Patent Publication Number: US-2023162643-A1

Title: Display device

Description:
This application claims priority to Korean Patent Application No. 10-2021-0160241, filed on Nov. 19, 2021, and all the benefits accruing therefrom under 35 U.S.C. § 119, the content of which in its entirety is herein incorporated by reference. 
     BACKGROUND 
     1. Field 
     Embodiments of the invention relate to a display device. More particularly, embodiments of the invention relate to a display device adjusting luminance of a displayed image. 
     2. Description of the Related Art 
     Generally, a display device may include a display panel and a display panel driver. The display panel driver may include a driving controller, gate driver, and a data driver. The display panel may include a plurality of gate lines, a plurality of data lines, and a plurality of pixels electrically connected to the gate lines and the data lines. The gate driver may provide gate signals to the gate lines. The data driver may provide data voltages to the data lines. The driving controller may control the gate driver and the data driver. 
     SUMMARY 
     A conventional display device adjusts luminance of a displayed image by adjusting a grayscale value of input image data according to an average image load (In other word, an average picture level; APL) of the input image data in order to reduce power consumption. Therefore, since the grayscale value is adjusted based on only the average image load, the conventional display device does not reflect an effect of other factors (e.g., a temperature of the display panel, etc.) in adjusting the grayscale of the input image data. 
     Embodiments of the invention provide a display device determining an operation mode for adjusting luminance of a displayed image according to a grayscale value of input image data. 
     Embodiments of the invention also provide determining an operation mode for adjusting luminance of a displayed image according to a temperature of a display panel. 
     In an embodiment of the invention, a display device includes a display panel including a plurality of pixels, and a display panel driver which determines an average image load of input image data, to determine an operation mode based on a grayscale value of the input image data and the average image load as a first operation mode or a second operation mode, applies a first scale factor to the input image data in the first operation mode, applies a second scale factor different from the first scale factor to the input image data in the second operation mode, and drives the display panel. 
     In an embodiment, the display panel driver may operate as the first operation mode when a number of pixels which display the grayscale value less than or equal to a first reference grayscale value, among the plurality of pixels, is greater than a first reference number and the average image load is less than or equal to a first reference load. 
     In an embodiment, the display panel driver may generate a histogram for the grayscale value of the input image data, and calculate the number of the pixels which display the grayscale value less than or equal to the first reference grayscale value based on the histogram. 
     In an embodiment, the display panel driver may determine a first load scale factor according to the average image load in the first operation mode, determine a first grayscale scale factor according to the grayscale value of the input image data in the first operation mode, determine the first scale factor based on the first load scale factor and the first grayscale scale factor, determine a second load scale factor according to the average image load in the second operation mode, determine a second grayscale scale factor according to the grayscale value of the input image data in the second operation mode, and determine the second scale factor based on the second load scale factor and the second grayscale scale factor. 
     In an embodiment, the first scale factor may decrease as the average image load increases in a period in which the average image load is greater than or equal to a second reference load, and may have a first reference value in a period in which the average image load is less than the second reference load. 
     In an embodiment, the second scale factor may decrease as the average image load increases in a period in which the average image load is greater than or equal to a first reference load greater than the second reference load, and may have a second reference value less than the first reference value in a period in which the average image load is less than the first reference load. 
     In an embodiment, the first scale factor may decrease as a number of pixels which display the grayscale value less than or equal to a first reference grayscale value, among the plurality of pixels, decreases in a period in which the number of the pixels which display the grayscale value less than or equal to the first reference grayscale value is less than or equal to a second reference number, and may have a first reference value in a period in which the number of the pixels which display the grayscale value less than or equal to the first reference grayscale value is greater than the second reference number. The second scale factor may decrease as the number of the pixels which display the grayscale value less than or equal to the first reference grayscale value decreases in a period in which the number of the pixels which display the grayscale value less than or equal to the first reference grayscale value is less than or equal to a first reference number less than the second reference number, and may have a second reference value less than the first reference value in a period in which the number of the pixels which display the grayscale value less than or equal to the first reference grayscale value is greater than the first reference number. 
     In an embodiment, the display device may operate as the first operation mode when a number of pixels which display the grayscale value less than or equal to a first reference grayscale value, among the plurality of pixels, is greater than a first reference number and an temperature of the display panel is lower than or equal to a first reference temperature. 
     In an embodiment, the display panel driver may determine a first load scale factor according to the average image load in the first operation mode, determine a first grayscale scale factor according to the grayscale value of the input image data in the first operation mode, determine a first temperature scale factor according to the temperature of the display panel in the first operation mode, to determine the first scale factor based on the first load scale factor, the first grayscale scale factor, and the first temperature scale factor, determine a second load scale factor according to the average image load in the second operation mode, determine a second grayscale scale factor according to the grayscale value of the input image data in the second operation mode, determine a second temperature scale factor according to the temperature of the display panel in the second operation mode, and determine the second scale factor based on the second load scale factor, the second grayscale scale factor, and the second temperature scale factor. 
     In an embodiment, the display panel driver may apply the second scale factor to the pixels in which a deterioration degree of the pixels is greater than a reference deterioration degree among the plurality of pixels. 
     In an embodiment, the display panel driver may increase the grayscale value of the input image data to which the first scale factor or the second scale factor is applied when the grayscale value of the input image data to which the first scale factor or the second scale factor is applied is greater than a second reference grayscale value. 
     In an embodiment, the display panel may be divided into panel blocks, the panel blocks may include a first panel block and a second panel block adjacent to the first panel block, and the display panel driver may increase the grayscale value of the input image data corresponding to the first panel block to which the first scale factor or the second scale factor is applied when an average image load of the first panel block is greater than a sum of an average image load of the second panel block and a third reference value. 
     In an embodiment of the invention, a display device includes a display panel including pixels, and a display panel driver which determines an average image load of input image data, determines an operation mode based on a temperature of the display panel and the average image load as a first operation mode or a second operation mode, applies a first scale factor to the input image data in the first operation mode, applies a second scale factor different from the first scale factor to the input image data in the second operation mode, and drives the display panel. 
     In an embodiment, the display panel driver may operate as the first operation mode when the temperature of the display panel is lower than or equal to a first reference temperature and the average image load is less than or equal to a first reference load. 
     In an embodiment, the display panel driver may determine a first load scale factor according to the average image load in the first operation mode, determine a first temperature scale factor according to the temperature of the display panel in the first operation mode, determine the first scale factor based on the first load scale factor and the first temperature scale factor, determine a second load scale factor according to the average image load in the second operation mode, determine a second temperature scale factor according to the temperature of the display panel in the second operation mode, and determine the second scale factor based on the second load scale factor and the second temperature scale factor. 
     In an embodiment, the first scale factor may decrease as the average image load increases in a period in which the average image load is greater than or equal to a second reference load, and may have a first reference value in a period in which the average image load is less than the second reference load. The second scale factor may decrease as the average image load increases in a period in which the average image load is greater than or equal to a first reference load greater than the second reference load, and may have a second reference value less than the first reference value in a period in which the average image load is less than the first reference load. 
     In an embodiment, the first scale factor may decrease as the temperature of the display panel increases in a period in which the temperature of the display panel is higher than or equal to a second reference temperature, and may have a first reference value in a period in which the temperature of the display panel is lower than the second reference temperature. The second scale factor may decrease as the temperature of the display panel increases in a period in which the temperature of the display panel is higher than a first reference temperature higher than the second reference temperature, and may have a second reference value less than the first reference value in a period in which the temperature of the display panel is lower than the first reference temperature. 
     In an embodiment, the display panel driver may determine the temperature of the display panel by accumulating the input image data. 
     In an embodiment, the display panel driver may determine the temperature of the display panel by sensing driving currents of the pixels. 
     In an embodiment of the invention a display device includes a display panel including pixels, and a display panel driver which determines an operation mode based on a temperature of the display panel and a grayscale value of input image data as a first operation mode or a second operation mode, applies a first scale factor to the input image data in the first operation mode, applies a second scale factor different from the first scale factor to the input image data in the second operation mode, and drives the display panel. 
     Therefore, even when an average image load of input image data is small, the display device may adjust luminance of a displayed image to be low when a number of the pixels displaying a low grayscale value is small by determining the average image load of the input image data, determining an operation mode based on a grayscale value of an input image data and the average image load as a first operation mode or a second operation mode, applying a first scale factor to the input image data in the first operation mode, and applying a second scale factor different from the first scale factor to the input image data in the second operation mode. So, the display device may reduce power consumption. 
     In addition, even when an average image load of input image data is small, the display device may adjust luminance of a displayed image to be low when a temperature of a display panel is high by determining an average image load of input image data, determining an operation mode based on a temperature of the display panel and the average image load as a first operation mode or a second operation mode, applying a first scale factor to the input image data in the first operation mode, and applying a second scale factor different from the first scale factor to the input image data in the second operation mode. 
     Further, even when an average image load of input image data is small, the display device may adjust luminance of a displayed image to be low when a temperature of a display panel is high and a number of the pixels displaying a low grayscale value is small by determining an operation mode based on a temperature of the display panel and a grayscale value of input image data as a first operation mode or a second operation mode, applying a first scale factor to the input image data in the first operation mode, and applying a second scale factor different from the first scale factor to the input image data in the second operation mode. 
     However, the effects of the invention are not limited to the above-described effects, and may be variously expanded without departing from the spirit and scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other exemplary embodiments, advantages and features of this disclosure will become more apparent by describing in further detail exemplary embodiments thereof with reference to the accompanying drawings, in which: 
         FIG.  1    is a block diagram illustrating a display device according to the invention. 
         FIG.  2    is a block diagram illustrating an embodiment of a driving controller of the display device of  FIG.  1   . 
         FIG.  3    is a diagram illustrating an embodiment of a histogram generated according to the display device of  FIG.  1   . 
         FIG.  4    is a graph illustrating an embodiment of a first scale factor of the display device of  FIG.  1   . 
         FIG.  5    is a graph illustrating an embodiment of a second scale factor of the display device of  FIG.  1   . 
         FIG.  6    is a graph illustrating an embodiment of a first scale factor of a display device according to the invention. 
         FIG.  7    is a graph illustrating an embodiment of a second scale factor of the display device of  FIG.  6   . 
         FIG.  8    is a diagram illustrating an embodiment in which a display device according to the invention determines a first scale factor and a second scale factor. 
         FIG.  9    is a block diagram illustrating an embodiment of a driving controller of a display device according to the invention. 
         FIG.  10    is a block diagram illustrating an embodiment of a driving controller of a display device according to the invention. 
         FIG.  11    is a block diagram illustrating an embodiment of a driving controller of a display device according to the invention. 
         FIG.  12    is a diagram illustrating an embodiment of a temperature of a display panel. 
         FIG.  13    is a graph illustrating an embodiment of a first scale factor of a display device according to the invention. 
         FIG.  14    is a graph illustrating an embodiment of a second scale factor of the display device of  FIG.  13   . 
         FIG.  15    is a diagram illustrating an embodiment in which a display device according to the invention determines a first scale factor and a second scale factor. 
         FIG.  16    is a block diagram illustrating an embodiment of a driving controller of a display device according to the invention. 
         FIG.  17    is a block diagram illustrating an embodiment of a driving controller of a display device according to the invention. 
         FIG.  18    is a block diagram illustrating an embodiment of a driving controller of a display device according to the invention. 
         FIG.  19    is a block diagram illustrating an embodiment of a driving controller of a display device according to the invention. 
         FIG.  20    is a diagram illustrating an embodiment in which a display device according to the invention determines a first scale factor and a second scale factor. 
         FIG.  21    is a diagram illustrating an embodiment in which a display device adjusts a grayscale value according to the invention. 
         FIG.  22    is a diagram illustrating an embodiment of a display panel of a display device according to the invention. 
         FIG.  23    is a diagram illustrating an embodiment in which the display device of  FIG.  22    adjusts a grayscale value. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, the invention will be explained in detail with reference to the accompanying drawings. 
     It will be understood that when an element is referred to as being “on” another element, it can be directly on the other element or intervening elements may be therebetween. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. 
     It will be understood that, although the terms “first,” “second,” “third” etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, “a first element,” “component,” “region,” “layer” or “section” discussed below could be termed a second element, component, region, layer or section without departing from the teachings herein. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms, including “at least one,” unless the content clearly indicates otherwise. “Or” means “and/or.” As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. 
     Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe one element&#39;s relationship to another element as illustrated in the Figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. In an embodiment, when the device in one of the figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The exemplary term “lower,” can therefore, encompasses both an orientation of “lower” and “upper,” depending on the particular orientation of the figure. Similarly, when the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below. 
     “About” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). The term “about” can mean within one or more standard deviations, or within ±30%, 20%, 10%, 5% of the stated value, for example. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the invention, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
       FIG.  1    is a block diagram illustrating a display device  1000  according to the invention. 
     Referring to  FIG.  1   , the display device  1000  may include a display panel  100  and a display panel driver  10 . The display panel driver  10  may include a driving controller  201 , a gate driver  300 , and a data driver  400 . In an embodiment, the driving controller  201  and the data driver  400  may be integrated into one chip. 
     The display panel  100  has a display region AA on which an image is displayed and a peripheral region PA adjacent to the display region AA. In an embodiment, the gate driver  300  may be integrated on the peripheral region PA of the display panel  100 . 
     The display panel  100  may include a plurality of gate lines GL, a plurality of data lines DL, and a plurality of pixels P electrically connected to the data lines DL and the gate lines GL. The gate lines GL may extend in a first direction D 1  and the data lines DL may extend in a second direction D 2  crossing the first direction D 1 . 
     The driving controller  201  may receive input image data IMG and an input control signal CONT from a host processor (e.g., a graphic processing unit (“GPU”)). In an embodiment, the input image data IMG may include red image data, green image data and blue image data, for example. In an embodiment, the input image data IMG may further include white image data. For another example, the input image data IMG may include magenta image data, yellow image data, and cyan image data. The input control signal CONT may include a master clock signal and a data enable signal. The input control signal CONT may further include a vertical synchronizing signal and a horizontal synchronizing signal. 
     The driving controller  201  may generate a first control signal CONT 1 , a second control signal CONT 2 , and output image data OIMG based on the input image data IMG and the input control signal CONT. 
     The driving controller  201  may generate the first control signal CONT 1  for controlling operation of the gate driver  300  based on the input control signal CONT and output the first control signal CONT 1  to the gate driver  300 . The first control signal CONT 1  may include a vertical start signal and a gate clock signal. 
     The driving controller  201  may generate the second control signal CONT 2  for controlling operation of the data driver  400  based on the input control signal CONT and output the second control signal CONT 2  to the data driver  400 . The second control signal CONT 2  may include a horizontal start signal and a load signal. 
     The driving controller  201  may receive the input image data IMG and the input control signal CONT, and generate the output image data OIMG. The driving controller  201  may output the output image data OIMG to the data driver  400 . 
     The gate driver  300  may generate gate signals for driving the gate lines GL in response to the first control signal CONT 1  input from the driving controller  201 . The gate driver  300  may output the gate signals to the gate lines GL. In an embodiment, the gate driver  300  may sequentially output the gate signals to the gate lines GL, for example. 
     The data driver  400  may receive the second control signal CONT 2  and the output image data OIMG from the driving controller  201 . The data driver  400  may convert the output image data OIMG into data voltages having an analog type. The data driver  400  may output the data voltage to the data lines DL. 
       FIG.  2    is a block diagram illustrating an embodiment of a driving controller  201  of the display device  1000  of  FIG.  1   ,  FIG.  3    is a diagram illustrating an embodiment of a histogram generated according to the display device  1000  of  FIG.  1   ,  FIG.  4    is a graph illustrating an embodiment of a first scale factor SF 1  of the display device  1000  of  FIG.  1   , and  FIG.  5    is a graph illustrating an embodiment of a second scale factor SF 2  of the display device  1000  of  FIG.  1   . 
     Referring to  FIGS.  1  to  5   , the display panel driver  10  may determine an average image load APL of the input image data IMG, determine an operation mode based on a grayscale value of the input image data IMG and the average image load APL as a first operation mode M 1  or a second operation mode M 2 , apply the first scale factor SF 1  to the input image data IMG in the first operation mode M 1 , and apply a second scale factor SF 2  different from the first scale factor SF 1  to the input image data IMG in the second operation mode M 2 . 
     In an embodiment, the display panel driver  10  may adjust the grayscale value of the input image data IMG by applying the first scale factor SF 1  or the second scale factor SF 2  to the input image data IMG, for example. Accordingly, luminance of a displayed image may be adjusted. A detailed description thereof will be given later. 
     The driving controller  201  may include an average image load determiner  210 , an operation mode determiner  221 , a scale factor determiner  230 , and a luminance controller  240 . In an embodiment, the driving controller  201  may further include a histogram generator  250 . 
     The average image load determiner  210  may receive the input image data IMG and determine the average image load APL of the input image data IMG. In an embodiment, the average image load determiner  210  may convert the input image data IMG of a RGB domain into the input image data of a luminance domain, and determine the average image load APL by dividing a sum of luminance of the input image data IMG of the luminance domain (i.e., the sum of luminance to be displayed in all pixels P) by the number of the pixels P, for example. 
     The average image load APL may be normalized to have a value ranging from 0% to 100%. In an embodiment, when the input image data IMG is a full white image, the average image load APL may be 100%, for example. In an embodiment, when the input image data IMG is a full black image, the average image load APL may be 0%, for example. 
     The operation mode determiner  221  may determine the operation mode as the first operation mode M 1  or the second operation mode M 2  based on the gray scale value of the input image data IMG and the average image load APL. The display panel driver  10  may operate in the second operation mode M 2  when the display panel driver  10  does not operate in the first operation mode M 1 , and operate in the first operation mode M 1  when the display panel driver  10  does not operate in the second operation mode M 2 . In an embodiment, the display panel driver  10  may operate as the first operation mode M 1  when the number NG of the pixels P displaying the grayscale value less than or equal to a first reference grayscale value RG 1  is greater than a first reference number RN 1  and the average image load APL is less than or equal to a first reference load RL 1 . In an embodiment, the display panel driver  10  may operate as the first operation mode M 1  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the first reference number RN 1  and the average image load APL is less than or equal to the first reference load RL 1 , operate as the second operation mode M 2  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is less than or equal to the first reference number RN 1  and the average image load APL is less than or equal to the first reference load RL 1 , operate as the second operation mode M 2  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the first reference number RN 1  and the average image load APL is greater than the first reference load RL 1 , and operate as the second operation mode M 2  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is less than or equal to the first reference number RN 1  and the average image load APL is greater than the first reference load RL 1 , for example. In an embodiment, the operation mode determiner  221  may output an operation mode signal MS including information on the operation mode to the scale factor determiner  230 , for example. The first reference grayscale value RG 1 , the first reference number RN 1 , and the first reference load RL 1  may be values set by a user. 
     The display panel driver  10  may generate the histogram for the grayscale value of the input image data IMG, and calculate the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  based on the histogram. 
     In an embodiment, the histogram generator  250  may receive the input image data IMG and generate the histogram for the grayscale value of the input image data IMG, for example. The histogram generator  250  may use the histogram to calculate the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1 . The operation mode determiner  221  may receive the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  from the histogram generator  250 . The operation mode determiner  221  may receive the average image load APL from the average image load determiner  210 . The operation mode determiner  221  may determine the operation mode based on the average image load APL and the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1 . 
     In an embodiment, referring to  FIG.  3   , the histogram generator  250  may divide the grayscale values of the input image data IMG into 16 sections, and generate the histogram representing the number of the pixels P displaying the grayscale value of each of sections, for example. It is assumed that sections including the grayscale value less than or equal to the first reference grayscale value RG 1  are section  0  and section  1 , and the first reference number RN 1  is 20000. Referring to a first example (CASE  1 ), the number of the pixels P displaying the grayscale value of the section  0  is 2000, and the number of the pixels P displaying the grayscale value in the section  1  is 10000. That is, in the first example (CASE  1 ), the number (N(0,1)) of the pixels P displaying the grayscale value of the section  0  and the section  1  is 12000. Accordingly, the number (N(0,1)) of the pixels P displaying the grayscale value of section  0  and section  1  is less than the first reference number RN 1 . Referring to a second example (CASE  2 ), the number of the pixels P displaying the grayscale value of the section  0  is 25000, and the number of the pixels P displaying the grayscale value of the section  1  is 25000. That is, in the second example (CASE 1 ), the number (N(0,1)) of the pixels P displaying the grayscale value of the section  0  and the section  1  is 50000. Accordingly, the number (N(0,1)) of the pixels P displaying the grayscale value of the section  0  and the section  1  is greater than the first reference number RN 1 . 
     The scale factor determiner  230  may operate in the first operation mode M 1  or the second operation mode M 2  in response to the operation mode signal MS. When operating in the first operation mode M 1 , the scale factor determiner  230  may generate the first scale factor SF 1 . When operating in the second operation mode M 2 , the scale factor determiner  230  may generate the second scale factor SF 2 . 
     The luminance controller  240  may apply the first scale factor SF 1  to the input image data IMG in the first operation mode M 1 , and apply the second scale factor SF 2  to the input image data IMG in the second operation mode M 2 . The luminance controller  240  may adjust the grayscale value of the input image data IMG by applying first and second scale factors SF 1  and SF 2  to the input image data IMG. That is, the luminance controller  240  may adjust the grayscale value of the input image data IMG so that luminance of the displayed image is adjusted by the first and second scale factors SF 1  and SF 2 . In an embodiment, the luminance controller  240  may adjust the grayscale value of the input image data IMG so that a peak luminance of the displayed image is adjusted by the first and second scale factors SF 1  and SF 2 . 
     The first and second scale factors SF 1  and SF 2  may have values between 0 and 1. Accordingly, the luminance controller  240  may lower the luminance of the displayed image by applying the first and second scale factors SF 1  and SF 2  to the input image data IMG. 
     In an embodiment, it is assumed that the luminance of the image is 1000 nit when displaying the image of 255 grayscale value, and the luminance of the image is 500 nit when displaying the image of 155 grayscale value 155G, for example. When the first scale factor SF 1  or the second scale factor SF 2  of 1 is applied to the input image data IMG of the 255 grayscale value, the luminance controller  240  may adjust the grayscale value of the input image data IMG so that the luminance of the image displayed by the input image data IMG of 255 grayscale value becomes 1000×1=1000 nit. Accordingly, the grayscale value of the input image data IMG′ to which the first scale factor SF 1  or the second scale factor SF 2  is applied may be 255 grayscale value. 
     In an embodiment, it is assumed that the luminance of the image is 1000 nit when displaying the image of 255 grayscale value, and the luminance of the image is 500 nit when displaying the image of 155 grayscale value, for example. When the first scale factor SF 1  of 0.5 or the second scale factor SF 2  of 0.5 is applied to the input image data IMG of the 255 grayscale value, the luminance controller  240  may adjust the grayscale value of the input image data IMG so that the luminance of the image displayed by the input image data IMG of 255 grayscale value becomes 1000×0.5=500 nit. Accordingly, the grayscale value of the input image data IMG′ to which the first scale factor SF 1  or the second scale factor SF 2  is applied may be 155 grayscale value 155G. As such, when the scale factor SF 1  or the second scale factor SF 2  less than 1 is applied to the input image data IMG, the luminance of the displayed image may be lowered. 
     The first scale factor SF 1  may decrease as the average image load APL increases in a period in which the average image load APL is greater than or equal to a second reference load RL 2 , and may have a first reference value RV 1  in a period in which the average image load APL is less than the second reference load RL 2 . 
     In an embodiment, as shown in  FIG.  4   , it is assumed that the first reference value RV 1  is 1, a second reference value RV 2  is 0.4, and a minimum value of the first scale factor SF 1  is 0.2, for example. The first scale factor SF 1  may decrease from 1 to 0.2 when the average image load APL is greater than or equal to the second reference load RL 2 . The first scale factor SF 1  may be 1 when the average image load APL is less than the second reference load RL 2 . 
     The second scale factor SF 2  may decrease as the average image load APL increases in a period in which the average image load APL is greater than or equal to the first reference load RL 1  greater than the second reference load RL 2 , and may have the second reference value RV 2  less than the first reference value RV 1  in a period in which the average image load APL is less than the first reference load RL 1 . 
     In an embodiment, as shown in  FIG.  5   , it is assumed that the first reference value RV 1  is 1, the second reference value RV 2  is 0.4, and a minimum value of the second scale factor SF 2  is 0.2, for example. The second scale factor SF 2  may decrease from 0.4 to 0.2 when the average image load APL is greater than or equal to the first reference load RL 1 . The second scale factor SF 2  may be 0.4 when the average image load APL is less than the second reference load RL 2 . 
     That is, in the second operation mode M 2 , the display panel driver  10  may adjust the luminance of the image displayed in a period in which the average image load APL is small (e.g., the average image load APL is less than or equal to the first reference load RL 1 ) to be lower than that of the first operation mode M 1 . 
     As a result, even when the average image load APL is small, the display device  1000  may adjust the luminance of the image displayed through the second operation mode M 2  to be low when the number of the pixels P displaying a low grayscale value (e.g., the grayscale value less than or equal to the first reference grayscale value RG 1 ) is small (e.g., the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is less than or equal to the first reference number RN 1 ). Also, even when the number of the pixels P displaying the low grayscale value is large (e.g., the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the first reference number RN 1 ), the display device  1000  may adjust the luminance of the image displayed through the second operation mode M 2  to be low when the average image load APL is large (e.g., the average image load APL is greater than the first reference load RL 1 ). 
       FIG.  6    is a graph illustrating an embodiment of the first scale factor SF 1  of a display device according to the invention, and  FIG.  7    is a graph illustrating an embodiment of the second scale factor SF 2  of the display device of  FIG.  6   . In  FIGS.  6  and  7   , it is assumed that the number of all pixels P is 1024. 
     The display apparatus according to the illustrated embodiment is substantially the same as the display apparatus  1000  of  FIG.  1    except for determining the first and second scale factors SF 1  and SF 2 . Thus, the same reference numerals are used to refer to the same or similar element, and any repetitive explanation will be omitted. 
     Referring to  FIGS.  6  and  7   , the first scale factor SF 1  may decrease as the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  decreases in a period in which the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is less than or equal to a second reference number RN 2 , and may have the first reference value RV 1  in a period in which the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the second reference number RN 2 . The second reference number RN 2  may be a value set by a user. 
     In an embodiment, as shown in  FIG.  6   , it is assumed that the first reference value RV 1  is 1, the second reference value RV 2  is 0.4, and a minimum value of the first scale factor SF 1  is 0.2, for example. The first scale factor SF 1  may decrease from 1 to 0.2 when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is less than or equal to the second reference number RN 2 . The first scale factor SF 1  may be 1 when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the second reference number RN 2 . 
     The second scale factor SF 2  may decrease as the number of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  decreases in a period in which the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is less than or equal to the first reference number RN 1  less than the second reference number RN 2 , and may have the second reference value RV 2  less than the first reference value RV 1  in a period in which the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the first reference number RN 1 . 
     In an embodiment, as shown in  FIG.  7   , it is assumed that the first reference value RV 1  is 1, the second reference value RV 2  is 0.4, and a minimum value of the second scale factor SF 2  is 0.2, for example. The second scale factor SF 2  may decrease from 0.4 to 0.2 when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is less than or equal to the first reference number RN 1 . The second scale factor SF 2  may be 0.4 when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the second reference number RN 2 . 
       FIG.  8    is a diagram illustrating an embodiment in which a display device according to the invention determines the first scale factor SF 1  and the second scale factor SF 2 . 
     The display apparatus according to the illustrated embodiment is substantially the same as the display apparatus  1000  of  FIG.  1    except for determining the first and second scale factors SF 1  and SF 2 . Thus, the same reference numerals are used to refer to the same or similar element, and any repetitive explanation will be omitted. 
     Referring to  FIGS.  1  and  8   , the display panel driver  10  may determine a first load scale factor LSF 1  according to the average image load APL in the first operation mode M 1 , determine a first grayscale scale factor NSF 1  according to the grayscale value of the input image data IMG in the first operation mode M 1 , and determine the first scale factor SF 1  based on the first load scale factor LSF 1  and the first grayscale scale factor NSF 1 . 
     In an embodiment, the first load scale factor LSF 1  may be determined in the same manner as in  FIG.  4   , and the first grayscale scale factor NSF 1  may be determined in the same manner as in  FIG.  6   , for example. In an embodiment, the display panel driver  10  may determine an average value of the first load scale factor LSF 1  and the first grayscale scale factor NSF 1  as the first scale factor SF 1 . In an embodiment, the display panel driver  10  may determine a minimum value of the first load scale factor LSF 1  and the first grayscale scale factor NSF 1  as the first scale factor SF 1 . 
     The display panel driver  10  may determine a second load scale factor LSF 2  according to the average image load APL in the second operation mode M 2 , determine a second grayscale scale factor NSF 2  according to the grayscale value of the input image data IMG in the second operation mode M 2 , and determine the second scale factor SF 2  based on the second load scale factor LSF 2  and the second grayscale scale factor NSF 2 . 
     In an embodiment, the second load scale factor LSF 2  may be determined in the same manner as in  FIG.  5   , and the second grayscale scale factor NSF 2  may be determined in the same manner as in  FIG.  7   , for example. In an embodiment, the display panel driver  10  may determine an average value of the second load scale factor LSF 2  and the second grayscale scale factor NSF 2  as the second scale factor SF 2 . In an embodiment, the display panel driver  10  may determine a minimum value of the second load scale factor LSF 2  and the second grayscale scale factor NSF 2  as the second scale factor SF 2 . 
       FIG.  9    is a block diagram illustrating an embodiment of a driving controller  202  of a display device according to the invention. 
     The display apparatus according to the illustrated embodiment is substantially the same as the display apparatus  1000  of  FIG.  1    except for the operation mode determiner  222 . Thus, the same reference numerals are used to refer to the same or similar element, and any repetitive explanation will be omitted. 
     Referring to  FIGS.  1 ,  4 ,  5 , and  9   , the display panel driver  10  may apply the second scale factor SF 2  to the pixels P in which a deterioration degree PD of the pixels P is greater than a reference deterioration degree. In an embodiment, the display panel driver  10  may apply the second scale factor SF 2  to the input image data IMG for an image displayed in the pixels P in which the deterioration degree PD of the pixels P is greater than the reference deterioration degree, for example. The reference deterioration degree may be a value set by a user. 
     The deterioration degree PD of the pixels P may be a degree of deterioration as the pixels P are driven. In an embodiment, the display panel driver  10  may sense a driving current of the pixels P to determine the degree of deterioration PD of the pixels P, for example. In an embodiment, the display panel driver  10  may determine the amount of deterioration due to the input image data IMG based on the input image data IMG, and accumulate the amount of deterioration due to the input image data IMG to determine the deterioration degree PD of the pixels P, for example. 
     The operation mode determiner  222  may receive the deterioration degree PD of the pixels P, and output the operation mode signal MS to apply the second scale factor SF 2  to the pixels P in which the deterioration degree PD of the pixels P is greater than the reference deterioration degree. That is, the operation mode determiner  222  may output the operation mode signal MS of the second operation mode M 2  with respect to the input image data IMG for an image displayed in the pixels P in which the deterioration degree PD of the pixels P is greater than the reference deterioration degree. 
     In an embodiment, when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the first reference number RN 1 , and the average image load APL is less than or equal to the first reference load RL 1 , the second scale factor SF 2  may be applied to the portion of the input image data IMG for the image displayed in the pixels P in which the deterioration degree PD of the pixels P is greater than the reference deterioration degree and the first scale factor SF 1  may be applied to the portion of the input image data IMG for the image displayed in the pixels P in which the deterioration degree PD of the pixels P is less than or equal to the reference deterioration degree, for example. 
     Accordingly, in the first operation mode M 1  in which the luminance of a displayed image is relatively higher than that of the second operation mode M 2 , the display panel driver  10  may convert the operation mode. So, the display device may prevent that an image having high luminance is displayed. 
       FIG.  10    is a block diagram illustrating an embodiment of a driving controller  203  of a display device according to the invention. 
     The display apparatus according to the illustrated embodiment is substantially the same as the display apparatus  1000  of  FIG.  1    except for the operation mode determiner  223 . Thus, the same reference numerals are used to refer to the same or similar element, and any repetitive explanation will be omitted. 
     Referring to  FIGS.  1 ,  4 ,  5 , and  10   , the operation mode determiner  223  may determine the operation mode as the first operation mode M 1  or the second operation mode M 2  based on the grayscale value of the input image data IMG. The display panel driver  10  may operate in the second operation mode M 2  when the display panel driver  10  does not operate in the first operation mode M 1 , and operate in the first operation mode M 1  when the display panel driver  10  does not operate in the second operation mode M 2 . In an embodiment, the display panel driver  10  may operate as the first operation mode M 1  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the first reference number RN 1 . In an embodiment, the display panel driver  10  may operate as the first operation mode M 1  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the first reference number RN 1 , and operate as the second operation mode M 2  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is less than or equal to the first reference number RN 1 , for example. In an embodiment, the operation mode determiner  223  may output the operation mode signal MS including information on the operation mode to the scale factor determiner  230 , for example. 
     As a result, even when the average image load APL is small, the display device  1000  may adjust the luminance of the image displayed through the second operation mode M 2  to be low when the number of the pixels P displaying a low grayscale value is small. 
       FIG.  11    is a block diagram illustrating an embodiment of a driving controller  204  of a display device according to the invention, and  FIG.  12    is a diagram illustrating an embodiment of a temperature PT of the display panel  100 . 
     The display apparatus according to the illustrated embodiment is substantially the same as the display apparatus  1000  of  FIG.  1    except for the operation mode determiner  224 . Thus, the same reference numerals are used to refer to the same or similar element, and any repetitive explanation will be omitted. 
     Referring to  FIGS.  1 ,  4 ,  5 ,  11 , and  12   , the operation mode determiner  224  may determine the operation mode as the first operation mode M 1  or the second operation mode M 2  based on the temperature PT of the display panel  100  and the average image load APL. The display panel driver  10  may operate in the second operation mode M 2  when the display panel driver  10  does not operate in the first operation mode M 1 , and operate in the first operation mode M 1  when the display panel driver  10  does not operate in the second operation mode M 2 . In an embodiment, the display panel driver  10  may operate as the first operation mode M 1  when the temperature PT of the display panel  100  is lower than or equal to the first reference temperature RT 1  and the average image load APL is less than or equal to the first reference load RL 1 . In an embodiment, the display panel driver  10  may operate as the first operation mode M 1  when the temperature PT of the display panel  100  is lower than or equal to the first reference temperature RT 1  and the average image load APL is less than or equal to the first reference load RL 1 , the display panel driver  10  may operate as the second operation mode M 2  when the temperature PT of the display panel  100  is higher than the first reference temperature RT 1  and the average image load APL is less than or equal to the first reference load RL 1 , the display panel driver  10  may operate as the second operation mode M 2  when the temperature PT of the display panel  100  is lower than or equal to the first reference temperature RT 1  and the average image load APL is greater than the first reference load RL 1 , and the display panel driver  10  may operate as the second operation mode M 2  when the temperature PT of the display panel  100  is higher than the first reference temperature RT 1  and the average image load APL is greater than the first reference load RL 1 , for example. In an embodiment, the operation mode determiner  224  may output the operation mode signal MS including information on the operation mode to the scale factor determiner  230 , for example. The first reference temperature RT 1  may be value set by a user. 
     In an embodiment, the display panel driver  10  may determine the temperature PT of the display panel  100  by accumulating the input image data IMG, for example. The display panel driver  10  may calculate a change amount of the temperature PT of the display panel  100  based on the input image data IMG. That is, the display panel driver  10  may calculate the change amount of the temperature PT of the display panel  100  based on the accumulated input image data IMG, and determine the temperature PT of the display panel  100  using the change amount of the temperature PT of the display panel  100 . 
     In an embodiment, the display panel driver  10  may sense the driving current of the pixels P to determine the temperature PT of the display panel  100 , for example. As the temperature PT of the display panel  100  changes, the driving current of the pixels P may change. Accordingly, the display panel driver  10  may sense the driving current of the pixels P and determine the temperature PT of the display panel  100  through the sensed driving current. 
     In an embodiment, as shown in  FIG.  12   , it is assumed that the temperature PT of the display panel  100  is higher than the first reference temperature RT 1  in periods between a time point at 10 seconds (s) and a time point at 15 s and between a time point at 18 s and a time point at 19 s, and the average image load APL is less than or equal to the first reference load RL 1 , for example. In this case, the display panel driver may operate in the first operation mode M 1  from a time point at 0 s to the time point at 10 s, operate in the second operation mode M 2  from the time point at 10 s to the time point at 15 s, and operate in the first operation mode M 1  from the time point at 15 s to the time point at 18 s and operate in the second operation mode M 2  from the time point at 18 s to the time point at 19 s. 
     As a result, even when the average image load APL is small, the display device  1000  may adjust the luminance of the image displayed through the second operation mode M 2  to be low when the temperature PT of the display panel  100  is high (i.e., the temperature PT of the display panel  100  is higher than the first reference temperature RT 1 .). 
       FIG.  13    is a graph illustrating an embodiment of the first scale factor SF 1  of the display device  100  according to the invention, and  FIG.  14    is a graph illustrating an embodiment of the second scale factor SF 2  of the display device of  FIG.  13   . 
     The display apparatus according to the illustrated embodiment is substantially the same as the display apparatus of  FIG.  11    except for determining the first and second scale factors SF 1  and SF 2 . Thus, the same reference numerals are used to refer to the same or similar element, and any repetitive explanation will be omitted. 
     Referring to  FIGS.  1 ,  4 ,  5 ,  13 , and  14   , the first scale factor SF 1  may decrease as the temperature PT of the display panel  100  increases in a period in which the temperature PT of the display panel  100  is higher than or equal to a second reference temperature RT 2 , and has the first reference value RV 1  in a period in which the temperature PT of the display panel  100  is lower than the second reference temperature RT 2 . The second reference temperature RT 2  may be value set by a user. 
     In an embodiment, as shown in  FIG.  13   , it is assumed that the first reference value RV 1  is 1, the second reference value RV 2  is 0.4, and a minimum value of the first scale factor SF 1  is 0.2, for example. The first scale factor SF 1  may decrease from 1 to 0.2 when the temperature PT of the display panel  100  is higher than or equal to the second reference temperature RT 2 . The first scale factor SF 1  may be 1 when the temperature PT of the display panel  100  is less than the second reference temperature RT 2 . 
     The second scale factor SF 2  may decrease as the temperature PT of the display panel  100  increases in a period in which the temperature PT of the display panel  100  is higher than the first reference temperature RT 1  higher than the second reference temperature RT 2 , and has the second reference value RV 2  less than the first reference value RV 1  in a period in which the temperature PT of the display panel  100  is lower than the first reference temperature RT 1 . 
     In an embodiment, as shown in  FIG.  14   , it is assumed that the first reference value RV 1  is 1, the second reference value RV 2  is 0.4, and a minimum value of the second scale factor SF 2  is 0.2, for example. The second scale factor SF 2  may decrease from 0.4 to 0.2 when the temperature PT of the display panel  100  is higher than or equal to the first reference temperature RT 1 . The second scale factor SF 2  may be 0.4 when the temperature PT of the display panel  100  is lower than the second reference temperature RT 2 . 
       FIG.  15    is a diagram illustrating an embodiment in which a display device according to the invention determines the first scale factor SF 1  and the second scale factor SF 2 . 
     The display apparatus according to the illustrated embodiment is substantially the same as the display apparatus of  FIG.  11    except for determining the first and second scale factors SF 1  and SF 2 . Thus, the same reference numerals are used to refer to the same or similar element, and any repetitive explanation will be omitted. 
     Referring to  FIGS.  1  and  15   , the display panel driver  10  may determine the first load scale factor LSF 1  according to the average image load APL in the first operation mode M 1 , determine a first temperature scale factor TSF 1  according to the temperature PT of the display panel  100  in the first operation mode M 1 , and determine the first scale factor SF 1  based on the first load scale factor LSF 1  and the first temperature scale factor TSF 1 . 
     In an embodiment, the first load scale factor LSF 1  may be determined in the same manner as in  FIG.  4   , and the first temperature scale factor TSF 1  may be determined in the same manner as in  FIG.  13   , for example. In an embodiment, the display panel driver  10  may determine an average value of the first load scale factor LSF 1  and the first temperature scale factor TSF 1  as the first scale factor SF 1 . In an embodiment, the display panel driver  10  may determine a minimum value of the first load scale factor LSF 1  and the first temperature scale factor TSF 1  as the first scale factor SF 1 . 
     The display panel driver  10  may determine the second load scale factor LSF 2  according to the average image load APL in the second operation mode M 2 , determine a second temperature scale factor TSF 2  according to the temperature PT of the display panel  100  in the second operation mode M 2 , and determine the second scale factor SF 2  based on the second load scale factor LSF 2  and the second temperature scale factor TSF 2 . 
     In an embodiment, the second load scale factor LSF 2  may be determined in the same manner as in  FIG.  5   , and the second temperature scale factor TSF 2  may be determined in the same manner as in  FIG.  14   , for example. In an embodiment, the display panel driver  10  may determine an average value of the second load scale factor LSF 2  and the second temperature scale factor TSF 2  as the second scale factor SF 2 . In an embodiment, the display panel driver  10  may determine a minimum value of the second load scale factor LSF 2  and the second temperature scale factor TSF 2  as the second scale factor SF 2 . 
       FIG.  16    is a block diagram illustrating an embodiment of a driving controller  205  of a display device according to the invention. 
     The display apparatus according to the illustrated embodiment is substantially the same as the display apparatus of  FIG.  11    except for the operation mode determiner  225 . Thus, the same reference numerals are used to refer to the same or similar element, and any repetitive explanation will be omitted. 
     Referring to  FIGS.  1 ,  4 ,  5 ,  12 , and  16   , the display panel driver  10  may apply the second scale factor SF 2  to the pixels P in which the deterioration degree PD of the pixels P is greater than the reference deterioration degree. In an embodiment, the display panel driver  10  may apply the second scale factor SF 2  to the input image data IMG for an image displayed in the pixels P in which the deterioration degree PD of the pixels P is greater than the reference deterioration degree, for example. 
     In an embodiment, when the temperature PT of the display panel  100  is lower than or equal to the first reference temperature RT 1 , and the average image load APL is less than or equal to the first reference load RL 1 , the second scale factor SF 2  may be applied to the portion of the input image data IMG for the image displayed in the pixels P in which the deterioration degree PD of the pixels P is greater than the reference deterioration degree and the first scale factor SF 1  may be applied to the portion of the input image data IMG for the image displayed in the pixels P in which the deterioration degree PD of the pixels P is less than or equal to the reference deterioration degree, for example. 
       FIG.  17    is a block diagram illustrating an embodiment of a driving controller  206  of a display device according to the invention. 
     The display apparatus according to the illustrated embodiment is substantially the same as the display apparatus of  FIG.  11    except for the operation mode determiner  226 . Thus, the same reference numerals are used to refer to the same or similar element, and any repetitive explanation will be omitted. 
     Referring to  FIGS.  1 ,  4 ,  5 ,  12 , and  17   , the operation mode determiner  226  may determine the operation mode as the first operation mode M 1  or the second operation mode M 2  based on the temperature PT of the display panel  100 . The display panel driver  10  may operate in the second operation mode M 2  when the display panel driver  10  does not operate in the first operation mode M 1 , and operate in the first operation mode M 1  when the display panel driver  10  does not operate in the second operation mode M 2 . In an embodiment, the display panel driver  10  may operate as the first operation mode M 1  when the temperature PT of the display panel  100  is lower than or equal to the first reference temperature RT 1 . In an embodiment, the display panel driver  10  may operate as the first operation mode M 1  when the temperature PT of the display panel  100  is lower than or equal to the first reference temperature RT 1 , and the display panel driver  10  may operate as the second operation mode M 2  when the temperature PT of the display panel  100  is higher than the first reference temperature RT 1 , for example. In an embodiment, the operation mode determiner  226  may output the operation mode signal MS including information on the operation mode to the scale factor determiner  230 , for example. 
     As a result, even when the average image load APL is small, the display device  1000  may adjust the luminance of the image displayed through the second operation mode M 2  to be low when the temperature PT of the display panel  100  is high. 
       FIG.  18    is a block diagram illustrating an embodiment of a driving controller  207  of a display device according to the invention. 
     The display apparatus according to the illustrated embodiment is substantially the same as the display apparatus of  FIG.  11    except for determining the operation mode. Thus, the same reference numerals are used to refer to the same or similar element, and any repetitive explanation will be omitted. 
     Referring to  FIGS.  1 ,  4 ,  5 ,  12 , and  18   , the display panel driver  10  may determine the operation mode as the first operation mode M 1  or the second operation mode M 2  based on the temperature PT of the display panel  100  and the grayscale value of the input image data IMG, apply the first scale factor SF 1  to the input image data IMG in the first operation mode M 1 , and apply the second scale factor SF 2  to the input image data IMG in the second operation mode M 2 . 
     The operation mode determiner  227  may determine the operation mode as the first operation mode M 1  or the second operation mode M 2  based on the temperature PT of the display panel  100  and the grayscale value of the input image data IMG. The display panel driver  10  may operate in the second operation mode M 2  when the display panel driver  10  does not operate in the first operation mode M 1 , and operate in the first operation mode M 1  when the display panel driver  10  does not operate in the second operation mode M 2 . In an embodiment, the display panel driver  10  may operate as the first operation mode M 1  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the first reference number RN 1  and the temperature PT of the display panel  100  less than or equal to the first reference temperature RT 1 . In an embodiment, the display panel driver  10  may operate as the first operation mode M 1  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the first reference number RN 1  and the temperature PT of the display panel  100  less than or equal to the first reference temperature RT 1 , the display panel driver  10  may operate as the second operation mode M 2  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is less than or equal to the first reference number RN 1  and the temperature PT of the display panel  100  less than or equal to the first reference temperature RT 1 , the display panel driver  10  may operate as the second operation mode M 2  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the first reference number RN 1  and the temperature PT of the display panel  100  higher than the first reference temperature RT 1 , the display panel driver  10  may operate as the second operation mode M 2  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is less than or equal to the first reference number RN 1  and the temperature PT of the display panel  100  higher than the first reference temperature RT 1 , for example. In an embodiment, the operation mode determiner  227  may output the operation mode signal MS including information on the operation mode to the scale factor determiner  230 , for example. 
     As a result, even when the temperature PT of the display panel  100  is low, the display device  1000  may adjust the luminance of the image displayed through the second operation mode M 2  to be low when the number of the pixels P displaying the low grayscale value is small. Also, even when the number of the pixels P displaying the low grayscale value is small, the display device  1000  may adjust the luminance of the image displayed through the second operation mode M 2  to be low when the temperature PT of the display panel  100  is high. 
     In an embodiment, the display panel driver  10  determine the first grayscale scale factor according to the grayscale value of the input image data IMG in the first operation mode M 1 , determine the first temperature scale factor according to the temperature PT of the display panel  100  in the first operation mode M 1 , and determine the first scale factor SF 1  based on the first grayscale scale factor and the first temperature scale factor. 
     In an embodiment, the first grayscale scale factor may be determined in the same manner as in  FIG.  6   , and the first temperature scale factor may be determined in the same manner as in  FIG.  13   , for example. In an embodiment, the display panel driver  10  may determine an average value of the first grayscale scale factor and the first temperature scale factor as the first scale factor SF 1 . In an embodiment, the display panel driver  10  may determine a minimum value of the first grayscale scale factor and the first temperature scale factor as the first scale factor SF 1 . 
     In an embodiment, the display panel driver  10  may determine the second grayscale scale factor according to the grayscale value of the input image data IMG in the second operation mode M 2 , determine the second temperature scale factor according to the temperature PT of the display panel  100  in the second operation mode M 2 , and determine the second scale factor SF 2  based on the second grayscale scale factor and the second temperature scale factor. 
     In an embodiment, the second grayscale scale factor may be determined in the same manner as in  FIG.  7   , and the second temperature scale factor may be determined in the same manner as in  FIG.  14   , for example. In an embodiment, the display panel driver  10  may determine an average value of the second grayscale scale factor and the second temperature scale factor as the second scale factor SF 2 . In an embodiment, the display panel driver  10  may determine a minimum value of the second grayscale scale factor and the second temperature scale factor as the second scale factor SF 2 . 
       FIG.  19    is a block diagram illustrating an embodiment of a driving controller  208  of a display device according to the invention. 
     The display apparatus according to the illustrated embodiment is substantially the same as the display apparatus of  FIG.  11    except for the operation mode determiner  228 . Thus, the same reference numerals are used to refer to the same or similar element, and any repetitive explanation will be omitted. 
     The operation mode determiner  228  may determine the operation mode as the first operation mode M 1  or the second operation mode M 2  based on the average image load APL, the temperature PT of the display panel  100 , and the grayscale value of the input image data IMG. The display panel driver  10  may operate in the second operation mode M 2  when the display panel driver  10  does not operate in the first operation mode M 1 , and operate in the first operation mode M 1  when the display panel driver  10  does not operate in the second operation mode M 2 . In an embodiment, the display panel driver  10  may operate as the first operation mode M 1  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the first reference number RN 1 , the temperature PT of the display panel  100  is lower than or equal to the first reference temperature RT 1 , and the average image load APL is less than or equal to the first reference load RL 1 . In an embodiment, the display panel driver  10  may operate as the first operation mode M 1  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the first reference number RN 1 , the temperature PT of the display panel  100  is lower than or equal to the first reference temperature RT 1 , and the average image load APL is less than or equal to the first reference load RL 1 , the display panel driver  10  may operate as the second operation mode M 2  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is less than or equal to the first reference number RN 1 , the temperature PT of the display panel  100  is lower than or equal to the first reference temperature RT 1 , and the average image load APL is less than or equal to the first reference load RL 1 , the display panel driver  10  may operate as the second operation mode M 2  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the first reference number RN 1 , the temperature PT of the display panel  100  is higher than the first reference temperature RT 1 , and the average image load APL is less than or equal to the first reference load RL 1 , the display panel driver  10  may operate as the second operation mode M 2  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the first reference number RN 1 , the temperature PT of the display panel  100  is lower than or equal to the first reference temperature RT 1 , and the average image load APL is greater than the first reference load RL 1 , the display panel driver  10  may operate as the second operation mode M 2  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is less than or equal to the first reference number RN 1 , the temperature PT of the display panel  100  is higher than the first reference temperature RT 1 , and the average image load APL is less than or equal to the first reference load RL 1 , the display panel driver  10  may operate as the second operation mode M 2  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is less than or equal to the first reference number RN 1 , the temperature PT of the display panel  100  is lower than or equal to the first reference temperature RT 1 , and the average image load APL is greater than the first reference load RL 1 , the display panel driver  10  may operate as the second operation mode M 2  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is greater than the first reference number RN 1 , the temperature PT of the display panel  100  is higher than the first reference temperature RT 1 , and the average image load APL is greater than the first reference load RL 1 , and the display panel driver  10  may operate as the second operation mode M 2  when the number NG of the pixels P displaying the grayscale value less than or equal to the first reference grayscale value RG 1  is less than or equal to the first reference number RN 1 , the temperature PT of the display panel  100  is higher the first reference temperature RT 1 , and the average image load APL is greater than the first reference load RL 1 , for example. In an embodiment, the operation mode determiner  228  may output the operation mode signal MS including information on the operation mode to the scale factor determiner  230 , for example. 
     As a result, even when the number of the pixels P displaying the low grayscale value is small and the temperature PT of the display panel  100  is low, the display device  1000  may adjust the luminance of the image displayed through the second operation mode M 2  to be low when the average image load APL is large. Also, even when the temperature PT of the display panel  100  is low and the average image load APL is small, the display device  1000  may adjust the luminance of the image displayed through the second operation mode M 2  to be low when the number of the pixels P displaying a low grayscale value is small. Also, even when the average image load APL is small and the number of the pixels P displaying the low grayscale value is small large, the display device  1000  may adjust the luminance of the image displayed through the second operation mode M 2  to be low when the temperature PT of the display panel  100  is high. 
       FIG.  20    is a diagram illustrating an embodiment in which a display device according to the invention determines the first scale factor SF 1  and the second scale factor SF 2 . 
     The display apparatus according to the illustrated embodiment is substantially the same as the display apparatus of  FIG.  11    except for determining the first and second scale factors SF 1  and SF 2 . Thus, the same reference numerals are used to refer to the same or similar element, and any repetitive explanation will be omitted. 
     Referring to  FIGS.  1  and  20   , the display panel driver  10  may determine the first load scale factor LSF 1  according to the average image load APL in the first operation mode M 1 , determine the first grayscale scale factor NSF 1  according to the grayscale value of the input image data IMG in the first operation mode M 1 , determine the first temperature scale factor TSF 1  according to the temperature PT of the display panel  100  in the first operation mode M 1 , and determine the first scale factor SF 1  based on the first load scale factor LSF 1 , the first grayscale scale factor NSF 1 , and the first temperature scale factor TSF 1 . 
     In an embodiment, the first load scale factor LSF 1  may be determined in the same manner as in  FIG.  4   , the first temperature scale factor TSF 1  may be determined in the same manner as in  FIG.  13   , and the first grayscale scale factor NSF 1  may be determined in the same manner as in  FIG.  6   , for example. In an embodiment, the display panel driver  10  may determine an average value of the first load scale factor LSF 1 , the first temperature scale factor TSF 1  and the first grayscale scale factor NSF 1  as the first scale factor SF 1 . In an embodiment, the display panel driver  10  may determine a minimum value of the first load scale factor LSF 1 , the first temperature scale factor TSF 1 , and the first grayscale scale factor NSF 1  as the first scale factor SF 1 . 
     The display panel driver  10  may determine the second load scale factor LSF 2  according to the average image load APL in the second operation mode M 2 , determine the second grayscale scale factor NSF 2  according to the grayscale value of the input image data IMG in the second operation mode M 2 , determine the second temperature scale factor TSF 2  according to the temperature PT of the display panel  100  in the second operation mode M 2 , and determine the second scale factor SF 2  based on the second load scale factor LSF 2 , the second grayscale scale factor NSF 2 , and the second temperature scale factor TSF 2 . 
     In an embodiment, the second load scale factor LSF 2  may be determined in the same manner as in  FIG.  5   , the second temperature scale factor TSF 2  may be determined in the same manner as in  FIG.  14   , and the second grayscale scale factor NSF 2  may be determined in the same manner as in  FIG.  7   , for example. In an embodiment, the display panel driver  10  may determine an average value of the second load scale factor LSF 2 , the second temperature scale factor TSF 2  and the second grayscale scale factor NSF 2  as the second scale factor SF 2 . In an embodiment, the display panel driver  10  may determine a minimum value of the second load scale factor LSF 2 , the second temperature scale factor TSF 2 , and the second grayscale scale factor NSF 2  as the second scale factor SF 2 . 
       FIG.  21    is a diagram illustrating an embodiment in which a display device adjusts a grayscale value according to the invention. 
     The display apparatus according to the illustrated embodiment is substantially the same as the display apparatus  1000  of  FIG.  1    except for adjusting the grayscale value of input image data IMG′ to which the first scale factor SF 1  or the second scale factor SF 2  is applied. Thus, the same reference numerals are used to refer to the same or similar element, and any repetitive explanation will be omitted. 
     Referring to  FIGS.  1  and  21   , the display panel driver  10  may increase the grayscale value of the input image data IMG′ to which the first scale factor SF 1  or the second scale factor SF 2  is applied when the grayscale value of the input image data IMG′ to which the first scale factor SF 1  or the second scale factor SF 2  is applied is greater than a second reference grayscale value RG 2 . 
     In an embodiment, as shown in  FIG.  21   , it is assumed that a 255 grayscale value 255G is displayed in a center area of the display panel  100  and a 100 grayscale value 100G is displayed in the remaining area when an image is displayed on the display panel  100  based on the input image data IMG to which the first scale factor SF 1  or the second scale factor SF 2  is not applied, and the second reference grayscale value RG 2  is a 150 grayscale value 50G, for example. A 155 grayscale value 155G lower than the 255 grayscale value 255G may be displayed in the center area of the display panel  100  and a 50 grayscale value 50G lower than the 100 grayscale value 100G may be displayed in the remaining area. The display panel driver  10  may increase the 155 grayscale value 155G greater than the second reference grayscale value RG 2  among the grayscale values of the input image data IMG′ to which the first scale factor SF 1  or the second scale factor SF 2  is applied. As a result, when an image is displayed based on input image data IMG″ having an increased grayscale value, a 200 grayscale value 200G greater than the 155 grayscale value 155G may be displayed in the center area of the display panel  100 , and a 50 grayscale value 50G may be displayed in the remaining area as it is. 
     Accordingly, the display panel driver  10  may adjust the overall luminance of the displayed image to be low through the first and second scale factors SF 1  and SF 2  and then increase the luminance of a portion displaying a high grayscale value to enhance a visibility. 
       FIG.  22    is a diagram illustrating an embodiment of the display panel  100  of a display device according to the invention, and  FIG.  23    is a diagram illustrating an embodiment in which the display device of  FIG.  22    adjusts a grayscale value. 
     The display apparatus according to the illustrated embodiment is substantially the same as the display apparatus  1000  of  FIG.  1    except for adjusting the grayscale value of input image data IMG′ to which the scale factor SF 1  or the second scale factor SF 2  is applied. Thus, the same reference numerals are used to refer to the same or similar element, and any repetitive explanation will be omitted. 
     Referring to  FIGS.  22  and  23   , the display panel  100  may be divided into panel blocks PB. The panel blocks PB may include a first panel block PB 1  and a second panel block PB 2  adjacent to the first panel block PB 1 . The panel blocks PB may include the pixels P. 
     The display panel driver  10  may receive the input image data IMG and determine an average image load of each of the panel blocks PB based on the input image data IMG. In an embodiment, the display panel driver  10  may convert the input image data IMG of the RGB domain into the input image data of the luminance domain, and determine the average image load of each of the panel blocks PB by dividing a sum of luminance for each of the panel blocks PB of the input image data IMG of the luminance domain (i.e., the sum of luminance to be displayed in each of the panel blocks PB) by the number of the pixels P included in each of the panel blocks PB, for example. The average image load of each of the panel blocks PB may be normalized to have a value ranging from 0% to 100%. In an embodiment, when the input image data IMG corresponding to a predetermined panel block is a full white image, the average image load of the predetermined panel block may be 100%, for example. In an embodiment, when the input image data IMG corresponding to a predetermined panel block is a full black image, the average image load of the predetermined panel block may be 0%, for example. 
     The display panel driver  10  may increase the grayscale value of the input image data IMG′ corresponding to the first panel block PB 1  to which the first scale factor SF 1  or the second scale factor SF 2  is applied when an average image load BAPL 1  of the first panel block PB 1  is greater than a sum of an average image load BAPL 2  of the second panel block PB 2  and a third reference value RV 3 . 
     In an embodiment, as shown in  FIG.  23   , it is assumed that the 255 grayscale value 255G is displayed in a first panel block PB 1  of the display panel  100  (i.e., an average of grayscale values of the pixels P included in the first panel block PB 1  is the 255 grayscale 255G), and the 100 grayscale value 100G is displayed in the second panel block PB 2  (i.e., an average of grayscale values of the pixels P included in the second panel block PB 2  adjacent to the first panel block PB 1  is the 100 grayscale 100G) when an image is displayed on the display panel  100  based on the input image data IMG to which the first scale factor SF 1  or the second scale factor SF 2  is not applied, the third reference value RV 3  is 40%, the average image load BAPL 1  of the first panel block PB 1  is 100%, and the average image load BAPL 2  of the second panel block PB 2  is 20%, for example. The 155 grayscale value 155G lower than the 255 grayscale value 255G may be displayed in the first panel block PB 1  (i.e., an average of grayscale values of the pixels P included in the first panel block PB 1  is the 155 grayscale 155G) and the 50 grayscale value 50G lower than the 100 grayscale value 100G may be displayed in the second panel block PB 2  (i.e., an average of grayscale values of the pixels P included in the second panel block PB 2  adjacent to the first panel block PB 1  is the 50 grayscale 50G). 
     Since the average image load BAPL 1  of the first panel block PB 1  of the input image data IMG′ to which the first scale factor SF 1  or the second scale factor SF 2  is applied is greater than the sum of the average image load BAPL 2  of the second panel block PB 2  and the third reference value RV 3 , the display panel driver  10  may increase the grayscale value of a portion corresponding to the first panel block PB 1 . As a result, when an image is displayed based on input image data IMG″ having an increased grayscale value, the 200 grayscale value 200G greater than the 155 grayscale value 155G may be displayed in the first panel block PB 1  (i.e., an average of grayscale values of the pixels P included in the first panel block PB 1  is the 200 grayscale 200G), and a 50 grayscale value 50G may be displayed in the second panel block PB 2  as it is. 
     Accordingly, the display panel driver  10  may adjust the overall luminance of the displayed image to be low through the first and second scale factors SF 1  and SF 2  and then increase the luminance of a portion displaying a high grayscale value to enhance the visibility. 
     The embodiments of the invention may be applied to any electronic device including the display device. The embodiments of the invention may be applied to a television (“TV”), a digital TV, a three dimensional (“3D”) TV, a mobile phone, a smart phone, a tablet computer, a virtual reality (“VR”) device, a wearable electronic device, a personal computer (“PC”), a home appliance, a laptop computer, a personal digital assistant (“PDA”), a portable multimedia player (“PMP”), a digital camera, a music player, a portable game console, a navigation device, etc. 
     The foregoing is illustrative of the invention and is not to be construed as limiting thereof. Although a few embodiments of the invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of the invention. Accordingly, all such modifications are intended to be included within the scope of the invention 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 the invention and is not to be construed as limited to the illustrative embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.