Method for encoding images, and an image coder
The invention relates to a method for encoding a digital image, in which method the digital image is divided into blocks (C, L, U, UL, UR). In the method a spatial prediction for a block (C) is performed to reduce the amount of information to be transmitted, wherein at least one prediction method (P 1 -P 13 ) is defined. In the method a classification is determined for at least one neighboring block (L, U) of said block (C) to be predicted according to the contents of the neighboring block (L, U), and a prediction method (P 1 -P 13 ) is selected for the current block (C) on the basis of at least one classification.
1. A method for encoding a digital image in a block-based manner into an encoded bitstream, the method comprising:
performing by an encoder a prediction for a block to be coded with respect to a reference block, wherein displacement between the block to be coded and the reference block is represented by a horizontal displacement and a vertical displacement;
defining by said encoder an ordered list of each possible horizontal and vertical displacements in a rank order; and
providing by said encoder a signal, in the encoded bitsream, representative of the rank of the horizontal displacement and the vertical displacement in the ordered list.
2. A method according to claim 1 , further comprising:
eliminating the vertical and horizontal displacement pairs that correspond to a reference block lying partially or entirely outside the frame from the ordered list.
3. A method for decoding an encoded bitstream representative of digital image in a block-based manner into an image, the method comprising:
receiving by a decoder a signal, from the encoded bitstream, representative of rank order in ordered list of horizontal and vertical displacements;
deriving by said decoder a horizontal displacement and a vertical displacement based on the received rank order and the ordered list of horizontal and vertical displacements;
deriving by said decoder a location of a reference block based on the horizontal displacement and the vertical displacement and the location of a block to be coded; and
forming by said decoder a prediction for the block to be coded using the reference block.
4. A method according to claim 3 , further comprising:
eliminating the vertical and horizontal displacement pairs that correspond to a reference block lying partially or entirely outside the frame from the ordered list.
5. An encoder for encoding a digital image in a block-based manner, wherein the encoder is arranged to:
perform a prediction for a block to be coded with respect to a reference block, wherein displacement between the block to be coded and the reference block is represented by a horizontal displacement and a vertical displacement;
define an ordered list of each possible horizontal and vertical displacements in a rank order; and
provide a signal representative of the rank of the horizontal displacement and the vertical displacement in the ordered list.
6. An encoder according to claim 5 , further arranged to:
eliminate the vertical and horizontal displacement pairs that correspond to a reference block lying partially or entirely outside the frame from the ordered list.
7. A decoder for decoding an encoded digital image in a block-based manner, the decoder is arranged to:
receive a signal representative of rank order in ordered list of horizontal and vertical displacements;
derive a horizontal displacement and a vertical displacement based on the received rank order and the ordered list of horizontal and vertical displacements;
derive a location of a reference block based on the horizontal displacement and the vertical displacement and the location of a block to be coded; and
form a prediction for the block to be coded using the reference block.
8. A decoder according to claim 7 , further arranged to:
eliminate the vertical and horizontal displacement pairs that correspond to a reference block lying partially or entirely outside the frame from the ordered list.
9. A method for encoding a digital image in a block-based manner into an encoded bitstream, the method comprising:
defining by an encoder an arrangement for a list of prediction methods in a rank order, said rank order determined based at least in part on block types of at least two neighboring blocks of a block to be coded, wherein each prediction method in the said list has a unique rank with respect to each of the other prediction methods;
selecting by said encoder a prediction method for the block to be coded from said list of prediction methods; and
providing by said encoder a signal, in the encoded bitstream, representative of rank of the selected prediction method.
10. A method according to claim 9 , comprising calculating a cost function representative of an error incurred when using a particular prediction method to form a spatial prediction for the block to be coded and selecting the prediction method for the block to be coded from said list of prediction methods that yields the smallest value for the cost function.
11. A method according to claim 10 , wherein the cost function includes a measure of an error incurred when using a particular prediction method to form a spatial prediction for the block to be coded and a measure of an amount of information required to be transmitted to a corresponding decoder when said particular prediction method is selected.
12. A method according to claim 9 , wherein the block type for a neighboring block is determined based at least in part on directionality in the image contents of the neighboring block.
13. A method for decoding an encoded bitstream representative of a digital image in a block-based manner into an image, the method comprising:
defining by a decoder an arrangement for a list of prediction methods in a rank order, said rank order determined based at least in part on block types of at least two neighboring blocks of a block to be coded, wherein each prediction method in the said list has a unique rank with respect to each of the other prediction methods;
receiving by said decoder a signal, from the encoded bitstream, indicative of rank order prediction method in said list of prediction methods; and
selecting by said decoder a prediction method for the block to be coded from said list of prediction methods, said prediction method having said rank order.
14. A method according to claim 13 , wherein the block type for a neighboring block is determined based at least in part on directionality in the image contents of the neighboring block.
15. An encoder for encoding a digital image in a block-based manner, the encoder comprises:
a prediction method selector arranged to:
define an arrangement for a list of prediction methods in a rank order, said rank order determined based at least in part on block types of at least two neighboring blocks of a block to be coded, wherein each prediction method in the said list has a unique rank with respect to each of the other prediction methods; and
select a prediction method for the block to be coded from said list of prediction methods;
a prediction estimator to form a spatial prediction for the block to be coded using the selected prediction method; and
a multiplexing unit to provide a signal representative of rank of the selected prediction method.
16. An encoder according to claim 15 , comprising a cost function calculator for calculating a cost function representative of an error incurred when using a particular prediction method for forming a spatial prediction for the block to be coded and the prediction method selector is arranged to select the prediction method for the block to be coded from said list of prediction methods that yields the smallest value for the cost function.
17. An encoder according to claim 16 , wherein the cost function includes a measure of an error incurred when using a particular prediction method to form a spatial prediction for the block to be coded and a measure of an amount of information required to be transmitted to a corresponding decoder when said particular prediction method is selected.
18. An encoder according to claim 15 , wherein the block type for a neighboring block is determined based at least in part on directionality in the image contents of the neighboring block.
19. A decoder for decoding an encoded digital image in a block-based manner, the decoder comprises:
a prediction method selector for defining an arrangement for a list of prediction methods in a rank order, said rank order determined based at least in part on block types of at least two neighboring blocks of a block to be coded, wherein each prediction method in the said list has a unique rank with respect to each of the other prediction methods;
a demultiplexing unit for receiving a signal indicative of rank order prediction method in said list of prediction methods;
the prediction method selector further arranged to select a prediction method for the block to be coded from said list of prediction methods, said prediction method having said rank order; and
a prediction estimator to form a spatial prediction for the block to be coded using the selected prediction method.
20. A decoder according to claim 19 , wherein the block type for a neighboring block is determined based at least in part on directionality in the image contents of the neighboring block.