Half-tone screen calibrations

An apparatus for configuring a first printer to simulate the grayscale printing characteristics of a second printer, comprising:

• means for characterizing the grayscale printing characteristics of the first printer and the second printer;
• means for determining a transform between the grayscale printing characteristics of the first printer and the grayscale printing characteristics of the second printer from the characterized grayscale printing characteristics of the first printer and the second printer;
• and
• means for modifying a first printer threshold matrix in accordance with the transform;
• wherein the means for characterizing the grayscale printing characteristics of the first and second printer comprises:
• a first printer and a second printer for printing patches of gray levels, each gray level patch corresponding to a gray level input command i;
• means for measuring the printed gray level of the printed patches;
• means for normalizing the measured printed gray level measurements;
• means for determining a functions R1(i) and a function R2(i) such that R1(i) characterizes a relationship between the gray level input commands i and the corresponding normalized measured printed gray levels for the patches printed by the first printer, and R2(i) characterizes a relationship between the gray level input commands i and the corresponding measured printed gray levels for the patches printed by the second printer;
• wherein the means for determining a transform between the grayscale printing characteristics of the first printer and the grayscale printing characteristics of the second printer comprises means for deriving a transform I(i)=R1−1 where R1−1 denotes the inverse of the function R1(i);
• and
• wherein the means for applying the transform to a first printer threshold matrix comprises means for replacing each value in a first printer threshold matrix by the product of I(i) and the value of the threshold matrix.

A method of rendering image data, comprising the steps of:

• receiving a grayscale command in a first halftoning device;
• applying a transform to a threshold matrix of the first halftoning device to modify the grayscale characteristics of the first halftoning device to emulate the grayscale characteristics of a second halftoning device;
• and
• rendering the image data with the transformed threshold matrix;
• wherein the transform is derived by performing the steps of:
• determining a normalized function R1(i) and a normalized function R2(i) such that R1(i) characterizes a relationship between a gray level input command i and a corresponding measured gray level rendered by the first halftoning device, and R2(i) characterizes a relationship between the gray level input command i and a corresponding measured gray level rendered by the second halftoning device;
• and
• deriving the transform I(i)=R1−1 where R1−1 denotes the inverse of the function R1.

An apparatus for rendering image data, comprising:

• means for receiving a grayscale command in a first halftoning device;
• means for applying a transform to a threshold matrix of the first halftoning device to modify the grayscale characteristics of the first halftoning device to emulate the grayscale characteristics of a second halftoning device;
• and
• means for rendering the image data with the transformed threshold matrix;
• wherein the transform is derived by performing the steps of:
• determining a normalized function R1(i) and a normalized function R2(i) such that R1(i) characterizes a relationship between a gray level input command i and a corresponding measured gray level rendered by the first halftoning device, and R2(i) characterizes a relationship between the gray level input command i and a corresponding measured gray level rendered by the second halftoning device;
• and
• deriving the transform I(i) R1−1 where R1−1 denotes the inverse of the function R1.

A program storage device, readable by a computer, tangibly embodying one or more programs of instructions executable by the computer to perform method steps of rendering image data, the method comprising the steps of:

• receiving a grayscale command in a first halftoning device;
• applying a transform to a threshold matrix of the first halftoning device to modify the grayscale characteristics of the first halftoning device to emulate the grayscale characteristics of a second halftoning device;
• and
• rendering the image data with the transformed threshold matrix;
• wherein the transform is derived by performing the steps of:
• determining a normalized function R1(i) and a normalized function R2(i) such that R1(i) characterizes a relationship between a gray level input command i and a corresponding measured gray level rendered by the first halftoning device, and R2(i) characterizes a relationship between the gray level input command i and a corresponding measured gray level rendered by the second halftoning device;
• and
• deriving the transform I(i)=R1−1 where R1−1 denotes the inverse of the function R1.