Abstract:
Image processing devices include a color extractor circuit configured to extract color information from input image data, a color shifter circuit configured to color shift the input image data according to the extracted color information and a definition enhancement circuit configured to detect a color difference from the color-shifted image data and to unsharp mask filter the color-shifted image data according to the detected color difference.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. non-provisional patent application claims priority under 35 U.S.C. §119 of Korean Patent Application No. 10-2009-0012036, filed on Feb. 13, 2009, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The present invention relates to image processing devices and methods, and more particularly, to apparatus and methods for enhancing image definition. 
     An image input/output devices, such as a digital still camera (DSC), a camcorder, and a digital television (DTV), may be costly due to the use of a high-definition image sensor capable of processing high-quality and high-definition images, and an accompanying larger memory compared to low-definition devices. Several techniques, such as zooming a low-definition image to a high-definition image, have been introduced for cost reduction. 
     During a zooming procedure, image degradation may occur because of the noise, blurring, and smearing of images, etc. To relieve such image degradation, definition enhancing techniques that emphasize details of an image and sharpen boundaries may be used. 
     A conventional definition enhancing technique may process the whole image using a single unsharp mask filter (UMF) coefficient. This technique may excessively enhance definition in an area where there is little color change in an image, thus leading to image degradation. In particular, there may be more areas with a slight color change in a high-definition image and, therefore, image degradation becomes more serious in the high-definition image. 
     SUMMARY 
     Some embodiments of the present invention provide image processing devices including a color extractor circuit configured to extract color information from input image data, a color shifter circuit configured to color shift the input image data according to the extracted color information and a definition enhancement circuit configured to detect a color difference from the color-shifted image data and to unsharp mask filter the color-shifted image data according to the detected color difference. 
     The extracted color information may include a minimum brightness value and a maximum brightness value and the color shifter circuit may be configured to color shift the input image data responsive to the minimum and maximum brightness values. The color shifter circuit may be further configured to determine a gain responsive to the extracted color information and the definition enhancement circuit may be configured to apply the determined gain to the unsharp mask filtered image data. 
     In some embodiments, the definition enhancement circuit may include a filter configured to unsharp mask filter the color-shifted image data, a color difference and gain controller circuit configured to detect the color difference from the color-shifted image data and to adaptively modify or replace the unsharp mask filtered image data according to the detected color difference to generate adaptively processed image data. The definition enhancement circuit may further include a gain multiplier circuit configured to apply the determined gain to the adaptively processed image data. 
     The color shifter circuit may be further configured to determine a high gain and a low gain responsive to the extracted color information. The gain multiplier circuit may be configured to generate low gain image data and high gain image data from the adaptively processed image data according to the determined high gain and low gain. 
     The definition enhancement circuit may further include a channel difference checker circuit configured to compare image data for center pixels of groups of pixels of the color-shifted image data to the high gain image data. The channel difference checker circuit may be configured to generate a gain select signal responsive to the comparison of the image data for the center pixels to the high gain image data and the definition enhancement circuit may further include a multiplexer configured to selectively output the high gain image data and the low gain image data responsive to the comparison. 
     In additional embodiments, the color difference and gain controller circuit may include a color difference detector circuit configured to detect the color difference by comparing image data for center pixels of respective groups of pixels of the color-shifted image data to image data for pixels surrounding the center pixels in the respective groups, and an image data modification circuit configured to modify the unsharp mask filtered image data according to the detected color difference. The image data modification circuit may include a first multiplexer configured to selectively provide the image data for the center pixels or unsharp mask filtered image data to the gain multiplier circuit and a gain controller circuit configured to control the first multiplexer responsive to the detected color difference. 
     The image data modification circuit may further include a shifter configured to scale the unsharp mask filtered image data and a second multiplexer configured to selectively provide the unsharp mask filtered image data or the scaled unsharp mask filtered image data to the first multiplexer. The gain controller circuit may be further configured to control the second multiplexer responsive to the detected color difference. The gain controller circuit and the first and second multiplexers may be configured to provide the image data for the center pixels to the gain multiplier circuit when the detected color difference is less than a first threshold, to provide the scaled unsharp mask filtered image data to the gain multiplier circuit when the detected color difference is greater than the first threshold and less than a second threshold and to provide the unsharp mask filtered image data to the gain multiplier when the detected color difference is greater than the second threshold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the inventive subject matter, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the inventive subject matter and, together with the description, serve to explain principles of the inventive subject matter. In the drawings: 
         FIG. 1  is a block diagram illustrating an image system according, to some embodiments of the inventive subject matter; 
         FIG. 2  is a block diagram illustrating interoperation of an image scaler circuit and detail creation circuit of  FIG. 1 ; 
         FIG. 3  is a block diagram illustrating and implementation of the detail creation circuit of  FIG. 2 ; 
         FIG. 4  is a block diagram illustrating an implementation of the definition enhancement circuit of  FIG. 3 ; 
         FIG. 5  is a block diagram illustrating an implementation of the color difference and gain controller circuit of  FIG. 4 ; 
         FIG. 6  illustrates operations for detecting a color difference according to some embodiments of the inventive subject matter; 
         FIG. 7  is a flowchart illustrating detail creation operations according to some embodiments of the inventive subject matter; 
         FIG. 8  illustrates an image before application of a UMF; 
         FIG. 9A  illustrates a portion of the image of  FIG. 8  before application of the UMF; 
         FIG. 9B  illustrates an image obtained by applying a high UMF coefficient to the image portion of  FIG. 9A ; 
         FIG. 9C  illustrates an image obtained by applying a low UMF coefficient to the image portion of  FIG. 9A ; 
         FIG. 9D  illustrates an image obtained by applying an adaptive UMF to the image portion of  FIG. 9A ; 
         FIG. 10A  illustrates a portion of the image of  FIG. 8  before a UMF is applied; 
         FIG. 10B  illustrates an image obtained by applying a high UMF coefficient to the image portion of  FIG. 10A ; 
         FIG. 10C  illustrates an image obtained by applying a low UMF coefficient to the image portion of  FIG. 10A ; 
         FIG. 10D  illustrates an image obtained by applying an adaptive UMF to the image portion of  FIG. 10A ; 
         FIG. 11  illustrates an image obtained by applying a high UMF coefficient to the image of  FIG. 8 ; 
         FIG. 12  illustrates an image obtained by applying a low UMF coefficient to the image of  FIG. 8 ; and 
         FIG. 13  illustrates an image obtained by applying an adaptive UMF to the image of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings to fully explain the inventive subject matter in such a manner that it may easily be carried out by a person with ordinary skill in the art to which the present invention pertains. 
     To enhance definition for a high-quality image, a degree of definition enhancement may be controlled by determining whether it is necessary to increase the image enhancement degree for each image block to be processed and then decreasing or increasing an unsharp mask filter (UMF) coefficient. Embodiments of the inventive subject matter provide apparatus and methods for effectively controlling definition enhancement by detecting, for an image processing block, an area requiring definition enhancement, and adjusting a UMF coefficient to provide appropriate definition enhancement. 
       FIG. 1  is a block diagram illustrating an image system  100  according to some embodiments of the inventive subject matter. The image system  100  includes an image scaler circuit  10 , a detail creation circuit  20 , a central processing unit (CPU)  30 , a memory controller circuit  40 , an external memory  50 , and a system bus  60 . 
     The image scaler circuit  10  changes a resolution of an image input thereto, and stores the image with changed resolution in the memory  50 . The image scaler circuit  10  also may remove an aliasing artifact phenomenon that may occur when changing the resolution of the input image. The detail creation circuit  20  enhances the definition of the input image, and will be more fully described with reference to  FIGS. 2 and 4 . The CPU  30  may include, for example, an ARM® processor. The memory  50  may include, for example, a DRAM. 
     The memory controller circuit  40  accesses the external memory  50  in response to the control of the CPU  30 . The external memory  50  stores an image scaled up by the image scaler circuit  10 , or stores an image definition enhanced by the detail creation circuit  20 . The system bus  60  interconnects the image scaler circuit  10 , the detail creation circuit  20 , the CPU  30 , and the memory controller circuit  40 . 
       FIG. 2  is a block diagram illustrating interoperation of the image scaler circuit  10  and the detail creation circuit  20  in  FIG. 1 . The image scaler circuit  10  stores the scaled-up (i.e., resolution-enhanced) image in the external memory  50 . The detail creation circuit  20  receives the resolution-enhanced image stored in the external memory  50  and enhances the definition thereof. The external memory  50  stores the scaled-up and definition-enhanced image. 
     The image scaler circuit  10  stores the resolution-enhanced image in an internal buffer memory, and the detail creation circuit  20  may receive the resolution-enhanced image stored in the internal buffer memory to thereby enhance the definition. 
       FIG. 3  is a block diagram illustrating an implementation of the detail creation circuit  20  of  FIG. 2 . The creation circuit  20  includes a major color extractor circuit  21 , a color shifter circuit  22 , a definition enhancement circuit  23 , and a memory interface circuit  24 . 
     The major color extractor circuit  21  reads out the image stored in an internal memory  25  though the memory interface circuit  24 , and extracts a major color (i.e., maximum value or minimum value) from the read-out image. Operations for extracting a major color according to some embodiments of the inventive subject matter are described below with reference to  FIG. 6 . 
     The major color extractor circuit  21  extracts the maximum value and the minimum value for brightness of each pixel from image data of 5×5 pixels (shown in  FIG. 6 ). The major color extractor circuit  21  calculates a distance signal (Distance) indicating a difference between the maximum value and the minimum value. The major color extractor circuit  21  amplifies the brightness of each pixel from the image data of 5×5 pixels by four to thereby generate image output data (Out_RGB). The major color extractor circuit  21  transmits the distance signal (Distance), a maximum value signal (Majcolor 0 ) and a minimum value signal (Majcolor 1 ), and the image output data (Out_RGB), to the color shifter circuit  22 . 
     The detail creation circuit  20  operates in response to a Fetch_start signal. In particular, when the minimum amount of image data (e.g., 5×5 pixels) is stored in the internal memory  25 , the Fetch_start signal is activated. 
     The color shifter circuit  22  shifts each image output data (Out_RGB) toward one of the maximum value (Majcolor 0 ) and the minimum value (Majcolor 1 ), which is closer thereto, by the use of the major color (i.e., maximum value or minimum value) extracted from the major color extractor circuit  21 . The color shifter circuit  22  calculates a gain (Gain) using the distance signal (Distance) transmitted from the major color extractor circuit  21 . The color shifter circuit  22  generates a gain (Gain) and output image data (O_RGB). 
     The definition enhancement circuit  23  adaptively applies a UMF to enhance the definition of the image. An implementation of the definition enhancement circuit  23  according to some embodiments of the inventive subject matter is described below with reference to  FIG. 4 . 
     The memory interface circuit  24  writes and reads image data to and from the internal memory  25 . Although rapid reading and storing may occur through the internal memory  25 , rapid reading and storing may be realized using the external memory  50  that is shown in  FIG. 1 . 
       FIG. 4  is a block diagram illustrating an implementation of the definition enhancement circuit  23  of  FIG. 3 . The definition enhancement circuit  23  includes a UMF  231 , a color difference and gain controller circuit  232 , a first multiplexer (MUX 1 )  233 , a gain multiplier circuit  234 , a channel difference checker (CDC) circuit  235 , a second multiplexer (MUX 2 ), and a third multiplexer (MUX 3 )  237 . 
     The UMF  231  outputs filtered RGB data UMF_RGB by applying an UMF to image data O_RGB. The color difference and gain controller circuit  232  receives the filtered RGB data UMF_RGB and performs an adaptive UMF operation. The color difference and gain controller circuit  232  outputs adaptively filtered data AUMF_RGB. An implementation of the color difference and gain controller circuit  232  is described below with reference to  FIG. 5 . 
     The first multiplexer  233  outputs the filtered RGB signal UMF_RGB or the adaptively filtered RGB signal AUMF_RGB in response to a mode signal Mode. When the mode signal Mode is activated, a result according to the adaptive UMF operation is output. When the mode signal Mode is deactivated, a result according to the general UMF operation is output. That is, whether to apply the adaptive UMF operation is determined depending on the activation/deactivation of the mode signal Mode. 
     The gain multiplier circuit  234  multiplies the output of the first multiplexer  233  by the gain Gain transmitted from the color shifter circuit  22 . The gain signal Gain may include a high gain signal and a low gain signal. The gain multiplier circuit  234  generates a high gain RGB signal High_RGB by multiplying the output of the first multiplexer  233  by the high gain signal. Likewise, the gain multiplier circuit  234  generates a low gain RGB signal Low_RGB by multiplying the output of the first multiplexer  233  by the low gain signal. The gain multiplier circuit  234  transmits the high gain and low gain RGB signals High_RGB, Low_RGB signals to the second multiplexer  236 . 
     The CDC circuit  235  receives center data RGB_Center of the input image data O_RGB and the high gain RGB signal High_RGB. The CDC circuit  235  compares the center data RGB_Center and the high gain RGB signal High_RGB, and then generates a gain select signal Gain_sel based on consideration of noise of these signals. Also, the CDC circuit  235  checks a grey valence for the center data RGB_Center to generate the gain select signal Gain_sel. 
     The gain select signal Gain_sel generated by the CDC circuit  235  controls the second multiplexer  236 . The grey valence means that a difference between the center data RGB-Center and each datum of the red (R), green (G) and blue (B) data is a predetermined bit or less. If the center data RGB_Center belong to a grey area meeting such a grey valence criterion, the second multiplexer  236  outputs the low gain RGB signal Low_RGB to the third multiplexer  237 . Otherwise, the second multiplexer  236  outputs the high gain RGB signal High_RGB to the third multiplexer  237 . 
       FIG. 5  is a block diagram illustrating an implementation of the color difference and gain controller circuit  232  of  FIG. 4 .  FIG. 6  illustrates operations for detecting, a color difference that may be implemented by the circuit of  FIG. 5 . 
     Referring to  FIGS. 4 and 5 , the color difference and gain controller circuit  232  includes a color difference detector circuit  232   a , a gain controller circuit  232   b , a 2-bit shifter  232   c , and first and second multiplexers  232   d  and  232   e . The color difference detector circuit  232   a  generates a signal indicating a color difference from the input image data O_RGB according to Equation 1 below:
 
Color_Diff=(|00-12|+|02-12|+|04-12|+≡10-11|+≡14-12≡+|20-11|+|22-14|+|24-12|)/8  (1)
 
In Equation 1, the numbers correspond to 5×5 pixels shown in  FIG. 6 .
 
     The gain controller circuit  232   b  receives the color difference signal output from the color difference detector circuit  232   a . The gain controller circuit  232   b  categorizes the color difference Color_Diff as shown below: 
     Case1: Color_Diff&lt;Threshold_low 
     Case2: Threshold_low&lt;Color_Diff&lt;Threshold_high 
     Case3: Color_Diff&gt;Threshold_high 
     It is assumed that the input data O_RGB of each of R, G and B has a value ranging from 0 to 255. 
     For example, some embodiments of the inventive subject matter may use a lower threshold Threshold_low of 4 and a higher threshold Threshold_high of 8. For these thresholds, the first case Case1 is that the color difference Color_Diff is less than 4. In this case, there is little or no color difference for the input data O_RGB. To bypass the output of the gain multiplier circuit  234 , the gain controller circuit  232   b  activates a gain bypass signal Gain_Bypass. The third multiplexer  237  is controlled by the gain bypass signal Gain_Bypass. 
     The second case Case2 is that the color difference Color_Diff is greater than 4 but less than 8. In this case, the color difference of the input data O_RGB is relatively small. The 2-bit shifter  232   c  reduces the filtered RGB data UMF_RGB by one quarter (¼). The 2-bit shifter  232   c  transmits the ¼-reduced filtered RGB data to the first multiplexer  232   d . The gain controller circuit  232   b  activates a gain detect signal Gain_Detect such that the ¼-reduced filtered RGB data is output to the second multiplexer  232   e  from the first multiplexer  232   d.    
     The third case Case3 is that the color difference Color_Diff is greater than 8. In this case, the color difference of the input data O_RGB is relatively large. The gain controller circuit  232   b  deactivates the gain detect signal Gain_Detect such that the filtered RGB data is output to the second multiplexer  232   e  from the first multiplexer  232   d.    
     Table 1 shows the cases described above: 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
             
             
               
                   
                 If(Color_Diff &lt; 4) 
                   
               
               
                   
                 Gain_Bypass =1; 
                 //Case1 
               
               
                   
                 else If(4 &lt; Color_Diff &lt; 8) 
                   
               
               
                   
                 Gain_Detect = 1; 
                 //Case2 
               
               
                   
                 else 
                   
               
               
                   
                 Gain_Bypass = Gain_Detect = 0; 
                 //Case3 
               
               
                   
               
             
          
         
       
     
     Referring to  FIGS. 4 through 6 , the input data includes 5×5 red input data (R) for, 5×5 green input data (G), and 5×5 blue input data (B). Data  12  corresponds to center data RGB_Center. According to some embodiments of the inventive subject matter, the maximum or minimum value is determined when comparing each of input data  00  to  11  and  13  to  24  and the center data  12 . In some embodiments of the inventive subject matter, only eight data among 5×5 input data are compared with the center data  12 . For example,  00 ,  02 ,  04 ,  10 ,  14 ,  20 ,  22  and  24  are compared with the center data  12 . The eight data  00 ,  02 ,  04 ,  10 ,  14 ,  20 ,  22  and  24  are the date referred to in Equation 1. 
       FIG. 7  is a flowchart illustrating operations of the detail creation circuit  20  in  FIG. 3 . The major color extractor circuit  21  divides input image data in units of blocks (for example, 5×5 pixels), and extracts the major color of each block (block S 01 ). The major color is set to the maximum or minimum value of the input image data. The color shifter circuit  22  shifts the color of the center pixel RGB_Center by the use of the major color (block S 02 ). In particular, the color shifter circuit  22  increases the color of the center pixel RGB_Center toward the maximum value if the center pixel is close to the maximum value, and the color shifter circuit  22  decreases the color of the center pixel RGB_Center toward the minimum value if the center pixel is close to the minimum value. The UMF  231  filters the input image data O_RGB (block S 03 ). The color difference and gain controller circuit  232  detects a color difference and controls the resultant gain (block S 04 ). The gain controller circuit  232   b  controls the gain value by comparing the center pixel RGB_Center and the maximum gain image data High_RGB (block S 05 ). The output image data output_RGB is output according, to the mode signal Mode (block S 06 ). 
       FIG. 8  illustrates an original image before UMF is applied. In  FIG. 8 , a portion A denotes an area with small color difference, and a portion B denotes an area with large color difference. 
       FIGS. 9B through 9D  respectively illustrate an image obtained when a high UMF coefficient is applied to the portion A of the original image shown in  FIG. 8  in a “strong” mode, an image obtained when a low UMF coefficient is applied in a “weak” mode, and an image obtained when an adaptive UMF applied in an “adaptive” mode.  FIGS. 10B through 10D  respectively illustrate an image obtained when a high UMF coefficient is applied to the portion B of the original image shown in  FIG. 8  in a “strong” mode, an image obtained when a UMF coefficient is applied in a “weak” mode, and an image obtained when an adaptive UMF is performed in an “adaptive” mode. 
       FIG. 9B  shows that the image of the portion A is very coarse in comparison with the portion A of the original image in  FIG. 9A . Such a coarse image typically appears when a UMF coefficient is high.  FIG. 9C  shows that the definition of the image of the portion A is worse than the image of  FIG. 9B .  FIG. 9D  shows very good image compared to the images in  FIGS. 9B and 9C . It appears that the adaptive UMF procedure enhances the definition by appropriately controlling a filter coefficient. 
       FIG. 10B  shows that the image of the portion B is very coarse in comparison with the portion B of the original image in  FIG. 10A . Such a coarse image typically appears when a UMF coefficient is high.  FIG. 10C  shows that the definition of the image of the portion B is worse than the image of  FIG. 10B .  FIG. 10D  shows a relatively good image compared to the images in  FIGS. 10B and 10C . 
       FIG. 11  illustrates an image obtained by applying high UMF coefficient to the original image in  FIG. 8 .  FIG. 12  illustrates an image obtained by applying low UMF coefficient to the original image in  FIG. 8 .  FIG. 13  illustrates an image obtained by applying adaptive unsharp mask filtering to the original image in  FIG. 8 . 
       FIG. 11  shows that the image is very coarse in comparison with the original image in  FIG. 8 .  FIG. 12  shows that the definition of the image is worse than the image in  FIG. 11 .  FIG. 13  shows relatively good image compared to the images in  FIGS. 11 and 12 . 
     In image processing apparatus according to some embodiments of the inventive subject matter, strong, weak and adaptive UMF modes may be provided. The strong mode uses a relatively high UMF coefficient, the weak mode uses a relatively low UMF coefficient and the adaptive mode uses an adaptive UMF coefficient. 
     Therefore, the mage processing device according to some embodiments of the inventive subject matter may enhance the definition for an input image depending on the various modes. Also, by controlling the UMF coefficient appropriately using the color difference of the input image, it is possible to enhance the definition.