Data encoding and decoding
A video coding or decoding method using inter-image prediction to encode input video data in which each chrominance component has 1/Mth of the horizontal resolution and 1/Nth of the vertical resolution of the luminance component, where M and N are integers equal to 1 or more, including storing one or more images preceding a current image, interpolating a higher resolution version of prediction units of the stored images so that the luminance component has a horizontal resolution P times that of the corresponding portion of the stored image and a vertical resolution Q times that of the corresponding portion of the stored image, detecting inter-image motion between a current image and the one or more interpolated stored images so as to generate motion vectors between a prediction unit of the current image and areas of the one or more preceding images, and generating a motion compensated prediction.
1. A video decoding apparatus for performing, with respect to blocks of spatial frequency data, frequency-transformation by applying a frequency transformation to generate blocks of video data samples which are each scaled, by a common scaling factor, with respect to the video data samples which would result from a normalized frequency-transformation of that block of spatial frequency data, and to dequantize according to a quantization step size, comprising:
circuitry configured to:
apply an n-bit shift to divide data processed by the apparatus by a factor of 2 n , where n is an integer;
detect a residual scaling factor, being the common scaling factor divided by 2 n ;
modify the quantization step size according to the residual scaling factor to generate a modified quantization step size;
multiply each data sample for dequantizing by a value dependent upon the modified quantization step size; and
apply the frequency transformation.
2. The apparatus according to claim 1 , wherein the circuitry is configured to select a quantization index, the quantization index defining a respective entry in a table of quantization step sizes.
3. The apparatus according to claim 2 , wherein the circuitry is configured to change the quantization index so as to select a different quantization step size, such that the ratio of the different quantization step size to the originally selected quantization step size is substantially equal to the residual scaling factor.
4. The apparatus according to claim 3 , wherein the circuitry is configured to select a quantization index in respect of luminance samples and to generate a quantization index offset, relative to the quantization index selected for the luminance samples, for samples of each or both chrominance components; and is configured to change the quantization index offset according to the residual scaling factor.
5. The apparatus according to claim 2 , wherein successive values of the quantization step sizes in the table are related logarithmically, so that a change in quantization index of m (where m is an integer) represents a change in quantization step size by a factor of p (where p is an integer greater than 1).
6. The apparatus according to claim 5 , wherein m=6 and p=2.
7. The apparatus according to claim 6 , wherein the data modifier is configured to modify the quantization index by +/−3.
8. The apparatus according to claim 6 , wherein in which the quantization index is associated with the quantization step and its inverse by one or more tables comprising 1.5 m entries.
9. The apparatus according to claim 8 , wherein the quantization index is associated with the quantization step and its inverse by one or both of the following tables:
Index
0
1
2
3
4
inverseQStep
26214
23302
20560
18396
16384
scaledQStep
40
45
51
57
64
Index
5
6
7
8
inverseQStep
14564
12945
11523
10280
scaledQStep
72
81
91
102
Index
−3
−2
−1
0
1
inverseQStep
36158
32768
29127
26214
23302
scaledQStep
29
32
36
40
45
Index
2
3
4
5
inverseQStep
20560
18396
16384
14564
scaledQStep
51
57
64
72.
10. The apparatus according to claim 1 , wherein the data modifier is configured to multiply the quantization step size by a factor dependent upon the residual scaling factor.
11. Apparatus according to claim 1 , in which at least some of the blocks of video data samples comprise M×N samples, where the square root of N/M is not equal to an integer power of 2.
12. The apparatus according to claim 11 , wherein the at least some of the blocks are blocks of chrominance samples.
13. The apparatus according to claim 12 , wherein the video data samples are in a 4:2:2 format.
14. The apparatus according to claim 1 ,
wherein the circuitry is configured to matrix-multiply a block of spatial frequency data by a transform matrix and the transposition of the transform matrix, in which the transform matrix comprises an array of integer values which are each scaled by the common scaling factor with respect to respective values of a normalized transform matrix.
15. The apparatus according to claim 14 , wherein the transform matrix comprises an array of integer values which are each scaled with respect to respective values of a normalized transform matrix by an amount dependent upon a dimension of the transform matrix.
16. The apparatus according to claim 1 , wherein
the dequantizing is configured to operate with respect to the blocks of quantized spatial frequency data to generate blocks of dequantized spatial frequency data; and
the circuitry is configured to operate with respect to the blocks of dequantized spatial frequency data to generate blocks of video data samples.
17. A video coding apparatus for generating blocks of spatial frequency data by performing frequency-transformation on blocks of video data samples and to quantize according to a selected quantization step size, the apparatus comprising:
circuitry configured to:
frequency-transform a block of video data samples to generate a block of spatial frequency coefficients which are each scaled, by a common scaling factor, with respect to the spatial frequency coefficients which would result from a normalized frequency-transformation of that block of video data samples;
select a quantization step size for quantizing; and
apply an n-bit shift to divide by a factor of 2 n , where n is an integer;
detect a residual scaling factor, being the common scaling factor divided by 2 n ;
modify the quantization step size according to the residual scaling factor to generate a modified quantization step size; and
divide each data value for quantizing by a value dependent upon the modified quantization step size and rounding the result to an integer value.
18. A video decoding method, comprising:
performing with respect to blocks of spatial frequency data, frequency-transformation by applying a frequency transformation to generate blocks of video data samples which are each scaled, by a common scaling factor, with respect to the video data samples which would result from a normalized frequency-transformation of that block of spatial frequency data, and to quantize according to a quantization step size;
applying an n-bit shift to divide data being processed by a factor of 2 n , where n is an integer;
detecting a residual scaling factor, being the common scaling factor divided by 2 n ;
modifying the quantization step size according to the residual scaling factor to generate a modified quantization step size; and
multiplying each of the data samples for dequantizing by a value dependent upon the modified quantization step size; and
applying the frequency-transformation.
19. A video coding method, comprising:
generating blocks of spatial frequency data by performing frequency-transformation on blocks of video data samples to generate spatial frequency coefficients which are each scaled, by a common scaling factor, with respect to the coefficients which would result from a normalized frequency-transformation of that block of video data samples, and to quantize according to a selected quantization step size;
frequency-transforming a block of video data samples;
selecting a quantization step size for quantizing;
applying an n-bit shift to divide by a factor of 2 n , where n is an integer;
detecting a residual scaling factor, being the common scaling factor divided by 2 n ;
modifying the quantization step size according to the residual scaling factor to generate a modified quantization step size; and
dividing each of the data values for quantizing by a value dependent upon the modified quantization step size and rounding the result to an integer value.
20. A non-transitory computer readable medium including computer program instructions, which when executed by a computer causes the computer to perform the method of claim 19 .
21. The apparatus according to claim 8 , wherein the table includes nine quantization index values each associated with the quantization step and its inverse.
22. The apparatus according to claim 21 , wherein the table includes the following values of quantization index (index), quantization step (scaledQstep) and its inverse (inverseQstep):
Index
0
1
2
3
4
5
inverseQStep
26214
23302
20560
18396
16384
14564
scaledQStep
40
45
51
57
64
72.