The assignee for this patent application is Canon Kabushiki Kaisha.
Reporters obtained the following quote from the background information supplied by the inventors: "In recent years high quality colour printers have become the norm. For inkjet printers, typical resolutions are 1200 dpi or higher, which translates into a printer ink dot size (and separation) of 20 microns or less. In many systems the inkjet printer may overprint regions multiple times to help minimise the effect of printer defects such as blocked print head nozzles. The optical density of a printed colour can be very sensitive to the precise value of the displacement between overprinted regions. This means, that at least for high quality, it is necessary to control or calibrate the exact displacement of the printer head between overprints.
"Many approaches have been proposed for calibrating the movements of the print head relative to the medium being printed upon. One approach to the calibration of print head position uses measurement of individual dot positions. Unfortunately, despite the simple experimental set-up and straightforward result analysis of this approach, it is quite unreliable due to the large variations in dot shape, position and size. There is also the difficulty of unambiguously locating isolated dots in large regions on the medium being printed upon.
"More robust methods have also been suggested to accommodate the aforementioned noise and ambiguity in order to achieve accurate measurement of print head position. Some methods measure the position of a print head by printing specially designed test charts and subsequently scanning the printed image to find the relative shift of each overprint using Fourier analysis. Although these methods are robust to noise, they involve complex computation and are not performed in real-time due to the separate printing and scanning processes that are involved.
"Other methods include a method described in US 2009/0268254 wherein an optical sensor is used to measure and correct print density error. However, the printing area to be corrected needs to be covered by the field of view of the sensor. Therefore, this method can be costly and require a considerable amount of computational power. Moreover, some print defects caused by line feed error cannot be corrected in this way."
In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventors' summary information for this patent application: "It is an object of the present invention to substantially overcome, or at least ameliorate, one or more disadvantages of existing arrangements.
"Disclosed are arrangements, referred to as Adaptive Dot Growth Correlation (ADGC) arrangements, that seek to address the above problems by improving correlation accuracy between a reference pattern of dots and a printed pattern of the same dots by adaptively growing the dots of the reference pattern dependent upon the locations of the dots in the reference pattern, thereby reducing correlation error between the reference pattern and the printed pattern. This improves the accuracy of measurements such as line feed error.
"According to a first aspect of the present invention, there is provided a method of determining a characteristic of an image forming apparatus, said method comprising the steps of: receiving print data, defining a plurality of dot locations, to be printed on a print medium by the image forming apparatus; determining from said plurality of dot locations a dot frequency measure reflecting a number of dots to be printed on at least a part of the print medium; forming a simulated reference image of the print data comprising a plurality of simulated dots corresponding to the plurality of dot locations in the print data; determining a size of the simulated dots in the reference image, said size being inversely related to the dot frequency measure; printing the print data on the print medium using the image forming apparatus to form a printed image; and determining a characteristic of the image forming apparatus based upon a comparison of the printed image and the simulated reference image.
"According to another aspect of the present invention, there is provided a method of determining a characteristic of an image forming apparatus, said method comprising the steps of: receiving print data, defining a plurality of dot locations, to be printed on a print medium by the image forming apparatus; forming a simulated reference image of the print data comprising a plurality of simulated dots corresponding to the plurality of dot locations in the print data, wherein a size of the simulated dots in the reference image is determined from the distances between the dot locations defined by the print data; printing the print data on the print medium using the image forming apparatus to form a printed image; and determining a characteristic of the image forming apparatus based upon a comparison of the printed image and the simulated reference image.
"Other aspects of the invention are also disclosed.
BRIEF DESCRIPTION OF THE DRAWINGS
"One or more embodiments of the invention will now be described with reference to the following drawings, in which:
"FIGS. 1A and 1B collectively form a functional block diagram representation of a printer upon which described ADGC arrangements can be practised;
"FIG. 2 depicts a simplified representation of the mechanical layout of an inkjet printer with a moving printing head;
"FIG. 3 depicts a layout of an inkjet print head and associated sensors;
"FIG. 4 shows a flow diagram of a process for measuring and calibrating the displacement of the printer head between overprints in a first ADGC arrangement;
"FIG. 5 shows a flow diagram of the swath construction process of FIG. 4;
"FIG. 6 illustrates the printing process of one overprint;
"FIGS. 7A and 7B provide a comparison of printed inkjet dots and simulated dots;
"FIGS. 8A, 8B and 8C depict relative positions of the overprints and the print head after a line feed;
"FIG. 9 shows a simplified flow diagram of a process for determining a vertical shift 6;
"FIG. 10 illustrates the relative positions of different sections of the print head and the printed swaths;
"FIGS. 11A and 11B show magnitude profiles for a captured/printed inkjet dot and a simulated dot;
"FIG. 12 shows a flow diagram of a process for simulating a reference image;
"FIGS. 13A, 13B and 13C show examples of simulated and real inkjet dot patterns;
"FIGS. 14A-14E illustrate the effect of changing a dot size parameter when simulating Gaussian dots;
"FIG. 15 shows a flow diagram for determining a suitable dot size parameter for simulation;
"FIG. 16 shows an example of a tile in a first ADGC arrangement and a magnified section thereof;
"FIG. 17 shows a jinc function profile;
"FIGS. 18A and 18B depict the effect of phase reversal in image correlation;
"FIG. 19 shows a flow diagram for determining a dot size parameter based on local dot density;
"FIG. 20 illustrates how comparison between a reference image and a captured target image can yield a relative displacement measurement;
"FIG. 21 depicts window regions for a halftone dot pattern;
"FIG. 22 depicts relationships between the image to be printed on a page, swaths and swath sections into which the image is decomposed;
"FIGS. 23A-23D illustrate a four-pass printing process;
"FIG. 24 shows a layout of a test chart in an alternate ADGC arrangement; and
"FIG. 25 shows experimental results for the ADGC arrangement."
For more information, see this patent application: CHONG, ERIC WAI-SHING; ASHIDA, JUMPEI. Real-Time Line Feed Measurement of Inkjet Printer. Filed
Keywords for this news article include: Canon Kabushiki Kaisha.
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