Compression of multiplane images

1 . A method of compressing a multiplane-image (MPI) video, the method comprising:

splitting the MPI video into a first frame sequence and a second frame sequence, the first frame sequence being a sequence of texture frames, with each of the texture frames representing a respective layer of a corresponding multiplane image of the MPI video, the second frame sequence being a sequence of alpha frames, with each of the alpha frames corresponding to a respective one of the texture frames of the first sequence;

applying a first set of preprocessing operations to convert the first frame sequence into a third frame sequence, the first set comprising:

a) generating a corresponding blurred image by applying a blur transformation to the corresponding source image; and

when the corresponding pixel value of the corresponding alpha frame of the second frame sequence is smaller than a first threshold value, assigning a corresponding pixel value from the corresponding blurred image to be the pixel value in the frame of the third frame sequence; or

b) generating a first thresholded image by nulling in the corresponding source image all pixel values for which the corresponding pixel value of the corresponding alpha frame of the second frame sequence is smaller than the first threshold value; and

generating a second thresholded image by nulling in a corresponding texture frame of the first sequence all pixel values for which the corresponding pixel value of the corresponding alpha frame of the second frame sequence is smaller than the first threshold value;

applying a second set of preprocessing operations to convert the second frame sequence into a fourth frame sequence, the second set including operations according to which a pixel value in a frame of the fourth frame sequence is determined based on a comparison of a corresponding pixel value of a corresponding source image with a second threshold value; and

applying video compression to the second frame sequence and to the fourth frame sequence.

2 . The method of claim 1 , further comprising applying video compression to a sequence of source images corresponding to the MPI video.

3 . The method of claim 2 , further comprising:

generating a metadata stream signaling parameters of the video compression;

generating an output bitstream by multiplexing the compressed third frame sequence, the compressed fourth frame sequence, the compressed sequence of source images, and the metadata stream; and

transmitting the output bitstream through a communication channel.

4 . The method of claim 1 , wherein option a) of the first set further comprises:

when the corresponding pixel value of the corresponding alpha frame of the second frame sequence is greater than the first threshold value, transferring a corresponding pixel value from the first frame sequence to the third frame sequence.

5 . The method of claim 1 , wherein the blur transformation is a Gaussian blur transformation with a square kernel including more than one pixel.

6 . The method of claim 1 , wherein option b) of the first set further comprises:

computing pixelwise difference values between the first thresholded image and the second thresholded image; and

computing a corresponding frame for the third frame sequence by adding a fixed offset value to the computed pixelwise difference values,

wherein the fixed offset value is selected based on an image resolution.

7 . The method of claim 1 , wherein the second set comprises generating a first thresholded image by nulling in the corresponding source image all pixel values for which the corresponding pixel value of the corresponding alpha frame of the second frame sequence is smaller than the second threshold value.

8 . The method of claim 7 , wherein the second set further comprises converting the first thresholded image into a corresponding grayscale image.

9 . The method of claim 8 , wherein the second set further comprises generating a corresponding blurred image by applying a blur transformation to the corresponding grayscale image.

10 . The method of claim 9 , wherein the second set further comprises:

computing pixelwise product values using the first thresholded image and the corresponding blurred image; and

computing a corresponding frame for the third frame sequence by applying normalization and clipping operations to the computed pixelwise product values,

wherein the normalization and clipping operations are configured based on an image resolution.

11 . The method of claim 1 , wherein the MPI video is one of a plurality of MPI videos corresponding to different respective camera positions of a plurality of camera positions arranged around a scene captured in the MPI video.

12 . A non-transitory computer-readable medium storing instructions that, when executed by an electronic processor, cause the electronic processor to perform operations comprising the method of claim 1 .

13 . An apparatus for compressing a multiplane-image (MPI) video, the apparatus comprising:

at least one processor; and

at least one memory including program code,

wherein the at least one memory and the program code are configured to, with the at least one processor, to perform the method of claim 1 .

14 . The method of claim 3 , further comprising:

receiving the output bitstream;

parsing the metadata stream signaling parameters;

decompressing the compressed third frame sequence, the compressed fourth frame sequence, and the compressed sequence of source images; and

generating a multiplane-image (MPI) video using the metadata stream signaling parameters, the decompressed third frame sequence, the decompressed fourth frame sequence, and the decompressed sequence of source images.

15 . The method of claim 14 , wherein the MPI video is one of a plurality of MPI videos corresponding to different respective camera positions of a plurality of camera positions arranged around a scene captured in the MPI video.

16 . A non-transitory computer-readable medium storing instructions that, when executed by an electronic processor, cause the electronic processor to perform operations comprising the method of claim 14 .