Patent Publication Number: US-2023141954-A1

Title: Sub-pixel rendering method for display panel

Description:
FIELD OF THE INVENTION 
     The present application relates generally to a rendering method, and particularly to a sub-pixel rendering method for a display panel. 
     BACKGROUND OF THE INVENTION 
     In a general display panel, sub-pixel structures are arranged in a matrix with each responsible for one of red, green, and blue colors. Three sub-pixel structures with each of the red, green, and blue colors may form a pixel. Nonetheless, not all display panels arrange a pixel with three sub-pixel structures. Thereby, the displaying quality is inferior. 
     To solve the above problem of inferior quality, according to the prior art, some manufacturers cooperated to propose a rendering technology for primary color sub-pixels. According to the technology, for a specific arrangement of the primary color sub-pixels, a specific sub-pixel rendering algorithm is designed. Unfortunately, the sub-pixel rendering algorithm according to the prior art does not include the human vision model. In other words, it neglects the visual perception of human eyes. 
     Accordingly, the present application provides a sub-pixel rendering method for a display panel. The method converts an input grayscale data of an input image according to a human vision model and gives adjustment luminance data for generating better target grayscale data. With the better target grayscale data, the grayscale images displayed on the display panels may comply with the visual perception of human eyes. 
     SUMMARY 
     An objective of the present application is to provide a sub-pixel rendering method for a display panel. The method converts an input grayscale data of an input image according to a human vision model for generating an adjustment luminance data, and samples the adjustment luminance values according to the sampling locations corresponding to the arrangement locations of the sub-pixels. Thereby, target grayscale values complying with the visual perception of human eyes will be given. 
     The present application discloses a sub-pixel rendering method for a display panel, which determines a plurality of sampling locations according to a plurality of arrangement locations of sub-pixels, converts an input grayscale data of an input image according to a human vision model for generating an adjustment luminance data, samples a plurality of adjustment luminance values of the adjustment luminance data according to the sampling locations, and generates a target grayscale data according to the sampled adjustment luminance values. The target grayscale data includes a plurality of target grayscale values corresponding to the sub-pixels. Thereby, the target grayscale values may comply with the visual perception of human eyes by avoiding distortion of the input image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows a block diagram of the sub-pixel rendering method according to an embodiment of the present application; 
         FIG.  2    shows a flowchart of the sub-pixel rendering method according to an embodiment of the present application; 
         FIG.  3    shows a schematic diagram of sub-pixel arrangement in the sub-pixel rendering method according to an embodiment of the present application; 
         FIG.  4    shows a flowchart of conversion of human vision in the sub-pixel rendering method according to an embodiment of the present application; 
         FIG.  5    shows a schematic diagram of conversion steps in the sub-pixel rendering method according to an embodiment of the present application; 
         FIG.  6    shows a curve of luminance versus grayscale in the sub-pixel rendering method according to an embodiment of the present application; 
         FIG.  7    shows a flowchart of sampling steps in the sub-pixel rendering method according to an embodiment of the present application; 
         FIG.  8    shows a schematic diagram of sampling steps in the sub-pixel rendering method according to an embodiment of the present application; and 
         FIG.  9    shows a schematic diagram of converting luminance to grayscale in the sub-pixel rendering method according to an embodiment of the present application. 
     
    
    
     DETAILED DESCRIPTION 
     In order to make the structure and characteristics as well as the effectiveness of the present application to be further understood and recognized, the detailed description of the present application is provided as follows along with embodiments and accompanying figures. 
     Since the sub-pixel rendering algorithm according to the prior art does not comply with the visual perception of human eyes, the present application proposes a sub-pixel rendering method for display panel for giving preferred target grayscale data. Thereby, the grayscale images displayed on the display panel may comply with the visual perception of human eyes. 
     In the specifications and subsequent claims, certain words are used for representing specific devices. A person having ordinary skill in the art should know that hardware manufacturers might use different nouns to call the same device. In the specifications and subsequent claims, the differences in names are not used for distinguishing devices. Instead, the differences in functions are the guidelines for distinguishing. In the whole specifications and subsequent claims, the word “comprising” is an open language and should be explained as “comprising but not limited to”. Besides, the word “couple” includes any direct and indirect electrical connection. Thereby, if the description is that a first device is coupled to a second device, it means that the first device is connected electrically to the second device directly, or the first device is connected electrically to the second device via other device or connecting means indirectly. 
     In the following, the properties and the accompanying structure of the sub-pixel rendering method for display panel disclosed in the present application will be further described. 
     First, please refer to  FIG.  1   , which shows a block diagram of the sub-pixel rendering method according to an embodiment of the present application. As shown in the figure, the display device  10  applying the sub-pixel rendering method for display panel according to the present application comprises an operational circuit  12 , a driving circuit  14 , and a display panel  16 . The operational circuit  12  receives an input image IN from a microprocessing unit  20  for performing a sub-pixel rendering operation RP on the input image IN and generating a target grayscale data to the driving circuit  14 . For example, the microprocessing unit  20  inputs a digital image to the operational circuit  12 . The driving circuit  14  generates a driving signal DR to the display panel  16  according to the target grayscale data GD and drives the display panel  16  to display the grayscale image corresponding to the input image IN. The operational circuit  12  according to the present embodiment may be a circuit with logic and floating-point operating capabilities. In addition, the operational circuit  12  according to the present application may be further integrated in the driving circuit  14 . 
     Please refer to  FIG.  2   , which shows a flowchart of the sub-pixel rendering method according to an embodiment of the present application. As shown in the figure, the sub-pixel rendering method according to the present application refers to the operating and processing processes of the operational circuit  12 , comprising steps of:
     Step S 10 : Determining the sampling locations according to the arrangement locations of the sub-pixels;   Step S 20 : Converting the input grayscale data of the input image according to a human vision model and generating an adjustment luminance data;   Step S 30 : Sampling adjustment luminance values from the adjustment luminance data according to the sampling locations; and   Step S 40 : Generating a target grayscale data according to the sampled adjustment luminance values.   

     In the step S 10 , the operational circuit  12  acquires a plurality of sampling locations  164  corresponding to the input grayscale values G 1  according to the arrangement locations of the sub-pixels  162  of the display panel  16 , as shown in  FIG.  3   . The operational circuit  12  determines the number of the sampling locations  164  according to the arrangement locations of the sub-pixels  162  and a display resolution of the display panel  16 . As shown in  FIG.  3   , the sub-pixels  162  according to the present embodiment include a plurality of first sub-pixels  1622 , a plurality of second sub-pixels  1624 , and a plurality of third sub-pixels  1626 . According to the present embodiment, the first sub-pixels  1622  are red pixels; the second sub-pixels  1624  are blue pixels; and the third sub-pixels  1626  are green pixels. Besides, the first sub-pixels  1622 , the second sub-pixels  1624 , and the third sub-pixels  1626  have their corresponding sampling locations  164 , respectively. Nonetheless, the present application is not limited to the embodiment. It may be applied to special display devices with other display conditions, for example, display panels with various arrangements of the sub-pixels. The operational circuit  12  determines the sampling locations  164  according to the arrangement locations of the sub-pixels  162 . 
     Next, in the step S 20 , the operational circuit  12  converts the input grayscale values G 1  of the input grayscale data ING according to a human vision model HV, as shown in  FIG.  5   . As shown in  FIG.  4   , the step S 20  includes the following steps:
     Step S 22 : Converting the input grayscale data according to a luminance versus grayscale curve and generating an input luminance data;   Step S 24 : Generating the adjustment luminance data according to a forward function of the human vision model and the input luminance data.   

     In the step S 22 , as shown in  FIG.  5   , the input grayscale data ING of the input image IN includes a plurality of input grayscale values G 1 . The operational circuit  12  converts the input grayscale values G 1  to a plurality of input luminance values B 1  according to a luminance versus grayscale curve CV as shown in  FIG.  6    and thus generating the input luminance data INB. 
     In the step S 24 , as shown in  FIG.  5   , the operational circuit  12  adjusts the input luminance values B 1  of the input luminance data INB according to a forward function EQ 1  of the human vision model HV and generates an adjustment luminance data ADB. The adjustment luminance data ADB includes a plurality of adjustment luminance values B 2 . According to the present embodiment, the operational circuit  12  adopts the forward function EQ 1  of the human vision model HV as the sampling function for sampling the input luminance values. The sampling process is similar to convolution operations and thus giving the adjustment luminance values B 2 . The human vision model HV according to the present application is a function of space, wavelength, environment, and physiology and determines the pupil size and the brightness and chromatic adaptation of optic nerves according to the ambient light. 
     Next, in the step S 30 , the operation circuit  12  samples the adjustment luminance values B 2  according to the sampling locations  164  corresponding to the sub-pixels  162  as described above. Furthermore, as shown in  FIG.  7   , the step S 30  may include steps of:
     Step S 32 : Sampling the adjustment luminance values according to the sampling locations; and   Step S 35 : Compensating the sampled luminance values according to a reverse function of the human vision model.   

     In the step S 32 , as shown in  FIG.  8   , the operational circuit  12  samples the adjustment luminance values B 2  corresponding to the input grayscale values G 1  according to the sampling locations  164  corresponding to the sub-pixels  162  as described above and generates a plurality of sampled luminance values B 3  and thus generates the sampled luminance data SPB. In other words, the operational circuit  12  samples the adjustment luminance values B 2  at corresponding locations according to the sampling locations  164  corresponding to the arrangement locations of the sub-pixels  162  and generates the sampled luminance values B 3  and the sampled luminance data SPB. In general, the number of the input grayscale values G 1  of the input image IN is greater than the number of the sub-pixels  162  of the display panel  16 . In addition, each input grayscale value G 1  corresponds to its location, as shown in  FIG.  3   . Once the resolution of the input image IN is different, the number of the input grayscale values G 1  of the input image IN will be different. Thereby, the sampling locations  164  will be different correspondingly. For example, if the resolution is larger, the number of the input grayscale values G 1  will be more. Correspondingly, the number of the input grayscale values G 1  distributed among the sampling locations  164  will be more. Contrarily, if the resolution is smaller, the number of the input grayscale values G 1  will be less. Correspondingly, the number of the input grayscale values G 1  distributed among the sampling locations  164  will be less. Thereby, the operational circuit  12  samples the adjustment luminance values B 2  according to the sampling locations  164  determined by the resolution of the display panel  16  and the arrangement locations of the sub-pixels  162 . Namely, for each sub-pixel  162 , the operational circuit  12  samples one of the adjustment luminance values B 2  where the location corresponding to the location of the sub-pixel  162 . Accordingly, even if the resolution of the display panel  16  is different from the number of the sub-pixels corresponding to the input image IN, the driving circuit  14  still may drive the display panel  16  to display the grayscale image corresponding to the input image IN according to the target grayscale data GD. 
     In the step S 35 , the operational circuit  12  compensates the sampled luminance values B 3  according to a reverse function EQ 2  of the human vision model and generates the compensated luminance values B 4 , and therefore generates compensated luminance data CB. To elaborate, the operational circuit  12  uses each of the sampling location  164  as center and samples the luminance values surrounding the center and compensates the luminance values of each sampling location  164  according to the reverse function EQ 2 . Thereby, the sampled luminance values B 3  are compensated and hence generating the compensated luminance values B 4 . 
     Next, in the step S 40 , as shown in  FIG.  9   , the operational circuit  12  converts the compensated luminance data CB to the target grayscale data GD according to the luminance versus grayscale curve CV shown in  FIG.  6   . In other word, the operational circuit  12  converts the compensated luminance values B 4  to the target grayscale values G 2  according to the luminance versus grayscale curve CV shown in  FIG.  6    and thus completing low-distortion image rendering. Then the driving circuit  14  generates the driving signal DR according to the target grayscale data GD for driving the display panel  16 . 
     Moreover, in the step S 24 , as shown in  FIG.  5   , the present application may further comprise a sensor  122  coupled to the operational circuit  12 . The sensor  122  senses ambient conditions and provides a sensing signals SEN to the operational circuit  12  for modifying the forward function EQ 1  of the human vision model HV, and therefore the forward function EQ 1  complies with the ambient conditions. For example, once the ambient brightness is different, the forward function EQ 1  will be different. Consequently, the operational circuit  12  modifies the forward function EQ 1  dynamically according to the ambient conditions. 
     To sum up, the present application provides the sub-pixel rendering method for display panel. The method converts the input grayscale data of the input image to the input luminance data and adjusts the input luminance data according to the forward function of the human vision model for generating the adjustment luminance data. Then the method samples the adjustment luminance data according to the sampling locations and generates the sampled luminance data. Next, according to the reverse function of the human vision model, the method compensates the sampled luminance data and generates the compensated luminance data for generating the target grayscale data. The driving circuit drives the display panel according to the target grayscale values of the target grayscale data. Thereby, in addition to providing target grayscale values complying with the resolution of the display panel for driving the sub-pixels of the display panel, the grayscale images displayed on the display panel may comply with the visual perception of human eyes. 
     Accordingly, the present application conforms to the legal requirements owing to its novelty, nonobviousness, and utility. However, the foregoing description is only embodiments of the present application, not used to limit the scope and range of the present application. Those equivalent changes or modifications made according to the shape, structure, feature, or spirit described in the claims of the present application are included in the appended claims of the present application.