Perceptually optimised color calibration method and system
Methods, devices, controllers and systems for color calibration of displays, non-volatile (non-transient) memory, controllers, display devices or display systems including a color calibration transform, operation of such controllers, display devices or systems and software for color calibration of a display are described are described that make use of a color transform having a distribution of color points across a full display gamut (hence optionally preserving full contrast and color saturation in the calibrated display) in an at least substantially perceptually uniform manner suitable for use as a color display calibration adapted for medical applications. A perceptually uniform spread of color points can be in terms of a distance metric such as deltaE2000 for color or JND for gray.
1. A color calibration method performed by a processor of a display device including non-volatile memory, the method comprising the steps:
expressing a first set of color points defining a color gamut in a first color space;
mapping said first set of color points from the first color space to a second color space, wherein the mapped first set of color points comprise a second set of color points;
redistributing the second set of points in the second color space wherein redistributing the second set of points in the second color space comprises linearizing the second set of points in the second color space by making the color points in the second color space equidistant throughout the second color space while preserving the color gamut of the first set of points,
mapping the second redistributed set of points from the second color space to a third color space, wherein the mapped second set of color points comprises a third set of color points;
storing the third set of points in the non-volatile memory for the display device as a calibration transform; and
applying the calibration transform to images to be displayed on the displayed device.
2. The color calibration method of claim 1 , wherein the third color space id the same as the first color space.
3. The color calibration method of claim 1 , further comprising the step:
measuring the first set of color points in the first color space to determine the color gamut.
4. The color calibration method of claim 1 , wherein the improved perceptional linearity is obtained by:
partitioning the color gamut in the first color space using polyhedrons;
obtaining improve perceptual linearity on the edges of each polyhedrons by redistributing the second set of color points on the edges of each polyhedron;
redistributing the second set of color points on the faces of each polyhedron to obtain improved perceptual linearity on the faces by replacing each such color point by an interpolated value obtained based on the redistributed color points surrounding points on edges of the polyhedron that form the boundaries of that face of the polyhedron; and
redistributing the second set of color points inside each polyhedron to obtain improved perceptual linearity by replacing each such color point by an interpolated value obtained based on the redistributed points surrounding faces of the polyhedron containing the inside color point.
5. The method of claim 4 , wherein the polyhedrons are tetrahedrons.
6. The color calibration method of claim 1 , wherein the improved perceptional linearity is obtained by:
partitioning the color gamut in the first color space using polyhedrons;
obtaining improved perceptual linearity on the edges of each polyhedrons by redistributing the second set of color points on the edges of each polyhedron;
redistributing the second set of color points on the faces of each polyhedron to obtain improved linearity of Euclidean distances between color points on the faces by replacing each such color point by an interpolated value obtained based on the redistributed points surrounding points on edges of the polyhedron that form the boundaries of that face of the polyhedron; and
redistributing the second set of color points inside each polyhedron to obtain improved linearity of the Euclidean distances between color points inside each polyhedron by replacing each such color point by an interpolated value obtained based on the redistributed surrounding faces of the polyhedron containing the inside color point.
7. The method of claim 6 , wherein the polyhedrons are tetrahedrons.
8. The color calibration method of claim 1 , wherein the color point linearizing procedure involves making color points that are spaced by a color distance metric of equidistance in the second color space.
9. The color calibration method of claim 8 , wherein a first distance metric is used in a first part of the second color space, and a second distance metric is used in another part of the second color space.
10. The color calibration method of claim 9 , wherein a second part of the second color space primarily contains a neutral grey part of the second color space and where the first part of the second color space primarily excludes the neutral grey part of the second color space.
11. The color calibration method according to claim 9 , further comprising applying a smoothing filter to reduce discontinuities in a border area between the first part of the second color space and a second part of the second color space.
12. The color calibration method of claim 1 , wherein the point linearizing procedure further comprises setting gray points in the second color space equidistant in terms of a second distance metric.
13. The color calibration method of claim 1 , further comprising ensuring Digital Imaging and Communications in Medicine (DICOM) Gray Scale Standard Display Function (GSDF) compliance for points that are gray.
14. A non-transient storage medium storing a computer program for executing the method of claim 1 .
15. A color calibration method used with a display device comprising a processor and non-volatile memory for the display device, the method comprising the steps:
expressing a first set of color points defining a color gamut in a first color space;
mapping said first set of color points from the first color space to a second color space, wherein the mapped first set of color points comprise a second set of color points;
redistributing the second set of points in the second color space wherein the redistributed second set of points has improved perceptional linearity compared to the first set of points while preserving the color gamut of the first set of points,
mapping the second redistributed set of points from the second color space to a third color space, wherein the mapped second set of color points comprises a third set of color points;
storing the third set of points in the non-volatile memory for the display device as a calibration transform; and
applying the calibration transform to images displayed on the display device;
wherein the improved perceptional linearity is obtained by:
partitioning the color gamut in the first color space using polyhedrons;
obtaining improved perceptual linearity on the edges of each polyhedron by redistributing the second set of color points on the edges of each polyhedron;
redistributing the second set of color points on the faces of each polyhedron to obtain improved perceptual linearity on the faces by replacing each such color point by an interpolated value obtained based on the redistributed color points surrounding points on edges of the polyhedron that form the boundaries of that face of the polyhedron; and
redistributing the second set of color points inside each polyhedron to obtain improved perceptual linearity by replacing each such color point by an interpolated value obtained based on the redistributed points surrounding faces of the polyhedron containing the inside color point.
16. The method of claim 15 , wherein the polyhedrons are tetrahedrons.
17. A color calibration method used with a display device comprising a processor and non-volatile memory for the display device, the method comprising the steps:
expressing a first set of color points defining a color gamut in a first color space;
mapping said first set of color points from the first color space to a second color space, wherein the mapped first set of color points comprise a second set of color points;
redistributing the second set of points in the second color space wherein the redistributed second set of points has improved perceptional linearity compared to the first set of points while preserving the color gamut of the first set of points,
mapping the second redistributed set of points from the second color space to a third color space, wherein the mapped second set of color points comprises a third set of color points;
storing the third set of points in the non-volatile memory for the display device as a calibration transform; and
applying the calibration transform to images displayed on the display device;
wherein the improved perceptional linearity is obtained by:
partitioning the color gamut in the first color space using polyhedrons;
obtaining improved perceptual linearity on the edges of each polyhedron by redistributing the second set of color points on the edges of each polyhedron;
redistributing the second set of color points on the faces of each polyhedron to obtain improved linearity of the Euclidean distances between color points on the faces by replacing each such color point by an interpolated value obtained based on the redistributed points surrounding points on edges of the polyhedron that form the boundaries of that face of the polyhedron; and
redistributing the second set of color points inside each polyhedron to obtain improved linearity of the Euclidean distances between color points inside each polyhedron by replacing each such color point by an interpolated value obtained based on the redistributed surrounding faces of the polyhedron containing the inside color point.
18. The method of claim 17 , wherein the polyhedrons are tetrahedrons.