Abstract:
A method includes: receiving, at a computing device, image data encoded by delta row encoding, the image data indicating two dimensionally arranged plurality of pixels, the image data including delta data indicating difference between N-th row line and (N−1)th row line in the two dimensionally arranged plurality of pixels; pre-decoding the image data for the N-th row line using the delta data if the delta data has a size equal to or larger than a threshold while keeping the image data for the N-th row line using the delta data if the delta data has a size smaller than the threshold so as to generate intermediate codes using the computing device; and decoding and rendering the kept undecoded lines in the generated intermediate codes while rendering the decoded lines in the generated intermediate codes using the computing device.

Description:
BACKGROUND 
     Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section. 
     This disclosure is related with an image-forming apparatus having a printing function such as printers, copiers, facsimile machines, and multi-function peripheral (MFP) having the functions of these apparatus. The image-forming apparatus processes images with high resolutions, which consume a large memory area. The memory area is saved by converting a print job of each page into intermediate codes after being divided into a plurality of bands. The intermediate codes are stored in the memory area while the image printing is performed on a page-by-page basis by rasterizing the stored intermediate codes into a bit image. 
     SUMMARY 
     A method according to one aspect of the disclosure includes: receiving, at a computing device, image data encoded by delta row encoding, the image data indicating two dimensionally arranged plurality of pixels, the image data including delta data indicating difference between N-th row line and (N−1)th row line in the two dimensionally arranged plurality of pixels; pre-decoding the image data for the N-th row line using the delta data if the delta data has a size equal to or larger than a threshold while keeping the image data for the N-th row line using the delta data if the delta data has a size smaller than the threshold so as to generate intermediate codes using the computing device; and decoding and rendering the kept undecoded lines in the generated intermediate codes while rendering the decoded lines in the generated intermediate codes using the computing device. 
     These as well as other aspects, advantages, and alternatives will become apparent to those of ordinary skill in the art by reading the following detailed description with reference where appropriate to the accompanying drawings. Further, it should be understood that the description provided in this summary section and elsewhere in this document is intended to illustrate the claimed subject matter by way of example and not by way of limitation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a block diagram representing a functional configuration of an image forming system  10  according to one embodiment of the disclosure. 
         FIG. 2  illustrates a schematic drawing representing a typical delta row decoding according to a comparative example. 
         FIG. 3  illustrates a schematic drawing representing a typical image rendering process according to the comparative example. 
         FIG. 4  illustrates a schematic drawing representing the typical image rendering process according to the comparative example. 
         FIG. 5  illustrates a flow chart representing an image process according to one embodiment. 
         FIG. 6  illustrates a flow chart representing a fast delta row (FDR) image process according to the one embodiment. 
         FIG. 7  illustrates a flow chart representing an image decoding process of the fast delta row image process according to the one embodiment. 
         FIG. 8  illustrates a schematic drawing representing an FDR decoding according to the one embodiment. 
         FIG. 9  illustrates a flow chart representing a fast delta row image decoding process according to the one embodiment. 
         FIG. 10  illustrates a schematic drawing representing an FDR decoding according to the one embodiment. 
         FIG. 11  illustrates a schematic drawing representing the FDR decoding according to the one embodiment. 
         FIG. 12  illustrates a schematic drawing representing the FDR decoding according to the one embodiment. 
         FIG. 13  illustrates a schematic drawing representing the FDR decoding according to the one embodiment. 
         FIG. 14  illustrates a flow chart representing an image rendering process of decoded image according to the one embodiment. 
         FIG. 15  illustrates a schematic drawing representing an image rendering process according to the one embodiment. 
         FIG. 16  illustrates a schematic drawing representing the image rendering process according to the one embodiment. 
         FIG. 17  illustrates a schematic drawing representing the image rendering process according to the one embodiment. 
         FIG. 18  illustrates a schematic drawing representing the image rendering process according to the one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Example apparatuses are described herein. Other example embodiments or features may further be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. In the following detailed description, reference is made to the accompanying drawings, which form a part thereof. 
     The example embodiments described herein are not meant to be limiting. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the drawings, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     The following describes embodiments of the disclosure (hereinafter referred to as, the “embodiments”) comparing with a comparative example with reference to the drawings. 
       FIG. 1  illustrates a block diagram representing a functional configuration of an image forming system  10  according to one embodiment of the disclosure. The image forming system  10  includes an image forming device  100  and a personal computer  200 . The personal computer  200  is connected to the image forming device  100  via a network (which is a LAN in this example). 
     The image forming device  100  includes a control unit  110 , an image forming unit  120 , an operation display unit  130 , a storage unit  140 , and a communication interface unit  150 . The personal computer  200  includes a control unit  210 , a delta row encoding unit  220 , an operation display unit  230 , a storage unit  240 , and a communication interface unit  250 . The delta row encoding unit  220  encodes image data to generate encoded image data using a delta row encoding. 
     The communication interface unit  150  and the communication interface unit  250  communicate using a Transmission Control Protocol/Internet Protocol (TCP/IP) suite. The communication interface unit  150  functions as a print data receiver in this embodiment. The print data receiver may receive print data via a discrete I/O interface. 
     The image forming unit  120  includes a delta row decoding unit  121 , an image rendering unit  122 , an image processing unit  123 , and an image output unit  124 . The delta row decoding unit  121  decodes the encoded image data by an inverse delta row encoding. The image rendering unit  122  renders the decoded image data to generate bit map data of the image. The image processing unit  123  processes the scan data in accordance with a print setting. The image output unit  124  prints an image on a printing medium based on the decoded print data. The image output unit  124  functions as a print executing unit. 
     The operation display unit  130  of the image forming device  100  includes a display  131  and an operation processing unit  132 . The operation display unit  230  of the personal computer  200  includes a display  231  and an operation processing unit  232 . The display  131 , which functions as a touch panel, displays various menus as a receiving screen. The operation processing units  132  and  232  accept an input operation of a user from the display  131 , which functions as a touch panel, and various kinds of buttons and switches (not illustrated). 
     The control units  110  and  210  include a main storage unit such as a RAM and a ROM, and a control unit such as a micro-processing unit (MPU) and a central processing unit (CPU). The control units  110  and  210  also include a controller function related to an interface such as various kinds of I/Os, a universal serial bus (USB), a bus, and other hardware, and control the entire image forming device  100  and the entire personal computer  200 , respectively. 
     The storage units  140  and  240  are storage devices formed of such as a hard disk drive and a flash memory, which are non-transitory recording mediums, and store control programs and data of processes performed by the control units  110  and  210 , respectively. 
       FIG. 2  illustrates a schematic drawing representing a typical delta row decoding according to a comparative example. This comparative example is described as one example of the delta row decoding process. 
       FIG. 2  illustrates delta row encoded image data CI and decoded image data DI. The delta row encoded image data CI is image data encoded from a plurality of pieces of original row data using the delta row encoding in the personal computer  200 . The decoded image data DI is image data decoded from the delta row encoded image data CI using the inverse delta row encoding in the image forming device  100 . 
     The delta row encoded image data CI includes the first encoded row data R 1 , the second encoded row data R 2 , and the third encoded row data R 3 . The decoded image data DI includes the first decoded row data D 1 , the second decoded row data D 2 , and the third decoded row data D 3 . The letters in pixels mean the respective colors of the pixels. The same letters indicate the same colors. The pixels in the first to fourth columns respectively include the letters “A,” “B,” “C,” and “D.” 
     The first encoded row data R 1  has an offset number of zero. The first decoded row data D 1  is generated by simply copying the first encoded row data R 1 . The second encoded row data R 2  includes a delta between the first original row data and the second original row data. The second encoded row data R 2  includes a part of image with an offset number of 6, which is calculated by 2 pixels times 3 colors for RGB. The part of image has the letters “K” and “L” in the third column and the fourth column, respectively. 
     The offset number of 6 means that there is no difference between the first original row data and the second original row data in the first and second columns of “A” and “B.” The offset number of six means that there is difference between the first original row data and the second original row data starting from the third column. 
     In the third column, the first original row data has the letter “C” while the second original row data has the letter “K.” In the fourth column, the first original row data has the letter “D” while the second original row data has the letter “L.” Thus, the third original row data is encoded into the second encoded row data R 2  having only the two columns (two pixels) of data. This encoding saves data for the rest of the columns (pixels), which include the first pixel, the second pixel, and the fifth to fourteenth pixels. 
     The delta row decoding unit  121  decodes the second encoded row data R 2  as follows. The delta row decoding unit  121  copies the first decoded row data D 1  and then updates the third and fourth pixels from “C” and “D” to “K” and “L.” This decoding process generates the second decoded row data D 2 . 
     The third encoded row data R 3  includes the first part of image R 31  and the second part of image R 32 . The first part of image R 31  has the first offset number of 12, which is calculated by 4 pixels times 3 colors for RGB, and has the letter “M” in the fifth and sixth columns. The second part of image R 32  has the second offset number of 0, which is calculated by 0 pixels times 3 colors for RGB from the first part of image R 31 , and has the letter “N” in the seventh to tenth columns. 
     The first offset number of 12 means that there is no difference between the second original row data and the third original row data in the first to fourth columns of “A,” “B,” “K,” and “L.” The part of image R 31  has the letter “M” in the fifth and sixth columns. The second offset number of 0 means that there is difference between the first original row data and the second original row data starting from the next or the seventh column. The second part of image R 32  has the letter “N” in the seventh to tenth columns. 
     The delta row decoding unit  121  decodes the third encoded row data R 3  as follows. The delta row decoding unit  121  copies the second decoded row data D 2  and then respectively updates the fifth and sixth columns from “E” and “F” to “M” and “M.” The delta row decoding unit  121  further updates the seventh to tenth columns from “G,” “G,” “H,” and “H” to “N,” “N,” “N,” and “N,” respectively. 
       FIG. 3  illustrates a schematic drawing representing a typical image rendering process according to the comparative example. The image rendering unit  122  renders the decoded image data DI to generate bit map data RD of the image by pixel replication. The scaling factor is 2 in X-direction (row direction) and Y-direction (column direction). 
     The image rendering unit  122  replicate the pixels in the first decoded row data D 1  in X-direction using a rendering one line work buffer RLB, thus generating the rendered line data RB 1 . The image rendering unit  122  replicates the pixels in the rendered line data RB 1  in Y-direction, thus generating the rendered rows data RD 1  and RD 2  in a page buffer PB. 
       FIG. 4  illustrates a schematic drawing representing the typical image rendering process according to the comparative example. The image rendering unit  122  replicate the pixels in the first decoded row data D 2  in X-direction using one line buffer LB, thus generating the rendered line data RB 2 . The image rendering unit  122  replicates the pixels in the rendered line data RB 2  in Y-direction, thus generating the rendered rows data RD 3  and RD 4  in the page buffer PB. 
       FIG. 5  illustrates a flow chart representing an image process according to one embodiment. At Step S 100 , the image forming device  100  receives a draw object from the personal computer  200  using the communication interface unit  250  and the communication interface unit  150 . 
     At Step S 200 , the image forming unit  120  analyzes the received draw object to find whether the received draw object is an image object or not. If the received draw object is found to be an image object, the image forming unit  120  advances the process to Step S 400 . If the received draw object is found to be an object, such as text and vector data, other than an image object, the image forming unit  120  advances the process to Step S 300 . At Step S 300 , the image forming unit  120  draws the object with a regular rendering process. 
     At Step S 400 , the image rendering unit  122  analyzes the received draw object to find whether the received draw object is compressed by delta row encoding. If the received draw object is found to be compressed by delta row encoding, the image forming unit  120  advances the process to Step S 500 . If the received draw object is not compressed by delta row encoding, the image forming unit  120  advances the process to Step S 300 . 
     At Step S 500 , the image rendering unit  122  analyzes the received draw object to find whether the image has the same orientation as the rendering page orientation or unrotated. If the image has the same orientation, the image forming unit  120  advances the process to Step S 700 . If the image does not have the same orientation, the image forming unit  120  advances the process to Step S 600 . At Step S 600 , the image forming unit  120  draws the image object with a regular image rendering process. 
       FIG. 6  illustrates a flow chart representing a fast delta row image process according to the one embodiment. At Step S 700 , the image rendering unit  122  performs a fast delta row image process (also referred to as FDR image process). The FDR image process includes a step of decoding images and a step of rendering the decoded images. 
       FIG. 7  illustrates a flow chart representing an image decoding process of the fast delta row image process according to the one embodiment. At Step S 711 , the delta row decoding unit  121  determines “processing as delta limit size,” which is also simply referred to as “delta limit size.” 
     The delta row decoding unit  121  reads out a predetermined “ratio for processing as delta limit” of 0.25 from the storage unit  140 . The delta row decoding unit  121  multiplies “input image one line buffer size” by the ratio for processing as delta limit of 0.25. The input image one line buffer size is 42, which is calculated by multiplying the number of pixels of 14 or image width in one line by 3 colors of RGB. Thus, the calculated delta limit size is 10.5. 
       FIG. 8  illustrates a schematic drawing representing an FDR decoding according to the one embodiment. At Step S 712 , the delta row decoding unit  121  prepares the work buffer WB. The work buffer WB has the same size as the input image one line buffer size. At Step S 713 , the delta row decoding unit  121  initializes the current line delta size sum to 0, which is also simply referred to as “delta size sum.” At Step S 714 , the delta row decoding unit  121  performs an FDR decoding process. 
       FIG. 9  illustrates a flow chart representing a fast delta row image decoding process according to the one embodiment. At Step S 741 , the delta row decoding unit  121  determines whether there is any delta left in this line or not. If there is any delta left in this line, the delta row decoding unit  121  advances the process to Step S 742 . If there is no left delta in this line, the delta row decoding unit  121  advances the process to Step S 715  (see  FIG. 7 ). 
     In this case, there is a delta of the first encoded row data R 1 . Thus, the delta row decoding unit  121  advances the process to Step S 742 . At Step S 742 , the delta row decoding unit  121  acquires the delta of the first encoded row data R 1 , the entire of which is the delta because there is no prior encoded row data. 
       FIG. 10  illustrates a schematic drawing representing the FDR decoding according to the one embodiment. At Step S 743 , the delta row decoding unit  121  updates the work buffer WB with the delta of the first encoded row data R 1  and adds the delta size of 42, which is one line buffer size, to the current line delta size sum. The delta size of 42 is calculated by multiplying the number of pixels of 14 or image width in one line by 3 colors of RGB because the entire line is updated. 
     At Step S 744 , the delta row decoding unit  121  determines whether the delta size sum is equal to or larger than the delta limit size or not. If the delta size sum is equal to or larger than the delta limit size, the delta row decoding unit  121  returns the process to Step S 741 . If the delta size sum is smaller than the delta limit size, the delta row decoding unit  121  advances the process to Step S 745 . In this case, the delta size sum is 42 while the delta limit size is 10.5 (which means YES). Thus, the delta row decoding unit  121  returns the process to Step S 741 . 
     At Step S 741 , the delta row decoding unit  121  determines whether there is any delta left in this line or not. If there is any delta left in this line, the delta row decoding unit  121  advances the process to Step S 742 . If there is no left delta in this line, the delta row decoding unit  121  advances the process to Step S 715  (see  FIG. 7 ). In this case, there is no left delta in the first encoded row data R 1 . Thus, the delta row decoding unit  121  advances the process to Step S 715  (see  FIG. 7 ). 
     At Step S 715 , the delta row decoding unit  121  determines whether the delta size sum is equal to or larger than the delta limit size or not. In this case, the delta size sum is 42 while the delta limit size is 10.5 (which means YES). Thus, the delta row decoding unit  121  advances the process to Step S 716 . 
     At Step S 716 , the delta row decoding unit  121  frees all the nodes for this line. At Step S 717 , the delta row decoding unit  121  acquires a node and a line buffer for this delta of the first encoded row data R 1 . The line buffer has the same size as the input image one line buffer size. The delta row decoding unit  121  copies the work buffer WB to this line buffer, which constitutes a part of an FDR compressed image FCI as FDR encoded row data FR 1 . 
     At Step S 718 , the delta row decoding unit  121  determines whether there is any other line or not. If there is any other line, the delta row decoding unit  121  returns the process to Step S 713 . If there is no line left, the delta row decoding unit  121  advances the process to Step S 750  (see  FIG. 6 ). In this case, there are other lines. Thus, the delta row decoding unit  121  returns the process to Step S 713 . 
     At Step S 713 , the delta row decoding unit  121  initializes the current line delta size sum to 0. At Step S 741 , the delta row decoding unit  121  determines whether there is any delta left in this line. In this case, there is a delta as the second encoded row data R 2 . Thus, the delta row decoding unit  121  advances the process to Step S 742 . At Step S 742 , the delta row decoding unit  121  acquires the delta of the second encoded row data R 2 . 
       FIG. 11  illustrates a schematic drawing representing the FDR decoding according to the one embodiment. At Step S 743 , the delta row decoding unit  121  updates the work buffer WB with the delta of the second encoded row data R 2  and adds the delta size of 6, which is calculated by 2 pixels times 3 colors for RGB, to the delta size sum. 
     At Step S 744 , the delta row decoding unit  121  determines whether the delta size sum is equal to or larger than the delta limit size or not. In this case, since the delta size sum of 6 is smaller than the delta limit size, the delta row decoding unit  121  advances the process to Step S 745 . 
     At Step S 745 , the delta row decoding unit  121  determines whether this is the first delta of current line or not. If this is the first delta of current line, the delta row decoding unit  121  advances the process to Step S 747 . If this is not the first delta of current line, the delta row decoding unit  121  advances the process to Step S 746 . At Step S 746 , the delta row decoding unit  121  extends the buffer for this the delta in the FDR compressed image FCI if the offset of this delta is 0 at Step S 748 . In this case, since this is the first delta of current line, the delta row decoding unit  121  advances the process to Step S 747 . 
     At Step S 747 , the delta row decoding unit  121  acquires a node and allocates a line buffer for the delta of the second encoded row data R 2 . The node has the offset number of 6. The line buffer has the same size as the delta size of 6. The delta row decoding unit  121  copies the work buffer WB to this line buffer, which constitutes a part of the FDR compressed image FCI as FDR encoded row data FR 2 . 
     The delta row decoding unit  121  returns the process to Step S 741 . In this case, there is no left delta in the second encoded row data R 2 . Thus, the delta row decoding unit  121  advances the process to Step S 715 . 
     At Step S 715 , the delta row decoding unit  121  determines whether the delta size sum is equal to or larger than the delta limit size or not. In this case, the delta size sum is 6 while the delta limit size is 10.5 (which means NO). Thus, the delta row decoding unit  121  advances the process to Step S 718 . 
     At Step S 718 , the delta row decoding unit  121  determines whether there is any other line or not. In this case, there is another line of the third encoded row data R 3 . Thus, the delta row decoding unit  121  returns the process to Step S 713 . 
     At Step S 713 , the delta row decoding unit  121  initializes the current line delta size sum to 0. At Step S 741 , the delta row decoding unit  121  determines whether there is any delta left in this line or not. In this case, there are two deltas in the third encoded row data R 3 . Thus, the delta row decoding unit  121  advances the process to Step S 742 . At Step S 742 , the delta row decoding unit  121  acquires the first delta R 31  in the third encoded row data R 3 . 
       FIG. 12  illustrates a schematic drawing representing the FDR decoding according to the one embodiment. At Step S 743 , the delta row decoding unit  121  updates the work buffer WB with the first delta R 31  in the third encoded row data R 3  and adds the delta size of 6, which is calculated by 2 pixels times 3 colors for RGB, to the delta size sum. 
     At Step S 744 , the delta row decoding unit  121  determines whether the delta size sum is equal to or larger than the delta limit size or not. In this case, the delta size sum of 6 is smaller than the delta limit size, the delta row decoding unit  121  advances the process to Step S 745 . 
     At Step S 745 , the delta row decoding unit  121  determines whether this is the first delta of current line or not. In this case, this is the first delta of current line. Thus, the delta row decoding unit  121  advances the process to Step S 747 . 
     At Step S 747 , the delta row decoding unit  121  acquires a node and allocates a line buffer for the first delta R 31  in the third encoded row data R 3 . The node has the first offset number of 12. The line buffer has the same size as the delta size of 6. The delta row decoding unit  121  copies the work buffer WB to this line buffer, which constitutes a part of the FDR compressed image FCI as FDR encoded row data FR 3   t , which is tentative due to the following second delta R 32 . 
     The delta row decoding unit  121  returns the process to Step S 741 . In this case, there is the second delta R 32  left in the third encoded row data R 3 . Thus, the delta row decoding unit  121  advances the process to Step S 742 . At Step S 742 , the delta row decoding unit  121  acquires the second delta R 32  in the third encoded row data R 3 . 
       FIG. 13  illustrates a schematic drawing representing the FDR decoding according to the one embodiment. At Step S 743 , the delta row decoding unit  121  updates the work buffer WB with the second delta R 32  in the third encoded row data R 3  and adds the delta size of 12, which is calculated by 4 pixels times 3 colors for RGB, to the delta size sum. This makes the delta size sum  18 . 
     At Step S 744 , the delta row decoding unit  121  determines whether the delta size sum is equal to or larger than the delta limit size of 10.5 or not. In this case, the delta size sum is 18 while the delta limit size is 10.5 (which means YES). Thus, the delta row decoding unit  121  advances the process to Step S 741 . 
     At Step S 744 , if the delta size sum were smaller than the delta limit size (which means NO), the delta row decoding unit  121  would advance the process to Step S 745 . In this case, since this is not the first delta of current line, the delta row decoding unit  121  advances the process to Step S 746 . Since the offset of this delta is 0 at Step S 746 , the delta row decoding unit  121  extends the existing buffer and copies this delta to this extended portion of this line buffer. Then, the delta row decoding unit  121  advances the process to Step S 741 . 
     At Step S 741 , the delta row decoding unit  121  determines whether there is any delta left in this line or not. In this case, there is no left delta in the third encoded row data R 3 . Thus, the delta row decoding unit  121  advances the process to Step S 715  (see  FIG. 7 ). 
     At Step S 715 , the delta row decoding unit  121  determines whether the delta size sum is equal to or larger than the delta limit size or not. In this case, the delta size sum is 18 while the delta limit size is 10.5 (which means YES). Thus, the delta row decoding unit  121  advances the process to Step S 716 . 
     At Step S 716 , the delta row decoding unit  121  frees all the nodes for the work buffer WB. At Step S 717 , the delta row decoding unit  121  acquires a node and allocates a line buffer for the entire third encoded row data R 3 . The line buffer has the same size as the input image one line buffer size. The delta row decoding unit  121  copies the work buffer WB to this line buffer, which constitutes a part of the FDR compressed image FCI as FDR encoded row data FR 3 . 
     At Step S 718 , the delta row decoding unit  121  determines whether there is any other line or not. In this case, there is no line left. Thus, the delta row decoding unit  121  advances the process to Step S 750  (see  FIG. 6 ). 
       FIG. 14  illustrates a flow chart representing an image rendering process of decoded image according to the one embodiment.  FIG. 15  illustrates a schematic drawing representing an image rendering process according to the one embodiment. At Step S 751 , the image rendering unit  122  allocates a decoded input one line buffer DLB. The decoded input one line buffer DLB has the same buffer size as the input image one line buffer size for the FDR encoded row data. 
     At Step S 752 , the image rendering unit  122  allocates a rendering one line work buffer RLB. The rendering one line work buffer RLB has a buffer size depending on a size of the original row data and the scaling factor in X-direction (row direction). 
     At Step S 753 , the delta row decoding unit  121  determines whether there is any delta left in this line. If there is any delta left in this line, the delta row decoding unit  121  advances the process to Step S 754 . If there is no left delta in this line, the delta row decoding unit  121  advances the process to Step S 756 . In this case, the delta row decoding unit  121  advances the process to Step S 754 . 
       FIG. 16  illustrates a schematic drawing representing the image rendering process according to the one embodiment. The first FDR encoded row data FR 1  has an offset number of zero. At Step S 754 , the first decoded input line data FD 1  is generated by simply copying the first FDR encoded row data FR 1 , which is one kind of update. 
     At Step S 755 , the image processing unit  123  converts the respective colors of the first decoded input line data FD 1  into CMY or CMYK, and subsequently the image rendering unit  122  renders the color converted data to generate one line bit map data RB 1  of the image by pixel replication using the rendering one line work buffer RLB. The scaling factor is 2 in X-direction (row direction) and Y-direction (column direction), which means that the destination height time is 2. 
     At Step S 753 , since there is no left delta in this line, the delta row decoding unit  121  advances the process to Step S 756 . At Step S 756 , the image rendering unit  122  copies the one line bit map data RB 1  and replicates or repeats the one line bit map data RB 1  in Y-direction, thus generating the rendered rows data RD 1  and RD 2  in a page buffer PB. 
       FIG. 17  illustrates a schematic drawing representing an image rendering process according to the one embodiment. At Step S 757 , since there is another line of the second FDR encoded row data FR 2 . Thus, the delta row decoding unit  121  returns the process to Step S 753 . 
     At Step S 753 , since there is a delta left the second decoded input line data FD 2 , the delta row decoding unit  121  advances the process to Step S 754 . At Step S 754 , the delta row decoding unit  121  updates the third and fourth pixels from “C” and “D” to “K” and “L” to generate the second decoded input line data FD 2 . 
     At Step S 755 , the image processing unit  123  converts the respective colors of the second decoded input line data FD 2 , and subsequently the image rendering unit  122  renders the color converted data to generate one line bit map data RB 2  of the image by pixel replication using the rendering one line work buffer RLB. 
     At Step S 753 , since there is no left delta in this line, the delta row decoding unit  121  advances the process to Step S 756 . At Step S 756 , the image rendering unit  122  copies the one line bit map data RB 2  and replicates or repeats the one line bit map data RB 2  in Y-direction, thus generating the rendered rows data RD 3  and RD 4  in the page buffer PB. 
       FIG. 18  illustrates a schematic drawing representing an image rendering process according to the one embodiment. At Step S 757 , since there is another line of the third FDR encoded row data FR 3 . Thus, the delta row decoding unit  121  returns the process to Step S 753 . 
     At Step S 753 , since there is a delta left the second decoded input line data FD 2 , the delta row decoding unit  121  advances the process to Step S 754 . 
     The third FDR encoded row data FR 3  has an offset number of zero. The third decoded input line buffer FD 3  is generated by simply copying the third FDR encoded row data FR 3 . The rest of the process is similar to the process for the first decoded input line buffer FD 1 . Thus, the image rendering unit  122  generates the rendered rows data RD 5  and RD 6  in the page buffer PB. 
     As described above, the image forming device  100  according to the one embodiment efficiently processes the delta row compressed image data by introducing another intermediate code. This new intermediate code is technically partially decoding or pre-decoding from the delta row compressed image data. This partial decoding process decodes the inefficiently encoded row data, which ends up with low compression ratio and consumes processing power for decoding. Thus, the image forming device  100  according to the one embodiment ensures the efficient use of its hardware resource. 
     Modifications 
     The disclosure will not be limited to respective embodiments described above, but modifications as follows are also possible. 
     Modification 1 
     While in the above-described embodiment the ratio for processing as delta limit is set to 0.25, the ratio may have any other value considering hardware resource including the memory area size and processing power of CPUs. 
     Modification 2 
     While in the above-described embodiment and the modification the ratio for processing as delta limit is preliminary set, the ratio may be automatically or semi-automatically changed based the hardware resource including the size of memory area and processing power of CPUs available for the image processing. 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.