal to modulate, based 01 .olor or other identifying criteria contained in the display signal. This embodiment is particularly useful to optimally display color information on a monochrome monitor. This invention has been described in considerable detail in order to comply with the Patent Statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. Although the present invention has been described with reference to the preferred embodiments, those skilled in the art will recognize changes that may be made in form or detail without departing from the spirit and scope of the invention. For example, these teachings are intended to cover any method or device which converts a display signal into a modified display signal based on a user selected transfer function. Although the preferred embodiments have directly taught the steps of producing a signal having a monochromatic luminance level, one skilled in the art can utilize the teachings contained herein to develop a device or method which allows a user to select a transfer function which will produce a modified display signal containing color information from a received display signal.

It is to be understood that the invention is not restricted to the particular embodiment that has been described and illustrated, but can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment details and operating procedures, can be accomplished without departing from the scope of the invention itself.

Claims

1. A method for optimizing the optical characteristics of information presented on a display comprising the steps of: receiving a display signal, said display signal characterizing an image to be displayed; and generating a modified display signal, capable of driving a display, from said display signal and a user selected transfer function.

2. The method as described in claim 1 wherein said modified display signal contains information indicative of a monochromatic luminance level.

3. The method as described in claim 1 wherein said display signal contains information designating said display signal as being either a primary display signal or a secondary display signal.

4. The method according to claim 3 wherein said user selected transfer function modulates the modified display signal generated from a secondary display signal.

5. The method according to claim 3 wherein the luminance level of the modified display signal generated from said primary display signal is greater than the luminance level of the modified display signal generated from said secondary display signal.

6. The method according to claim 1 wherein the transfer function is time variant.

7. The method according to claim 1 wherein the transfer function is nonlinear.

8. A method for optimizing the optical characteristics of information presented on a display comprising the steps of: receiving a display signal, said display signal characterizing an image to be displayed; providing a plurality of transfer functions; receiving a user input to select a transfer function from said plurality of transfer functions; and generating a modified display signal, from said display signal and said user selected transfer function.

9. The method as described in claim 8 wherein said modified display signal contains information indicative of a monochromatic luminance.

10. The method as described in claim 8 wherein said display signal contains information designating said display signal as being either a primary display signal or a secondary display signal.

11. The method according to claim 10 wherein the user selected transfer function modulates the modified display signal generated from a secondary display signal.

12. The method according to claim 10 wherein the luminance level of the modified display signal generated from said primary display signal is greater than the luminance level of the modified display signal generated from said secondary display signal.

13. The method according to claim 8 wherein at least one of said plurality of transfer functions is time variant.

14. The method according to claim 8 wherein at least one of said plurality of transfer functions is nonlinear.

15. A method for optimizing the optical characteristics of information presented on a display comprising the steps of: receiving a plurality of display signals characterizing an image to be displayed; providing a plurality of transfer functions; receiving a user input to select a transfer function from said plurality of transfer functions; and generating a modified display signal, from at least one of said plurality of display signals and said user selected transfer function.

16. The method as described in claim 15 wherein said modified display signal contains information indicative of a monochromatic luminance.

17. The method as described in claim 15 wherein said plurality of display signals contains information designating at least one of said plurality of display signals as being either a primary display signal or a secondary display signal.

18. The method according to claim 17 wherein said user selected transfer function modulates the modified display signal generated from said secondary display signal.

19. The method according to claim 17 wherein the luminance level of the modified display signal generated from said primary display signal is greater than the luminance • level of the modified display signal generated from said secondary display signal.

20. The method according to claim 15 wherein at least one of said plurality of transfer functions is time variant.

21. The method according to claim 15 wherein at least one of said transfer functions is nonlinear.

22. An apparatus for optimizing the optical characteristics of information presented on a display comprising: means for receiving a display signal characterizing an image to be displayed; and means for generating a modified display signal, capable of driving a display, as a function of said display signal and a user selected transfer function.

23. An apparatus according to claim 22 wherein the modified display signal contains information indicative of a monochromatic luminance level.

24. An apparatus according to claim 20 wherein said display signal contains information designating said display signal as being either a primary display signal or a secondary display signal.

25. An apparatus according to claim 24 wherein said user selected transfer function modulates the modified display signal generated from a secondary display signal.

26. An apparatus according to claim 24 wherein the luminance level of the modified display signal generated from said primary display signal is greater than the luminance level of the modified display signal generated from said secondary display signal.

27. An apparatus according to claim 24 wherein said user selected transfer function is a look-up table.

28. A method for optimizing the optical characteristics of information presented on a display comprising the steps of: receiving a display signal, said display signal characterizing an image to be displayed; receiving a user input to generate a transfer function for said display signal; and generating a modified display signal, from said display signal and said user generated transfer function.

29. The method as described in claim 28 wherein said modified display signal contains information indicative of a monochromatic luminance.

30. The method as described in claim 28 wherein said display signal contains information designating said display signal as being either a primary display signal or a secondary display signal.

31. The method according to claim 30 wherein the user generated transfer function modulates the modified display signal generated from a secondary display signal.

32. The method according to claim 30 wherein the luminance level of the modified display signal generated from said primary display signal is greater than the luminance level of the modified display signal generated from said secondary display signal.

33. The method according to claim 28 wherein the user generated transfer function is time variant.

34. The method according to claim 28 wherein the user generated transfer function is nonlinear.