Determining an optimal color space direction for selecting color modulations

• US 6,023,525 A
• Filed: 10/23/1997
• Issued: 02/08/2000
• Est. Priority Date: 10/23/1997
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Cass, Todd A.
• Primary Examiner(s): Tran, Phuoc
• Application Number:
  US08/956,326
• Time in Patent Office: 838 Days
• Field of Search: 382/162, 382/163, 382/166, 382/232, 358/515, 358/518, 235/469, 235/494, 380/9, 380/54, 283/72, 283/114
• US Class Current: 382/162
• CPC Class Codes: G06V 10/56 relating to colour
• CPC Class Codes: H04N 1/6058 Reduction of colour to a range of reproducible colours, e.g. to ink- reproducible colour gamut

Abstract

This technique for determining an optimal color space direction for a respective input color mathematically models the determination of the color space direction as an optimization problem and uses models of human perception and scanner response that produce quantitative measurements of color changes. A given input color and a direction in color space away from the givien input color define a color change away from the input color. An objective function simultaneously minimizes the quantitative color difference of the color change measured by a human perception model and maximizes the color response difference of a scanner response model to find an optimal color space direction for the respective input color.

Claims

1. A method for operating a processor-controlled machine to determine, for a given input color, an optimal direction in color space that includes the given input color and that satisfies a set of constraints;

the machine including an output device, a processor, and a memory device for storing data;

the data stored in the memory device including instruction data the processor executes to operate the machine;

the processor being connected to the memory device for accessing and executing the instruction data stored therein;

the method comprising;

obtaining an input color defined in coordinates of a multi-dimensional color space;

specifying an objective function that balances measurements of a human perceptual response and a digital image capture device response to a color change;

the color change being defined by a color space direction away from the input color;

the objective function simultaneously minimizing the human perceptual response measurement and maximizing the digital image capture device response measurement to the color change;

determining an output color defined as an optimal color space direction in the multi-dimensional color space away from the input color using the objective function;

encoding data as a pattern comprising one or more picture elements in an output color and one or more picture elements in the input color; and

outputting, on the output device, the encoded data such that the pattern is minimally visually perceptible to humans while, at the same time is maximally detectable by the digital image capture device.

2. A method for operating a processor-controlled machine to determine, for a given input color, an optimal direction in color space that includes the given input color and that satisfies a set of constraints;

the machine including an output device, a processor, and a memory device for storing data;

the data stored in the memory device including instruction data the processor executes to operate the machine, the processor being connected to the memory device for accessing and executing the instruction data stored therein, the method comprising;

obtaining an input color defined in coordinates of a multi-dimensional color space;

specifying an objective function that balances measurements of a human perceptual response and a digital image capture device response to a color change, the color change being defined by a color space direction away from the input color, the objective function simultaneously minimizing the human perceptual response measurement and maximizing the digital image capture device response measurement to the color change;

determining a range of output colors defined as optimal color space directions in the multi-dimensional color space away from the input color using the objective function;

encoding data as a pattern comprising a plurality of picture elements in one or more output colors of the range of output colors; and

outputting, on the output device, the encoded data such that the pattern is generally visually non-perceptible to humans while, at the same time is detectable by the digital image capture device.

3. The method of claim 2, wherein determining a range of output colors comprises determining an optimal output color, such that human visual discriminability is minimized while, at the same time, machine discriminability is maximized.

4. The method of claim 2, wherein determining a range of output colors comprises determining a minimally sufficient output color which is minimally visually non-discriminable to humans while, at the same time, is minimally machine discriminable.

5. The method of claim 2, wherein the output color is determined by:

representing the input color as a direction in a multi-dimensional color space;

determining a human visual response to the input color;

determining a machine response to the input color;

determining an objective function by balancing the human visual response and the machine response; and

determining an output color which is a direction in the multi-dimensional color space away from the direction of the input color using the objective function.

6. The method of claim 2, wherein:

determining an output color comprises determining two output colors, both of which are different than the input color, which, when output as adjoining picture elements, are imperceptible to humans as being different colors, but which are discriminable as being different colors by machine; and

wherein

rendering the image to include the encoded data among the input color in the selected portion of the image comprises replacing at least some picture elements of the selected portion of the image with picture elements of the two output colors.

7. The method of claim 6, wherein the two output colors are selected such that when they are output as adjoining picture elements, they are imperceptible to humans as being different from the input color.