Interpolation method and prediction method using same

1. An inter prediction method comprising the steps of:

calculating a motion vector for generating a predicted block;

performing an interpolation process of generating pixel samples in the unit of sub pixels when the motion vector indicates a sub pixel position; and

generating the predicted block on the basis of the pixel samples in the unit of sub pixels,

wherein, in the interpolation process, reconstructed pixel samples of a current picture and reference pixel samples of a reference picture are together used with predetermined interpolation filter coefficients for generating the pixel samples in the unit of sub pixels,

wherein the step of generating the pixel samples in the unit of sub pixels is based on an integer sample set including integer pixel samples to which the interpolation process is applied,

wherein the integer sample set includes at least one current integer sample out of the reconstructed pixel samples,

wherein the at least one current integer sample is used to generate the pixel samples in the unit of sub pixels, and

wherein the pixel samples in the unit of sub pixels correspond to offset positions relative to a predetermined reference pixel sample out of the integer pixel samples.

2. The inter prediction method according to claim 1 , wherein the reconstructed pixel samples of the current picture are located in an upper or left area of a current prediction unit in the current picture, and the reference pixel samples of the reference picture are positioned in at least one of a below area and right area of a reference block in the reference picture.

3. The inter prediction method according to claim 1 , wherein a smoothing process using at least one of the reconstructed pixel samples of the current picture and at least one of the reference pixel samples of the reference picture is performed on the reconstructed pixel samples of the current picture before the step of performing the interpolation process.

4. The method of claim 1 , wherein the interpolation process is regarding to luma pixels, and

wherein the step of generating the pixel samples in the unit of sub pixels includes setting a predetermined number of current integer samples to be included in the integer sample set depending on the position of the reference pixel sample.

5. The method of claim 4 , wherein three current integer samples are included in the integer sample set when the reference pixel sample is located in a first integer sample column or row from a boundary between a reconstructed pixel sample area of the current picture and a reference sample area of the reference picture used for the interpolation,

wherein two current integer samples are included in the integer sample set when the reference pixel sample is located in a second integer pixel sample column or row from the boundary, and

wherein one current integer sample is included in the integer sample set when the reference pixel sample is located in a third integer pixel sample column or row form the boundary.

6. The method of claim 5 , further comprising a step of applying a smoothing filter, which uses at least one reference pixel sample and at least one reconstructed pixel sample of the current picture, to at least one current integer sample out of the current integer samples before generating the pixel samples in the unit of sub pixels.

7. The method of claim 1 , wherein the interpolation process is regarding to chroma pixels, and

wherein the step of generating the pixel samples in the unit of sub pixels includes setting a predetermined number of current integer samples to be included in the integer sample set depending on the position of the reference pixel sample.

8. The method of claim 7 , wherein one current integer sample is included in the integer sample set when the reference pixel sample is located in a first integer sample column or row from a boundary between a reconstructed pixel sample area of the current picture and a reference sample area of the reference picture which are used for the interpolation.

9. The method of claim 8 , further comprising a step of applying a smoothing filter, which uses at least one reference pixel sample and at least one reconstructed pixel sample of the current picture, to at least one current integer sample out of the current integer samples before generating the pixel samples in the unit of sub pixels.

10. The method of claim 1 , further comprising a step of determining whether an implicit or explicit instruction to use the integer pixel samples of the current picture to generate the pixel samples in the unit of sub pixels is transmitted from an encoder,

wherein when it is determined that the instruction is transmitted, the integer pixel samples of the current picture are used to generate the pixel samples in the unit of sub pixels.

11. The method of claim 10 , wherein the explicit instruction is 1-bit flag information which is transmitted from the encoder to a decoder along with pixel position information and information on an array of reference pixel samples.

12. The method of claim 10 , wherein when a difference between a motion vector of a current prediction unit and a motion vector of a neighboring block of the current prediction unit is equal to or less than a predetermined threshold value, it is determined that an implicit instruction to use the integer pixel samples of the current picture to generate the fractional pixel samples is transmitted.

13. The method of claim 1 , wherein the interpolation process is regarding to luma pixels, and

wherein the integer pixel samples of the current picture are used for the interpolation when a reference integer sample is located within a third integer sample row or column from an upper or left boundary of a reference sample area of a reference picture used for the interpolation.

14. The method of claim 1 , wherein the interpolation method is regarding to chroma pixels, and

wherein the integer pixel samples of the current picture are used for the interpolation when a reference integer sample is located within a first integer sample row or column from an upper or left boundary of a reference sample area of a reference picture used for the interpolation.