Method of processing images of a users eye, associated systems and computer programs

1. A computer-implemented method of selecting a sequence of images of a user's eye for an eye tracking application wherein each image is captured when a stationary stimulus point is displayed to the user, the method comprising, for a plurality of different pairs of the images:

comparing the pair of images with each other to determine an image-score that represents a degree of difference between the compared images; and

calculating a sequence-score based on the image-scores for the plurality of pairs of images.

2. The method of claim 1 , wherein:

each of the images in the sequence comprises a gaze-location-identifier that represents the location of the stimulus on a screen that was presented to the user when the image was captured; and

the gaze-location-identifier is the same for each image in the sequence of images.

3. The method of claim 1 , further comprising controlling how the sequence of images is passed to a downstream eye gaze tracking operation based on the sequence-score.

4. The method of claim 1 , further comprising:

setting a discard-flag for at least a portion of the sequence of images if the sequence-score is greater than a discard-threshold.

5. The method of claim 1 , further comprising:

discarding at least a portion of the sequence of images if the sequence-score is greater than a discard-threshold.

6. The method of claim 4 , further comprising:

setting an inspection-flag for at least a portion of the sequence of images if the sequence-score is greater than an inspection-threshold, wherein the inspection-threshold is less than the discard-threshold; and

if the inspection-flag is set, then providing the at least a portion of the sequence of images to a user for manually setting the discard-flag.

7. The method of claim 4 , further comprising:

performing a downstream eye gaze tracking operation on sequences of images for which the discard-flag is not set, and not performing the eye gaze tracking operation on sequences of images for which the discard-flag is set.

8. The method of claim 4 , further comprising:

performing a downstream eye gaze tracking operation on the sequence of images irrespective of whether or not the associated discard-flag is set; and

aggregating performance evaluation statistics on sequences of images for which the discard-flag is not set, and not aggregating performance evaluation statistics on sequences of images for which the discard-flag is set.

9. The method of claim 1 , further comprising:

identifying a plurality of spaced apart sub-sequences of images in the sequence of images, wherein each sub-sequence comprises a plurality of consecutive images in the sequence of images that satisfy a sub-sequence-score-threshold; and

concatenating the plurality of sub-sequences of images to provide a concatenated-sequence of images; and

providing the concatenated-sequence of images to a downstream eye gaze tracking operation.

10. The method of claim 7 , wherein the eye gaze tracking operation comprises:

a training algorithm for setting one or more trainable parameters of a machine learning model for performing eye gaze tracking on received images;

a calibration algorithm;

a verification algorithm; and/or

a performance evaluation algorithm.

11. The method of claim 10 , wherein:

each sequence of images comprises a gaze-location-identifier that represents the location of a stimulus on a screen that was presented to the user when the sequence of images was captured; and

the eye gaze tracking operation performs its function based on the images and the gaze-location-identifier.

12. The method of claim 1 , wherein calculating the sequence-score based on the image-scores comprises:

summing the image-scores to provide an accumulated-sequence-score.

13. The method of claim 1 , wherein calculating the sequence-score based on the image-scores comprises:

setting a peak-sequence-score as the maximum value of the image-scores.

14. The method of claim 13 , further comprising:

setting a blink-flag for the sequence of images if the peak-sequence-score is greater than a blink-threshold; and

if the blink-flag is set, then passing the sequence of images to a downstream eye gaze tracking operation that requires a presence of a blink in the sequence of images; or

if the blink-flag is not set, then passing the sequence of images to a downstream eye gaze tracking operation that requires the absence of a blink in the sequence of images.

15. The method of claim 13 , further comprising:

setting a movement-flag for the sequence of images if the peak-sequence-score is greater than a movement -threshold; and

if the movement-flag is set, then passing the sequence of images to a downstream eye gaze tracking operation that requires a presence of a movement in the sequence of images; or

if the movement-flag is not set, then passing the sequence of images to a downstream eye gaze tracking operation that requires the absence of movement in the sequence of images.

16. The method of claim 1 , wherein the method further comprises:

causing a screen to display a stationary stimulus point to the user in accordance with a gaze-location-identifier; and

capturing the sequence of images of the user's eye while the screen is displaying the stationary stimulus point to the user.

17. The method of claim 1 , wherein:

each of the images comprises a plurality of pixel positions, and each pixel position has a pixel-value that represents a brightness or hue of the pixel; and

comparing the pair of images comprises:

comparing pixel-values at corresponding pixel-positions in the pair of images to determine pixel-value-differences; and

determining the image-score as a function of the pixel-value-differences.

18. The method of claim 1 , wherein:

each of the images comprises:

a plurality of pixel positions that represent a subset of pixels from a full-sensor-image, and

a crop-identifier that represents a location of the subset of pixels in the full-sensor-image; and

comparing the pair of images comprises determining a crop-offset-value as the difference between the crop-identifiers of the two images;

the method further comprises:

setting a discard-sequence-threshold based on the crop-offset-values; and

setting a discard-flag for the sequence of images if the sequence-score is greater than the discard-sequence-threshold.

19. A processor configured to:

receive a sequence of images of a user's eye for an eye tracking application;

for a plurality of different pairs of the images:

compare the pair of images with each other to determine an image-score that represents a degree of difference between the compared images; and

calculate a sequence-score based on the image-scores for the plurality of pairs of images.

20. A non-transitory computer-readable storage medium storing instructions which, when executed by a cause the computer to carry out the steps of:

selecting a sequence of images of a user's eye for an eye tracking application wherein each image is captured when a stationary stimulus point is displayed to the user,

comparing a plurality of different pairs of the images with each other to determine an image-score that represents a degree of difference between the compared images; and

calculating a sequence-score based on the image-scores for the plurality of pairs of images.