Patent Publication Number: US-8116580-B2

Title: Embedded high frequency image details

Description:
TECHNICAL FIELD 
     The present invention relates to a method, process, and system for embedding high frequency image details into a digital image file. 
     BACKGROUND 
     There are a multitude of devices and techniques for creating digital representations of images. For example, digital images of physical objects can be created using digital imaging devices such as digital cameras, scanners, and radars while computer graphics and imaging programs directly generate digital images. Regardless of source, a digital image is commonly arranged as a 2-dimensional (2D) array of pixels. Each pixel of an image has a specific position and a value. For example, the value of a red-green-blue (RGB) color digital image pixel is commonly represented by a triplet of values, one for each of the red, green or blue color channels. The raw pixel data generated by digital imaging devices and computer graphics is typically converted and stored as a digital image file. 
     There are many different types of digital image file formats. Some common examples of digital image file formats include windows bitmap (bmp), graphics interchange format (gif), exchangeable image file (exif), RAW image format (RAW), and portable network graphics (png). Another commonly used file format is the Tagged Image File Format (TIFF). Two of the most commonly used formats are the Joint Photographic Experts Group (JPEG) and a new wavelet-based compression technique referred as JPEG2000. Many of these digital image file formats include some method of either lossy or lossless compression of the images to reduce the amount of memory necessary to store the image and the bandwidth consumed during transmission of the image. 
     Some of the challenges in storing and transmitting digital image files is balancing the desire for reduced image file size against the need for higher resolution and 1197899 thus, additional information. Lossless compression techniques can only reduce the overall file by a finite amount. Therefore, many digital image file formats compress images using a lossy compression technique by reducing and eliminating the rapidly changing or high frequency components of the image. The elimination of these rapidly changing elements may result in blurring of images and other negative effects, particularly high frequency information as might be generated by text or other line art present in the digital image. 
     A second challenge in storing and transmitting digital image files may be the presence of incompatible digital image file formats. Typically a digital image is first encoded to a digital image file using an encoder. After the digital image file is generated it must be decoded by a decoder prior to being rendered for either viewing or printing. Incompatibilities between digital file formats and decoders may render digital image files unreadable on many computers and reduce the prevalence and portability of different types of digital images files. 
     Therefore, there is a need for a method, process, and system for embedding high frequency image images into an image file that remains compatible with existing image rendering systems while providing additional image resolution when rendered with a compliant viewer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying figures depict multiple embodiments of a system, process, and method for embedded high frequency image details. A brief description of each figure is provided below. Elements with the same reference numbers in each figure indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawings in which the reference number first appears. 
         FIG. 1  is a block diagram detailing an imaging system; 
         FIG. 2  is a flow chart detailing an operation of image separator system; 
         FIG. 3  is a flow chart detailing an operation of a low frequency encoder; 
         FIG. 4  is a flow chart detailing an operation of a high frequency encoder; 
         FIG. 5  is a flow chart detailing an operation of a file creator; 
         FIG. 6  is a flow chart detailing an operation of a non-compliant digital image decoder; 
         FIG. 7  is a flow chart detailing an operation of a compliant digital image decoder; 
         FIG. 8  is an example of low frequency and high frequency subimages created by the image separator system of  FIG. 2 ; and 
         FIG. 9  is an example of low frequency and high frequency subimages created by three passes of the image separator system of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a block diagram detailing an imaging system  100 . The imaging system  100  comprises an image separator system  104 , low frequency encoder  112 , high frequency encoder  114 , and a file creator  118 , wherein the imaging system  100  receives an input digital image  102  and generates a final digital image  122  which embeds both low and high frequency data. The imaging system  100  also comprises both a non-compliant digital image decoder  120  and a compliant digital image decoder  124 . The non-compliant decoder is typically a decoder or viewer for images in proprietary file formats and is usually created by the supplier of such format. A compliant decoder is a generally known and available image viewer or decoder for commonly recognized image file formats, such as JPEG, JPEG2000, TIFF, GIF, PNG, Exif and bmp. 
     The non-compliant digital image decoder  120  receives the final digital image  122  and decodes only the low frequency data, resulting in a low frequency digital image  126 . For example, any conventional imaging software program can read in the final digital image  122  and process the low frequency data. In contrast, the compliant digital image decoder  124  receives the final digital image  122  and decodes both the low and high frequency data, resulting in a high frequency, or high-resolution, digital image  128 . Once generated, the low frequency digital image  126  and the high frequency digital image  128  are available for display, editing, storing, or printing. 
     The operation of the image separator system  104  is shown in  FIG. 2 . Processing starts  202  and proceeds a the block image operation  204 . In the block image operation  204 , the image separator system  104  receives the input digital image  102  and blocks the image  102  into non-overlapping pixel blocks, thereby creating a blocked image  206 . Preferably, the input digital image  102  is blocked into non-overlapping 2×2 pixel blocks which contains a total of four pixels. In alternative embodiments, the input digital image  102  is blocked into square or rectangular pixel blocks having a different number of pixels, such as 1×2, 3×3, 4×4 or 8×8. Thus, the resulting pixel blocks of the blocked image  206  may be either of a uniform or a non-uniform size. Also, the block image operation  204  of the input digital image  102  may occur sequentially or as a batch process. 
     Once the blocked image  206  is created, the image separator system  104  proceeds to a create pixel vector operation  208 , which orients each pixel block of the blocked image  206  as a pixel vector. For example, the image separator system  104  retrieves a current pixel block from the blocked image  206 , orients the current pixel block as a vector as shown in Expression 1, and stores the vector as pixel vector data  210 . 
     
       
         
           
             
               
                 
                   
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     The image separator system  104  performs an apply wavelet transform operation  212 . The apply wavelet transform operation  212  applies a wavelet transform function to the pixel vector data  210 , as shown in Expression 2, to generate a low frequency subimage  106  and a high frequency subimage  108 . 
     
       
         
           
             
               
                 
                   
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     Expression 2 provides the preferred Haar wavelet transform; however, other wavelet transforms may be used. The preferred wavelet transform parameters [a, b, c, d] of Expression 2 represent different components of information from the pixel vector data  210 . The wavelet parameter a represents the average value of the pixel vector data  210 , and as such, is considered a low frequency representation of the corresponding pixel vector and is used to generate the low frequency subimage  106 . The wavelet parameters b, c, and d represent edge information or higher frequency data regarding the pixel vector data  210  and are used to generate the high frequency subimage  108 . Alternative embodiments may utilize other types of wavelet transforms, including, but not limited to, Daubechies, Cohen-Daubechies-Feauveau, and symlet wavelet transforms. 
     In an alternative embodiment, the wavelet parameter a is used to create the low frequency subimage  106 . The low frequency subimage  106  is an accumulation of all of the a parameters from the successive application of the wavelet transform operation  212  to the non-overlapping pixel blocks of the blocked image  206 . In addition to the low frequency subimage  106 , a similar set of three high frequency subimages  108  are created by accumulating all of the b, c, and d parameters from successive application of the wavelet transform operation  212  to the non-overlapping pixel blocks of the blocked image  206 . After the respective wavelet transform parameters are accumulated for a specific pixel block of the blocked image  206 , the image separator system  104  determines  214  if the entire blocked image  206  has been transformed into high frequency subimages  108  and low frequency subimage  106 . If the blocked image  206  has not been completely transformed, then the image separator system  104  selects the next non-overlapping pixel block  216 , and the process repeats. In this embodiment, a 2×2 pixel block is extracted from the blocked image  206  with each iteration of the image separator system  104 . When the processing is finished of all pixel blocks of the blocked image  206 , the wavelet transform operation  212  has been applied to the entire blocked image  206 , and the resulting wavelet parameters have been separated into respective low frequency subimage  106  and high frequency subimages  108  creating a first pass composite image output. 
       FIG. 8  shows the first pass composite image  800  output after one pass through the image separator system  104 . The resulting low-level (LL) frequency subimage  802 , which represents the wavelet transform parameter a, is an average of the 2×2 pixel blocks of the blocked image  206 . Therefore, the LL frequency subimage  802  is ¼ the original size of the entire input digital image  102 . The first pass composite image  800  also contains three high frequency subimages: the Low-High (LH) level subimage  804 ; the High-Low (HL) level subimage  806 ; and, the High-High (HH) level subimage  808 . These high frequency subimages,  804 ,  806 , and  808 , and in particular the HH subimage  808  are nearly all zeros, while the LL subimage  802  is still recognizable as the original image albeit with reduced resolution. 
     Referring back to  FIG. 2 , after the first pass processing of the input digital image  102  and creating a composite image  800 , the image separator system  104  determines in operation  218  whether another pass through the image separator system  104  is needed (described in detail below). If another pass is required, the image separator system  104  proceeds to operation  222  and sets the input digital image  102  equal to the low frequency subimage  106 , for example, as shown as LL frequency subimage  802  in  FIG. 8 . Since the next pass through the image separator system  104  is only applied to the low frequency subimage  106 , the high frequency subimages  108 , for example, LH level subimage  804 , HL level subimage  806 , and HH level subimage  808  of  FIG. 8 , are passed directly through to the high frequency encoder  114 . 
       FIG. 9  illustrates multiple passes of an input digital image  102  (shown as composite image  900 ) through the image separator system  104 , and in particular shows low frequency subimages  106  and high frequency subimages  108  created by three passes through the image separator system  104 . A second pass through the image separator system  104  inputs the first LL frequency subimage  802  as the input digital image  102 . The output of a second pass through the image separator system  104  is a second LL frequency subimage  904 , a second LH level subimage  906 , a second HL level subimage  908 , and a second HH level subimage  910 . 
     A third pass through the image separator system  104  inputs the second LL frequency subimage  904  as the input digital image  102 . The output of a third pass through the image separator system  104  is a third LL frequency subimage  912  and the following third pass high frequency subimages  108 : third pass LH subimage  914 , third pass HL subimage  916 , and third pass HH subimage  918 . 
     The three pass composite image  900  demonstrates the ability to successively apply the image separator system  104  to the low level frequency subimage  106  of a given blocked image  206 . Each successive pass through the image separator system  104  reduces the overall size of the low frequency subimage  106  and the resulting resolution and size of the original, base input digital image  102 . In the preferred embodiment, the number of passes through the image separator system  104  is selectable by the user based on the desired reduction of original image resolution and other parameters such as a user tunable low frequency image resolution selection threshold or a scaling parameter. After separation of the low frequency subimage  106  from the high frequency subimages  108  from the first, second and third passes through the image separator system  104 , the low frequency image  106  (e.g., third LL frequency subimage  912 ) is output to the low frequency encoder  112  while the high frequency images  108  are output to a high frequency encoder  114 . 
     Multiple passes may be made through the image separator system  104  until operation  218  determines that no additional passes on the low frequency subimage  106  are desired. If no such additional processing is desired, the image separator system  104  has completed its processing  220  of the input digital image  102 . 
     The low frequency encoder  112  processes only the output of the low frequency subimage  106  and is shown on  FIG. 3 . The low frequency encoder  112  uses a standard or established image encoding technique in order to ensure compatibility with the greatest number of image rendering systems. A number of different types of image encoding techniques are used in different embodiments. In the preferred embodiment, the image encoding technique used is the JPEG process, as it is a well-known process and easy to implement. 
     After starting  302 , the low frequency encoder  112  inputs the low frequency subimage  106  and blocks it into n×n pixel blocks in operation  304 . In this embodiment, the standard JPEG process is applied to an 8×8 pixel non-overlapping block. The resulting pixel blocks are then processed in operation  306  using a discrete cosine transform (DCT), as shown in Expression 3. The preferred DCT is related to a discrete Fourier transform (DFT), but using only real numbers that provide a representation of the 8×8 pixel block. This preferred DCT concentrates most of the signal information in a 8×8 pixel block in a few low frequency components in order to compact the signal. This successive application of the DCT transform to the pixel blocks creates the DCT transform data of operation  306 . 
     
       
         
           
             
               
                 
                   
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     After creating the DCT Transform data, the low frequency encoder  112  proceeds to operation  308  and quantizes the DCT transform data by dividing each coefficient of the DCT transform data by a predefined number. The quantization effectively reduces the values of higher frequency information produced by the DCT transform operation  306 . A common quantization matrix for a JPEG image process is shown in Expression 4, below. After the DCT transform data has been divided by the quantization matrix, a threshold or rounding process is applied to the resulting coefficients to eliminate values near zero and fractional values. The result is a plurality of quantized DCT parameters. The larger the quantization values are, the greater the degree of compression of the signal, and typically the greater the loss of high frequency subimage details. 
     
       
         
           
             
               
                 
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     The quantized DCT parameters created in operation  308  are next encoded in operation  310  using an entropy encoding technique. Entropy encoding compresses data by replacing symbols represented by equal-length codes with symbols represented by codes proportional to the negative logarithm of the probability. Thus, the most common symbols use the shortest codes. For the JPEG process, a common entropy encoding process is Huffman coding. The Huffman coding process allows for lossless data compression of the quantized DCT parameters resulting in encoded DCT parameters. 
     After the quantized DCT parameters are created, the low frequency encoder  112  creates the compressed low frequency image  110 . The compressed low frequency image  110  is created by outputting the encoded DCT parameters and associated information into a standard image file format associated with the compression standard used. In this embodiment, the JPEG file format is used. Once the compressed low frequency image  110  is created, the low level encoder  112  has completed its operation  312 . 
     The high frequency encoder  114 , shown in  FIG. 4 , compresses the high frequency subimages  108  which will subsequently be embedded with the compressed low frequency image  110 . Processing starts  402  and immediately proceeds to operation  404  wherein the high frequency encoder  114  replaces the LL frequency subimage  912  component of the overall set, or fills in the gap with, a zero image. The high frequency subimages  108  are the full set of high frequency subimages from the first pass (LH level subimage  804 , HL level subimage  806 , and HH level subimage  808 ), the second pass (second LH level subimage  906 , a second HL level subimage  908 , and a second HH level subimage  910 ), and the third pass (third pass LH subimage  914 , third pass HL subimage  916 , and third pass HH subimage  918 ), and are input into the high frequency encoder  114 . Together, the zero image created at operation  404  and the high frequency subimages  108  create a square high frequency subimage  406 . 
     The high frequency encoder  114  proceeds to operation  408 , wherein the square high frequency subimage  406  is quantized in operation  408  to produce quantized high frequency data. The quantization process in the preferred embodiment uses a rounding process to remove fractional coefficients from the square high frequency subimage  406  to create the quantized high frequency data. Continuing, the high frequency encoder  114  compresses the quantized high frequency data with a lossless encoding technique in operation  410 . In one embodiment, the preferred encoding technique is a Lempel-Ziv-Walch (LZW) process. In other embodiments, other lossless encoding techniques, such as Huffman coding and run length encoding, may be used. The encoded high frequency data is then stored as the compressed high frequency image  116 . Once the compressed high frequency image  116  is created, the high level encoder  114  has completed its operation  412 . 
     The file creator  118  of the imaging system  100  creates a final digital image  122  by combining both the compressed low frequency image  110  and the compressed high frequency image  116 , which is compatible with standard rendering systems. In this embodiment, the JPEG file format is used. The operation of the file creator  118  is shown in  FIG. 5 . 
     The file creator  118  starts  502  its processing in operation  504  by appending a high frequency data tag  506  to the end of the compressed low frequency image  110 . The data tag  506  is a delimiter for separating the compressed low frequency image  110  from the compressed high frequency image  116  in the final digital image  122 . After appending the data tag  506 , the file creator  118  proceeds to operation  508  and appends the compressed high frequency image  116  after the data tag  506 , thereby creating the final digital image  122 . The resulting final digital image  122  with compressed low frequency image  110  and compressed high frequency image  116  is compatible with most existing image rendering systems and may provide enhanced higher resolution details for a compliant image rendering system. Once the final digital image  122  is created, the file creator  118  has completed its operation  510 . 
     In other embodiments, the file creator  118  embeds additional information in the final digital image  122 . The additional information may be embedded anywhere in the final digital image  122  so long as it is easily delimited from the other data, such as at the end of the digital image  122 . 
       FIG. 6  illustrates the operation of a non-compliant digital image decoder  120  for creating a low resolution (low frequency) digital image  126  from the final digital image  122  containing the compressed low frequency image  110  embedded with compressed high frequency image  116 . The non-compliant digital image decoder  120  starts  602  its processing with operation  604  by reading the final digital image  122  as it would any conventional compressed digital image file of a type used to encode a low frequency subimage. Thus, the non-compliant digital image decoder  120  extracts the compressed low frequency image  110  from the final digital image  122 . 
     Proceeding to operation  606 , non-compliant digital image decoder  120  uses a symbol decoder and reconstructs the DCT transformed data from the extracted compressed low frequency image  110 . The DCT transformed data is then inverse transformed in operation  608  using an inverse DCT to output a series of n×n pixel blocks. The non-compliant digital image decoder  120  then performs operation  610  and merges the n×n pixel blocks into the low frequency digital image  126  using conventional rendering processes. When the non-compliant digital image decoder  120  reads the high frequency data tag  506 , it stops processing because it does not have the means to render an image from the remaining data, i.e., the compressed high frequency image  116 , in the final digital image  122 . Thus, the non-compliant digital image decoder  120  terminates  612  after it finishes rendering the low frequency digital image  126 . 
       FIG. 7  illustrates the operation of a compliant digital image decoder  124  for creating a high frequency digital image  128  from the final digital image  122 . The compliant digital image decoder  124  starts  702  its processing with invoking the non-compliant digital image decoder  120  to extract the compressed low frequency image  110  from the final digital image  122  and create the low frequency digital image  126 . 
     Unlike the non-compliant digital image decoder  120 , upon encountering the data tag  506 , the compliant digital image decoder  124  continues processing of the compressed high frequency image  116  in the final digital image  122  to render a high frequency digital image  128 . In particular, after creating the low frequency digital image  126 , the compliant digital image decoder  122  proceeds to operation  704  to extract and decompress, or decode, the compressed high frequency image  116  using the inverse process to that used, such as an LZW decoder, to re-create the high frequency subimages  706 . 
     The next operation  708  in the rendering process recreates the composite image  800  (or composite image  900 ) by merging the low frequency digital image  126  with the high frequency subimages  706 . Continuing to operation  710 , the compliant digital image decoder  124  separates the composite image  800  into the respective pass subimage blocks. In the described embodiment of three passes, the first reverse application extracts the third LL frequency subimage  912  and the third pass high frequency subimages: third pass LH subimage  914 , third pass HL subimage  916  and third pass HH subimage  918 . These subimages are input to the construct wavelet parameter blocks operation  712  which performs the inverse wavelet transform on the subimages  912 ,  914 ,  916 ,  918 . The inverse wavelet transform operation  712 , see Expression 5, is used to recreate the respective 2×2 pixel block, see Expression 1, that was used originally to create the wavelet parameters. Proceeding to operation  714 , the resulting 2×2 pixel block is then reintegrated to create the second pass LL frequency subimage (not shown, but is at position  904  on  FIG. 9 ). The compliant digital image decoder  122  determines in operation  716  if another pass of the LL frequency subimage is needed. The inverse wavelet transform is thus successively applied to the number of passes of the block image operation  204  performed by the image separator system  104  on the original input digital image  102 . After the final pass  716 , processing is complete  718 , and a high frequency digital image  128  is available for display or printing. 
     
       
         
           
             
               
                 
                   
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     A scanner is a common digital image generation device. A digital image generated by a scanner is encoded using the system and process outlined above to create a final digital image file  122  with a compressed low frequency image  110  and a compressed high frequency image  116 . In the preferred embodiment, the software for creating the final digital image file  122  of the present invention with compressed high frequency image  116  resides in the scanner interface software. The user has the option to save a scanned image with embedded high frequency subimages  108  or to use a standard image file format. Then, a compliant digital image decoder  124 , which is embedded in an authorized compliant image viewing and rendering system, enables viewing of the final digital image file  122  with the compressed high frequency image  116  to be viewed at high resolution. In an alternative embodiment, the compliant digital image decoder  124  is embedded within a printer driver or printer controller whereby the printer driver or printer controller utilizes the high frequency information embedded within the final digital image file  122  with compressed high frequency image  116  to create high resolution output. 
     The embodiments of the present invention shown in the drawings and described above are exemplary of numerous embodiments that may be made within the scope of the appended claims. It is contemplated that numerous other configurations, methods, processes and applications of the embedded high frequency image detail system may be created taking advantage of the disclosed approach. Therefore, it is the applicant&#39;s intention that the scope of the patent issuing herefrom will be limited only by the scope of the appended claims.