Method, device and computer program product for encoding a distorted image frame

1. A method for encoding, using a block-based video encoding algorithm, a distorted image frame produced via at least one image sensor, depicting a scene, each pixel in the distorted image frame corresponding to a field of view, FOV, in the scene, the method comprising:

determining a map of maximum pixel block sizes corresponding to the distorted image frame, wherein the map of maximum pixel block sizes is determined based on a spatial resolution distribution corresponding to a distribution of extents of the corresponding FOV per pixel in the distorted image frame, such that for a first portion of the distorted image frame having a first spatial resolution, the maximum pixel block size corresponding to the first portion is set to a first value, and for a second portion of the distorted image frame having a second spatial resolution being lower than the first spatial resolution, the maximum pixel block size corresponding to the second portion is set to a second value being lower than the first value; and

encoding, using the block-based video encoding algorithm, the distorted image frame, wherein the map of maximum pixel block sizes is used for defining maximum block sizes for encoding blocks of the block-based video encoding algorithm.

2. The method according to claim 1 , wherein the block-based video encoding algorithm is h.265 or AV1, and wherein the map of maximum pixel block sizes is used for defining maximum sizes of coding units of the block-based video encoding algorithm.

3. The method according to claim 1 , further comprising:

determining a map of mum pixel block sizes corresponding to the distorted image frame, wherein the map of minimum pixel block sizes comprises areas having different minimum pixel block sizes, and wherein the map of minimum pixel block sizes is determined based on the spatial resolution distribution such that for the first portion of the distorted image frame having the first spatial resolution, the minimum pixel block size corresponding to the first portion is set to a third value being lower than the first value, and for the second portion of the distorted image frame having the second spatial resolution, the minimum pixel block size corresponding to the second portion is set to a fourth value being lower than the second value and the third value; and

wherein, in the step of encoding the distorted image frame, the map of minimum pixel block sizes is used for defining minimum block sizes for encoding blocks of the block-based video encoding algorithm.

4. The method according to claim 3 , wherein the block-based video encoding algorithm is h.265, and wherein the map of minimum pixel block sizes is used for defining the minimum sizes of prediction units, PU, and/or transform units, TU, of the block-based video encoding algorithm.

5. The method according to claim 1 , wherein the distorted image frame are produced by capturing by one image sensor through a wide-angle lens.

6. The method according to claim 5 , wherein the wide-angle lens is a fisheye lens.

7. The method according to claim 1 , wherein the distorted image frame are produced by capturing by one image sensor through an optical dome.

8. The method according to claim 1 , wherein each distorted image frame is produced by a stitching, based on a projection algorithm, of a plurality of primary image frames captured by one or more image sensors.

9. The method according to claim 5 , wherein a first area of the map of maximum pixel sizes corresponding to the first portion of the distorted image frame and a second area of the map of maximum pixel sizes corresponding to the second portion of the distorted image frame form elliptical patterns radially extending from a reference position of the map of maximum pixel sizes; and

wherein a radial distance between the reference position and the first area is smaller than a radial distance between the reference position and the second area.

10. A non-transitory computer-readable medium including instructions that, when executed by circuitry on a device, cause the circuitry to perform the method according to claim 1 .

11. An encoder for encoding, using a block-based video encoding algorithm, distorted image frame produced via at least one image sensor, depicting a scene, each pixel in the distorted image frame corresponding to a field of view, FOV, of the scene, the encoder being configured to:

determine a map of maximum pixel block sizes corresponding to the distorted image frame, wherein the map of maximum pixel block sizes is determined based on a spatial resolution distribution corresponding to a distribution of extents of the corresponding FOY per pixel in the distorted image frame, such that for a first portion of the distorted image frame having a first spatial resolution, the maximum pixel block size corresponding to the first portion is set to a first value, and for a second portion for the distorted image frame having a second spatial resolution being lower than the first spatial resolution, the maximum pixel block size corresponding to the second portion is set to a second value being lower than the first value; and

encode, using the block-based video encoding algorithm, the distorted image frame, wherein the map of maximum pixel block sizes is used by the block-based video encoding algorithm for defining maximum block sizes for encoding blocks of the block-based video encoding algorithm.

12. A camera comprising the encoder according to claim 11 .

13. The camera according to claim 12 , further comprising a wide-angle lens through which images are captured by one image sensor of the camera.

14. The camera according to claim 12 , further comprising a plurality of image sensors, and wherein the encoder is further configured to stitch image frame from a plurality of primary images captured by the plurality of image sensors.