Patent Document

BACKGROUND 
     1. Technical Field 
     The disclosure generally relates to a multi-function printer and a method for calibrating the multi-function printer. 
     2. Description of Related Art 
     Multi-function printers (MFPs) including scanner units and printer units are used widely because MFPs are relatively small in size with low noise and can perform color copying, printing, and scanning at low cost. The scanner head of a scanner unit in an MFP may include an image sensor such as a charge coupled device (CCD) and a contact image sensor (CIS). The printer unit of an MFP may include an inkjet printer or a laser printer. 
     The output quality by the printer unit of an MFP may vary over time due to factors such as media variability, aging of the printer unit&#39;s components, and changes in the printer unit&#39;s environment. To achieve a consistent performance of the printer unit of an MFP, there is a need for a technique for dynamically calibrating the print unit of the MFP according to its latest status and/or environment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a functional block diagram of a multi-function printer (MFP) which is an example of an image processing apparatus according to one embodiment. 
         FIG. 2  shows a first calibration pattern. 
         FIG. 3  is a flowchart showing one embodiment of a method for calibrating the MFP of  FIG. 1  using the first calibration pattern. 
         FIG. 4  is an image level histogram representing an image level distribution of a scanned image obtained by the MFP of  FIG. 1 . 
         FIG. 5  is a flowchart showing another embodiment of a method for calibrating the MFP of  FIG. 1  using the first calibration pattern. 
         FIG. 6  shows a second calibration pattern. 
         FIG. 7  is a flowchart showing one embodiment of a method for calibrating the MFP of  FIG. 1  using the second calibration pattern. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
     In general, the word “module”, as used herein, refers to logic embodied in hardware or firmware, or to a collection of software instructions, written in a programming language, such as, Java, C, or assembly. One or more software instructions in the modules may be embedded in firmware, such as in an EPROM. The modules described herein may be implemented as either software and/or hardware modules and may be stored in any type of non-transitory computer-readable medium or other storage device. Some non-limiting examples of non-transitory computer-readable media include CDs, DVDs, BLU-RAY, flash memory, and hard disk drives. 
       FIG. 1  is a functional block diagram of a multi-function printer (MFP)  100  which is an example of an image processing apparatus according to one embodiment. The MFP  100  comprises a CPU  101 , a ROM  102 , a RAM  103 , a printer unit  104 , a scanner unit  105 , an image processing unit  106 , an I/F (interface)  107 , an operation unit  108 , a display unit  109 , a DMA controller  110 , and a setting unit  111 . 
     The CPU  101  is a processor capable of controlling the overall MFP  100 . The MFP  100  is controlled by running a program (firmware) stored in the ROM  102 . 
     The ROM  102  is non-volatile memory capable of storing the program for controlling the MFP  100 . 
     The RAM  103  is volatile memory which is used as a working area when the CPU  101  runs the program stored in the ROM  102 . The RAM  103  is also used as buffer memory for temporarily storing image data from the scanner unit  105 . 
     The printer unit  104  may print image data on a sheet of paper, an OHP sheet, or other medium (hereinafter referred to as a “printing medium”). In one embodiment, the printer unit  104  is an inkjet printer which comprises a printhead, a motor, and an ink cartridge. The printer unit  104  causes a carriage having the printhead to scan on the printing medium in a reciprocating manner and apply ink to the printing medium. Printing is performed by transporting the printing medium according to the scanning perpendicularly to the scanning direction of the carriage. 
     The scanner unit  105  may scan images on a sheet of paper, a plastic sheet, a film, and so on and generate image data. The scanner unit  105  temporarily buffers, in the RAM  103 , image data having been generated by the scanned images. 
     The scanner unit  105  may comprise a scanner head which has a scanning width corresponding to an overall width of the largest readable medium (for example, A4-size paper). In the scanner head, a plurality of CCDs (or CISs) may be in a scanning width direction. Image data is obtained by electrically scanning the plurality of CCDs. Further, the scanner head may be mechanically scanned by a motor perpendicularly to the scanning width direction of the CCDs. Overall image of the medium can be scanned by combining the electrical scanning and the mechanical scanning. In the present embodiment, a direction of electrical scanning is called “main scanning direction” and a direction of mechanical scanning is called “sub scanning direction.” 
     The scanner unit  105  may scan images line-by-line and generate color image data, wherein the color components, including RGB (red, green, blue) components, are represented in, for example, 8 bits (0 to 255). A number of bits representing each pixel can be freely set within the capability of the CCDs or CISs. The number of bits is called “image level” or “color depth.” 
     The image processing unit  106  may perform digital image processing such as level analysis, color correction, and filter processing on image data which have been buffered in the RAM  103  by the scanner unit  105 . 
     The I/F  107  is an interface for allowing the MFP  100  to communicate with various external devices. External devices may include, for example, a personal computer (PC), and a drive for reading and writing data in a storage medium such as a memory card. I/F  107  may include USB and IEEE 1394. 
     The operation unit  108  may be operated by a user to provide the MFP  100  with various instructions. Instructions may be a scan instruction to cause the scanner unit  105  to scan images on a medium, or a print instruction to cause the printer unit  104  to print images on a printing medium. The instructions to the MFP  100  may be provided from a PC, or the like, through the I/F  107 . 
     The display unit  109  may display information to the user, and be made up of an LCD, an LED, or the like. The information displayed to the user may be a state of the MFP  100  (scanning, printing, or idling), or a setting menu of the MFP  100 . 
     The DMA controller  110  is a controller for transferring data between the constituent elements of the MFP  100  through DMA transfer. 
     The printer unit  104  may print a calibration pattern on a printing medium. The scanner unit  105  may obtain a scanned image by scanning the medium. The image processing unit  106  may detect any defects of the scanned image by comparing the scanned image against the calibration pattern; and the setting unit  111  may adjust print settings of the printer unit  104  according to the defects in the scanned image. 
     The setting unit  111  may disable or enable overall settings of the MFP  100  or components of the MFP, such as the printer unit  104  and the scanner unit  105 . 
       FIG. 2  shows a first calibration pattern  20 . The first calibration pattern  20  is an image filled with pixels each having a same, preset image level. For example, all the pixels of the first calibration pattern  20  have the same image level of “130”. 
       FIG. 3  is a flowchart showing one embodiment of a method for calibrating the MFP  100  using the first calibration pattern  20 . The method comprises the following steps: 
     In step S 301 , the printer unit  104  prints the calibration pattern  20  on a printing medium. 
     In step S 302 , the scanner unit  105  obtains a scanned image by scanning the printed medium. 
     In step S 303 , the image processing unit  106  generates an image level distribution of the scanned image such as  FIG. 4 .  FIG. 4  shows an image level histogram representing the image level distribution of the scanned image. An x-axis of the image level histogram represents image levels of the scanned image, and a y-axis of the image level histogram represents a number of pixels. The image level histogram is a statistical chart primarily illustrating the number of pixels in each image level. Therefore, the image level histogram of  FIG. 4  reveals the image level distribution conditions of the scanned image. The gray area under the curve of the image level histogram represents a total number of pixels of the scanned image. In  FIG. 4 , the range of image levels is from 0 to 255. 
     In step S 304 , the image processing unit  106  derives a reference image level which has a maximal number of pixels from the image level distribution. For example, according to the image level histogram of  FIG. 4 , an image level of “130” has the maximal number of pixels. The image level “130” may be the reference image level. 
     In step S 305 , the image processing unit  106  counts up a first number of pixels which have an image level outside the range based on the reference image level. For example, in  FIG. 4 , a range of (110, 150) may be defined as inside the range based on the reference image level of 130. If the image level of a pixel is outside the defined range of (110, 150), the pixel may be counted into the first number. 
     In step S 306 , the image processing unit  106  calculates a first proportion which is a ratio of the first number relative to the total number of pixels of the scanned image. 
     In step S 307 , if the first proportion of the first number relative to the total number of pixels exceeds a threshold, such as 10%, the flow goes to step S 308 . If the first proportion is equal to, or less than the threshold, calibration of the MFP  100  has completed and the flow ends. 
     In step S 308 , the setting unit  111  enables and applies de-noising settings of the printer unit  104  to eliminate potential noises introduced by the printer unit  104 . 
       FIG. 5  is a flowchart showing another embodiment of a method for calibrating the MFP  100  using the first calibration pattern  20 . The method comprises the following steps: 
     In step S 401 , the printer unit  104  prints the calibration pattern  20  on a printing medium. 
     In step S 402 , the scanner unit  105  obtains a scanned image by scanning the printed medium. 
     In step S 403 , the image processing unit  106  calculates an average image level of the scanned image. In one embodiment, an average image level is an arithmetic average of the image level distribution of the scanned image. 
     In step S 404 , the image processing unit  106  calculates an image level difference between the average image level of the scanned image and the preset image level of the first calibration pattern  20 . 
     In step S 405 , if the image level difference exceeds a threshold, such as 30, the flow goes to step S 406 . If the image level difference is equal to, or less than the threshold, calibration of the MFP  100  has completed and the flow ends. 
     In step S 406 , the setting unit  111  enables and applies image level compensation settings of the printer unit  104  to drive the image level difference between the average image level of the scanned image and the preset image level of the first calibration pattern  20  down to zero. 
       FIG. 6  shows a second calibration pattern  30 . The second calibration pattern  30  is an image including a plurality of black stripes. 
       FIG. 7  is a flowchart showing one embodiment of a method for calibrating the MFP  100  using the second calibration pattern  30 . The method comprises the following steps: 
     In step S 601 , the printer unit  104  prints the calibration pattern  30  on a printing medium. 
     In step S 602 , the scanner unit  105  obtains a scanned image by scanning the printed medium. 
     In step S 603 , the image processing unit  106  examines edges of the plurality of black stripes in the scanned image and determines whether the edges are jagged or not. 
     In step S 604 , the image processing unit  106  counts up a second number of black stripes which have jagged edges in the scanned image. If a black stripe has at least one edge that is jagged, the black stripe will be counted into the second number. 
     In step S 605 , the image processing unit  106  calculates a second proportion which is a ratio of the second number relative to a total number of stripes in the plurality of black stripes of the scanned image. 
     In step S 606 , if the second proportion of the second number relative to the total number of stripes of the scanned image exceeds a threshold, the flow goes to step S 607 . If the second proportion is equal to, or less than the threshold, calibration of the MFP  100  has completed and the flow ends. 
     In step S 606 , the setting unit  111  enables and applies edge enhancement settings of the printer unit  104  to make edges of images printed by the printer unit  104  smoother and more distinct. 
     Although numerous characteristics and advantages have been set forth in the foregoing description of embodiments, together with details of the structures and functions of the embodiments, the disclosure is illustrative only and changes may be made in detail, especially in the matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 
     Depending on the embodiment, certain steps or methods described may be removed, others may be added, and the sequence of steps may be altered. The description and the claims drawn for or in relation to a method may include some indication in reference to certain steps. However, any indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps.

Technology Category: h