Methods and systems for assigning pixels distance-cost values using a flood fill technique

1. A method comprising:

obtaining video data depicting a head of a user;

obtaining depth data associated with the video data;

selecting seed pixels for a hair-identification flood fill for identifying pixels depicting hair of the head of the user, the seed pixels selected at least in part by using the obtained depth data;

performing the hair-identification flood fill from the selected seed pixels, the hair-identification flood fill assigning respective distance-cost values to pixels of the video data based on respective position-space-cost values and respective color-space-cost values, wherein performing the hair-identification flood fill comprises:

identifying a plurality of neighbor pixels of a current pixel;

determining respective step-cost values from the current pixel to each pixel in the plurality of neighbor pixels; and

assigning each pixel in the plurality of neighbor pixels a respective distance-cost value based on a distance-cost value of the current pixel and the respective step-cost values; and

identifying, using a foreground identification process, a persona of the user from the video data, wherein the respective distance-cost values assigned to pixels by the hair-identification flood fill is one of a plurality of inputs of the foreground identification process.

2. The method of claim 1 , wherein selecting seed pixels for the hair-identification flood fill further comprises selecting seed pixels for the hair-identification flood fill at least in part by using the video data.

3. The method of claim 1 , further comprising:

obtaining a head contour that estimates an outline of the depicted head of the user, the head contour being based at least in part on the depth data associated with the video data,

wherein the selected seed pixels are on an upper contour, wherein the upper contour is an upper portion of the head contour.

4. The method of claim 3 , wherein the selected seed pixels are equally distributed along the upper contour.

5. The method of claim 3 , wherein the selected seed pixels are of colors that are found in a user-hair-color model.

6. The method of claim 1 , wherein selecting seed pixels for the hair-identification flood fill comprises:

identifying pixels having noisy depth values over a series of frames; and

selecting the identified noisy depth-pixels as seed pixels for the hair-identification flood fill.

7. The method of claim 6 , wherein the selected seed pixels are located within an extended head box.

8. The method of claim 6 , wherein the selected seed pixels have intermittent depth values that are within a threshold tolerance of a depth value corresponding to the head of the user.

9. The method of claim 6 , wherein the selected seed pixels are of colors that are found in a user-hair-color model.

10. The method of claim 1 , wherein a first set of the selected seed pixels are on an upper contour and a second set of the selected seed pixels have noisy depth values over a series of frames, wherein the upper contour is an upper portion of a head contour that estimates an outline of the depicted head of the user, the method further comprising:

initializing the distance-cost values of the seed pixels in the first set to be zero; and

initializing the distance-cost values of the seed pixels in the second set to be non-zero.

11. The method of claim 1 , wherein performing the hair-identification flood fill comprises:

determining a minimum distance-cost value from at least one of the selected seed pixels to a current pixel; and

assigning the current pixel a distance-cost value that is the determined minimum distance-cost value.

12. The method of claim 11 , wherein determining a minimum distance-cost value comprises:

comparing a current distance-cost value corresponding with a current flood-fill path to a prior distance-cost value corresponding with a prior flood-fill path.

13. The method of claim 12 , wherein the current flood-fill path and the prior flood-fill path originate from a common seed pixel.

14. The method of claim 12 , wherein the current flood-fill path and the prior flood-fill path originate from different seed pixels.

15. The method of claim 1 , wherein performing the hair-identification flood fill comprises performing the hair-identification flood fill along a plurality of flood-fill paths, the method further comprising:

terminating the hair-identification flood fill along a current flood-fill path in response to at least one termination criteria, the termination criteria comprising:

a current pixel not being a user-hair color according to a user-hair-color model;

the current pixel being a background color according to a background-color model;

a distance-cost value to the current pixel being greater than a distance-cost threshold; and

a step-cost value to the current pixel being greater than a step-cost threshold.

16. A system comprising:

a communication interface;

a processor; and

data storage containing instructions executable by the processor for causing the system to carry out a set of functions, the set of functions including:

obtaining video data depicting a head of a user;

obtaining depth data associated with the video data;

selecting seed pixels for a hair-identification flood fill for identifying pixels depicting hair of the head of the user, the seed pixels selected at least in part by using the depth data;

performing the hair-identification flood fill from the selected seed pixels, the hair-identification flood fill assigning respective distance-cost values to pixels of the video data based on respective position-space-cost values and respective color-space-cost values, wherein performing the hair-identification flood fill comprises:

identifying a plurality of neighbor pixels of a current pixel;

determining respective step-cost values from the current pixel to each pixel in the plurality of neighbor pixels; and

assigning each pixel in the plurality of neighbor pixels a respective distance-cost value based on a distance-cost value of the current pixel and the respective step-cost values; and

identifying, using a foreground identification process, a persona of the user from the video data, wherein the respective distance-cost values assigned to pixels by the hair-identification flood fill is one of a plurality of inputs of the foreground identification process.