Patent Publication Number: US-8970636-B2

Title: System and method for color correction between displays with and without average picture dependency

Description:
This application claims the benefit, under 35 U.S.C. §365 of International Application PCT/US 2007/014966, filled Jun. 27, 2007, which was published in accordance with PCT Article 21(2) on Dec. 31,2008 in English. 
     TECHNICAL FIELD 
     The present invention generally relates to color correction, and more particularly, to systems and methods for editing colors in anticipation of average brightness dependency differences between reference and target displays. 
     BACKGROUND OF THE INVENTION 
     Many displays, mainly in the consumer field, include a dependency between local brightness and global picture brightness, or local color information and global color information. This is called “Average Brightness Dependency”, or ABD. Another term is “APL” dependency, standing for “average picture level” or “average power level” dependency. ABD can be described as: a behavior, where a grey spot is displayed on a screen; then, the absolute brightness of that grey spot will depend not only on its code value but also on its geometrical size relative to the screen size, and further on the code value of the remaining area of the screen. In one example, for a cathode ray tube (CRT), it is mainly the power supply for the electron guns that is responsible for a limited total light output of the display system. In a plasma system, it is again the power supply, but also the power load for the so-called “line drivers” that puts constraints on the total light output of the display system. 
     Another example includes a function that can be found in today&#39;s displays, which is called “Dynamic Black”. It can be found in liquid crystal displays (LCD), direct view, LCD, DLP, and LCOS rear projection displays, and LCD, DLP, and LCOS front projection displays. All of these displays are based on a “passive” light modulator that spatially modulates light coming from a light source. Display engineers have found that the total contrast range of such a display can be much higher if the light source is modulated itself, depending on the picture requirements. Circuitry driving the light modulation generally decreases light from the light source for dark pictures and increases light from the light source for bright pictures, thus creating an ABD. A display that does not exhibit an ABD or exhibits an ABD that is fundamentally different from a target display results in colors that may not look correct or may have a dissatisfying appearance on the target display. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention address the deficiencies of the prior art by providing a method and system for compensating for average brightness dependency (ABD) differences between displays with and without average brightness dependency (ABD). 
     In one embodiment of the present invention, a method for compensating for average brightness dependency (ABD) differences between displays includes color correcting source picture content on a reference display to produce color corrected picture content and applying an ABD compensation characteristic to the color corrected picture content for correctly displaying the source picture content on a display with different ABD characteristics than the reference display. 
     In an alternate embodiment of the present invention, a system for compensating for average brightness dependency (ABD) differences between displays includes a color correction module configured to color correct source picture content on a reference display to produce color corrected picture content, a simulation module configured to receive the color corrected picture content and simulate the look of the corrected source picture content on the reference display on a display with ABD characteristics different from the reference display, and a compensation module configured to receive the color corrected picture content and information from the simulation module and to apply an ABD compensation characteristic to the color corrected picture content for correctly displaying the source picture content on a display with different ABD characteristics than the reference display. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  depicts a graph illustrating an average brightness level dependency test picture; 
         FIG. 2  depicts a graph illustrating a total brightness level versus average brightness level for CRT and plasma displays; 
         FIG. 3  depicts a graph illustrating a total brightness level versus average brightness level for dynamic black displays; 
         FIG. 4  depicts an illustrative example of a problem in a conventional process of display content creation using consumer display systems; 
         FIG. 5  depicts a block diagram of a process for ABD compensation for a display with different ABD behavior than a reference display in accordance with an embodiment of the present invention; 
         FIG. 6  depicts a high level block diagram of an ABD simulation unit in accordance with one embodiment of the present invention; 
         FIG. 7  depicts a block diagram of a process for ABD simulation to provide correction for a plurality of displays with different ABD behaviors in accordance with an embodiment of the present invention; 
         FIG. 8  depicts an illustrative example of a split screen for displaying multiple reference images in accordance with an embodiment of the present invention; 
         FIG. 9  depicts a block diagram of a process for ABD simulation for providing at least two masters for displays with similar and different ABD behaviors in accordance with an embodiment of the present invention; 
         FIG. 10  depicts a block diagram of a process for ABD simulation for providing correction for a plurality of displays with different ABD behaviors using metadata from a simulation process in accordance with an embodiment of the present invention; 
         FIG. 11  depicts a block diagram of a process for ABD simulation for providing correction information through metadata to an ABD compensation module for displays with ABD behavior different from a reference display in accordance with an embodiment of the present invention; 
         FIG. 12  depicts a block diagram of a process for ABD simulation based on a subsequent color correction process using an additional reference display to generate one master and provide correction for a display with different ABD behavior and a second master created by a previous color correction process for a display with the same ABD behavior in accordance with an embodiment of the present invention; 
         FIG. 13  depicts a block diagram of a process for ABD simulation based on a subsequent color correction process using an additional reference display to generate one master and provide correction for a display with different ABD behavior by computing a color transform based on simulation metadata and color correction metadata and a second master created by a previous color correction process for a display with the same ABD behavior in accordance with an alternate embodiment of the present invention; and 
         FIG. 14  depicts a high level block diagram of a module for computing a color transform specification in accordance with an embodiment of the present invention. 
       It should be understood that the drawings are for purposes of illustrating the concepts of the invention and are not necessarily the only possible configuration for illustrating the invention. To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention provide methods and systems for editing colors (color correction, color grading) in anticipation of an average brightness dependency (ABD) behavior of target displays. Embodiments in accordance with the present principles provide that ABD characteristics used during the content production process are used to predict/produce desired brightness/color characteristics on reproduction displays. There exist displays with many different ABD characteristics; in some cases, those ABD characteristics are designed into the display by means of signal processing. In other cases, display technologies exhibit their own characteristic ABD. However, in various embodiments of the present invention, an exact reproduction of consumer display behavior is not required; as long as the content that is produced using the approximation will produce a better match to the original intent than pictures created without such a model. To further improve the result, a reproduction display can be calibrated to a “reference” model or display. 
     The functions of the various elements shown in the figures can be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions can be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which can be shared. Moreover, explicit use of the term “processor” or “controller” should not be construed to refer exclusively to hardware capable of executing software, and can implicitly include, without limitation, digital signal processor (“DSP”) hardware, read-only memory (“ROM”) for storing software, random access memory (“RAM”), and non-volatile storage. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure). 
     Thus, for example, it will be appreciated by those skilled in the art that the block diagrams presented herein represent conceptual views of illustrative system components and/or circuitry embodying the principles of the invention. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudocode, and the like represent various processes which may be substantially represented in computer readable media and so executed by a computer or processor, whether or not such computer or processor is explicitly shown. 
       FIG. 1  depicts a graph illustrating an average brightness level dependency test picture. In  FIG. 1 , an exemplary test picture  10  is depicted to measure an average brightness dependency (ABD) of a display. The test picture  10  of  FIG. 1  includes a black picture  12  with a grey spot  14 . In one embodiment of the present invention, to measure the ABD, the picture levels of the spot  14  are kept constant while the spot size is increased. In alternate embodiments of the present invention, however, other known methods for measuring ABD are also contemplated. 
     Referring to  FIG. 2 ,  FIG. 2  depicts a graph illustrating a total brightness level versus average brightness level for, for example, CRT and plasma displays. More specifically,  FIG. 2  depicts a graph of luminance over spot size in percent for a given code value for the exemplary displays. That is, in  FIG. 2  a characteristic example curve  20  of an average brightness behavior of a CRT or Plasma display is shown. Such a characteristic curve  20  typically has one to three segments, but is not limited to three segments. To explain the characteristic, a test picture with a white spot on a black background is assumed. X (or ABD Act ) denotes the spot size in percentage of the total picture size. For instance, on a high definition (HD) picture with 1920×1080 pixels, a spot with the size of 644×644 pixels is 20% of the picture size, thus X=20 for that spot size. Segment one from spot size zero to spot size X1 or ABD1 (in percent) is a segment where many displays exhibit a behavior of constant brightness Y2 for any spot sizes between 0 and X1. Between spot sizes X1 (ABD1) and X2 (ABD2), the brightness follows a characteristic described by a function or by a Look Up Table (LUT). For example, the brightness may follow the law of constant picture power, meaning that the picture power defined as spot size in percent times the brightness is kept constant using, for example, Equation one (1), which follows:
 
ABD out (ABD Act )=( Y 1+( Y 2 −Y 1)(1/(ABD Act −ABD1)))/max( Y 1 ,Y 2),  (1)
 
where ABD Act  is the spot size in percent (%), and ABD out  is the output ABD (or Y). More specifically, X is the input value of ABD, and Y is the output value of ABD of a display with ABD.
 
     Referring back to  FIG. 2 , a third segment may exhibit constant normalized brightness Y1 for spot sizes above X2. However, on current plasma or CRT displays, this third segment does not exist, but it may be used in future display systems. It should be noted that the thresholds, absolute brightness and functions can be different for each color channel (e.g., red (R), green (G), and blue (B)). As such, the picture modification can be described as:
 
 R   out   =f   abd r ( R   in );
 
 G   out   =f   abd g ( G   in );
 
 B   out   =f   abd b ( B   in );
 
     where f abd  a function which converts the color component input (e.g., R in ) to the output (e.g., R out ). The subscripts r, g and b designate the respective color components. 
     Taking the relationship of Equation 1, it follows that for each color component (R, G, B), 
               R   out     =               R     i   ⁢           ⁢   n     *     ⁢   Y   ⁢           ⁢     1   r       ⁢                       for   ⁢           ⁢     ABD     Act   ⁢           ⁢   r         &lt;     ABD   ⁢           ⁢     1   r         ⁢                         R     i   ⁢           ⁢   n     *     ⁢       ABD     out   ⁢           ⁢   r       ⁡     (     ABD     Act   ⁢           ⁢   r       )               for   ⁢           ⁢   ABD   ⁢           ⁢       1   r     [       ABD     Act   ⁢           ⁢   r       [     ABD   ⁢           ⁢     2   r                           R     i   ⁢           ⁢   n     *     ⁢   Y   ⁢           ⁢     2   r       ⁢                       for   ⁢           ⁢   ABD   ⁢           ⁢     2   r       &lt;     ABD     Act   ⁢           ⁢   r         ⁢                                 G   out     =               G     i   ⁢           ⁢   n     *     ⁢   Y   ⁢           ⁢     1   g       ⁢                       for   ⁢           ⁢     ABD     Act   ⁢           ⁢   g         &lt;     ABD   ⁢           ⁢     1   g         ⁢                         G     i   ⁢           ⁢   n     *     ⁢       ABD     out   ⁢           ⁢   g       ⁡     (     ABD     Act   ⁢           ⁢   g       )               for   ⁢           ⁢   ABD   ⁢           ⁢       1   g     [       ABD     Act   ⁢           ⁢   g       [     ABD   ⁢           ⁢     2   g                           G     i   ⁢           ⁢   n     *     ⁢   Y   ⁢           ⁢     2   g       ⁢                       for   ⁢           ⁢   ABD   ⁢           ⁢     2   g       &lt;     ABD     Act   ⁢           ⁢   g         ⁢                                   B   out     =               B     i   ⁢           ⁢   n     *     ⁢   Y   ⁢           ⁢     1   b       ⁢                       for   ⁢           ⁢     ABD     Act   ⁢           ⁢   b         &lt;     ABD   ⁢           ⁢     1   b         ⁢                         B     i   ⁢           ⁢   n     *     ⁢       ABD     out   ⁢           ⁢   b       ⁡     (     ABD     Act   ⁢           ⁢   b       )               for   ⁢           ⁢   ABD   ⁢           ⁢       1   b     [       ABD     Act   ⁢           ⁢   b       [     ABD   ⁢           ⁢     2   b                           B     i   ⁢           ⁢   n     *     ⁢   Y   ⁢           ⁢     2   b       ⁢                       for   ⁢           ⁢   ABD   ⁢           ⁢     2   b       &lt;       ABD     Act   ⁢           ⁢   b       .       ⁢                     ⁢                 
The indexes r, g, b denote parameters related respectively to the color components R, G and B.
 
       FIG. 3  depicts a graph illustrating a total brightness level versus average brightness level for dynamic black displays. Referring to  FIG. 3 , a characteristic average brightness level dependency of a display featuring the aforementioned “dynamic black” behavior is illustratively shown. More specifically, there may be a range of spot sizes from 0 to X1 with a constant brightness Y1. In addition, there is a range of spot sizes of size X1&lt;spot size&lt;X2 that follows, a relationship of increased brightness with increasing spot size. Then, most displays will have a third segment, with a constant brightness Y2 for spot sizes equal to or above the spot size X2. The function in the second segment may differ from one display to another depending on, for example, model, technology and manufacturer. The example shown in  FIG. 3  uses the simplest implementation: a linear increase of brightness with spot size, however, in accordance with alternate embodiments of the present invention other functions (e.g., non-linear functions) may also be applied. For example, it should be noted that plasma displays, for example, have a per channel average brightness dependency, meaning that each color Red, Green, Blue has an independent characteristic. 
     CRT&#39;s, however, have an additive behavior, meaning that the average brightness depends on the additive brightness of Red, Green, and Blue. “Dynamic Black” displays normally are white level oriented, where white may be defined as min(Red, Green, Blue), as an example. In accordance with embodiments of the present principles, there are average brightness characteristics used during the content production process which are determined to be able to predict/produce a desired color reproduction on target displays. It is assumed that an exact reproduction of the average brightness dependency specification is difficult to realize on the content production side due to the fact that there exist a large variety of such specifications; in fact, each particular model of a display manufacturer may have a different characteristic. 
       FIG. 4  depicts an illustrative example of a problem in a conventional process of display content creation using consumer display systems.  FIG. 4  includes a content creation side  101  which includes the facilities needed to provide color correction or other adjustments to video content and a content consumer side  103  which includes equipment to view the video content. Referring to  FIG. 4 , a diagram depicts color correction using a display  102  with no ABD in accordance with a conventional set up. Picture source content  110  is input to a color correction process  112 . In conjunction with the color correction process  112 , the reference display  102  is used without ABD correction to provide color adjustments to images of the content. Color corrected picture content  114  is then provided to consumers. When color correcting on a display  102  without ABD correction, the colors on a display  106  having ABD will be reproduced incorrectly. For example, if two displays  106  and  108  are compared, both with the same peak brightness, for example, the display  106  with ABD and the display  108  without ABD, pictures with higher brightness will look significantly darker on the display  106  having ABD. Dark pictures, on the other hand, can look the same on both displays  106  and  108 . As a result, bright scenes get attenuated versus dark scenes, and as an effect, the color intent may be lost or degraded. Low light components may disappear in brighter pictures, and the visual effect on scene transitions may be degraded. 
     In some displays, the brightness achieved in a first segment (up to X1) may be significantly higher than the brightness that was achieved with the reference display. The spot sizes for which this brightness can be maintained is rather limited, e.g., X1=5. In this case, all darker scenes experience a significantly higher gain versus displays with no ABD. In this case, when the gain, and thus the opto-electrical transfer function (gamma), is significantly different to the transfer function used in the reference display, a side effect is that picture quantization artifacts and picture compression artifacts become visible which were not visible on the reference display with no ABD. 
       FIG. 5  depicts a block diagram of a process for ABD compensation for a display with different ABD behavior than a reference display in accordance with an embodiment of the present invention. Referring to  FIG. 5 , a diagram depicts color correction of a reference display  102  with no ABD. In accordance with one embodiment, an ABD compensation module  202  is used prior to displaying a picture on a consumer display  106  with ABD behavior. One way of retrieving the original look of the picture may include compensating for the ABD of the display  106  by applying an inverse characteristic in the ABD compensation module  202  and then routing the resultant signal to the display  106  with ABD. This solution may have the drawback that a display with ABD may provide a very poor display image when all ABD is compensated out. There may either be a lot of clipping artifacts introduced by this solution, when retaining the dynamic range of the display, or, in another case, when the peak white is set equal to the minimum peak white for all spot sizes, the dynamic range will be really low, and quantization problems are likely to become apparent since only parts of all code values will be used. 
     In accordance with an embodiment of the present invention, the compensation module  202  can include the ability to determine the type of reference display  102  where the color corrected picture content  114  was produced. As such, the inverse characteristic is referenced for the display type of display  106 . Next, the inverse characteristic is applied to compensate for the ABD not present in the referenced display  102  to provide a better match between the reference display  102  and the content consumer display  106 . It should be understood that while the figures include a content creation side  101  and a content consumer side  103 , the elements depicted on the content consumer side  103  can be implemented on the content creation side  101  and vice versa. In addition, content creation  101  can include production facilities for rendering video for cable or other networks, television, movie studios, DVD&#39;s, VHS tapes or any other content production. The content consumer  103  can include movie theatres, televisions, or any other content consumer. The determined ABD information in accordance with various embodiments of the present invention can be embodied in a look up table, analytical transfer function, data graph or any other relationship between spatial resolution and brightness. It should be kept in mind however, that the color correction process provides changes to the ABD information. As such, alternatively, ABD compensation can be performed by comparing ABD information between the consumer display ( 106 ) and the reference display  102  and compensating for the differences to achieve the same or similar result as the reference display  102 . 
     ABD on a plasma display, for example, can be defined according to Equation two (2), which follows: 
     ABD out (ABD Act )=(Y1+(Y2−Y1)(1/(ABD Act −ABD1))/max(Y1,Y2) for all spot sizes ABD act  above minimum spot size ABD1, and constant for all ABD act  below or equal to ABD1. 
     More generally:
 
ABD out (ABD Act )=( Y 1+( Y 2 −Y 1) f   abd (ABD Act −ABD1)/max( Y 1 ,Y 2).  (2)
 
     In the embodiment described above, there are three color components, and in one exemplary embodiment, there is assumed to be no correlation between the three color components. To simulate an ABD on a display with no ABD, however, the video signals can be modified by means of a mathematical function or by means of a LUT (Look-Up Table). Such a modification is explained with reference to the system of  FIG. 6 . 
       FIG. 6  depicts a high level block diagram of an ABD simulation unit in accordance with one embodiment of the present invention. Referring to  FIG. 6 , an ABD simulation unit  250  is illustratively depicted, (which can be used for simulation module  302  or  604 , as will be described below). In  FIG. 6 , a source picture  252  includes a Red component, P1 R , a Green component, P1 G , and a Blue component, P1 B . In the embodiment of the invention of  FIG. 6 , the P1 components are analyzed for average brightness for each color component in an ABD analysis block  254 . The average brightness can be characterized according to equation three (3), which follows: 
     
       
         
           
             
               
                 
                   
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     0 [ABD R [ 100, where HSIZE is equal to the horizontal size of the picture and VSIZE is equal to the vertical size of the picture. P1 R min  depicts the minimum red component of the source picture and P1 R max  depicts the maximum red component of the source picture. The values for ABD G , and ABD B  are obtained the same way by calculating the global average out of P1 G , and P1 B , respectively. 
     In the ABD control block  256 , a target ABD function is applied, and a resultant multiplication factor is produced, one for each color component (ABD R M , ABD G M , ABD B M ). An exemplary target function as described in Equation 1, above, is applied per color component. Following the theory of a three segmented function, it needs specification of one set of brightness references, Y1, Y2, and ABD1, ABD2 spot sizes (=average brightness levels), but also of the function that ABD out  follows depending on ABD Act , Y1, Y2, ABD1, and ABD2. A picture modification device  258 , then, applies the ABD multiplication factor to the picture, either by means of, in one embodiment, simple multiplication, or by a more complex function, or Look-Up Tables. The ABD compensation (P2 R , P2 G , P2 B ) is, as such, provided to a respective picture display  260  (e.g., display  106  of  FIG. 5 , for example). 
       FIG. 7  depicts a block diagram of a process for ABD simulation to provide correction for a plurality of displays with different ABD behaviors in accordance with an embodiment of the present invention. Referring to  FIG. 7 , a system for predicting variations in color reproduction between displays with and without ABD during the content creation process is illustratively depicted. As such, the composition on a display is known during content production and compensation for ABD variances can applied on the content creation side  101  of the process. Predicting the color variations between displays with ABD  106  and displays without ABD ( 102  and  102 ′) during the content creation process enables the color composition on a consumer display  106  to be known even during content creation  101  and compensation can be applied using an ABD simulation module  302  in accordance with the present invention. 
     Differences in the look of images presented on displays with ABD versus displays with no ABD and/or displays with different types of ABD, during content creation, can be predicted, and color decisions can be made to make sure that the artistic intent is not compromised by one of the displays taken into consideration in accordance with the present invention. More specifically, in one embodiment of the present invention a best compromise for all displays can be determined and implemented using a master content source  114 . This can mean that not all desired color compositions are possible on all displays even though some displays would have the potential to support them. The resultant picture material  114  would be color corrected to meet the least common denominator among all displays expected to be employed. 
     In one embodiment, reference display  102 , which employs ABD and is used during content creation, could be a reference display of a given type with well characterized and documented characteristics, or display  102  could be a reference display of another type, for example, with no ABD (as shown in the  FIG. 7 ), with ABD simulation circuitry  302 . The advantage of a reference with no ABD, however, is in the possibility of viewing different display characteristics on one display without the need of an arrangement of several displays for color correction. 
     In one embodiment, during content creation  101 , reference display  102  which is affected by ABD is compared to a different reference display  102 ′ with no ABD effects. In this embodiment, the simulation module  302  includes the capability of adjusting the ABD of display  102 ′ to arrive at a satisfactory picture reproduction. The adjustments made in the simulation module  302  can be employed to create an inverse characteristic curve or a new ABD setting to be used with consumer displays (e.g., display  106  in  FIG. 7 ) of the same type as the reference display  102 ′. As previously described however, the displays  102  and  102 ′ can be the same display type with different ABD characteristics, different display types with the same ABD or different display types with different ABD. Advantageously, using the simulation circuitry  302  in this way offers the opportunity of having different display characteristics on one display without the need of an arrangement of several displays in a color correction process. 
       FIG. 8  depicts an illustrative example of a split screen for displaying multiple reference images in accordance with an embodiment of the present invention. As shown in  FIG. 8 , a split screen display  402  can be provided for comparing the two display characteristics on a single display. Display  402  can include a partial screen  404  which employs a first ABD characteristic (or lack thereof) and a second partial screen  406  that employs a different ABD characteristic (or lack thereof). The split screen display  402  provides a very practical solution since a side-by-side comparison between different settings can be performed. In alternate embodiments of the present invention, however, a screen  402  can be segmented into any number of partial screens more than two. Using the embodiment of  FIG. 8 , however, it is possible to use a split screen display to compare two display characteristics on one display. 
       FIG. 9  depicts a block diagram of a process for ABD simulation for providing at least two masters for displays with similar and different ABD behaviors in accordance with an embodiment of the present invention. Referring to  FIG. 9 , an ABD specification is employed during color correction ( 112 ), resulting in two masters: one master (color corrected picture content)  516  for displays  106  with ABD, and one master (color corrected picture content)  514  for displays without ABD. Here, the color correction  112  is actually done on the master  516  with ABD, and the master  514  with no ABD will be a derivative of master  516  using ABD simulation module  302 . 
     Good results can be achieved with this embodiment. Good color matching can be achieved between a consumer ABD display  106  and a non-ABD display  108  provided that the ABD specifications of master  514  and master  516  match with the specification needed for displays in the field, or the display in the field is calibrated to the specification used in the color correction process  112 . 
     However, there is a singular specification for a display with no ABD, and yet multiple ABD specifications will have to be considered for the ABD versions. It would be advantageous if the parent version were the version with no ABD. In addition, the color correction process  112  can be a bit labor intensive since the colors are modified before any ABD is applied, because the simulation module or circuitry  302  is disposed between the color correction  112  and the reference display  102 . A colorist in a content creation facility can, for example, raise the contrast of a picture, but the ABD simulation can work against this and reduce the contrast. Advantageously, in contrast with the embodiment of  FIG. 7 , there will be no colors in the master  516  that cannot be displayed by a display  106  with ABD. 
       FIG. 10  depicts a block diagram of a process for ABD simulation for providing correction for a plurality of displays with different ABD behaviors using metadata from a simulation process in accordance with an embodiment of the present invention. Referring to  FIG. 10 , another embodiment is depicted where display  106  has ABD behavior while the reference display  102  does not. In addition, display  108  has no ABD behavior. Color correction  112  provides color corrected content ( 514 ) for displays with ABD and displays without ABD. ABD simulation  302  is performed using reference display  102  without ABD during color correction. This results in one master  514  for displays with average brightness dependency (ABD). Simulation module  302  outputs metadata  602  describing a transformation of the picture with ABD into a picture without ABD. As described above, it follows the theory of a three segmented ABD, with two flat regions and one variable region in between, therefore the metadata  602  can describe the thresholds in average brightness and the corresponding absolute brightnesses, plus a description of the function in between. In one embodiment of the present invention, a function description can be a parameter that indexes different functions, such as a linear function, an 1/x function, or the like. 
     Based on an ABD description as depicted in  FIG. 2  or  3 , for example, a list of illustrative parameters that can be transmitted as metadata  602  can be characterized according to Table 1, which follows: 
                     TABLE 1                  Examples of Metadata                         Parameter   Description   Value               X1 = ABD1   Threshold that determines the   Value between 0 and 100. 0 for a           lower threshold for ABD (as   very dark picture, 100 for a picture           defined in Eq. 3), below which   with very high average brightness.           there is no change in picture           brightness by the average           brightness of the picture.       X2 = ABD2,   Threshold that determines the   0 for a very dark picture, 100 for a           upper threshold for ABD (as   picture with very high average           defined in Eq. 3), above which   brightness. Display of technology           there is no change in picture   type Plasma or CRT do not have this           brightness by the average   segment, in which case the           brightness of the picture.   X2 = ABD2 = 100. However, displays of               technology type LCD with “dynamic               black” feature typically do have such a               segment, therefore X2 = ABD2 &lt; 100.       Y1   Relative brightness level in   For displays of technology type           percent. Brightness level after   Plasma or CRT, ABD typically does           ABD for ABD&#39;s &lt; ABD1   not modify the brightness in this               segment, therefore Y1 = 100.               However, displays of technology type               LCD with “dynamic black” feature               typically modify brightness in this               segment, therefore Y1 &lt; 100       Y2   Relative brightness level in   For displays of technology type LCD           percent. Brightness level after   with “dynamic black” feature, ABD           ABD for ABD&#39;s &gt; ABD2   typically does not modify the               brightness in this segment, therefore               Y2 = 100. However, displays of               technology type Plasma or CRT               typically modify brightness in this               segment, therefore Y2 &lt; 100       FUNC_SEL   Selection flag for analytical   Examples:           function (f abd  of Eq. 2)   FUNC_SEL = 0 for f abd (x) = 1/x               FUNC_SEL = 1 for f abd (x) = x       CORR_SEL   Correlation Flag, determines inter-   CORR_SEL = 0: Every color channel           channel dependency of average   is treated independently,           brightness dependency   CORR_SEL = 1: The channel with the               most effect to ABD determines the               ABD for all channels,               CORR_SEL = 2: The channel with the               least effect to ABD determines the               ABD for all channels,               CORR_SEL = 3: for ABD, an average               of all channels is used.               CORR_SEL = 4: for ABD, a weighted               average (weight (w)) of all channels is               used, ABD out  = ⅓ * (w r  * ABD out r  +               w g  * ABD out g  + w b  * ABD out b )       w r     Weighting Factor for the Red   0 . . . 1           channel for CORR_SEL = 4       w g     Weighting Factor for the Green   0 . . . 1           channel for CORR_SEL = 4       w b     Weighting Factor for the Blue   0 . . . 1           channel for CORR_SEL = 4                    
Additional metadata or a variety of different forms of metadata can be used to address other and more complex ABD characteristics. Other metadata formats can also be applied, such as, for example, multi-dimensional Look Up Tables. An ABD simulation module  604  transforms input from the single master  514  to provide ABD simulation signals which permit a match in display images between displays  106  and  108 .
 
     Advantageously, a single inventory master  514  is provided, and metadata  602  describing the difference between the colors for a display with ABD and a display without ABD are provided. A color transform described by the metadata is similar to the color transform defined by the reference ABD specification for display  102 . 
       FIG. 11  depicts a block diagram of a process for ABD simulation for providing correction information through metadata to an ABD compensation module for displays with ABD behavior different from a reference display in accordance with an embodiment of the present invention. Referring to  FIG. 11 , in this embodiment, the display  106  includes ABD behavior which is compensated for by an ABD compensation module  702  in accordance with the present invention. The display  106  has different behavior from the reference display  102  (which has no ABD). The color correction process  112  adjusts the reference display  102  to make the picture suitable for the display  106  with ABD. This is performed using ABD simulation module  302 . The simulation results in one master  514  for displays  108  without ABD behavior like the reference display  102 . In addition, metadata  602  describing a transformation of the picture for use on the display  106  with ABD is provided. The metadata  602  may be, for example, a description of an inverse transform of the ABD simulation transform (from ABD simulation  302 ) used for color correction. The metadata  602  can be employed by the compensation module  702  that applies the inverse of the function specified by the metadata to the picture content  514  to produce a matching image result to display  108  (or with the reference display  102 ). The difference between the embodiment shown in  FIG. 11  and the embodiment shown in  FIG. 10  is that the single inventory master  514  is based on a display without ABD behavior. 
     Using the example of Eq. 1, the inverse function can be characterized according to equation four (4), which follows:
 
ABD Act =( Y 2 −Y 1)/(ABD out   −Y 1)+ABD1,  (4)
 
     where ABD Act  is the input ABD value of the display and ABD out  is the output ABD value of the ABD display. 
       FIG. 12  depicts a block diagram of a process for ABD simulation based on a subsequent color correction process using an additional reference display to generate one master and provide correction for a display with different ABD behavior and a second master created by a previous color correction process for a display with the same ABD behavior in accordance with an embodiment of the present invention. Referring to  FIG. 12 , in this embodiment, one master is provided for displays without ABD in a first color correction process, and a subsequent color correction is used to create a secondary master for displays with ABD. Picture source content  110  is color corrected by color correction process  112  using the reference display  102 . The color corrected picture content is forwarded to create a first master  514  for displays without ABD behavior. A subsequent color correction is provided using reference display  102 ′ by a color correction process  112 ′ for creating a secondary master  514 ′ for displays  106  with ABD behavior where the ABD behavior is adjusted to match the reference display  102 ′ by using the simulation module  302  to make adjustments. 
     In the embodiment of  FIG. 12 , a two step color correction is advantageously performed. In a first step, color correction  112  is applied where the colors are corrected for the reference display  102  with no ABD behavior. Then, the picture is put onto the display  102 ′ with no ABD behavior and a simulation is performed to adjust for display  106  with ABD behavior. In the secondary color correction process  112 ′, the colorist is given the ability to adjust the colors and parameters in a way to preserve artistic intent on the display  106  with ABD behavior using reference display  102 ′. However, in this scenario it is accepted that the two versions of the picture for display  106  and display  108  will not match exactly, but will preserve artistic intent. The two versions can then be stored as separate masters  514  and  514 ′. 
       FIG. 13  depicts a block diagram of a process for ABD simulation based on a subsequent color correction process using an additional reference display to generate one master and provide correction for a display with different ABD behavior by computing a color transform based on simulation metadata and color correction metadata and a second master created by a previous color correction process for a display with the same ABD behavior in accordance with an alternate embodiment of the present invention. Referring to  FIG. 13 , in this embodiment, one master is preferably created for displays without ABD, and a subsequent color correction creates a second version for displays with ABD. Instead of creating two masters, a color transform is calculated using the subsequent color transform information and the ABD simulation specification. The combined metadata is provided to the consumer device which is then able to reconstruct the version for displays with ABD using a color transform that uses the color transform specification. 
     As shown in  FIG. 13 , one master  514  is created for displays  108  with no ABD behavior based on the reference display  102 . This master  514  is created by a color correction process  112 . A subsequent color correction process  112 ′ is performed on the output of the first color correction process  112  for creating a second version for displays  106  with ABD behavior based on color decisions made using the reference display  102 ′. Instead of creating two masters, a color transform  806  is calculated using the subsequent color correction process  112 ′ transform information. The transform information can be generated from simulation module  302  and/or from the color correction process  112 ′ of reference display  102 ′, which is the same or similar to display  106 . 
     A color transform specification calculation  808  is performed to generate ABD compensation and color change metadata  804 . The combined metadata  804  would then be provided to a consumer device in the form of the color transform  806  which is then able to reconstruct the version for displays with different ABD behavior in accordance with behavior of the reference display  102 ′ using a signal transform that uses the color transform specification  806 . 
     In some applications, it may not be preferable to have separate or multiple masters for different ABD characteristics or different display types. In such cases, it is preferable to have a single source of content and metadata describing a color transform  806  that is necessary to retrieve the characteristic version needed. On the consumer side, color transform  806  (which can be implemented as a circuit or in software) can be provided which connects a signal source with a display ( 106 ) with an ABD behavior different from the ABD behavior of the reference display  102 . This transform  806  can be implemented in hardware or in software, and can provide the signal transform to generate the version of ABD specification needed out of the signal for displays with ABD. In one embodiment of the present invention, the transform  806  can be provided with the signal transform specification from the content provider by means of metadata  804 . The signal transform specification from transform  806  includes two major components, a specification of the color change from the subsequent color correction, and a specification of an ABD compensation (by inverting the ABD simulation specification used during color correction). Since it may not be desirable to have separate masters for different ABD situations, it is preferable to have one parent or main content and metadata describing the color transform that is necessary to retrieve the ABD version needed. 
       FIG. 14  depicts a high level block diagram of a module for computing a color transform specification in accordance with an embodiment of the present invention.  FIG. 14  depicts an embodiment of a module  802  that combines the two components used to create a color transform  806 . A signal transform specification  910  is output to color transform  806  after two major component signals are combined. These components include an input color transform specification  908  for color changes from the subsequent color correction, and ABD simulation information from ABD simulation  302 . This includes an ABD specification  902  for ABD compensation. An output color transform specification  910  is derived in block  904  by creating ABD compensation, for example, by inverting the ABD simulation specification used during color correction and applying the inverse ABD simulation specification to the input color transform specification  908 . To further explain this, a color change (cc) can be characterized according to equation five (5), which follows:
 
 R   cc   =f   cc r ( R   in   , G   in   , B   in )
 
 G   cc   =f   cc g ( R   in   , G   in   , B   in )
 
 B=f   cc b ( R   in   , G   in   , B   in ),  (5)
 
     where f cc  is a color change function for a particular color channel (r, g, b) based on input values for R in , G in , B in . For ABD, the resultant color change can be characterized according to equation six (6), which follows:
 
 R   cc abd   =f   abd r ( f   cc r ( R   in   ,Gin,B   in )
 
 G   cc abd   =f   abd g ) f   cc g ( R   in   ,G   in   ,B   in )
 
 B   cc abd   =f   abd b ( f   cc b ( R   in   , G   in , B in ),  (6)
 
     with component color change (C cc ) being C cc =CC×C in  where CC is a color matrix characterized according to equation seven (7), which follows: 
     
       
         
           
             
               
                 
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                                                   g 
                                                 
                                               
                                               , 
                                               
                                                 Y 
                                                 ⁢ 
                                                 
                                                     
                                                 
                                                 ⁢ 
                                                 
                                                   2 
                                                   g 
                                                 
                                               
                                             
                                             ) 
                                           
                                         
                                         * 
                                       
                                       ⁡ 
                                       
                                         [ 
                                         
                                           
                                             R 
                                             
                                               i 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               n 
                                             
                                           
                                           ; 
                                           
                                             G 
                                             
                                               i 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               n 
                                             
                                           
                                           ; 
                                           
                                             B 
                                             
                                               i 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               n 
                                             
                                           
                                         
                                         ] 
                                       
                                     
                                     * 
                                   
                                   ⁡ 
                                   
                                     [ 
                                     
                                       
                                         
                                           
                                             c 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             21 
                                           
                                         
                                         
                                           
                                             c 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             22 
                                           
                                         
                                         
                                           
                                             c 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             23 
                                           
                                         
                                       
                                     
                                     ] 
                                   
                                 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           for 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           ABD 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             
                               1 
                               g 
                             
                             [ 
                             
                               
                                 ABD 
                                 
                                   act 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   g 
                                 
                               
                               [ 
                               
                                 ABD 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   
                                     2 
                                     g 
                                   
                                   . 
                                 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   
                     Y 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       
                         
                           
                             2 
                             g 
                             * 
                           
                           ⁡ 
                           
                             [ 
                             
                               
                                 R 
                                 
                                   i 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   n 
                                 
                               
                               ; 
                               
                                 G 
                                 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     i 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     n 
                                   
                                 
                               
                               ; 
                               
                                 B 
                                 
                                   i 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   n 
                                 
                               
                             
                             ] 
                           
                         
                         * 
                       
                       ⁡ 
                       
                         [ 
                         
                           
                             
                               
                                 c 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 21 
                               
                             
                             
                               
                                 c 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 22 
                               
                             
                             
                               
                                 c 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 23 
                               
                             
                           
                         
                         ] 
                       
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     for 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     ABD 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       
                         2 
                         g 
                       
                       [ 
                       
                         
                           ABD 
                           
                             act 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             g 
                           
                         
                         . 
                       
                     
                   
                 
               
             
           
         
       
       
         
           
             
               
                 B 
                 
                   cc 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   abd 
                 
               
               = 
               
                 
                   
                     
                       
                         
                           
                             
                               
                                 
                                   Y 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     
                                       
                                         
                                           1 
                                           b 
                                           * 
                                         
                                         ⁡ 
                                         
                                           [ 
                                           
                                             
                                               R 
                                               
                                                 i 
                                                 ⁢ 
                                                 
                                                     
                                                 
                                                 ⁢ 
                                                 n 
                                               
                                             
                                             ; 
                                             
                                               G 
                                               
                                                 i 
                                                 ⁢ 
                                                 
                                                     
                                                 
                                                 ⁢ 
                                                 n 
                                               
                                             
                                             ; 
                                             
                                               B 
                                               
                                                 i 
                                                 ⁢ 
                                                 
                                                     
                                                 
                                                 ⁢ 
                                                 n 
                                               
                                             
                                           
                                           ] 
                                         
                                       
                                       * 
                                     
                                     ⁡ 
                                     
                                       [ 
                                       
                                         
                                           
                                             
                                               c 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               31 
                                             
                                           
                                           
                                             
                                               c 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               32 
                                             
                                           
                                           
                                             
                                               c 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               33 
                                             
                                           
                                         
                                       
                                       ] 
                                     
                                   
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   for 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     
                                       ABD 
                                       
                                         act 
                                         ⁢ 
                                         
                                             
                                         
                                         ⁢ 
                                         b 
                                       
                                     
                                     [ 
                                     
                                       ABD 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       
                                         1 
                                         b 
                                       
                                     
                                   
                                 
                               
                             
                             
                               
                                 
                                   
                                     
                                       ABD 
                                       
                                         out 
                                         ⁢ 
                                         
                                             
                                         
                                         ⁢ 
                                         b 
                                       
                                     
                                     ⁡ 
                                     
                                       ( 
                                       
                                         ABD 
                                         
                                           act 
                                           ⁢ 
                                           
                                               
                                           
                                           ⁢ 
                                           b 
                                         
                                       
                                       ) 
                                     
                                   
                                   / 
                                   
                                     
                                       
                                         
                                           
                                             max 
                                             ⁡ 
                                             
                                               ( 
                                               
                                                 
                                                   Y 
                                                   ⁢ 
                                                   
                                                       
                                                   
                                                   ⁢ 
                                                   
                                                     1 
                                                     b 
                                                   
                                                 
                                                 , 
                                                 
                                                   Y 
                                                   ⁢ 
                                                   
                                                       
                                                   
                                                   ⁢ 
                                                   
                                                     2 
                                                     b 
                                                   
                                                 
                                               
                                               ) 
                                             
                                           
                                           * 
                                         
                                         ⁡ 
                                         
                                           [ 
                                           
                                             
                                               R 
                                               
                                                 i 
                                                 ⁢ 
                                                 
                                                     
                                                 
                                                 ⁢ 
                                                 n 
                                               
                                             
                                             ; 
                                             
                                               G 
                                               
                                                 i 
                                                 ⁢ 
                                                 
                                                     
                                                 
                                                 ⁢ 
                                                 n 
                                               
                                             
                                             ; 
                                             
                                               B 
                                               
                                                 i 
                                                 ⁢ 
                                                 
                                                     
                                                 
                                                 ⁢ 
                                                 n 
                                               
                                             
                                           
                                           ] 
                                         
                                       
                                       * 
                                     
                                     ⁡ 
                                     
                                       [ 
                                       
                                         
                                           
                                             
                                               c 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               31 
                                             
                                           
                                           
                                             
                                               c 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               32 
                                             
                                           
                                           
                                             
                                               c 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               33 
                                             
                                           
                                         
                                       
                                       ] 
                                     
                                   
                                 
                               
                             
                           
                         
                       
                       
                         
                           
                             for 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             ABD 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               
                                 1 
                                 b 
                               
                               [ 
                               
                                 
                                   ABD 
                                   
                                     act 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     b 
                                   
                                 
                                 [ 
                                 
                                   ABD 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     
                                       2 
                                       b 
                                     
                                     . 
                                   
                                 
                               
                             
                           
                         
                       
                     
                   
                 
                 
                   
                     
                       Y 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         
                           
                             
                               2 
                               b 
                               * 
                             
                             ⁡ 
                             
                               [ 
                               
                                 
                                   R 
                                   
                                     i 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     n 
                                   
                                 
                                 ; 
                                 
                                   G 
                                   
                                     i 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     n 
                                   
                                 
                                 ; 
                                 
                                   B 
                                   
                                     i 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     n 
                                   
                                 
                               
                               ] 
                             
                           
                           * 
                         
                         ⁡ 
                         
                           [ 
                           
                             
                               
                                 
                                   c 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   31 
                                 
                               
                               
                                 
                                   c 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   32 
                                 
                               
                               
                                 
                                   c 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   33 
                                 
                               
                             
                           
                           ] 
                         
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       for 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       ABD 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         
                           2 
                           b 
                         
                         [ 
                         
                           
                             ABD 
                             
                               act 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               b 
                             
                           
                           . 
                         
                       
                     
                   
                 
               
             
             ⁢ 
             
                 
             
           
         
       
     
     In another exemplary application where both the ABD specification  902  and the input color transform  908  are implemented as Look Up Tables (LUTs), the resultant color transform specification  910  will be a Look Up Table produced by inverting the Look Up Table that described the ABD characteristic used during color correction. This Look Up Table is then concatenated with a Look Up Table generated from the color transform, where the color correction transform comes first followed by the ABD compensation. 
     In accordance with the present principles, it is often discriminated between a picture version for displays with ABD and a picture version for displays without ABD, or metadata for reconstructing the picture for displays with ABD. As mentioned above, there are several ABD specifications to be addressed, e.g., at least one for the CRT and Plasma kinds of behavior, and at least one for the “dynamic black” type of behavior. 
     Having described preferred embodiments for systems and methods for compensating for average brightness dependency (ABD) differences between displays with and without average brightness dependency (ABD) (which are intended to be illustrative and not limiting), it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope and spirit of the invention as outlined by the appended claims. While the forgoing is directed to various embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof.