Patent Publication Number: US-10311799-B2

Title: Display device and method for controlling peak luminance of the same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2016-0081865, filed on Jun. 29, 2016 in the Korean Intellectual Property Office (KIPO), the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Field 
     Example embodiments of the inventive concept relate to electronic devices. More particularly, example embodiments of the inventive concept relate to display devices and methods for controlling peak luminance of the same. 
     2. Discussion of Related Art 
     Organic light emitting diode (OLED) displays can display information such as images and characters by emitting light generated from an organic layer. This light is generated in the organic layer via the combination of holes supplied from an anode and electrons supplied from a cathode. OLED displays have advantages over traditional displays such as low power consumption, wide viewing angles, fast response times, stability at low temperatures, etc. 
     The organic light emitting display device applies peak luminance control (PLC) driving method for controlling peak luminance of display image based on RGB image data to reduce power consumption. The PLC driving method decreases the peak luminance according to an increase of an average grayscale level (or an average signal level of the image) to reduce the power consumption. 
     However, the conventional PLC driving method determines the peak luminance without considering environments such as contrast of the image, ambient light, temperature, etc, and thus visibility of the image decreases and the image deterioration occurs. 
     SUMMARY 
     Example embodiments provide a display device adaptively controlling peak luminance based on contrast and load of images. 
     Example embodiments provide a method for controlling adaptively controlling peak luminance of a display device based on contrast and load of images. 
     Example embodiments provide a display device adaptively controlling peak luminance based on contrast and load of images, ambient light and temperature. 
     According to example embodiments, a display device may comprise an image analyzer configured to calculate contrast and load of an image of a frame based on R, G, and B image data input corresponding to the frame, an image processor configured to control a peak control coefficient applied to W image data to adaptively control peak luminance based on the contrast and the load, and to respectively generate R′, G′, and B′ image data by subtracting a product of the W image data and the peak control coefficient from each of the R, G, and B image data, a display panel including a plurality of pixels, a data driver configured to generate a data signal based on the R′, G′, B, and W image data, and to provide the data signal to the display panel, and a scan driver configured to provide a scan signal to the display panel. 
     In example embodiments, the peak luminance may increase when the peak control coefficient decreases. 
     In example embodiments, the image analyzer may determine the image of the frame as a normal image when the contrast is less than a predetermined first reference or the load is greater than a predetermined second reference; and wherein the image analyzer determines the image of the frame as a peak image which requires an increase of the peak luminance when the contrast is greater than the first reference and the load is less than the second reference. 
     In example embodiments, the image analyzer may comprise a calculator configured to calculate the contrast and the load based on a histogram of the R, G, and B image data, and a comparator configured to compare the contrast with the first reference and to compare the load with the second reference. 
     In example embodiments, the image processor may comprise a coefficient determiner configured to determine the peak control coefficient corresponding to the contrast, and a data converter configured to generate the W image data based on a minimum value among grayscales of the respective R, G, and B image data, and to generate the R′, G′, and B′ image data by subtracting the product of the W image data and the peak control coefficient from the respective R, G, and B image data. 
     In example embodiments, the coefficient determiner may determine the peak control coefficient to 1 when the image of the frame is the normal image. The coefficient determiner may determine the peak control coefficient to a real number within a range greater than or equal to 0 and less than 1 based on the contrast when the image of the frame is the peak image. 
     In example embodiments, the peak control coefficient may have a uniform value regardless of the contrast when the image of the frame is the peak image. 
     In example embodiments, the peak control coefficient may decrease as a step function according to an increase of the contrast when the image of the frame is the peak image. 
     In example embodiments, the peak control coefficient may decrease linearly according to an increase of the contrast when the image of the frame is the peak image. 
     In example embodiments, the peak control coefficient may decrease as a step function according to an increase of a grayscale level when the image of the frame is the peak image. 
     In example embodiments, a first peak luminance corresponding to a first grayscale range may be less than a second peak luminance corresponding to a second grayscale range that has grayscales higher than grayscale levels within the first grayscale range. 
     In example embodiments, the data converter may comprise a minimum value selector configured to generate the W image data by selecting the minimum value among the grayscales of the R, G, and B image data, a coefficient applier configured to generate W′ image data by multiply the W image data by the peak control coefficient, and a subtractor configured to subtract the W′ image data from each of the R, G, and B image data to generate the R′, G′, and B′ image data, respectively. 
     In example embodiments, peak control coefficients applied to the respective R, G, and B image data may be the same each other. 
     In example embodiments, at least one of peak control coefficients applied to the respective R, G, and B image data may be different. 
     In example embodiments, the image analyzer may determine whether or not an image displayed on a predetermined pixel block is the peak image, and wherein the peak control coefficient is independently calculated per the predetermined pixel block. 
     In example embodiments, the display device may further comprise an illuminance sensor configured to detect ambient light around the display panel, and a peak controller configured to determine a sub peak control coefficient based on the ambient light and to provide the sub peak control coefficient to the image processor, the sub peak control coefficient being additionally applied to the W image data. 
     In example embodiments, the peak controller may decrease the sub peak control coefficient at a predetermined interval according to an increase of the ambient light, when the ambient light is greater than a predetermined reference ambient light, and the image processor may generate R′, G′, and B′ image data by subtracting a product of the W image data, the peak control coefficient and the sub peak control coefficient from each of the R, G, and B image data. 
     In example embodiments, the display device may further comprise a temperature sensor configured to detect a temperature of the display panel, and a peak controller configured to determine a sub peak control coefficient based on the temperature and to provide the sub peak control coefficient to the image processor, the sub peak control coefficient being additionally applied to the W image data. 
     In example embodiments, the peak controller may decrease the sub peak control coefficient at a predetermined interval according to a decrease of the temperature, when the temperature is less than a predetermined reference temperature, and the image processor may generate R′, G′, and B′ image data by subtracting a product of the W image data, the peak control coefficient and the sub peak control coefficient from each of the R, G, and B image data. 
     In example embodiments, the image analyzer may further calculate a total sum of saturation of the image based on the R, G, and B image data when the image of the frame is the peak image. 
     In example embodiments, the display device may further comprise a peak controller configured to compare the total sum of saturation with a predetermined third reference, to determine a sub peak control coefficient and to provide the sub peak control coefficient to the image processor, the sub peak control coefficient being additionally applied to the W image data. 
     In example embodiments, the peak controller may decrease the sub peak control coefficient at a predetermined interval according to a decrease of the total sum of saturation, when the total sum of saturation is less than the third reference, and the image processor may generate R′, G′, and B′ image data by subtracting a product of the W image data, the peak control coefficient and the sub peak control coefficient from each of the R, G, and B image data. 
     According to example embodiments, a method for controlling peak luminance of a display device may comprise calculating contrast and load of an image of a frame based on R, G, and B image data input corresponding to the frame, determining a peak control coefficient for adaptively controlling peak luminance based on the contrast and the load, generating W image data based on a minimum value among grayscales of the R, G, and B image data, generating R′, G′, and B′ image data by subtracting a product of the W image data and the peak control coefficient from the R, G, and B image data, respectively, and generating a data signal based on the R′, G′, B′, and W image data. 
     In example embodiments, the peak luminance may increase when the peak control coefficient decreases. 
     In example embodiments, determining the peak control coefficient may comprise determining the image of the frame as a normal image when the contrast is less than a predetermined first reference or the load is greater than a predetermined second reference, and determining the peak control coefficient to 1 when the image of the frame is the normal image. 
     In example embodiments, determining the peak control coefficient may further comprise determining the image of the frame as a peak image which requires an increase of the peak luminance when the contrast is greater than the first reference and the load is less than the second reference, and determining the peak control coefficient to a real number within a range greater than or equal to 0 and less than 1 based on the contrast when the image of the frame is the peak image. 
     In example embodiments, the peak control coefficient may have a uniform value regardless of the contrast or decreases as a step function according to an increase of the contrast, when the image of the frame is the peak image. 
     According to example embodiments, a display device may comprise an image analyzer configured to calculate contrast and load of an image of a frame based on R, G, and B image data input corresponding to the frame, an image processor configured to control a peak control coefficient applied to W image data to adaptively control peak luminance based on the contrast and the load, and to respectively convert the R, G, and B image data into R′, G′, B′, and W image data based on the peak control coefficient, an illuminance sensor configured to detect ambient light around the display panel, a first peak controller configured to determine a first sub peak control coefficient based on the ambient light and to provide the sub peak control coefficient to the image processor, the first sub peak control coefficient being additionally applied to the W image data, a temperature sensor configured to detect a temperature of the display panel, a second peak controller configured to determine a second sub peak control coefficient based on the temperature and to provide the sub peak control coefficient to the image processor, the second sub peak control coefficient being additionally applied to the W image data, a display panel including a plurality of pixels, a data driver configured to generate a data signal based on the R′, G′, B, and W image data, and to provide the data signal to the display panel, and a scan driver configured to provide a scan signal to the display panel. 
     In example embodiments, the image analyzer may determine the image of the frame as a normal image when the contrast is less than a predetermined first reference and the load is greater than a predetermined second reference. The image analyzer may determine the image of the frame as a peak image which requires an increase of the peak luminance when the contrast is greater than the first reference and the load is less than the second reference. 
     According to example embodiments, a display device may comprise an image analyzer configured to decide a frame image characteristic, wherein the frame image characteristic includes a peak image which requires an increase of the peak luminance and a normal image, and is decided according to contrast and load of a frame image which is generated based on R, G, and B image data input of a frame, an image processor configured to receive the contrast and the frame image characteristic from the image analyzer and generate R′, G′, B′, and W image data, a display panel including a plurality of pixels; a data driver configured to generate a data signal based on the R′, G′, B, and W image data, and to provide the data signal to the display panel, and a scan driver configured to provide a scan signal to the display panel, wherein the W image data W corresponds to a minimum value among the R image data R, G image data G, and B image data B, The R′ G′, and B′ image data correspond to (R−W*PCC), (G−W*PCC), and (W*PCC), respectively, where PCC represents a peak control coefficient. The PCC is 1 when the frame image characteristic is the normal image and PCC is equal to or greater than 0 and less than 1 when the frame image characteristic is the peak image. The PCC may decrease as the contrast increases when the frame image characteristic is the peak image. 
     In example embodiments, the display device may further comprise an illumination sensor configured to detect ambient light around the display panel and a peak controller configured to determine a sub peak control coefficient based on the ambient light and to provide the sub peak control coefficient to the image processor. The sub peak control coefficient may decrease as the ambient light increases when the frame image characteristic is the peak image. The PCC may decrease as the sub peak control coefficient decreases. 
     In example embodiments, the display device may further comprise a temperature sensor configured to detect temperature of the display panel and a peak controller a sub peak configured to determine control coefficient based on the temperature of the display panel and to provide the sub peak control coefficient to the image processor. The sub peak control coefficient may increase as the temperature of the display panel increases when the frame image characteristic is the peak image. The PCC may decrease as the sub peak control coefficient decreases. 
     In example embodiments, the display device may further comprise a peak controller configured to compare a total sum of saturation with a predetermined reference to determine a sub peak control coefficient. The image analyzer may further calculate the total sum of saturation of the image based on the R, G, and B image data when the image characteristic is the peak image. The sub peak control coefficient may increase as the total sum of saturation of the image increases when the frame image characteristic is the peak image. The PCC may decrease as the sub peak control coefficient decreases. 
     In example embodiments, the display device may further comprise an illumination sensor configured to detect ambient light around the display panel and a first peak controller configured to determine a first sub peak control coefficient based on the ambient light and to provide the first sub peak control coefficient to the image processor; and a temperature sensor configured to detect temperature of the display panel and a second peak controller configured to determine a second sub peak control coefficient based on the temperature of the display panel and to provide the second sub peak control coefficient to the image processor. The first sub peak control coefficient may decrease as the ambient light increases when the frame image characteristic is the peak image. The second sub peak control coefficient may increase as the temperature of the display panel increases when the frame image characteristic is the peak image. The PCC may decrease as the first sub peak control coefficient or the second peak control coefficient decreases. 
     Therefore, the display device according to example embodiments may determine whether the peak image or not every frame and adaptively increase the peak luminance with respect to the peak image that has high contrast and low load, so that the visibility, reality and immersion of the image may be improved. Further, the peak luminance may be controlled by an adaptive image data conversion based on the peak control coefficient so that deterioration of the image quality may be reduced. 
     In addition, the display device may adaptive control the peak luminance based on at least one of the ambient light, the temperature of the display panel, the total sum of saturation of the image, etc with the contrast. Thus, the visibility of display may be improved and deterioration of display may be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example embodiments can be understood in more detail from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram of a display device according to example embodiments, 
         FIG. 2  is a block diagram illustrating an example of an image analyzer included in the display device of  FIG. 1 , 
         FIGS. 3A and 3B  illustrate examples of which the image analyzer of  FIG. 2  analyzes an image, 
         FIG. 4  is a block diagram illustrating an example of an image processor included in the display device of  FIG. 1 , 
         FIG. 5A  is a graph illustrating an example of a peak control coefficient determined by the image processor of  FIG. 4 , 
         FIG. 5B  is a graph illustrating another example of a peak control coefficient determined by the image processor of  FIG. 4 , 
         FIG. 5C  is a graph illustrating still another example of a peak control coefficient determined by the image processor of  FIG. 4 , 
         FIG. 6  is a graph illustrating an example of a peak control coefficient by the image processor of  FIG. 4  based on grayscales, 
         FIG. 7A  is a block diagram illustrating an example of a data converter included in the image processor of  FIG. 4 , 
         FIG. 7B  is a diagram illustrating an example of image data converted by the data converter of  FIG. 7A , 
         FIG. 8  is a block diagram of a display device according to example embodiments, 
         FIG. 9A  is a graph illustrating an example of a sub-peak control coefficient determined by ambient light, 
         FIG. 9B  is a graph illustrating an example of a peak control coefficient determined based on the sub-peak control coefficient of  FIG. 9A , 
         FIG. 10  is a graph illustrating another example of a sub-peak control coefficient determined by ambient light, 
         FIG. 11  is a block diagram of a display device according to example embodiments, 
         FIG. 12A  is a graph illustrating an example of a sub-peak control coefficient determined by a temperature of a display panel, 
         FIG. 12B  is a graph illustrating an example of a peak control coefficient determined based on the sub-peak control coefficient of  FIG. 12A , 
         FIG. 13  is a graph illustrating another example of a sub-peak control coefficient determined by a temperature of a display panel, 
         FIG. 14  is a block diagram of a display device according to example embodiments, 
         FIG. 15  is a graph illustrating another example of a sub-peak control coefficient determined by saturation of an image, 
         FIG. 16  is a block diagram of a display device according to example embodiments, 
         FIG. 17  is a flow chart of a method for controlling peak luminance of a display device according to example embodiments, 
         FIG. 18  is a flow chart illustrating an example of determining a peak control coefficient of the method of  FIG. 17 , 
         FIG. 19  is a block diagram of an electronic device according to example embodiments, 
         FIG. 20A  is a diagram illustrating an example of the electronic device of  FIG. 19  implemented as a television, and 
         FIG. 20B  is a diagram illustrating an example of the electronic device of  FIG. 19  implemented as a smart phone. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Exemplary embodiments will be described more fully hereinafter with reference to the accompanying drawings, in which various embodiments are shown. 
       FIG. 1  is a block diagram of a display device according to example embodiments. 
     Referring to  FIG. 1 , the display device  1000  may include a display panel  100 , an image analyzer  200 , an image processor  300 , a timing controller  400 , a scan driver  500 , and a data driver  600 . 
     In one embodiment, the display device  1000  may be implemented as an organic light emitting display device or a liquid crystal display device. Since these are examples, the display device  1000  is not limited thereto. 
     The display panel  100  may display images. The display panel  100  may include a plurality of scan lines SL 1  through SLn and a plurality of data lines DL 1  through DLm. The display panel  100  may also include the pixels P connected to the scan lines SL 1  through SLn and the data lines DL 1  through DLm. For example, the pixels P may be arranged in a matrix form. In some embodiments, the number of pixels P may be equal to n×m, where n and m are integers greater than 0. In some embodiments, each of the pixels P may include 4 sub pixels, for example, a red sub pixel R, a green sub pixel G, a blue sub pixel B, and a white sub pixel W. Since an arrangement of the sub pixels illustrated in  FIG. 1  is an example, the arrangement of the sub pixels is not limited thereto. 
     Each of the sub pixels may include a switching transistor, a driving transistor, a storage capacitor, and an organic light emitting diode (OLED). Some embodiments, the OLED may be a white OLED which emit white light in which the red, green and blue sub pixels may be implemented by color filters having a red, green and blue color filters, respectively. Since these are examples, structures of the sub pixels are not limited thereto. 
     The image analyzer  200  may calculate contrast CON and load LOAD of an image of a frame based on R, G, and B image data R, G, B input corresponding to the frame. The R, G, and B image data R, G, B may correspond to red image data R, green image data G, and blue image data B, respectively. The contrast CON may be a proportion of a low-grayscale range to a high-grayscale range in a whole image of one frame. The load LOAD may be a proportion of an average signal level (e.g., an average grayscale) of the present frame to a signal level of a full-white image. In some embodiments, the image analyzer  200  may include a calculator configured to calculate the contrast CON and the load LOAD based on a histogram of the R, G, and B image data R, G, B and a comparator configured to compare the contrast CON with a predetermined first reference and to compare the load LOAD with a predetermined second reference. 
     The image analyzer  200  may provide the R, G, and B image data R, G, B, the contrast CON and the load LOAD to the image processor  300 . 
     The image analyzer  200  may determine the image of the frame as a normal image or a peak image, which requires an increase of peak luminance, based on the contrast CON and the load LOAD provided from the image analyzer  200 . In some embodiments, the image analyzer  200  may determine the image of the frame as the normal image when the contrast CON is less than the first reference or the load LOAD is greater than the second reference. In some embodiments, the image analyzer  200  may determine the image of the frame as the peak image which requires an increase of the peak luminance when the contrast CON is greater than the first reference and the load LOAD is less than the second reference. For example, when a high grayscale (or high luminance) portion partially exists in a dim image, the peak luminance may be increased and visibility may be improved. 
     The image processor  300  may control a peak control coefficient applied to W image data to adaptively control peak luminance according to the contrast CON and the load LOAD, and convert the R, G, and B image data R, B into R′, G′, B′, and W image data R′, G′, B′, W based on the peak control coefficient. The W image data W may be converted image data obtained using the R, G, and B image data R, G, B to emit white light. In some embodiments, the image processor  300  may include a coefficient determiner configured to determine the peak control coefficient corresponding to the contrast CON, and a data converter configured to generate the W image data W based on a minimum value among grayscales of the R, G, and B image data R, B, and to generate the R′, G′, and B′ image data R′, G′, B′ by subtracting the product of the W image data W and the peak control coefficient from the respective R, G, and B image data R, G, B. 
     In some embodiments, the peak luminance may increase when the peak control coefficient decreases. 
     The peak control coefficient may be determined as 1 when the image of the frame is the normal image. Thus, the peak luminance in this case may be determined by only the W image data W and an emission of the white sub pixel. 
     The peak control coefficient may be determined to a real number within a range greater than or equal to 0 and less than 1 when the image of the frame is the peak image for increasing the peak luminance. In this, the peak luminance may be determined by the W image data W and at least one of the R, G, and B image data R, G, B. Thus, the peak luminance may be greater than that of the normal image. 
     The peak control coefficient may have a uniform value regardless the contrast CON or decrease as a step function according to an increase of the contrast CON when the image of the frame is the peak image. In some embodiments, peak control coefficients applied to the respective R, G, and B image data R, G, B may have the same value. In contrast, at least one of the peak control coefficients applied to the respective R, G, and B image data R, G, B may have a different value. 
     In some embodiments, the peak control coefficient may changes according to a grayscale level in the peak image. For example, the peak control coefficient may decrease as a step function according to an increase of the grayscale level. 
     In some embodiments, the contrast CON and load LOAD calculation may be performed with a predetermined pixel block as a unit. Accordingly, conversions of the R, G, and B image data R, G, B may be performed independently. Thus, the peak control coefficient determined by each pixel block may be different each other. 
     The image processor  300  may provide the converted R′, G′, B′, and W image data R′, G′, B′, and W to the timing controller  400 . 
     The timing controller  400  may control the scan driver  500  and the data driver  600  based on a control signal CLR received from external devices, for example, a graphic controller. The control signal CLR may include a vertical synchronization signal, a horizontal synchronization signal, a data enable signal, a clock signal, and so on. The timing controller  400  may generate a first control signal CLT 1  for controlling a driving timing of the scan driver  500  and provide the first control signal CLT 1  to the scan driver  500 . In some embodiments, the timing controller  400  may provide the R′, G′, B′, and W image data R′, G′, B′, W to the data driver  600 . The timing controller  400  may generate a second control signal CLT 2  for controlling a driving timing of the data driver  600  and provide the second control signal CLT 2  to the data driver  600 . In some embodiments, the timing controller  400  may generate a data signal (e.g., digital data signals) corresponding to operating conditions of the display panel  100  based on the R′, G′, B′, and W image data R′, G′, B′, W and provide the data signal to the data driver  600 . 
     In some embodiments, at least one of the image analyzer  200  and the image processor  300  may be included in the timing controller  400 . 
     The scan driver  500  may provide a plurality of scan signals to the display panel  100 . The scan driver  500  may output the scan signals to the display panel  100  via the scan lines SL 1  through SLn in response to the first control signal CLT 1  received from the timing controller  400 . 
     The data driver may convert the R′, G′, B′, and W image data R′, G′, B′, W or the data signal into an analog type data voltage in response to a second control signal CLT 2  received from the timing controller  400  and may apply the data voltage to the data lines DL 1  through DLm. 
     As described above, the display device  1000  may determine whether the frame image is the peak image or not in every frame and adaptively increase the peak luminance when the frame image is the peak image that has high contrast and low load, so that the visibility, reality and immersion of the image may be improved. Further, the peak luminance may be controlled by an adaptive image data conversion using the peak control coefficient so that deterioration of the image quality may be reduced. 
       FIG. 2  is a block diagram illustrating an example of an image analyzer included in the display device of  FIG. 1 .  FIGS. 3A and 3B  illustrate examples of which the image analyzer of  FIG. 2  analyzes an image. 
     Referring to  FIGS. 2 through 3B , the image analyzer  200  may include a calculator  220  and a comparator  240 . 
     The calculator  220  may calculate the contrast CON and the load LOAD based on a histogram of the R, G, and B image data R, G, B. The calculator  220  may calculate the contrast CON and the load LOAD at a predetermined frame interval. In some embodiments, the calculator  220  may calculate the contrast CON and the load LOAD every frame. 
     The calculator  220  may calculate a luminance histogram of all pixels from the R, G, and B image data R, G, B as illustrated in  FIGS. 3A and 3B . An X axis of the histogram represents the luminance (or the grayscale level) and a Y axis represents the number of pixels. For example,  FIG. 3A  shows the histogram of an image having a relatively high contrast CON, and  FIG. 3B  shows the histogram of an image having a relatively low contrast CON. 
     The luminance of the image data may be defined by a plurality of grayscales. For example, the luminance may be divided into 0 to 255 grayscale levels and the luminance may increase according to an increase of the grayscale level. A low-grayscale proportion Rlow, a mid-grayscale proportion Rmid and a high-grayscale proportion Rhigh may be calculated from the histogram. For example, a low-grayscale range for calculating the low-grayscale proportion Rlow may include a 0 grayscale level to a 64 grayscale level and a high-grayscale range for calculating the high-grayscale proportion Rhigh may include a 200 grayscale level to a 255 grayscale level. A mid-grayscale range may correspond to between the low-grayscale range and the high-grayscale range. The contrast CON may be calculated based on the low-grayscale proportion Rlow, the mid-grayscale proportion Rmid and the high-grayscale proportion Rhigh. 
     Further, the load LOAD that is a proportion of an average signal level of a present frame to a signal level of a full-white image may be calculated by the histogram. 
     The comparator  240  may determine the frame image as a peak image PEAKI for increasing peak luminance or a normal image NORI based on the contrast CON and the load LOAD. In some embodiments, the comparator  240  may compare the contrast CON with a predetermined first reference and compare the load LOAD with a predetermined second reference. The frame image may be determined as the peak image PEAKI by satisfying a condition that the contrast CON is higher than the first reference and the load LOAD is lower than the second reference. 
     In some embodiments, the comparator  240  may determine the image of the frame as the peak image PEAKI when the contrast CON is greater than the first reference and the load is less than the second reference. In contrast, the comparator  240  may determine the image of the frame as the normal image NORI when the contrast CON is less than the first reference or the load LOAD is greater than the second reference. 
     For example, the first reference may include a reference value with respect to the low-grayscale proportion Rlow and a reference value with respect to the high-grayscale proportion Rhigh. For example, when the low-grayscale proportion Rlow is over about 60% and the high-grayscale proportion Rhigh is over about 10%, the image of the frame may be the high contrast image. The contrast CON may be digitized by the calculation. The higher the digitized contrast CON is, the wider areas of low-grayscale portion and high-grayscale portion exist. And, in the high contrast CON, the image of the frame may provide sufficient contrast. 
     In some embodiments, the second reference may be determined to about 15%. That is, the peak image PEAKI may have entirely dim image including high-grayscale portions. For example, the peak image PEAKI may be a night scene image partially having high-grayscale portions. 
     Accordingly, when the load LOAD is lower than 15% and the low-grayscale proportion Rlow is over about 60% and the high-grayscale proportion Rhigh is over about 10%, the image of the frame may be determined as the peak image PEAKI. 
     However, this is an example, and the references for determining whether the image is the peak image PEAKI or not are not limited thereto. 
     The calculator  220  and the comparator  240  may provide the contrast CON and the result of the determination to the image processor  300 . 
     In some embodiments, the calculations of the contrast CON and the load LOAD and the determination whether or not an image displayed on a predetermined pixel block is the peak image PEAKI. Accordingly, the peak control coefficient PCC may be independently calculated per pixel block. 
     The peak luminance of the frame may be adaptively controlled by the determination whether the image is the peak image PEAKI or not. 
       FIG. 4  is a block diagram illustrating an example of an image processor included in the display device of  FIG. 1 . 
     Referring to  FIG. 4 , the image processor  300  may include a coefficient determiner  320  and a data converter  340 . 
     The coefficient determiner  320  may determine a peak control coefficient PCC according to the contrast CON. In some embodiments, the coefficient determiner  320  may determine the peak control coefficient PCC based on the normal image NORI and the peak image PEAKI. The peak control coefficient PCC may be multiplied to the W image data W to control the peak luminance. In some embodiments, the lower the peak control coefficient PCC is, the higher the peak luminance is. 
     When the image of the frame is the normal image NORI, the coefficient determiner  320  may determine the peak control coefficient PCC to 1. When the peak luminance of the normal image NORI is about 500 nit, the peak luminance may be represented by an emission of only white sub pixels (i.e., only the W image data). 
     When the image of the frame is the peak image PEAKI, the coefficient determiner  320  may determine the peak control coefficient PCC based on the contrast CON. Here, the peak control coefficient PCC may be real number within a range greater than or equal to 0 and less than 1. In some embodiments, the coefficient determiner  320  may determine the peak control coefficient PCC to have a uniform value regardless the contrast CON. In some embodiments, the coefficient determiner  320  may determine the peak control coefficient PCC to be changed according to a value of the contrast CON. For example, the coefficient determiner  320  may include a lookup table having a relation between the contrast CON and the peak control coefficient PCC, or may change the peak control coefficient PCC using a formula (or a function) that has a contrast CON as a variable. 
     The coefficient determiner  320  may provide the peak control coefficient PCC to the data converter  340 . 
     The data converter  340  may generate the W image data W based on a minimum value among grayscales of the respective R, G, and B image data R, G, B. The respective grayscales may represent luminances of the respective R, G, and B image data R, G, B. For example, each of the grayscales may be implemented by 8 bit digital data (e.g., 0 to 255 grayscale levels). The data converter  340  may extract the minimum value (e.g., a minimum grayscale level) from the digitized grayscale levels (or the digitized luminances). However, this is an example, and forms of the digital data representing the grayscale levels are not limited thereto. 
     Luminance efficiency of the respective red sub pixel, green sub pixel, and blue sub pixel are different from each other. Thus, even though all of the R, G, and B image data R, G, B have the same grayscale level, the red, green, and blue sub pixels may emit light each having different luminance. For example, when all of the R, G, and B image data R, G, B have 255 grayscale level (i.e., a maximum grayscale level), the red sub pixel may emit light with about 100 nit, the green sub pixel may emit light with about 300 nit, and the blue sub pixels may emit light with about 50 nit. Here, the peak luminance may correspond to about 450 nit that is a sum of the luminances of the red, green, and blue sub pixels. 
     In some embodiments, the W image data W may be calculated by Equation 1.
 
 W =min( R,G,B )  Equation 1
 
     In Equation 1, the W image data W may correspond to the minimum value among the R, G, and B image data R, G, B. For example, when all of the R, G, and B image data R, G, B have the 255 grayscale level (i.e., the maximum grayscale level), the minimum value may correspond to the 255 grayscale level and the W image data W may have digital data corresponding to the 255 grayscale level. 
     The data converter  340  may generate the R′, G′, and B′ image data R′, G′, B′ by subtracting the product of the W image data W and the peak control coefficient PCC from the respective R, G, and B image data R, G, B. In some embodiments, the R′, G′, and B′ image data R′, G′, B′ may be converted from the R, G, and B image data R, G, B by Equation 2, respectively.
 
 R′=R−W*PCC  
 
 G′=G−W*PCC  
 
 B′=B−W*PCC   Equation 2
 
     The peak control coefficient PCC may be 1 when the image of the frame is the normal image NORI. Thus, the R′, G′, and B′ image data R′, G′, B′ may correspond to (R−W), (G−W), and (B−W), respectively. When the image of the frame is the peak image PEAKI, the peak control coefficient PCC is less than 1 so that the R′, G′, and B′ image data R′, G′, B′ may be respectively greater than (R−W), (G−W), and (B−W). Thus, when all of the R, G, and B image data R, G, B have the 255 grayscale level (i.e., the maximum grayscale level), the W image data W may have the digital data corresponding to the 255 grayscale level and the respective R′, G′, and B′ image data R′, G′, B′ may have specific grayscale levels greater than 0. Accordingly, all the red, green, blue, and white sub pixels may emit light and the peak luminance may increase. 
     In some embodiments, peak control coefficients PCC applied to the respective R, G, and B image data R, G, B may have the same value. In some embodiments, at least one of peak control coefficients applied to the respective R, G, and B image data R, G, B may have a different value. Accordingly, the peak control coefficient PCC may be different according to the R, G, and B image data R, G, B in consideration of each of the emission efficiencies of the sub pixels. 
     In some embodiments, the data converter  340  may include a minimum value selector, a coefficient applier, and a subtractor to generate the R′, G′, and B′ image data R′, G′, B′. 
       FIG. 5A  is a graph illustrating an example of a peak control coefficient determined by the image processor of  FIG. 4 .  FIG. 5B  is a graph illustrating another example of a peak control coefficient determined by the image processor of  FIG. 4 .  FIG. 5C  is a graph illustrating still another example of a peak control coefficient determined by the image processor of  FIG. 4 . 
     Referring to  FIGS. 4 through 5C , the peak control coefficient PCC may be adaptively controlled according to the peak image PEAKI and the normal image NORI. The peak control coefficient PCC may further controlled according to the contrast CON in the peak image PEAKI. 
     In some embodiments, the peak control coefficient PCC may be determined to 1 in the normal image NORI. 
     As illustrated in  FIG. 5A , the peak control coefficient PCC may have a uniform value regardless the contrast CON in the peak image PEAKI that the contrast CON of the image of the frame is greater than a reference contrast TH. For example, the peak control coefficient PCC may be determined to 0.5 in the peak image PEAKI. Thus, in the same R, G, and B image data, peak luminance of the peak image PEAKI may be relatively higher than peak luminance of the normal image NORI. 
     As illustrated in  FIG. 5B , the peak control coefficient PCC may decrease as a step function according to an increase of the contrast CON in the peak image PEAKI that the contrast CON of the image of the frame is greater than a reference contrast TH. Accordingly, the peak control coefficient PCC may be changed based on specific contrast ranges. Here, as the contrast CON increases, the peak luminance may increase as a step function. 
     As illustrated in  FIG. 5C , the peak control coefficient PCC may linearly decrease according to an increase of the contrast CON in the peak image PEAKI that the contrast CON of the image of the frame is greater than a reference contrast TH. Here, as the contrast CON increases, the peak luminance may increase. 
     However, these are examples, and methods for adjusting the peak control coefficient PCC are not limited thereto. For example, the peak control coefficient PCC may change as an exponential function in the peak image PEAKI. 
     Accordingly, the peak control coefficient PCC in the peak image PEAKI is lower than the peak control coefficient PCC in the normal image NORI, so that the peak luminance in the peak image PEAKI that has relatively higher contrast than the normal image NORI may be higher than the peak luminance in the normal image NORI. Further, the peak luminance may increase according to the increase of the contrast CON of the peak image PEAKI. 
       FIG. 6  is a graph illustrating an example of a peak control coefficient obtained by the image processor of  FIG. 4  according to grayscales. 
     Referring to  FIGS. 4 and 6 , the peak control coefficient PCC may be adaptively controlled according to a grayscale level GRAY in the peak image. 
       FIG. 6  shows the peak control coefficient PCC changes according to the grayscale level GRAY in a specific contrast. In some embodiments, the peak control coefficient PCC may decrease as a step function according to an increase of the grayscale level GRAY. Accordingly, the peak control coefficient PCC may be determined by predetermined grayscale ranges G 1 , G 2 , G 3 , . . . . Thus, in the peak image, a first peak luminance corresponding to a first grayscale range G 1  may be lower than a second peak luminance corresponding to a second grayscale range G 2 . Therefore, a luminance range in the first grayscale range G 1  (e.g., a low-grayscale range) may be less than a luminance range in the second grayscale range G 2 . 
     However, this is an example, and methods for adjusting the peak control coefficient PCC are not limited thereto. For example, the number of the grayscale ranges and a range of each grayscale range are set by experiments. And, the peak control coefficient PCC may change as an exponential function, a linear function, and so on, in the peak image PEAKI. 
     As described above, the peak control coefficient PCC may be changed according to the grayscale level GRAY so that a rapid increase of the luminance in the low-grayscale range by the increase of the peak luminance can be prevented. 
       FIG. 7A  is a block diagram illustrating an example of a data converter included in the image processor of  FIG. 4 .  FIG. 7B  is a diagram illustrating an example of image data converted by the data converter of  FIG. 7A . 
     Referring to  FIGS. 2 through 7B , the data converter  340  may include a minimum value selector  342 , a coefficient applier  344 , and a subtractor  346 . 
     The minimum value selector  342  may generate the W image data W by selecting the minimum value among the grayscales of the R, G, and B image data R, G, and B. The grayscale of the R image data R may represent luminance corresponding to the R image data R. The grayscale of the G image data G may represent luminance corresponding to the G image data G The grayscale of the B image data B may represent luminance corresponding to the B image data B. The minimum value selector  342  may receive the R, G, and B image data R, G, and B from the image analyzer  200  or an external graphic source and extract the minimum value of digitized luminance (e.g., a minimum grayscale level). In some embodiments, the minimum value selector  342  may calculate the W image data W using the Equation 1. 
     For example, as illustrated in  FIG. 7B , the luminance of the respective R, G, and B image data R, G, and B may be divided into 0 to 255 grayscale levels. Emission luminances of the maximum grayscale level with respect to the respective R, G, and B image data R, G, and B may be about 100 nit, 300 nit, and 50 nit, respectively. Thus, the peak luminance by the R, G, and B image data R, G, and B may correspond to about 450 nit. When all of the R, G, and B image data have the 255 grayscale level (i.e., the maximum grayscale level), the minimum value may correspond to the 255 grayscale level and the W image data W may have digital data corresponding to the 255 grayscale level. A white sub pixel arranged in the display panel may emit light based on the W image data W. 
     The coefficient applier  344  may generate W′ image data W′ by multiply the W image data W by the peak control coefficient PCC (i.e., W′=W*PCC). In some embodiments, the peak control coefficient PCC may be greater than or equal to 0 and less than 1 when the image of the frame is the peak image PEAKI. Thus, the W′ image data W′ may be less than the W image data W in the peak image PEAKI. 
     The subtractor  346  may subtract the W′ image data W′ from each of the R, G, and B image data R, G, and B to generate the R′, G′, and B′ image data R′, G′, and B′, respectively. Accordingly, the Equation 2 may be expressed by Equation 3.
 
 R′=R−W′ 
 
 G′=G−W′ 
 
 B′=B−W′   Equation 3
 
     Accordingly, the R, G, and B image data R, G, and B may be converted into the R′, G′, and B′ image data R′, G′, and B′, respectively. The R′, G′, and B′ image data R′, G′, and B′ may have newly updated grayscale levels, respectively. 
     As illustrated in  FIG. 7B , when the peak control coefficient PCC is 0.5, the W′ image data W′ may be half of the W image data W and the R′, G′, and B′ image data R′, G′, and B′ may be respectively half of the R, G, and B image data R, G, and B. The red, green, and blue sub pixels may emit lights based on the R′, G′, and B′ image data R′, G′, and B′, respectively. Accordingly, all the red, green, blue, and white sub pixels may emit lights and the peak luminance may be about 675 nit. 
     In contrast, as illustrated in  FIG. 7B , when the peak control coefficient PCC is 1 (i.e., in the normal image NORI), the R′, G′, and B′ image data R′, G′, and B′ may be 0 (e.g., the 0 grayscale level) and the red, green, and blue sub pixels may not emit light. Here, only the white sub pixel may emit light and the peak luminance may be about 450 nit. 
     Accordingly, the peak luminance in the peak image PEAKI may be improved about 1.5 times of the normal image NORI, when the peak control coefficient PCC is 0.5. Thus, the visibility, reality and immersion of the peak image PEAKI having relatively low load and high contrast may be improved. 
       FIG. 8  is a block diagram of a display device according to example embodiments. 
     The display device of the present example embodiments are substantially the same as the display device explained with reference to  FIGS. 1 through 7B  except for constructions of an illuminance sensor, a peak controller, and an image processor. Thus, the same reference numerals will be used to refer to the same or like parts as those described in the example embodiments of  FIGS. 1 through 7B , and any repetitive explanation concerning the above elements will be omitted. 
     Referring to  FIG. 8 , the display device  1000 A may include a display panel  100 , an image analyzer  200 , an image processor  300 A, a timing controller  400 , a scan driver  500 , a data driver  600 , an illuminance sensor  700 , and a peak controller  750 . 
     The display panel  100  may include a plurality of pixels P each having a red sub pixel, a green sub pixel, a blue sub pixel, and a white sub pixel. 
     The image analyzer  200  may calculate contrast CON and load LOAD of an image of a frame based on R, G, and B image data R, G, B input corresponding to the frame. The image analyzer  200  may provide the R, G, and B image data R, B, the contrast CON and the load LOAD to the image processor  300 A. The image analyzer  200  may determine the image of the frame as a normal image or a peak image. 
     The image processor  300 A may control a peak control coefficient applied to W image data to adaptively control peak luminance according to the contrast CON and the load LOAD. The image processor  300 A may receive a sub peak control coefficient S_PCC 1  generated based on an ambient light IL from the peak controller  750 . The sub peak control coefficient S_PCC 1  may be used to determine the peak control coefficient or the W image data W. In some embodiments, the peak control coefficient may be affected by the sub peak control coefficient S_PCC 1 . For example, the sub peak control coefficient S_PCC 1  may be multiplied to the peak control coefficient to get a corrected peak control coefficient. The image processor  300 A may convert the R, G; and B image data R, B into R′, G′, and B′ image data R′, G′, B′ based on the corrected peak control coefficient which is determined considering the sub peak control coefficient S_PCC 1 . In some embodiments, the image processor  300 A may adaptively control the peak luminance based on the contrast CON, the load LOAD, and the ambient light IL. 
     The illuminance sensor  700  may detect the ambient light around the display panel  100 . When the ambient light is high, the visibility of the image may be reduced by a reflection of external light. Accordingly, the detected ambient light IL may be additionally applied to the R, G, and B image data R, G, B to control the peak luminance. 
     The peak controller  750  may determine the sub peak control coefficient S_PCC 1  based on the ambient light IL. The peak controller  750  may provide the sub peak control coefficient S_PCC 1  to the image processor  300 A. In some embodiments, the peak controller  750  may only be activated when the ambient light IL is greater than a predetermined reference ambient light. The peak controller  750  may decrease the sub peak control coefficient S_PCC 1  at a predetermined interval according to an increase of the ambient light IL. Accordingly, the corrected peak control coefficient to which the sub peak control coefficient S_PCC 1  is considered may decrease according to the increase of the ambient light IL. Thus, the peak luminance may increase according to the increase of the ambient light IL, so that the visibility of the image in the high ambient light (or bright surroundings) and/or the high contrast image may be improved. 
     In some embodiments, the peak controller  750  may be included in the image processor  300 A. 
     In some embodiments, when the ambient light IL is less than or equal to the reference ambient light, the peak controller  750  is disabled. Thus, the peak luminance control operations as described above with reference to  FIGS. 1 through 7B  may be performed. 
     The timing controller  400  may control the scan driver  500  and the data driver  600  based on a control signal CLT received from external devices. The scan driver  500  may provide a plurality of scan signals to the display panel  100 . The data driver may convert the R′, G′, B′, and W image data R′, G′, B′, W or the data signal into an analog type data voltage based on a second control signal CLT 2  received from the timing controller  400  and may apply the data voltage to the data lines DL 1  through DLm. 
     As described above, the display device  1000 A may adaptively control the peak luminance based on the contrast CON, the load LOAD, and the ambient light IL. Thus, the visibility, reality and immersion of the image may be improved. Further, the peak luminance may be controlled by an adaptive image data conversion based on the corrected peak control coefficient so that deterioration of the image quality may be reduced. 
       FIG. 9A  is a graph illustrating an example of a sub-peak control coefficient determined by ambient light.  FIG. 9B  is a graph illustrating an example of a corrected peak control coefficient determined based on the sub-peak control coefficient of  FIG. 9A . 
     Referring to  FIGS. 9A and 9B , the sub peak control coefficient S_PCC 1  may be changed according to the ambient light IL and the corrected peak control coefficient PCC′ may be changed according to the sub peak control coefficient S_PCC 1 . 
     In some embodiments, the peak control coefficient PCC may be determined to 1 when the ambient light IL is lower than or equal to a reference ambient light TH. In this, the ambient light IL may not affect the peak luminance. In some embodiments, the peak controller  750  may be disabled when the ambient light IL is lower than or equal to the reference ambient light TH. 
     As illustrated in  FIG. 9A , the sub peak control coefficient S_PCC 1  may decrease as a step function according to an increase of the ambient light IL when the ambient light IL is higher than the reference ambient light TH. Thus, as the ambient light IL increases, the peak luminance of the image may increase. The sub peak control coefficient S_PCC 1  may be determined regardless whether the image is the normal image NORI or the peak image PEAKI. 
       FIG. 9B  shows changes of relation between the corrected peak control coefficient PCC′ and the contrast CON according to a change of the sub peak control coefficient S_PCC 1 . As illustrated in  FIG. 9B , in the normal image NORI, as the ambient light increases, the corrected peak control coefficient PCC′ may decrease and the peak luminance may increases. Similarly, in the peak image PEAKI having the same contrast CON, as the ambient light increases, the corrected peak control coefficient PCC′ may decrease. 
     Accordingly, the peak luminance of the image may be adaptively controlled based on the load, contrast CON, and the ambient light IL. Thus, the visibility in the high-ambient light environment may be improved. 
       FIG. 10  is a graph illustrating another example of a sub-peak control coefficient determined by ambient light. 
     Referring to  FIG. 10 , the sub peak control coefficient S_PCC 1  may be changed according to the ambient light IL. 
     In some embodiments, the sub peak control coefficient S_PCC 1  may be determined to 1 when the ambient light IL is lower than or equal to a reference ambient light TH. In this, the ambient light IL may not influence on the peak luminance. In some embodiments, the peak controller  750  may not be operated when the ambient light IL is lower than or equal to the reference ambient light TH. 
     The sub peak control coefficient S_PCC 1  may linearly decrease according to an increase of the ambient light IL when the ambient light IL is higher than the reference ambient light TH. Thus, as the ambient light IL increases, the peak luminance of the image may increase. The sub peak control coefficient S_PCC 1  may be determined regardless whether the image is the normal image NORI or the peak image PEAKI. 
     However, this is an example, and forms of the decrease of the peak control coefficient S_PCC 1  based on the ambient light IL are not limited thereto. 
       FIG. 11  is a block diagram of a display device according to example embodiments. 
     The display device of the present example embodiments are substantially the same as the display device explained with reference to  FIGS. 1 through 7B  except for constructions of a temperature sensor, a peak controller, and an image processor. Thus, the same reference numerals will be used to refer to the same or like parts as those described in the example embodiments of  FIGS. 1 through 7B , and any repetitive explanation concerning the above elements will be omitted. 
     Referring to  FIG. 11 , the display device  1000 B may include a display panel  100 , an image analyzer  200 , an image processor  300 B, a timing controller  400 , a scan driver  500 , a data driver  600 , a temperature sensor  800 , and a peak controller  850 . 
     The display panel  100  may include a plurality of pixels P each having a red sub pixel, a green sub pixel, a blue sub pixel, and a white sub pixel. 
     The image analyzer  200  may calculate contrast CON and load LOAD of an image of a frame based on R, G, and B image data R, G, B input corresponding to the frame. The image analyzer  200  may provide the R, G, and B image data R, B, the contrast CON and the load LOAD to the image processor  300 B. The image analyzer  200  may determine the image of the frame as a normal image or a peak image. 
     The image processor  300 B may control a peak control coefficient applied to W image data to adaptively control peak luminance based on the contrast CON and the load LOAD. The image processor  300 B may receive a sub peak control coefficient S_PCC 2  generated based on a temperature TEMP from the peak controller  850 . The sub peak control coefficient S_PCC 2  may be used to determine the peak control coefficient or the W image data W. In some embodiments, the peak control coefficient may be changed by the sub peak control coefficient S_PCC 2 . For example, the sub peak control coefficient S_PCC 2  may be multiplied to the peak control coefficient to get a corrected peak control coefficient. The image processor  300 B may convert the R, G, and B image data R, B into R′, G′, and B′ image data R′, G′, B′ based on the corrected peak control coefficient which is determined using the sub peak control coefficient S_PCC 2 . In some embodiments, the image processor  300 B may adaptively control the peak luminance based on the contrast CON, the load LOAD, and the temperature TEMP of the display panel  100 . 
     The temperature sensor  800  may detect the temperature TEMP of the display panel  100 . The display device  1000 B may increase the peak luminance to improve the visibility when the temperature TEMP of the display panel  100  is lower than a specific reference. The display device  1000 B may decrease the peak luminance to reduce the deterioration of the mage quality when the temperature TEMP of the display panel  100  is relatively high. The temperature TEMP of the display panel  100  detected by the temperature sensor  800  may be additionally applied to the R, G, and B image data R, G, B to control the peak luminance. 
     The peak controller  850  may determine the sub peak control coefficient S_PCC 2  according to the temperature TEMP. The peak controller  850  may provide the sub peak control coefficient S_PCC 2  to the image processor  300 B. In some embodiments, the peak controller  850  may only be operated when the temperature TEMP is lower than a predetermined reference temperature. The peak controller  850  may decrease the sub peak control coefficient S_PCC 2  at a predetermined interval according to a decrease of the temperature TEMP. In the peak image, the corrected peak control coefficient may decrease according to the decrease of the temperature TEMP. Thus, the peak luminance may increase according to the decrease of the temperature TEMP. In some embodiments, when a temperature of the display panel  100  is higher than the reference temperature, the peak luminance control operations as described above with reference to  FIGS. 1 through 7B  may be performed. 
     The timing controller  400  may control the scan driver  500  and the data driver  600  according to a control signal CLT received from external devices. The scan driver  500  may provide a plurality of scan signals to the display panel  100 . The data driver may convert the R′, G′, B′, and W image data R′, G′, B′, W or the data signal into an analog type data voltage based on a second control signal CLT 2  received from the timing controller  400  and may apply the data voltage to the data lines DL 1  through DLm. 
     As described above, the display device  1000 B may adaptively control the peak luminance based on the contrast CON, the load LOAD, and the temperature TEMP of the display panel  100  every frame. Thus, the visibility, reality and immersion of the image may be improved. Further, the peak luminance may be controlled by an adaptive image data conversion based on the corrected peak control coefficient so that deterioration of the image quality may be reduced. 
       FIG. 12A  is a graph illustrating an example of a sub-peak control coefficient determined by a temperature of a display panel.  FIG. 12B  is a graph illustrating an example of a corrected peak control coefficient determined based on the sub-peak control coefficient of  FIG. 12A . 
     Referring to  FIGS. 11 through 12B , the sub peak control coefficient S_PCC 2  may be changed according to the temperature TEMP of the display panel  100  and the corrected peak control coefficient PCC″ may be changed according to the sub peak control coefficient S_PCC 2 . 
     In some embodiments, the peak controller  850  may be operated when the image of the frame is the peak image. 
     In some embodiments, the sub peak control coefficient S_PCC 2  may be determined to 1 when the temperature TEMP is higher than or equal to a reference temperature TH. In this, the temperature TEMP may not influence on the peak luminance. In some embodiments, the peak controller  850  may not be operated when the temperature TEMP is higher than or equal to the reference temperature TH. 
     As illustrated in  FIG. 12A , the sub peak control coefficient S_PCC 2  may decrease as a step function according to a decrease of the temperature TEMP when the temperature TEMP of the display panel  100  is lower than the reference temperature TH. Thus, as the temperature TEMP decreases, the peak luminance of the image may increase. 
       FIG. 12B  shows changes of relation between the corrected peak control coefficient PCC″ and the contrast CON according to a change of the sub peak control coefficient S_PCC 2 . As illustrated in  FIG. 12B , in the peak image PEAKI having the same contrast CON, as the temperature TEMP decreases, the corrected peak control coefficient PCC″ may decrease and the peak luminance may increases. 
     Accordingly, the peak luminance of the image may be adaptively controlled based on the load, contrast CON, and the temperature TEMP. Thus, the visibility may be improved and the deterioration may be reduced. 
       FIG. 13  is a graph illustrating another example of a sub-peak control coefficient determined by a temperature of a display panel. 
     Referring to  FIG. 13 , the sub peak control coefficient S_PCC 2  may be changed according to the temperature TEMP. 
     In some embodiments, the sub peak control coefficient S_PCC 2  may be additionally multiplied to the peak control coefficient to get a corrected peak control coefficient PCC″. Accordingly, the W image data may be multiplied by the sub peak control coefficient S_PCC 2  and the peak control coefficient to get a corrected peak control coefficient PCC″. 
     In some embodiments, the sub peak control coefficient S_PCC 2  may be determined to 1 when the temperature TEMP is higher than or equal to a reference temperature TH. In this, the temperature TEMP may not influence on the peak luminance. In some embodiments, the peak controller  850  may not be operated when the temperature TEMP is higher than or equal to the reference temperature TH. 
     The sub peak control coefficient S_PCC 2  may linearly decrease according to a decrease of the temperature TEMP when the temperature is lower than the reference temperature TH. Thus, as the temperature TEMP decreases, the peak luminance of the image may increase. However, this is an example, and forms of the decrease of the peak control coefficient S_PCC 2  based on the temperature TEMP are not limited thereto. 
       FIG. 14  is a block diagram of a display device according to example embodiments. 
     The display device of the present example embodiments are substantially the same as the display device explained with reference to  FIGS. 1 through 7B  except for constructions of an image analyzer, a peak controller, and an image processor. Thus, the same reference numerals will be used to refer to the same or like parts as those described in the example embodiments of  FIGS. 1 through 7B , and any repetitive explanation concerning the above elements will be omitted. 
     Referring to  FIG. 14 , the display device  1000 C may include a display panel  100 , an image analyzer  201 , an image processor  300 C, a timing controller  400 , a scan driver  500 , a data driver  600 , and a peak controller  900 . 
     The display panel  100  may include a plurality of pixels P each having a red sub pixel, a green sub pixel, a blue sub pixel, and a white sub pixel. An image displayed on the display panel  100  may have areas having a large difference in saturation (or chroma). For example, an achromatic color image such as a white image, etc may be displayed at a first area A and a primary color image such as a red image, etc may be displayed at a second area B. There is a large difference of the saturation between the first and second areas A and B. Here, when the entire image of the display panel  100  emit light with a high luminance, a color shift may be seen and the visual discomfort may occur. 
     The image analyzer  201  may calculate contrast CON and load LOAD of an image of a frame based on R, G, and B image data R, G, B input corresponding to the frame. The image analyzer  201  may provide the R, G, and B image data R, G, B the contrast CON and the load LOAD to the image processor  300 C. The image analyzer  201  may determine the image of the frame as a normal image or a peak image. 
     In some embodiments, the image analyzer  201  may further calculate a total sum of saturation CSUM of the entire image based on the R, G, and B image data R, G, B when the image of the frame is the peak image. For example, a saturation of a specific pixel may be calculated by Equation 4 and the total sum of saturation CSUM may be calculated by Equation 5. 
     
       
         
           
             
               
                 
                   
                     C 
                     ⁡ 
                     
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                       ⁡ 
                       
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                       min 
                       ⁡ 
                       
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                           B 
                         
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                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   4 
                 
               
             
             
               
                 
                   CSUM 
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                         x 
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                               1 
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                               1 
                             
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                         ( 
                         
                           N 
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                     ⁢ 
                     
                       C 
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                   Equation 
                   ⁢ 
                   
                       
                   
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                   5 
                 
               
             
           
         
       
     
     In Equation 4 and Equation 5, C(x, y) represents a saturation of a pixel corresponding to an (x, y) coordinate of the display panel  100 , max(R, G, B) represents a maximum value among the R, G; and B image data R, B, min(R, G, B) represents a minimum value among the R, G, and B image data R, G, B, and CSUM represents the total sum of saturation. (1, 1) may represent a leftmost and uppermost coordinate of pixel in the display panel  100 , N represents the number of pixel columns, and M represents the number of pixel rows. Referring to Equation 5, as the difference of saturation (or chroma) increases, the total sum of saturation CSUM may increase. 
     The image processor  300 C may control a peak control coefficient applied to W image data to adaptively control peak luminance based on the contrast CON and the load LOAD. The image processor  300 C may receive a sub peak control coefficient S_PCC 3  generated based on the total sum of saturation CSUM from the peak controller  900 . The sub peak control coefficient S_PCC 3  may be applied to the peak control coefficient or the W image data W. In some embodiments, the peak control coefficient may be affected by the sub peak control coefficient S_PCC 3 . For example, the sub peak control coefficient S_PCC 3  may be multiplied to the peak control coefficient to get a corrected peak control coefficient. The image processor  300 C may convert the R, G, and B image data R, G, B into R′, G′, and B′ image data R′, G′, B′ based on the corrected peak control coefficient. In some embodiments, the image processor  300 C may adaptively control the peak luminance based on the contrast CON, the load LOAD, and the total sum of saturation CSUM. 
     The peak controller  900  may compare the total sum of saturation CSUM with a predetermined reference and determine the sub peak control coefficient S_PCC 3 . The sub peak control coefficient S_PCC 3  may be additionally applied to the W image data W. The peak controller  900  may provide the sub peak control coefficient S_PCC 3  to the image processor  300 C. In some embodiments, the peak controller  900  may be operated when the total sum of saturation CSUM is lower than the reference value. The peak controller  900  may decrease the sub peak control coefficient S_PCC 3  at a predetermined interval according to a decrease of the total sum of saturation CSUM. Accordingly, the corrected peak control coefficient may increase according to an increase of total sum of saturation CSUM. Thus, the peak luminance may decrease according to the increase of the total sum of saturation CSUM. Thus, the color shift in the image having a large difference of saturation may be prevented and the visibility may be improved. 
     In some embodiments, the peak controller  900  may be included in the image processor  300 C. 
     In some embodiments, when the total sum of saturation CSUM is greater than or equal to the reference, the peak luminance control operations as described above with reference to  FIGS. 1 through 7B  may be performed. 
     As described above, the display device  1000 C may adaptively control the peak luminance based on the contrast CON, the load LOAD, and the total sum of saturation CSUM of the display panel  100  every frame. Thus, the visibility, reality and immersion of the image may be improved and the color shift in the image having the large difference of saturation may be prevented. Further, the peak luminance may be controlled by an adaptive image data conversion based on the corrected peak control coefficient so that deterioration of the image quality may be reduced. 
       FIG. 15  is a graph illustrating another example of a sub-peak control coefficient determined by saturation of an image. 
     Referring to  FIGS. 14 and 15 , the sub peak control coefficient S_PCC 3  may change based on the total sum of saturation CSUM. 
     In some embodiments, the peak control coefficient S_PCC 3  may be additionally multiplied to the peak control coefficient. Accordingly, the W image data may be multiplied by the sub peak control coefficient S_PCC 3  and the peak control coefficient. 
     In some embodiments, the sub peak control coefficient S_PCC 3  may be determined to 1 when the total sum of saturation CSUM is higher than or equal to a third reference TH. In this, the total sum of saturation CSUM may not influence on the peak luminance. In some embodiments, the peak controller  900  may not operate when the total sum of saturation CSUM is higher than or equal to the third reference TH. 
     As illustrated in  FIG. 15 , the sub peak control coefficient S_PCC 3  may decrease as a step function according to a decrease of the total sum of saturation CSUM when the total sum of saturation CSUM is lower than the third reference TH. In some embodiments, the sub peak control coefficient S_PCC 3  may have a uniform positive real number less than 1 when the total sum of saturation CSUM is lower than the third reference TH. 
     Accordingly, the peak luminance may be adaptively controlled based on the load, the contrast, and the total sum of saturation CSUM. Thus, the visibility may be improved and the deterioration may be reduced. 
       FIG. 16  is a block diagram of a display device according to example embodiments. 
     The display device of the present example embodiments are substantially the same as the display device explained with reference to  FIGS. 1 through 7B  except for constructions of a temperature sensor, a illuminance sensor, a first peak controller, a second peak controller, and an image processor. Thus, the same reference numerals will be used to refer to the same or like parts as those described in the example embodiments of  FIGS. 1 through 13 , and any repetitive explanation concerning the above elements will be omitted. 
     Referring to  FIG. 16 , the display device  1000 D may include a display panel  100 , an image analyzer  200 , an image processor  300 D, a timing controller  400 , a scan driver  500 , a data driver  600 , an illuminance sensor  700 , a first peak controller  750 , a temperature sensor  800 , and a second peak controller  850 . 
     The display panel  100  may include a plurality of pixels P each having a red sub pixel, a green sub pixel, a blue sub pixel, and a white sub pixel. 
     The image analyzer  200  may calculate contrast CON and load LOAD of an image of a frame based on R, G, and B image data R, G, B input corresponding to the frame. The image analyzer  200  may provide the R, G, and B image data R, B, the contrast CON and the load LOAD to the image processor  300 B. The image analyzer  200  may determine the image of the frame as a normal image or a peak image. 
     The image processor  300 D may control a peak control coefficient applied to W image data to adaptively control peak luminance based on the contrast CON and the load LOAD. The image processor  300 D may receive a first sub peak control coefficient S_PCC 1  generated based on an ambient light IL from the first peak controller  750 . The image processor  300 D may receive a second sub peak control coefficient S_PCC 2  generated based on a temperature TEMP from the second peak controller  850 . The image processor  300 D may adaptively control the peak luminance based on the contrast CON, the load LOAD, the ambient light IL, and the temperature TEMP of the display panel  100 . 
     The first peak controller  750  may determine the first sub peak control coefficient S_PCC 1  based on the ambient light IL. The first peak controller  750  may provide the first sub peak control coefficient S_PCC 1  to the image processor  300 D. The second peak controller  850  may determine the second sub peak control coefficient S_PCC 2  based on the temperature TEMP. The second peak controller  850  may provide the second sub peak control coefficient S_PCC 2  to the image processor  300 D. 
     In some embodiments, the first sub peak control coefficient S_PCC 1  and the second sub peak control coefficient S_PCC 2  may be additionally multiplied to the peak control coefficient to get a corrected peak control coefficient. Accordingly, the W image data may be multiplied by the first and second sub peak control coefficients S_PCC 1  and S_PCC 2  and the peak control coefficient to get a corrected peak control coefficient. 
     Since the illuminance sensor  700  and the first peak controller  750  are described above referred to  FIGS. 8 through 10  and the temperature sensor  800  and the second peak controller  850  are described above referred to  FIGS. 11 through 13 , duplicate descriptions will not be repeated. 
     As described above, the display device  1000 D may adaptively control the peak luminance based on the contrast CON, the load LOAD, the ambient light IL, and the temperature TEMP every frame. Thus, the visibility, reality and immersion of the image may be improved. Further, the peak luminance may be controlled by an adaptive image data conversion based on the corrected peak control coefficient so that deterioration of the image quality may be reduced. 
       FIG. 17  is a flow chart of a method for controlling peak luminance of a display device according to example embodiments. 
     Referring to  FIG. 17 , the method for controlling peak luminance of the display device may include calculating contrast and load of an image of a frame based on R, G, and B image data input corresponding to the frame S 100 , determining a peak control coefficient for adaptively controlling peak luminance based on the contrast and the load S 200 , generating W image data based on a minimum value among grayscales of the R, G, and B image data S 300 , generating R′, G′, and B′ image data by subtracting a product of the W image data and the peak control coefficient from the R, G, and B image data, respectively S 400 , and generating a data signal based on the R′, G′, B′, and W image data S 500 . 
     In some embodiments, the peak luminance increases when the peak control coefficient decreases. The peak luminance may be adaptively controlled based on at least one of an ambient light surrounding the display panel, a temperature of the display panel, and a total sum of saturation of the image of the frame. 
     Since the methods for controlling peak luminance of the display device are described above referred to  FIGS. 1 through 16 , duplicate descriptions will not be repeated. 
       FIG. 18  is a flow chart illustrating an example of determining a peak control coefficient of the method of  FIG. 17 . 
     Referring to  FIG. 18 , determining the peak control coefficient S 200  may include comparing the contrast with a predetermined first reference and comparing the load with a predetermined second reference S 220 , and determining the peak control coefficient S 240  and S 260 . 
     In some embodiments, the image of the frame may be determined as a peak image which requires an increase of the peak luminance when the contrast is greater than the first reference and the load is less than the second reference S 230 . The peak control coefficient may be determined to a real number within a range greater than or equal to 0 and less than 1 based on the contrast when the image of the frame is the peak image S 240 . 
     In some embodiments, the image of the frame may be determined as a normal image when at least one situation that the contrast is less than the first reference and the load is greater than the second reference S 250 . The peak control coefficient may be determined to 1 when the image of the frame is the normal image S 260 . 
     Since the methods for controlling peak luminance of the display device are described above referred to  FIGS. 1 through 16 , duplicate descriptions will not be repeated. 
     Accordingly, the method for controlling peak luminance of the display device may adaptively control the peak luminance of the image based on the contrast, the load, and so on, every frame. Thus, the visibility, reality and immersion of the image may be improved. Further, the peak luminance may be controlled by an adaptive image data conversion based on the peak control coefficient so that deterioration of the image quality may be reduced. 
       FIG. 19  is a block diagram of an electronic device according to example embodiments.  FIG. 20A  is a diagram illustrating an example of the electronic device of  FIG. 19  implemented as a television.  FIG. 20B  is a diagram illustrating an example of the electronic device of  FIG. 19  implemented as a smart phone. 
     Referring to  FIGS. 19 through 20B , the electronic device  10000  may include a processor  1010 , a memory device  1020 , a storage device  1030 , an input/output (I/O) device  1040 , a power supply  1050 , and a display device  1060 . Here, the display device  1060  may correspond to one of the display devices of  FIGS. 1 through 16 . In addition, the electronic device  10000  may further include a plurality of ports for communicating with a video card, a sound card, a memory card, a universal serial bus (USB) device, other suitable electronic devices, etc. In one embodiment, as illustrated in  FIG. 20A , the electronic device  10000  may be implemented in a television. In one embodiment, as illustrated in  FIG. 20B , the electronic device  10000  may be implemented in a smart phone. However, these are examples and the electronic device  10000  is not limited thereto. For example, the electronic device  10000  may be implemented in a cellular phone, a video phone, a smart pad, a smart watch, a tablet, a personal computer, a navigation for vehicle, a monitor, a notebook, a head mounted display (HMD), and/or the like. 
     The processor  1010  may perform various suitable computing functions. The processor  1010  may be a microprocessor, a central processing unit (CPU), etc. The processor  1010  may be coupled to other suitable components via an address bus, a control bus, a data bus, etc. Furthermore, the processor  1010  may be coupled to an extended bus such as a peripheral component interconnection (PCI) bus. 
     The memory device  1020  may also store data for operations of the electronic device  10000 . For example, the memory device  1020  may include at least one non-volatile memory device, such as an erasable programmable read-only memory (EPROM) device, an electrically erasable programmable read-only memory (EEPROM) device, a flash memory device, a phase change random access memory (PRAM) device, a resistance random access memory (RRAM) device, a nano floating gate memory (NFGM) device, a polymer random access memory (PoRAM) device, a magnetic random access memory (MRAM) device, a ferroelectric random access memory (FRAM) device, etc., and/or at least one volatile memory device, such as a dynamic random access memory (DRAM) device, a static random access memory (SRAM) device, a mobile DRAM device, and/or the like. 
     The storage device  1030  may store data for operations of the electronic device  10000 . The storage device  1030  may be a solid state drive (SSD) device, a hard disk drive (HDD) device, a CD-ROM device, and/or the like. 
     The I/O device  1040  may be an input device, such as a keyboard, a keypad, a touchpad, a touch-screen, a mouse, and/or the like, and an output device, such as a printer, a speaker, and/or the like. 
     The power supply  1050  may provide power for operating the electronic device  1000 . 
     The display device  1060  may be connected to other elements via the buses or other communication links. According to some example embodiments, the display device  1060  may be included in the I/O device  1040 . As described above, the display device  1060  may adaptively control peak luminance of every frame based on a contrast and a load of an image of the frame. The display device may include an image analyzer configured to calculate the contrast and the load of the image of the frame based on R, G, and B image data input corresponding to the frame, an image processor configured to control a peak control coefficient applied to W image data to adaptively control peak luminance based on the contrast and the load, and to respectively generate R′, G′, and B′ image data by subtracting a product of the W image data and the peak control coefficient from each of the R, G, and B image data, a display panel including a plurality of pixels, a data driver configured to generate a data signal based on the R′, G′, B, and W image data, and to provide the data signal to the display panel, and a scan driver configured to provide a scan signal to the display panel. 
     As described above, in the electronic device  10000  including the display device  1060 , the visibility, reality and immersion of the image may be improved. 
     The present embodiments may be applied to any display device and any system including the display device having white sub pixels. For example, the present embodiments may be applied to a television, a computer monitor, a laptop, a digital camera, a cellular phone, a smart phone, a smart pad, a personal digital assistant (PDA), a portable multimedia player (PMP), a MP3 player, a navigation system, a game console, a video phone, etc. 
     The foregoing is illustrative of example embodiments, and is not to be construed as limiting thereof. Although a few example embodiments have been described, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the novel teachings and advantages of example embodiments. Accordingly, all such modifications are intended to be included within the scope of example embodiments as defined in the claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Therefore, it is to be understood that the foregoing is illustrative of example embodiments and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed example embodiments, as well as other example embodiments, are intended to be included within the scope of the appended claims. The inventive concept is defined by the following claims, with equivalents of the claims to be included therein.