Generation of inverse transfer function for image rendering device

• US 8,705,115 B1
• Filed: 04/26/2006
• Issued: 04/22/2014
• Est. Priority Date: 04/26/2006
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Bhachech, Miheer M., DiCarlo, Jeffrey M., Shaw, Mark Q.
• Primary Examiner(s): Vo, Quang N
• Application Number:
  US11/411,451
• Time in Patent Office: 2,918 Days
• Field of Search: 358/1.9, 358/504, 358/518, 358/525, 358/530
• US Class Current: 358/1.9
• CPC Class Codes: H04N 1/6019 using look-up tables H04N1/6025 takes precedence
• CPC Class Codes: H04N 1/603 controlled by characteristics of the picture signal generator or the picture reproducer

Abstract

An inverse transfer function is computed from a forward transfer function of an image rendering device. During the computation, device-dependent values are extrapolated for border nodes. The extrapolated values are out-of-gamut.

Claims

1. A method executed by a computer for computing an inverse transfer function from a forward transfer function of an image rendering device, comprising:

extrapolating device-dependent values for border nodes of the inverse transfer function, and

computing, from the device-dependent values, values for at least some in-gamut nodes, wherein the in-gamut nodes are within a color gamut of the image rendering device, the border nodes are outside the color gamut and adjacent to the in-gamut nodes along a curve representing the color gamut, and the device-dependent values extrapolated for the border nodes are out-of-gamut.

2. The method of claim 1, wherein the border nodes are used to interpolate the in-gamut nodes.

3. The method of claim 1, wherein the forward transfer function is generated with the image rendering device, and wherein a gamut is computed for the image rendering device.

4. The method of claim 3, further comprising:

classifying nodes of the inverse transfer function with respect to a device gamut, the classifying includes the in-gamut nodes, the border nodes, and non-border nodes; and

wherein the device-dependent values for the border nodes and the non-border nodes are extrapolated from values in the forward transfer function.

5. The method of claim 1, wherein extrapolating a device-dependent value for a border node includes extrapolating a device-dependent value from a device-independent value of the border node and from device-dependent and device-independent values of training points, which lie within a region surrounding the border node.

6. The method of claim 5, wherein:

all border simplices S_b having border node N_b as a node are identified;

all training data points lying inside the border simplices S_b are added to a training vertices set;

in-gamut nodes N_i that connect directly to border node N_b are found;

for each in-gamut node N_i, all simplices S_i containing that node N_i are found;

training data points lying inside the simplices S_i are added to the training vertices set; and

device-dependent values at border node N_b are extrapolated using the device-dependent and device-independent values for its training vertices set, as well as the device-independent value for the border node.

7. The method of claim 1, wherein the device-dependent values extrapolated for the border nodes that are out-of-gamut nodes that influence interpolation of in-gamut colors.

8. The method of claim 7, wherein a device-dependent value of non-border node is extrapolated from a device-independent value of a node, the device-independent value depending on location of the node from a maximum extrapolation limit.

9. The method of claim 8, wherein the device-independent value of the node is used for extrapolation if the node lies within a convex hull of border nodes, and wherein the device-independent value mapped to the convex hull is used for extrapolation if the node lies outside the convex hull.

10. The method of claim 1, further comprising encoding the device-dependent values to fit within a gamut of the image rendering device.

11. The method of claim 1, wherein the image rendering device is a printer, and the border nodes are out-of-gamut nodes that influence interpolation of in-gamut colors.

12. The method of claim 1, wherein the borders nodes are out-of-gamut nodes that have colors that cannot be reproduced by the image rendering device.

13. The method of claim 1, wherein the image rendering device is a printer that is programmed with the inverse transfer function.

14. An article comprising memory encoded with the inverse transfer function of claim 1.

15. An apparatus for computing an inverse transfer function for an image rendering device, comprising:

a memory storing a program; and

a processor that executes the program for;

extrapolating device-dependent values for out-of-gamut nodes that influence interpolation of in-gamut nodes and that are adjacent the in-gamut nodes along a curve of a color gamut; and

interpolating device-dependent values for the in-gamut nodes, wherein the in-gamut nodes are within a device gamut of the image rendering device, the out-of-gamut nodes are outside the device gamut, and the extrapolated device-dependent values are out-of-gamut.

16. The apparatus of claim 15, wherein a device-dependent value for an out-of-gamut node is extrapolated from its device-independent value and from device-dependent and device-independent values of regional in-gamut nodes, the device-dependent and device-independent values of the regional in-gamut nodes taken from a forward transfer function of the image rendering device.

17. The apparatus of claim 15, wherein the extrapolated device-dependent values are obtained from border nodes that are out-of-gamut nodes outside the curve that represents the color gamut for the image rendering device.

18. The apparatus of claim 15, wherein the processor further executes the program for extrapolating device-dependent values for the out-of-gamut nodes that do not influence the interpolation of the in-gamut nodes.

19. The apparatus of claim 18, wherein extrapolation of a non-influencing out-of gamut node is a function of a device-independent value that is subject to a maximum limit.

20. A computer, comprising:

a memory encoded with data; and

a processor that retrieves the data to;

compute an inverse transfer function from a forward transfer function of an image rendering device; and

extrapolate, from the forward transfer function, out-of-gamut device-dependent values for border nodes of the inverse transfer function, wherein the border nodes are outside a color gamut of the image rendering device and adjacent in-gamut nodes along a curve of the color gamut.