White balance calibration method

1 . A method comprising:

(i) applying a respective value of a first plurality of values of a first control parameter to each light source of a plurality of light sources of a projector system, each light source of the plurality of light sources configured to output a different wavelength of light, wherein applying each of the first plurality of values of the first control parameter causes each light source of the plurality of light sources to output light having a respective first output luminance;

(ii) measuring a first luminance and first colour space coordinates of a light pattern displayed by the projector system, wherein the light pattern is generated by applying the first plurality of values of the first control parameter to the plurality of light sources;

(iii) converting the first luminance and first colour space coordinates to corresponding tristimulus values;

(iv) calculating, based on the corresponding tristimulus values, a respective colour luminance value corresponding to each light source of the plurality of light sources,

wherein the calculation comprises solving a plurality of linear equations, each linear equation of the plurality of linear equations being derived from a sum of the contributions of the plurality of light sources to a respective tristimulus value, to obtain each colour luminance value;

(v) calculating a linear relationship between the first control parameter and each colour luminance value based on:

(a) the respective colour luminance value;

(b) either a previous colour luminance value from a previous iteration or an initial colour luminance value;

(c) the respective first value of the first control parameter; and

(d) either a previous value of the first control parameter from a previous iteration or an initial value of the first control parameter;

(vi) determining a second plurality of values of the first control parameter based on the linear relationships and a target colour luminance value for each light source; and

(vii) applying the second plurality of values of the first control parameter to the plurality of light sources, wherein applying each of the second plurality of values of the first control parameter causes each light source of the plurality of light sources to output light having a respective second output luminance.

2 . The method of claim 1 , wherein the plurality of light sources comprises a first light source configured to output a first wavelength of light having colour space coordinates x R , y R , z R =(1−x R −y R ), a second light source configured to output a second wavelength of light having colour space coordinates x G , y G , z G =(1−x G −y G ), and a third light source configured to output a third wavelength of light having colour space coordinates x B , y B , z B =(1−x B −y B ).

3 . The method of claim 2 , wherein the first wavelength is in the range of 620 to 750 nm, the second wavelength is in the range of 490 to 570 nm, and the third wavelength is in the range of 450 to 495 nm, and wherein the first wavelength and the second wavelength are separated by at least 150 nm, and the second wavelength and the third wavelength are separated by at least 60 nm.

4 . The method of claim 2 , wherein the conversion of the first luminance and first colour space coordinates into respective tristimulus values, X, Y and Z, comprises the calculations:

X

=

Lv

⁢

x

y

,

Y

=

Lv

,

and

Z

=

Lv

⁢

(

1

-

x

-

y

)

y

,

wherein Lv is the first luminance and (x, y) are the first colour space coordinates.

5 . The method of claim 4 , wherein the calculation of the respective colour luminance values comprises solving the three linear equations:

X

=

L

⁢

v

R

⁢

x

R

y

R

+

L

⁢

v

G

⁢

x

G

y

G

+

L

⁢

v

B

⁢

x

B

y

B

,

Y

=

L

⁢

v

R

+

L

⁢

v

G

+

L

⁢

v

B

,

and

Z

=

L

⁢

v

R

⁢

z

R

y

R

+

L

⁢

v

G

⁢

z

G

y

G

+

L

⁢

v

B

⁢

z

B

y

B

,

wherein x γ , y γ , z γ =(1−x γ −y γ ), are the colour space coordinates for the first wavelength, second wavelength, and third wavelength, such that γ={R, G, B}, in order to obtain a first colour luminance value Lv R corresponding to the first light source, a second colour luminance value Lv G corresponding to the second light source, and a third colour luminance value Lv B corresponding to the second light source.

6 . The method of claim 5 , wherein the linear relationship between the first control parameter and the respective colour luminance value is determined based on the calculation:

m

γ

=

P

i

γ

-

P

i

-

1

γ

Lv

i

γ

-

Lv

i

-

1

γ

,

b

γ

=

P

i

γ

-

m

γ

⁢

L

⁢

v

i

γ

,

wherein

P

i

γ

is the respective value of the first control parameter of the first plurality of values corresponding to each respective light source,

P

i

-

1

γ

is the previous value of the first control parameter from the previous iteration or the initial value of the first control parameter corresponding to each respective light source,

L

⁢

v

i

γ

is the colour luminance value for each respective light source,

L

⁢

v

i

-

1

γ

is the colour luminance value from the previous iteration or the initial colour luminance value, m γ is the gradient of the respective linear relationship, and b γ is the offset of the respective linear relationship.

7 . The method of claim 6 , wherein each of the second plurality of values of the first control parameter,

P

i

+

1

γ

,

is determined based on the calculation of:

P

i

+

1

γ

=

m

γ

⁢

L

⁢

v

t

γ

+

b

γ

,

wherein

L

⁢

v

t

γ

is the target colour luminance value for each light source.

8 . The method of claim 1 , wherein steps (i) to (vii) form an initial iteration in which calculating the linear relationship between the first control parameter and each colour luminance value is based on:

(a) the respective colour luminance value;

(b) an initial colour luminance value;

(c) the respective first value of the first control parameter; and

(d) an initial value of the first control parameter;

wherein the method steps (i) to (vii) are repeated for one or more further iterations in which calculating the linear relationship between the first control parameter and each colour luminance value is based on:

(a) the respective colour luminance value;

(b) a previous colour luminance value from a previous iteration;

(c) the respective first value of the first control parameter; and

(d) a previous value of the first control parameter from a previous iteration.

9 . The method of claim 8 , wherein the one or more iterations are performed while a difference between the first luminance and a target luminance is below a first threshold and a difference between the first colour space coordinates and target colour space coordinates is below a second threshold.

10 . The method of claim 8 , wherein the method steps of claim 1 are repeated at a first temperature of the projector system.

11 . The method of claim 10 , wherein the first temperature and the second plurality of values of the first control parameter is saved in a lookup table implemented on a computing device in communication with the projector system when the difference between the first luminance and a target luminance is below a first threshold and a difference between the first colour space coordinates and target colour space coordinates is below a second threshold.

12 . The method of claim 1 , wherein the first control parameter comprises one of the group comprising: a pulse width modulation parameter for each of the plurality of light sources, a digital-analogue converter parameter for each of the plurality of light sources, a photodiode signal parameter for each of the plurality of light sources, and a scaling factor applied to a uniformity map for controlling the amount of light projected by each of the light sources.

13 . The method of claim 12 , wherein the selection from the group is determined based on the measured value of the first luminance.

14 . The method of claim 13 , wherein a first one of the group is selected for a first range of measured first luminance values, and a second one of the group is selected for a second range of measured first luminance values.

15 . The method of claim 12 , further comprising applying a first plurality of values of a second control parameter each corresponding to a respective one of the plurality of light sources, wherein the second control parameter is a different one of the group than the first control parameter, wherein the second control parameter is used to control an overall luminance of the projector system.

16 . A projector system comprising:

a plurality of light sources, each configured to output a different wavelength of light;

a display device configured to display a hologram, such that a light pattern is displayed at an image plane when the display device is illuminated by the plurality of light sources;

a measurement device configured to measure a first luminance and first colour space coordinates of the light pattern displayed at the image plane; and

a computing device in communication with the plurality of light sources and the measurement device, wherein the computing device is configured to:

apply a respective value of a first plurality of values of a first control parameter to each of the plurality of light sources, wherein applying each value of the first plurality of values of the first control parameter causes each light source of the plurality of light sources to output light having a respective first output luminance;

receive the first luminance and first colour space coordinates from the measurement device;

convert the first luminance and first colour space coordinates to corresponding tristimulus values;

calculate, based on the corresponding tristimulus values, a respective colour luminance value corresponding to each light source of the plurality of light sources,

wherein the calculation comprises solving a plurality of linear equations, each linear equation of the plurality of linear equations being derived from a sum of the contributions of the plurality of light sources to a respective tristimulus value, to obtain each colour luminance value,

calculate a linear relationship between the first control parameter and each colour luminance value based on:

(a) the respective colour luminance value;

(b) either a previous colour luminance value from a previous iteration or an initial colour luminance value;

(c) the respective first value of the first control parameter; and

(d) either a previous value of the first control parameter from a previous iteration or an initial value of the first control parameter;

determine a second plurality of values of the first control parameter based on the linear relationships and a target luminance value for each light source; and

apply the second plurality of values of the first control parameter to the plurality of light sources, wherein applying each of the second plurality of values of the first control parameter causes each light source of the plurality of light sources to output light having a respective second output luminance.

17 . A method of projection comprising:

applying a respective value of a first plurality of values of a first control parameter to each light source of a plurality of light sources of a projector system, each light source of the plurality of light sources configured to output a different wavelength of light, wherein applying each of the first plurality of values of the first control parameter causes each light source of the plurality of light sources to output light having a respective first output luminance;

projecting a first light pattern by applying the first plurality of values of the first control parameter to the plurality of light sources and illuminating a hologram corresponding to the light pattern with the plurality of light sources;

measuring a first luminance and first colour space coordinates of the light pattern;

converting the first luminance and first colour space coordinates to corresponding tristimulus values;

calculating, based on the corresponding tristimulus values, a respective colour luminance value corresponding to each light source of the plurality of light sources,

wherein the calculation comprises solving a plurality of linear equations, each linear equation of the plurality of linear equations being derived from a sum of the contributions of the plurality of light sources to a respective tristimulus value, to obtain each colour luminance value;

calculating a linear relationship between the first control parameter and each colour luminance value based on:

(a) the respective colour luminance value;

(b) either a previous colour luminance value from a previous iteration or an initial colour luminance value;

(c) the respective first value of the first control parameter; and

(d) either a previous value of the first control parameter from a previous iteration or an initial value of the first control parameter;

determining a second plurality of values of the first control parameter based on the linear relationships and a target colour luminance value for each light source; and

projecting a second light pattern by applying the second plurality of values of the first control parameter to the plurality of light sources, wherein applying each of the second plurality of values of the first control parameter causes each light source of the plurality of light sources to output light having a respective second output luminance.

18 . A non-transitory computer readable medium comprising instructions which, when executed by one or more processors, cause the one or more processors to:

(i) apply a respective value of a first plurality of values of a first control parameter to each light source of a plurality of light sources of a projector system, each light source of the plurality of light sources configured to output a different wavelength of light, wherein each of the first plurality of values of the first control parameter determines an output luminance of a corresponding light source of the plurality of light sources;

(ii) measure a first luminance and first colour space coordinates of a light pattern displayed by the projector system, wherein the light pattern is generated by applying the first plurality of values of the first control parameter to the plurality of light sources;

(iii) convert the first luminance and first colour space coordinates to corresponding tristimulus values;

(iv) calculate, based on the corresponding tristimulus values, a respective colour luminance value corresponding to each light source of the plurality of light sources,

wherein the calculation comprises solving a plurality of linear equations, each linear equation of the plurality of linear equations being derived from a sum of the contributions of the plurality of light sources to a respective tristimulus value, to obtain each colour luminance value;

(v) calculate a linear relationship between the first control parameter and each colour luminance value based on: the respective colour luminance value, a previous colour luminance value from a previous iteration or an initial colour luminance value, the respective first value of the first control parameter, and a previous value of the first control parameter from a previous iteration or an initial value of the first control parameter;

(vi) determine a second plurality of values of the first control parameter based on the linear relationships and a target colour luminance value for each light source; and

(vii) control the plurality of light sources using the second plurality of values of the first control parameter.