# US 10,373,585 B2 · Metamerically stable RGBW display

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- Number: US 10,373,585 B2
- Document ID: US10373585B2
- Status: Granted
- Kind: B2
- Application number: 15/704,708
- Filed: 2017-09-14
- Published: 2018-03-22
- Granted: 2019-08-06
- Earliest claimed: 2016-09-19
- Assignees: Dolby Laboratories Licensing Corporation
- Applicants: Dolby Laboratories Licensing Corporation
- Inventors: Robin Atkins
- Web page: https://patentgrep.com/patent/US10373585B2

## CPC

- G09G 5/02: characterised by the way in which colour is displayed {(details of colour display specific for CRTs G09G1/28; specific for flat matrix panels other than liquid crystal displays G09G3/2003; specific for liquid crystal displays G09G3/3607)}
- G09G 3/2003: {Display of colours (specific for liquid crystal displays G09G3/3607)}
- H04N 1/6022: {Generating a fourth subtractive colour signal, e.g. under colour removal, black masking}
- G09G 2300/0452: Details of colour pixel setup, e.g. pixel composed of a red, a blue and two green components
- G09G 2320/0271: Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping
- G09G 2320/0666: for control of colour parameters, e.g. colour temperature
- G09G 2340/06: Colour space transformation
- G09G: ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION (arrangements for transferring data between digital computers and displays G06F3/14; static indicating arrangements comprising an association of a number of separate sources or light control cells G09F9/00; static indicating arrangements comprising integral associations of a number of light sources H01J, H01K, H10H, H05B33/12; scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission, details thereof H04N1/00)
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

Methods for designing metamerically stable RGBW displays are presented. Display parameters are selected so that given a reference spectral power distribution (SPD) for the white color primary (e.g., one based on D65), and a test spectral power distribution for the white color primary, deviations in color appearance measurements between the two SPDs among N different observers are minimized. Given a display with a metamerically stable white (W), given linear input R, G, and B values, output R, G, B, and W values are generated to optimize metameric stability instead of reducing power consumption or to increase total brightness.

## Claims

### Claim 1

A method to design a metamerically stable RGBW display, the method comprising:
accessing a reference spectral power distribution (SPD) function for a white color primary;
accessing a first test SPD function for the white color primary for a display based on a first set of display parameters;
computing reference XYZ values based on the reference SPD and color matching functions for N observers;
computing first test XYZ values based on the test SPD and the color matching functions for the N observers;
translating the reference XYZ values and the first test XYZ values into color values in a perceptually uniform color space to generate reference color values and first test color values, wherein the perceptually uniform color space comprises the ICtCp color space;
computing first difference values based on the reference color values and the first test color values; and
computing a first measure of metameric stability based on the first difference values.

### Claim 2 (depends on 1)

The method of claim 1, further comprising:
determining a second test SPD function for the white color primary for the display based on a second set of display parameters;
computing second test XYZ values based on the second test SPD and the color matching functions for the N observers;
translating the second test XYZ values into color values in the perceptually uniform color space to generate second test color values;
computing second difference values based on the reference color values and the second test color values;
computing a second measure of metameric stability based on the second difference values; and
if the first measure of metameric stability is smaller than the second measure of metameric stability selecting the first set of design parameters for the display, otherwise selecting the second set of design parameters.

### Claim 3 (depends on 2)

A method for a metamerically stable RGBW display, the method comprising:
determining, according to claim 2, design para meters for a display with a metamerically stable white color primary (W);
receiving in the display an input image comprising pixels, wherein each pixel comprises three input color components R, G, and B; for a pixel in the input image:
adjusting the output W value as the minimum of the input R, G, and B values; and setting:
output R=input R−output W;
output G=input G−output W;
output B=input B−output W.

### Claim 4 (depends on 3)

The method of claim 3, further comprising removing any non-linearity from the input image before computing the output RGBW values.

### Claim 5 (depends on 3)

The method of claim 3, further comprising re-applying a non-linearity to the output RGBW signal values.

### Claim 6 (depends on 3)

The method of claim 3, wherein input RGB values and output RGB and W values are normalized to be between 0 and 1.

### Claim 7 (depends on 2)

A method for a metamerically stable RGBW display, the method comprising:
determining, according to claim 2, design parameters for a display with a metamerically stable white color primary (W);
receiving in the display an input image comprising pixels, wherein each pixel comprises three input color components R, G, and B, wherein each of the components comprises values between 0 and RGB_in_max;
for a pixel in the input image:
if the pixel color is white, then setting:
output R=output G=output B=RGB_out_max;
output W=Wmax,
wherein RGB_out_max denotes a maximum value for the output RGB values and Wmax denotes a maximum allowed value of W;
if the pixel color is mid gray, then setting
output R=output G=output B=0;
output W=Wmax;
else,
multiplying each input RGB component by a scaler to generate scaled input R, G, and B values;
computing a first output W value as the minimum of the scaled input R, G, and B values;
computing output W=min(first output W, Wmax);
computing
output R=scaled input R−output W;
output G=scaled input G−output W;
output B=scaled input B−output W; and
clamping each of the output R, G, and B values between 0 and RGB_out_max.

### Claim 8 (depends on 7)

The method of claim 7, wherein a pixel is determined to be white if for that pixel
input R=input G=input B=RGB_in_max, and a pixel is determined to be mid-gray if for that pixel input R=input G=input B=RGB_in_max/2.

### Claim 9 (depends on 1)

The method of claim 1, wherein the design parameters comprise one or more combinations of light emitters, phosphors, quantum dots, and display filters.

### Claim 10 (depends on 1)

The method of claim 1, wherein the measure of metameric stability comprises the standard deviation of the difference values across all N observers.

### Claim 11 (depends on 1)

The method of claim 1, wherein the square of the difference value for an observer comprises the sum of the squares of the color differences between the reference color values and the test color values for the observer.

### Claim 12 (depends on 1)

The method of claim 1, wherein the reference SPD function for the white color primary comprises the CIE daylight, D65, definition.

### Claim 13 (depends on 1)

An apparatus comprising a processor and configured to perform the method recited in claim 1.

### Claim 14 (depends on 1)

A non-transitory computer-readable storage medium having stored thereon computer-executable instruction for executing a method with one or more processors in accordance with claim 1.