Quantization processes for residue differential pulse code modulation
In an example, system and method for coding encoded video data. A quantized residue differences block associated with a current block of a picture is generated and a reconstructed prediction residue for each quantized residue difference in the block of quantized residue differences is generated. Each reconstructed prediction residue is added to its corresponding original prediction value to produce a current block of a picture. Generating the reconstructed prediction residue includes performing inverse quantization on blocks of quantized residue differences, wherein the inverse quantization reconstructs data to which uniform quantization residue differential pulse code modulation (RDPCM) has been applied and wherein the quantization is of the form: Δ X q =floor(( X+αQ )/ Q ) where Q is quantization step and α is quantization offset.
1. A method of encoding video data, the method comprising:
subtracting a prediction block from a current block of a picture to form a prediction residual block; and
applying a Residue Differential Pulse-Code Modulation (RDPCM) process to the prediction residual block, wherein applying the RDPCM process comprises:
for each respective residue pixel in the prediction residual block other than residue pixels in a first row or first column of the prediction residual block:
calculating a respective residue difference by subtracting a reconstructed left or above neighbor residue pixel from the respective residue pixel;
generating a respective quantized residual difference by applying a uniform quantization to the respective residue difference according to a formula:
Δ
X
q
=
floor
(
X
+
α
Q
Q
)
where X is the respective residue difference, ΔX q is a quantized value, floor is a floor function, Q is a quantization step, and a is a quantization offset, wherein α is equal to ½; and
entropy encoding the quantized value.
2. The method of claim 1 , wherein the quantization step is a constant.
3. The method of claim 1 , wherein the quantization step increases or decreases down rows of the prediction residual block.
4. The method of claim 1 , wherein the quantization step increases or decreases across columns of the prediction residual block.
5. The method of claim 1 , wherein a value of the quantization step is dependent on a direction mode of the RDPCM process.
6. The method of claim 1 , wherein a value of the quantization step is dependent on whether the prediction block is generated using an inter prediction mode or an intra prediction mode.
7. The method of claim 1 , wherein applying the RDPCM process further comprises:
for each respective residue pixel in the first row or the first column of the prediction residual block:
quantizing the respective residual pixel according to the quantization formula to generate a quantized version of the respective residual pixel;
entropy coding the quantized version of the respective residual pixel;
inverse quantizing the quantized version of the respective residual pixel to generate a reconstructed version of the respective residual pixel; and
for each residue pixel of the prediction residual block not in the first row or the first column of the prediction residual block:
entropy coding the respective quantized residual difference; and
generating a reconstructed version of the respective residual pixel at least in part by inverse quantizing the respective quantized residual difference and adding the inverse quantized residual difference to a reconstructed version of a left or above neighbor residual value.
8. A device for encoding video data, the device comprising:
a memory configured to store the video data; and
a video encoder configured to:
subtracting a prediction block from a current block to generate a prediction residual picture; and
apply a Residue Differential Pulse-Code Modulation (RDPCM) process to the prediction residual block, wherein as part of applying the RDPCM process to the prediction residual block, for each respective residue pixel in the prediction residual block other than the residue pixel in a first row or first column of the prediction residual block, the video encoder:
calculates a respective residue difference by subtracting a reconstructed left or above neighbor residue pixel from the respective residue pixel;
generates a respective quantized residual difference by applying a uniform quantization to the respective residual difference according to a formula:
Δ
X
q
=
floor
(
X
+
α
Q
Q
)
where X is the respective residue difference, ΔX q is a quantized value, floor is a floor function, Q is a quantization step, and a is a quantization offset, wherein α is equal to ½; and
entropy encoding the quantized value.
9. The device of claim 8 , wherein the quantization step is a constant.
10. The device of claim 8 , wherein one or more of:
the quantization step increases or decreases down rows of the prediction residual block, or
the quantization step increases or decreases across columns of the prediction residual block.
11. The device of claim 8 , wherein the video encoder is configured such that, as part of applying the RDPCM process, the video encoder:
for each respective residue pixel in the first row or the first column of the prediction residual block:
quantizes the respective residual pixel according to the quantization formula to generate a quantized version of the respective residual pixel;
entropy codes the quantized version of the respective residual pixel;
inverse quantizes the quantized version of the respective residual pixel to generate a reconstructed version of the respective residual pixel by; and
for each residue pixel of the prediction residual block not in the first row or the first column of the prediction residual block:
entropy codes the respective quantized residual difference; and
generates a reconstructed version of the respective residual pixel at least in part by inverse quantizing the respective quantized residual difference and adding the inverse quantized residual difference to a reconstructed version of a left or above neighbor residual value.
12. A non-transitory computer-readable medium having instructions stored thereon that, when executed, cause one or more processors to:
subtract a prediction block from a current block of a picture to form a prediction residual block; and
apply an Residue Differential Pulse-Code Modulation (RDPCM) process to the prediction residual block, wherein applying the RDPCM process comprises:
for each respective residue pixel in the prediction residual block other than residue pixels in a first row or first column of the prediction residual block:
subtract a reconstructed left or above neighbor residue pixel from the respective residue pixel to calculate a respective quantized residue difference; and
generate a respective quantized residual difference by applying a uniform quantization to the respective residual difference according to a formula:
Δ
X
q
=
floor
(
X
+
α
Q
Q
)
where X is the respective residue difference, ΔX q is a quantized value, floor is a floor function, Q is a quantization step, and a is a quantization offset, wherein α is equal to ½; and
entropy encoding the quantized value.
13. The non-transitory computer-readable medium of claim 12 , wherein one or more of:
the quantization step increases or decreases down rows of the prediction residual block, or
the quantization step increases or decreases across columns of the prediction residual block.