Depth estimation using variant features

1 . A method comprising:

accessing an initial image, captured by a first camera, of an object comprising a size-invariant feature and a size-variant feature;

determining a size of the size-invariant feature in the initial image;

determining, based on the determined size of the size-invariant feature in the initial image, a distance between the camera and the object;

determining a size of the size-variant feature in the initial image;

determining, based on the determined distance between the camera and the object and based on the determined size of the size-variant feature in the initial image, an actual size of the size-variant feature;

accessing a subsequent image, captured by a second camera, of at least the size-variant feature;

determining a size of the size-variant feature in the subsequent image; and

determining, based on the determined actual size of the size-variant feature and the determined size of the size-variant feature in the subsequent image, a distance between the second camera and an object comprising the size-variant feature.

2 . The method of claim 1 , further comprising:

determining that an appearance of the size-invariant feature in the initial image satisfies one or more visibility criteria; and

determining the size of the size-invariant feature in the initial image in response to the determination that the size-invariant feature in the initial image satisfies the one or more visibility criteria.

3 . The method of claim 1 , wherein the accessed initial image is a first one of a plurality of accessed initial images of the object, the method further comprising:

determining, for each of the plurality of accessed initial images, a visibility of the size-invariant feature in that image;

selecting, based on the determined visibility of the size-invariant feature in each of the plurality of accessed initial images, a particular initial image as the first one of the plurality initial images.

4 . The method of claim 1 , wherein the object comprising the size-variant feature in the subsequent image is the same object comprising the size-invariant feature and the size-variant feature in the initial image.

5 . The method of claim 1 , wherein the first camera is the same as the second camera.

6 . The method of claim 4 , wherein the size-variant feature is a first size-variant feature of a plurality of size-variant features of the object, the method further comprising:

determining, for each of the plurality of size-variant features, a visibility of the size-variant feature in the subsequent image; and

selecting, based on the determined visibility of the size-variant features, a particular size-variant feature as the first size-variant feature.

7 . The method of claim 6 , wherein the determined visibility is based on one or more of:

an occlusion of the respective size-variant feature;

a coverage area of the respective size-variant feature relative to a coverage threshold;

an angle between a plane of the subsequent image and the respective size-variant feature; or

a rotation of the object.

8 . The method of claim 4 , further comprising determining, based on the determined distance between the second camera and the object, a distance between the object and a device.

9 . The method of claim 8 , further comprising automatically adjusting a position of the device based on the determined distance between the object and the device.

10 . The method of claim 9 , wherein the object comprises a person's face, and the device comprises a display screen.

11 . The method of claim 10 , further comprising automatically adjusting the position of the display screen based on one or more preferences of the person.

12 . The method of claim 10 , wherein the display screen is part of a computer monitor.

13 . The method of claim 10 , further comprising:

identifying the person; and

associating the actual size of the size-variant feature with the identity of the person.

14 . An apparatus comprising one or more non-transitory computer readable storage media storing instructions; and one or more processors coupled to the non-transitory computer readable storage media, the one or more processors operable to execute the instructions to:

access an initial image, captured by a first camera, of an object comprising a size-invariant feature and a size-variant feature;

determine a size of the size-invariant feature in the initial image;

determine, based on the determined size of the size-invariant feature, a distance between the camera and the object;

determine a size of the size-variant feature in the initial image;

determine, based on the determined distance between the camera and the object and based on the determined size of the size-variant feature, an actual size of the size-variant feature

access a subsequent image, captured by a second camera, of at least the size-variant feature;

determine a size of the size-variant feature in the subsequent image; and

determine, based on the determined actual size of the size-variant feature and the determined size of the size-variant feature in the subsequent image, a distance between the second camera and an object comprising the size-variant feature.

15 . The apparatus of claim 14 , wherein the object comprising the size-variant feature in the subsequent image is the same object comprising the size-invariant feature and the size-variant feature in the initial image.

16 . A method comprising:

accessing a subsequent image, captured by a second camera, of an object comprising a size-variant feature;

determining a size of the size-variant feature in the subsequent image;

accessing an actual size of the size-variant feature, wherein the actual size of the size-variant feature is based on:

a determined size of the size-invariant feature in an initial image, captured by a first camera, of an object comprising a size-invariant feature and the size-variant feature;

a distance, determined based on the determined size of the size of the size-invariant feature in the initial image captured by the first camera, between the first camera and the object in the initial image; and

a size of the size-variant feature in the initial image captured by the first camera; and

determining, based on the actual size of the size-variant feature and the determined size of the size-variant feature in the subsequent image, a distance between the second camera and the object comprising the size-variant feature.

17 . The method of claim 16 , wherein the object comprising the size-variant feature in the subsequent image is the same object comprising the size-invariant feature and the size-variant feature in the initial image.

18 . The method of claim 16 , further comprising determining, based on the determined distance between the second camera and the object, a distance between the object and a device.

19 . The method of claim 18 , further comprising automatically adjusting a position of the device based on the determined distance between the object and the device.

20 . The method of claim 19 , wherein the object comprises a person's face, and the device comprises a display screen.