Color registration system for a printing press

A system for generating signals representative of color registration offsets between cyan, magenta, yellow and black inks of a printed image, wherein first, second, third and fourth printing units are disposed to print cyan, magenta, yellow and black ink on a web, the system comprising:

• a memory which stores first, second, third and fourth reference arrays of digital data representative of the cyan, magenta, yellow and black inks in at least a portion of a printed image, respectively;
• an imaging device in optical communication with the web to produce first, second, third and fourth analog signals representative of the cyan, magenta, yellow and black inks, respectively, in the portion of the image;
• a converter circuit, operatively associated with the memory and the imaging device, which converts the first, second, third and fourth analog signals to cyan, magenta, yellow and black data arrays of digital on-press data respectively, wherein the cyan, magenta, yellow and black data arrays are representative of the cyan, magenta, yellow and black inks, respectively;
• and
• a processing circuit in communication with the converter circuit and the memory, wherein the processing circuit phase correlates the cyan, magenta, yellow and black reference arrays with the cyan, magenta, yellow and black on-press arrays, respectively, when determining registration offsets between the cyan, magenta, yellow and black inks.

A system for generating a signal representative of color registration offset between at least first and second colors of an image printed on a web, wherein a first printing unit prints the first color of the image and a second printing unit prints the second color of the image, the system comprising:

• memory means for storing a first reference array of digital data representative of the first color in at least a portion of the image and a second reference array of digital data representative of the second color of the portion of the image;
• imaging means in optical communication with the web for producing a first analog signal representative of the first color of the portion of the image and a second analog signal representative of the second color of the portion of the image;
• a converter means operatively associated with the imaging means and the memory means for converting the first analog signal to a first color array of digital on-press data, converting the second analog signal to a second color array of digital on-press data, and storing the first and second on-press arrays;
• and
• a processing means in communication with the converter means and the memory means, wherein the processing means phase correlates the first reference array with the first on-press array to produce first data and phase correlates the second reference array with the second on-press array to produce second data, the processing means comparing the first data and the second data to determine a registration offset between the first and second colors and producing a signal representative of the registration offset between the first color and the second color.

A system for generating a signal representative of color registration rotational offset between at least first and second colors of an image printed on a web, wherein a first printing unit prints the first color of the image and a second printing unit prints the second color of the image, the system comprising:

• a memory disposed to store a first reference array of digital data representative of the first color of at least first and second portions of the image and a second reference array of digital data representative of the second color of the first and second portions of the image, wherein the first portion is displaced from the second portion;
• an imaging device in optical communication with the web to produce a first analog signal representative of the first color of the portions of the image and a second analog signal representative of the second color of the portions of the image;
• a converter circuit, operatively associated with the imaging device and the memory, which converts the first analog signal to a first color array of digital on-press data, and converts the second analog signal to a second color array of digital on-press data, wherein the first and second color arrays of on-press data are stored in the memory;
• and
• a processing circuit in communication with the converter circuit and the memory, wherein the processing circuit phase correlates the first reference array with the first on-press array to produce first data and phase correlates the second reference array with the second on-press array to produce second data, the processing circuit comparing the first data and the second data to determine a registration offset between the first and second colors at the first and second portions, and producing a signal representative the skew offset between the colors based upon the registration offset between the first and second colors.

A method of generating a first reference array of first digital data representative of a first color and a second reference array of second digital data representative of a second color for use in a registration control system of a printing apparatus, the printing apparatus printing an image on at least a portion of a web, the method comprising the steps of:

• (A) applying ink of a first color to the web;
• (B) optically communicating with web after said step (A) to generate a first signal representative of the ink of the first color on the web;
• (C) converting the first signal after said step (B) to generate a first reference array representative of the first ink of the first color on the web;
• (D) applying ink of a second color to the web after said step (C);
• (E) optically communicating with the web after said step (D) to generate a second signal representative of the ink of the second color on the web;
• (F) converting the second signal after said step (E) to generate a second reference array representative of the second ink of the second color on the web;
• and
• (G) storing the first and the second reference arrays in a memory.

A system for generating a first reference array of first digital data and a second reference array of second digital data for use in a registration control system of a printing apparatus, the printing apparatus printing an image on at least a portion of a web, the printing apparatus including a first printing unit which prints a first color of the image on the portion of the web and a second printing unit which prints a second color of the image on the portion of the web, the system comprising:

• means for printing sequential ink reference images on the web and for producing reference data arrays from the reference images, the means for printing sequential ink reference images including
• a print controller coupled to the first printing unit and the second printing unit, the print controller configured to have the first print unit apply the first color to the web, and the second print unit apply the second color to the web,
• a memory disposed to store the first reference array of digital data representative of the first color of at least a reference area of the image and a second reference array of digital data representative of the second color of the reference area,
• an imaging system, in optical communication with the web, the imaging system being configured to produce a first analog signal representative of the first color of the reference area of the image and a second analog signal representative of the second color of the reference area of the image, and
• a converter circuit, operatively associated with the imaging device and the memory, which converts the first analog signal to the first reference array of digital data, and converts the second analog signal to the second reference array of digital data;
• and
• a processor configured to perform cross correlation on the first reference array and the second reference array to generate register offset data representative of original color-to-color misregistration.

A system for generating a cyan reference array, a magenta reference array, a yellow reference array, and a black reference array for a printed image, wherein a cyan printing unit, a magenta printing unit, a yellow printing unit, and a black printing unit are disposed to print cyan, magenta, yellow and black ink, respectively, on a web, the system comprising;

• a print controller coupled to the printing units, the print controller configured to have the printing units first print a first reference area of the image in yellow ink, next print a second reference area of the image in magenta ink, next print a third reference area of the image in cyan ink, and next print a fourth reference area in black ink;
• a memory configured to store the yellow, magenta, cyan, and black reference arrays of digital data representative of the yellow ink, the magenta ink, the cyan ink, and the black ink, respectively, in the first reference area, the second reference area, the third reference area, and the fourth reference area;
• a camera assembly in optical communication with the web, the camera assembly further comprising an imaging system configured to produce in order first, second, third and fourth analog signals representative of the yellow, magenta, cyan and black reference areas, respectively, of the image;
• and
• a converter circuit, operatively associated with the imaging device and the memory, which converts the first analog signal to the yellow reference array of digital data, converts the second analog signal to the magenta reference array of digital data, converts the third analog signal to the cyan reference array of digital data, and converts the fourth analog signal to the black reference array of digital data.

A system for generating a signal representative of color registration offset between at least first and second colors of an image printed on a web, where a first printing unit prints the first color of the image and a second printing unit prints the second color of the image, the system comprising:

• an imaging device in optical communication with the web to produce a first analog signal representative of the first color of the portion of the image and a second analog signal representative of the second color of the portion;
• a memory for storing digital data;
• a converter circuit, operatively associated with the imaging device and memory, which converts the first analog signal to a first color array of digital data, and converts the second analog signal to a second color array of digital data, where the first and second color arrays are stored in said memory;
• a transform circuit disposed to transform the data in the color arrays to data referenced to a frequency domain;
• a correlation circuit which correlates the transformed data from the first color array with the transformed data from the second color array to produce a product array;
• an inverse transform circuit disposed to transform the data in the product array to a spatial array having data referenced to a spatial domain;
• a maximum value determining circuit which determines the maximum value in the spatial array to determine a registration offset between the first and second colors and produces a signal representative of the registration offset between the colors.