Printing calibration

Abstract

In an example, a print target may be printed with a calibration target. The calibration target may comprise an first printing fluid figure printed on the print target and a second printing fluid figure printed on the print target. A geometric figure may be defined by the second printing fluid figure. The geometric figure may be negatively outlined in the second printing fluid figure. In an example, the calibration target may be processed to define a geometric relationship between an first printing fluid reference point and a second printing fluid reference point.

What is claimed is: 
     
         1 . A method, comprising:
 printing a calibration target on a print target by:
 printing, with an ink printing system included in a printing system, an ink figure on the print target; and 
 printing, with a fixative printing system included in the printing system, a fixative figure on the print target, wherein the fixative figure defines a geometric figure including a reference point that allows a position of the ink figure to be compared with a position of the fixative figure; 
   determining, based on the position of the ink figure to the position of the fixative figure, a misalignment between the ink printing system and the fixative printing system; and   aligning the ink printing system and the fixative printing system to correct the misalignment between the ink printing system and the fixative printing system.   
     
     
         2 . The method of  claim 1 , further comprising printing the ink figure with ink from a first set of printing dies in the ink printing system. 
     
     
         3 . The method of  claim 2 , further comprising printing the fixative figure with the substantially transparent fixative from a second set of printing dies in the fixative printing system. 
     
     
         4 . The method of  claim 3 , further comprising printing the fixative figure with a transparent fixative. 
     
     
         5 . The method of  claim 1 , further comprising printing the fixative figure wherein the geometric figure is negatively outlined in the fixative figure. 
     
     
         6 . The method of  claim 5 , wherein the geometric figure further comprises two negatively outlined lines that have opposing slopes and intersect to form the reference point. 
     
     
         7 . The method of  claim 6 , wherein the geometric figure further comprises two negatively outlined lines that are perpendicular and intersect to form the reference point. 
     
     
         8 . The method of  claim 1 , wherein the reference point further comprises a fixative reference point, wherein the calibration target further comprises an ink reference point, and wherein determining the misalignment further comprise determining a distance between the ink reference point and the fixative reference point. 
     
     
         9 . The method of  claim 8 , wherein the distance is a distance between the ink reference point and the fixative reference point in an X′-Y′ plane in a Cartesian coordinate system, and wherein the X′-Y′ plane in a Cartesian coordinate system corresponds to a printing plane in the fixative printing system, a printing plane in the ink printing system, or both. 
     
     
         10 . A method comprising:
 printing a calibration target on a print target by:
 printing an ink figure on the print target; 
 printing a fixative figure printed with a fixative from a fixative printing system on the print target, wherein the fixative figure defines a geometric figure negatively outlined in the fixative figure, and wherein the fixative is transparent; 
   capturing an image of the calibration target, the image having a first region of interest relating to the ink figure and a second region of interest relating to the fixative figure;   processing image data relating to the first region of interest to locate the borders of the ink figure;   determining the location of an ink reference point on the print target based upon the located borders of the ink figure;   processing image data relating to the second region of interest to locate geometric features of the geometric figure defined by the fixative figure;   determining the location of a fixative reference point on the print target by matching the located geometric features with reference geometric features from a reference geometric figure; and   determining a geometric relationship between the ink reference point and the fixative reference point so that an ink printing process and a fixative printing process can be aligned during operation of a printing system.   
     
     
         11 . The method of  claim 10 , wherein processing the image data relating to the first region of interest to locate the borders of the ink figure comprises:
 converting the image data for the first region of interest into a monochrome image;   filtering the monochrome image using 2D median filtering;   cleaning noise from the monochrome image; and   analyzing the monochrome image to detect outer borders of the ink figure.   
     
     
         12 . The method of  claim 10 , wherein processing the image data relating to the second region of interest of the image to locate the geometric features of the geometric figure comprises:
 determining a threshold for the fixative in the image data relating to the second region of interest;   producing a logical image from the image data relating to the second region of interest by comparing pixels in the image data with the threshold and assigning the pixels a binary digit based on the comparison;   filtering anomalous features out of logical image;   thinning lines in the logical image; and   performing a Hough transform on the logical image to locate lines within the second region of interest.   
     
     
         13 . The method of  claim 12 , wherein determining the location of the fixative reference point comprises:
 filtering the located lines from the logical image by comparing the length and/or slope of the located lines with reference geometric lines in the reference geometric figure;   selecting located lines from the logical image by matching located lines with reference geometric lines in the reference geometric figure; and   determining the location of the fixative reference point by matching reference geometric points in the reference geometric figure with corresponding points derived from the selected lines in the logical image.   
     
     
         14 . The method of  claim 13 , wherein the selected lines are two intersecting lines having opposing slopes that match two intersecting reference geometric lines having corresponding opposing slopes and wherein the location of the fixative reference point is determined from the intersection point of the selected lines. 
     
     
         15 . A printing system, comprising:
 an ink printing system;   a fixative printing system; and   a controller including processor to execute instructions to:
 print a calibration target on a print target, comprising:
 an ink figure printed on the print target; and 
 a transparent fixative figure printed on the print target that defines a geometric figure negatively outlined in the transparent fixative figure; 
 
 determine the location of an ink reference point; 
 determine the location of a fixative reference point; 
 determine a geometric relationship between the ink reference point and the fixative reference point; and 
 align, based on the geometric relationship, the ink printing system and the fixative printing system so ink printed by the ink printing system and fixative printed by the fixative prinking system are aligned during operation of the printing system. 
   
     
     
         16 . The printing system of  claim 15 , wherein processor is further to execute instructions to:
 obtain image data relating to a first region of interest in an image of the calibration target   process the image data relating to the first region of interest to locate the borders of the ink figure; and   determine the location of the ink reference point based upon the detected borders of the ink figure.   
     
     
         17 . The printing system of  claim 16 , wherein processor is further to execute instructions to:
 obtain image data relating to a second region of interest in the image of the calibration target;   process the image data relating to the second region of interest to locate geometric features of the geometric figure defined by the transparent fixative figure; and   determine the location of a fixative reference point on the print target by matching the located geometric features with reference geometric features from a reference geometric figure.   
     
     
         18 . The printing system of  claim 15 , wherein the ink printing system includes a first set of dies to print ink. 
     
     
         19 . The printing system of  claim 18 , wherein the fixative printing system includes a second set of dies to print a transparent fixative. 
     
     
         20 . The printing system of  claim 19 , wherein processor is further to execute instructions to align the first set of dies in the ink printing system and the second set of dies in the fixative printing system so the ink printed by the ink printing system and the transparent fixative printed by the fixative prinking system are aligned during operation of the printing system.