Sample sets and new down-sampling schemes for linear component sample prediction
The disclosure regards cross-component prediction and methods for deriving of a linear model for obtaining a first-component sample for a first-component block from an associated reconstructed second-component sample of a second-component block in the same frame, the method comprising determining the parameters of a linear equation representing a straight line passing through two points, each point being defined by two variables, the first variable corresponding to a second-component sample value, the second variable corresponding to a first-component sample value, based on reconstructed samples of both the first-component and the second-component; and deriving the linear model defined by the straight line parameters; wherein said determining the parameters uses integer arithmetic.
1. A method of deriving parameters of a linear model for obtaining a chroma sample of a target area from an associated luma sample of the target area, the method comprising:
determining two points for determining the parameters of the linear model, each of the two points being defined by two variables, a first variable of the two variables corresponding to a luma sample, a second variable of the two variables corresponding to a chroma sample;
determining the parameters of the linear model including a parameter corresponding to a slope of the linear model by using the two points,
wherein determining the parameter corresponding to the slope uses integer arithmetic; and
restricting a magnitude of the parameter corresponding to the slope so that a number of bits to represent the slope in integer arithmetic does not exceed 5 bits.
2. The method of claim 1 , wherein the parameter corresponding to the slope of the linear model is estimated by calculating a difference between values of the first variable of the two points, and the size of the difference is restricted by applying a bit-shift to the difference.
3. The method of claim 2 , wherein a value of the bit-shift is dependent to the bit-depth of the sample.
4. The method according to claim 1 , wherein determining the parameter corresponding to the slope of the linear model comprises determining a division, said determining comprising reducing the magnitude of the division by applying a bitshift to said division.
5. The method according to claim 4 , wherein reducing the magnitude comprises restricting the number of bits wherein the number of bits depends on the bit-depth of the sample.
6. A device for encoding images by deriving parameters of a linear model for obtaining a chroma sample of a target area from an associated luma sample of the target area, wherein the device comprises:
a deriving unit for deriving parameters of the linear model;
a determining unit for determining two points for determining the parameters of the linear model, each of the two points being defined by two variables, a first variable of the two variables corresponding to a luma sample, a second variable of the two variables corresponding to a chroma sample;
determining the parameters of the linear model including a parameter corresponding to a slope of the linear model by using the two points,
wherein determining the parameter corresponding to the slope uses integer arithmetic; and
restricting a magnitude of the parameter corresponding to the slope so that a number of bits to represent the slope in integer arithmetic does not exceed 5 bits.
7. A device for decoding images by deriving parameters of a linear model for obtaining a chroma sample of a target area from an associated luma sample of the target area, wherein the device comprises:
a deriving unit for deriving parameters of the linear model;
a determining unit for determining the two points for determining the parameters of the linear model, each of the two points being defined by two variables, a first variable of the two variables corresponding to a luma sample, a second variable of the two variables corresponding to a chroma sample;
determining the parameters of the linear model including a parameter corresponding to a slope of the linear model by using the two points,
wherein determining the parameter corresponding to the slope uses integer arithmetic; and
restricting a magnitude of the parameter corresponding to the slope so that a number of bits to represent the slope in integer arithmetic does not exceed 5 bits.
8. A non-transitory computer readable carrier medium comprising processor executable code for a programmable apparatus, comprising a sequence of instructions for implementing a method of deriving parameters of a linear model for obtaining a chroma sample of a target area from an associated luma sample of the target area, the method comprising:
determining two points for determining the parameters of the linear model, each of the two points being defined by two variables, a first variable of the two variables corresponding to a luma sample, a second variable of the two variables corresponding to a chroma sample;
determining the parameters of the linear model including a parameter corresponding to a slope of the linear model by using the two points,
wherein determining the parameters corresponding to the slope uses integer arithmetic; and
restricting a magnitude of the parameter corresponding to the slope so that a number of bits to represent the slope in integer arithmetic does not exceed 5 bits.