Method for calculating colorant error from reflectance measurement
AssigneeXerox Corporation
InventorR. Klassen
Life of this patent
Estimating the term…
Abstract
Color error associated with an image rendered by a rendering device is calculated in the no more than N−1 dimensions of an associated color sensor color space. The color error is assumed to be small. A differential of a mapping from an N dimensional rendering device color space to the associated color sensor color space is used to calculate a colorant error in the N dimensions of the rendering device color space. Where necessary, appropriate assumptions are used to constrain an underdetermined system of equations. Where calculated colorant error is unreasonable, the calculated colorant error is clipped and colorant error is recalculated based on the clipped value.
Claims20
A method for calculating rendering error in a rendering device color space having N dimensions, from measurements in a sensor color space having no more than N−1 dimensions, the method comprising:
- predetermining a mapping from coordinates in the N dimensional rendering device color space to coordinates in the sensor color space having no more than N−1 dimensions;
- receiving a color description in one of the rendering device color space coordinates and the sensor device color space coordinates;
- converting the color description to rendering device color space coordinates, if the color description is received in sensor color space coordinates, based on the predetermined mapping, thereby generating a converted color description;
- rendering an image based on the received color description or the converted color description;
- measuring a color of the rendered image, thereby generating a measurement in sensor color space coordinates;
- and
- calculating a rendering error in rendering device color space coordinates based on the predetermined mapping, the received color description and/or the converted color description and the measurement.
A method for calculating colorant error in a rendering device color space having N dimensions from measurements in a sensor color space having no more than N−1 dimensions in a system having a mapping from coordinates in the N dimensional rendering device color space to coordinates in the sensor color space having no more than N−1 dimensions, the method comprising:
- receiving a color description in at least one of the rendering device color space coordinates and the sensor device color space coordinates;
- converting the color description to rendering device color space coordinates, if the color description is received in sensor color space coordinates, based on the mapping, thereby generating a converted color description;
- converting the received color description to sensor color space coordinates, if the color description is received in rendering device color space coordinates, based on the mapping, thereby generating an expected sensor color space color description;
- using the received color description as the expected sensor color space color description, if the received color description is in sensor color space coordinates;
- rendering an image based on the received color description or the converted color description;
- measuring a color of the rendered image, thereby generating a measurement in sensor color space coordinates;
- determining a Jacobian matrix of at least a portion of the mapping from coordinates in the rendering device color space to coordinates in the sensor color space;
- calculating a rendering error in sensor color space coordinates based on the expected sensor color space color description, and the measurement;
- creating a system of equations relating the calculated rendering error to an error expressed in rendering device color space coordinates through the Jacobian matrix and at least one additional constraining equation;
- and
- solving the system of equations for the rendering error expressed in rendering device color space coordinates.
16 The method of claim 11 wherein determining the Jacobian matrix comprises:
- analytically differentiating the mapping from coordinates in the rendering device color space to coordinates in the sensor color space.
17 The method of claim 11 wherein determining the Jacobian matrix comprises:
- solving for the parameters of a parametric function.
A document rendering system comprising:
- a print engine that is operative to render images with N rendering device color separations;
- a sensor that is operative to examine output of the rendering device and provide color measurements reported in N−1 sensor color space dimensions;
- a map that provides information for transforming color descriptions based on the N rendering device color separations to color descriptions based on the N−1 sensor color space dimensions;
- a sensor color space color description comparator that is operative to receive an expected color sensor color space color description based on a color description input to the system, to receive a sensor color space based measurement from the sensor, and to determine a difference between the expected color sensor color space color description and the measurement from the sensor, thereby generating a sensor color space rendering error signal;
- and
- a sensor color space to rendering device color space converter that is operative to receive the sensor color space rendering error signal from sensor color space color description comparator and convert it to a rendering device color space rendering error signal, based on a differentiation of information from the map.
A method for calculating rendering error in a rendering device color space having N dimensions from measurements in a sensor color space having no more than N−1 dimensions, the method comprising:
- determining a target color of a rendered image;
- and
- calculating a rendering error in rendering device color space coordinates based on the target color, a measurement of a color of an image rendered based on the target color, the measurement being in coordinates of the no more than N−1 dimension sensor color space, and on a predetermined mapping from coordinates in the N dimensional rendering device color space to coordinates in the no more than N−1 dimension sensor color space.
Dependencies are inferred from the claim text.