Image data encoding and decoding

1. An image encoding apparatus comprising:

circuitry configured to:

select, from a set of candidate prediction operations each defining at least a prediction direction, a prediction operation for prediction of samples of a current region of a current image, the current region comprising an array of two or more rows and two or more columns of samples;

derive predicted samples of the current region with respect to one or more of a group of reference samples of the same image in dependence upon a prediction direction, defined by the selected prediction operation, between a current sample to be predicted and a reference position amongst the reference samples, wherein for at least some of the candidate prediction operations, the group of reference samples comprises two or more parallel linear arrays of reference samples disposed at different respective separations from the current region;

detect whether samples of any of the two or more parallel linear arrays of reference samples are unavailable for use in prediction of samples of the current region; and

if any of the two or more parallel linear arrays of reference samples are unavailable including a case where one of the two or more parallel linear arrays of reference samples is unavailable and another of the two or more parallel linear arrays of reference samples is available, inhibit selection of a candidate prediction operation dependent upon the reference samples of the two or more parallel linear arrays of reference samples.

2. The apparatus according to claim 1 , wherein the circuitry is further configured to:

detect for the current region of the current image whether the two or more parallel linear arrays are available for use in the prediction of samples of the current region; and

allow selection, as the prediction operation of a candidate prediction operation dependent upon the available parallel linear arrays.

3. The apparatus according to claim 1 , wherein:

for at least some of the candidate prediction operations, the group of reference samples comprises one or more predetermined values; and

the circuitry is further configured to:

detect for the current region of the current image if none of the two or more parallel linear arrays is available for use in the prediction of samples of the current region; and

allow selection, as the prediction operation, of a candidate prediction operation for the current region dependent upon the predetermined values as reference samples.

4. The apparatus according to claim 1 , wherein the circuitry is configured to detect whether the samples corresponding to any of the two or more parallel linear arrays of reference samples are unavailable for use in the prediction of samples of the current region based on an image location of the current region.

5. The apparatus according to claim 4 , wherein the circuitry is configured to detect whether the current region is adjacent an edge of the current region such that sample locations corresponding to at least some of the two or more parallel linear arrays of reference samples lie outside the current image.

6. The apparatus according to claim 4 , wherein:

the image encoding apparatus is configured to encode the current image as successive coding units of samples;

the image encoding apparatus comprises a sample storage to store samples corresponding to a region of the current image other than the current region; and

the circuitry is configured to detect whether, for an image region at a location within a coding unit adjacent to a previous coding unit, any of the two or more parallel linear arrays of reference samples are held by the sample storage.

7. The apparatus according to claim 1 , wherein the circuitry is configured to:

detect, separately for reference sample positions disposed vertically with respect to the current image region and for reference sample positions disposed horizontally with respect to the current image region, whether samples corresponding to any of the two or more parallel linear arrays of reference samples are unavailable for use in the prediction of samples of the current region; and

if any of the two or more parallel linear arrays of reference samples are unavailable for the reference sample positions disposed vertically with respect to the current image region or the reference sample positions disposed horizontally with respect to the current image region inhibit selection of a candidate prediction operation dependent upon the reference samples of the two or more parallel linear arrays of reference samples.

8. The apparatus according to claim 1 , wherein the circuitry is responsive to configuration data defining one or more parameters of a decoding apparatus to detect whether the samples corresponding to any of the two or more parallel linear arrays of reference samples will be available for use in the prediction of samples of the current region at the decoding apparatus.

9. A video storage, capture, transmission, or reception apparatus comprising the apparatus according to claim 1 .

10. An image decoding apparatus comprising circuitry configured to:

select, from a set of candidate prediction operations each defining at least a prediction direction, a prediction operation for prediction of samples of a current region of a current image, the current region comprising an array of two or more rows and two or more columns of samples;

derive predicted samples of the current region with respect to one or more of a group of reference samples of the same image in dependence upon a prediction direction, defined by the selected prediction operation, between a current sample to be predicted and a reference position amongst the reference samples, wherein for at least some of the candidate prediction operations, the group of reference samples comprises two or more parallel linear arrays of reference samples disposed at different respective separations from the current region;

detect whether samples of any of the two or more parallel linear arrays of reference samples are unavailable for use in prediction of samples of the current region; and

if any of the two or more parallel linear arrays of reference samples are unavailable including a case where one of the two or more parallel linear arrays of reference samples is unavailable and another of the two or more parallel linear arrays of reference samples is available, inhibit selection of a candidate prediction operation dependent upon the reference samples of the two or more parallel linear arrays of reference samples.

11. The apparatus according to claim 10 , wherein the circuitry is further configured to:

detect for the current region of the current image whether the two or more parallel linear arrays are unavailable for use in the prediction of samples of the current region; and

allow selection, as the prediction operation, of a candidate prediction operation dependent upon the available parallel linear arrays.

12. The apparatus according to claim 10 , wherein:

for at least some of the candidate prediction operations, the group of reference samples comprises one or more predetermined values; and

the circuitry is further configured to:

detect for the current region of the current image if none of the two or more parallel linear arrays is available for use in the prediction of samples of the current region; and

allow selection, as the prediction operation, of a candidate prediction operation for the current region dependent upon the predetermined values as reference samples.

13. The apparatus according to claim 10 , wherein the circuitry is configured to detect whether the samples corresponding to any of the two or more parallel linear arrays of reference samples are unavailable for use in the prediction of samples of the current region based on an image location of the current region.

14. The apparatus according to claim 13 , wherein the circuitry is configured to detect whether the current region is adjacent an edge of the current region such that sample locations corresponding to at least some of the two or more parallel linear arrays of reference samples lie outside the current image.

15. The apparatus according to claim 13 , wherein:

the image decoding apparatus is configured to decode the current image as successive coding units of samples;

the image decoding apparatus comprises a sample storage to store samples corresponding to a region of the current image other than the current region; and

the circuitry is configured to detect whether, for an image region at a location within a coding unit adjacent to a previous coding unit, any of the two or more parallel linear arrays of reference samples are held by the sample storage.

16. The apparatus according to claim 10 , wherein the circuitry is configured to:

detect, separately for reference sample positions disposed vertically with respect to the current image region and for reference sample positions disposed horizontally with respect to the current image region, whether samples corresponding to any of the two or more parallel linear arrays of reference samples are unavailable for use in the prediction of samples of the current region; and

if any of the two or more parallel linear arrays of reference samples are unavailable for reference sample positions disposed vertically with respect to the current image region or the reference sample positions disposed horizontally with respect to the current image region inhibit selection of a candidate prediction operation dependent upon the reference samples of the two or more parallel linear arrays of reference samples.

17. A video storage, capture, transmission, or reception apparatus comprising the apparatus according to claim 10 .

18. An image encoding method comprising:

selecting, from a set of candidate prediction operations each defining at least a prediction direction, a prediction operation for prediction of samples of a current region of a current image, the current region comprising an array of two or more rows and two or more columns of samples;

deriving intra-image predicted samples of the current region with respect to one or more of a group of reference samples of the same image in dependence upon a prediction direction, defined by the selected prediction operation, between a current sample to be predicted and a reference position amongst the reference samples, wherein for at least some of the candidate prediction operations, the group of reference samples comprises two or more parallel linear arrays of reference samples disposed at different respective separations from the current region;

detecting whether samples of any of the two or more parallel linear arrays of reference samples are unavailable for use in prediction of samples of the current region; and

inhibiting selection by the selecting step, if any of the two or more parallel linear arrays of reference samples are unavailable including a case where one of the two or more parallel linear arrays of reference samples is unavailable and another of the two or more parallel linear arrays of reference samples is available, of a candidate prediction operation dependent upon the reference samples of the two or more parallel linear arrays of reference samples.

19. A non-transitory computer readable medium including computer program instructions, which when executed by a computer, cause the computer to perform the method of claim 18 .

20. An image decoding method comprising:

selecting, from a set of candidate prediction operations each defining at least a prediction direction, a prediction operation for prediction of samples of a current region of a current image, the current region comprising an array of two or more rows and two or more columns of samples;

deriving intra-image predicted samples of the current region with respect to one or more of a group of reference samples of the same image in dependence upon a prediction direction, defined by the selected prediction operation, between a current sample to be predicted and a reference position amongst the reference samples, wherein for at least some of the candidate prediction operations, the group of reference samples comprises two or more parallel linear arrays of reference samples disposed at different respective separations from the current region;

detecting whether samples of any of the two or more parallel linear arrays of reference samples are unavailable for use in prediction of samples of the current region; and

inhibiting selection by the selecting step, if any of the two or more parallel linear arrays of reference samples are unavailable including a case where one of the two or more parallel linear arrays of reference samples is unavailable and another of the two or more parallel linear arrays of reference samples is available, of a candidate prediction operation dependent upon the reference samples of the two or more parallel linear arrays of reference samples.

21. A non-transitory computer readable medium including computer program instructions, which when executed by a computer, cause the computer to perform the method of claim 20 .