2. Principle of H.264/AVC Normal Quantization Scheme

2.1. Scalar dead-zone quantization

In this section the principle of H.264/AVC normal quantization scheme is described in a generalized form.

A scalar quantizer for input signal W can be decomposed into a function Z=C[W] called a classification rule that selects an integer-valued class identifier called the quantization index at the encoder, and a reconstruction rule that produces a real-valued output W’=R[Z] at the decoder. Video encoder applies entropy coding to the quantization indices and communicates to the decoder. Although H.264/AVC JM reference software implements some classification functions, only reconstruction function is standardized.

In the quantization step of the encoder, the transform coefficients of the prediction error are quantized. This quantization is used to reduce the precision of the coefficients. Furthermore, the quantizer is designed to map insignificant coefficient values to zero whilst retaining a reduced [......]

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Permanent Link: Quantization Techniques in JM/KTA – Part 2

1. Overview

Currently most image and video coding systems and standards, such as MPEG-1/2 and H264/AVC, use transform-based techniques followed by quantization and entropy coding. The key idea is that transforms de-correlate the signal and compact the energy of a block into a few coefficients, which still represent the signal rather accurately after quantization and de-quantization. Nevertheless, this quantization/de-quantization process needs to be carefully designed in order to have the best possible subjective and objective quality.

In the encoder of H.264/AVC reference software, the scalar dead-zone quantization is adopted. In order to improve further the performance, other two adaptive quantization techniques are also introduced, which are both based on how to adjust the size of dead-zone and control the rounding behavior. In this tutorial, we will first introduce the principle of H.264/AVC normal quantization scheme, then discuss the adaptive rounding method which select adaptive[......]

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Permanent Link: Quantization Techniques in JM/KTA – Part 1

The technique of 1/8-pel interpolation [AD09] was proposed for motion-compensated prediction (MCP) and adopted in KTA software. Three types of interpolation filters are used for 1/2-, 1/4-, and 1/8-pel sub positions, respectively.

• [-3, 12, -39, 158, 158, -39, 12, -3]/256 for 1/2-pel sub positions.
• [-3, 12, -37, 229, 71, -21, 6, -1]/256 and [-1, 6, -21, 71, 229, -37, 12, -3]/256 for 1/4-pel sub positions.
• Bilinear filter for 1/8-pel sub positions.

  The frequency response of the interpolation filter is shown in the following figure. As can be seen, it is almost an ideal low-pass filter with a gain of 8 and a cutoff frequency π/8.

  According to the performance reported in the proposal, the gain on CIF/QCIF sequences is quite significant, i.e., up to 14% bit-rate reduction. I tested this technique based on a set of HD sequences. As shown in Table 1, the R-D performance is measured by BDPSNR [1], i.e., PSNR improvement at the same bit-rate or bit-rate reduction at the same PSNR.

 

 

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Permanent Link: R-D Performance of 1/8-pel MCP on HD Sequences

In the Geneva meeting held in Feb. 2009, a proposal with the title “Video Coding Using Extended Block Sizes” was adopted by KTA, where the MB size is extended up to 64×64 and the motion partitions are scaled accordingly. At the same time, a 2D order-16 transform was also proposed for transforming the residual blocks with the size larger than or equal to 16×16. The transformation matrix of the proposed 2D order-16 transform is given as below, which is obtained by scaling the transformation matrix of 2D order-16 DCT by the factor 128 and rounding, and is non-orthogonal.

  Non-orthogonality will inevitably introduce transform error. Before analyzing the transform error quantitatively, let’s recall two properties of orthogonal transforms. Firstly, signals can be reconstructed perfectly if no quantization is performed in the transform domain. Secondly, if quantization is performed in the transform domain, the average variance (or energy) of the reconstruction er[......]

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Permanent Link: Transform Error Introduced by Non-orthogonality

The latest KTA software is JM11KTA2.3, which integrates the coding tools adopted in the Geneva meeting (Jan. 2009) and before.  

1. Inter prediction
   1. Adaptive interpolation filter (AIF)
      • 2-D non-separable AIF (AD08, AE16)
      • Separable AIF (COM16-C219, AG10)
      • Directional AIF (DAIF) (AG21, AG22, AH17, AH18)
      • Enhanced DAIF (E-DAIF) (AI12,  COM16-C126)
      • Enhanced DAIF 2 (E-DAIF2) (COM16-C125)
      • Enhanced AIF (EAIF) (COM16-C464, AI38, AJ30)
      • Switch interpolation filters with offsets (SIFO) (COM16-C463, AI35, AJ29, COM16-C126)
      • High precision filter (HPF) (AI33)
      • Single-Pass Encoding (AJ29, AK26)
   2. 1/8-pel MCP (AD09)
   3. Extended MCP block size (COM16-C123)
   4. Competition-based MV prediction (AC06r1)
2. Transform and quantization
   1. Mode-dependent directional transform (MDDT) (AF15, AG11, AH20, AJ24, AI36)
   2. Very large block transform (COM16-C123)
   3. Adaptive prediction error coding (APEC) (AB06, AD07, AE15)
   4. Adaptive quantization matrix selection (AQMS) (AC07, AD06, AF08, AI19)
   5. Rate-distortion optimized quantization (RDO[......]

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Permanent Link: KTA Software JM11KTA2.3

H.265 is a long-term video coding standard, launched by VCEG. As indicated in ITU-T SG16′s homepage, VCEG plans to complete the requirement definition and begin the detailed algorithm design for H.265 in the study period 2005-2008, and if the progress in contribution technology is sufficient, H.265 is expected to be finalized in 2009-2010.

Currently, H.265 hasn’t been formalized and VCEG keeps seeking proposals and information regarding the possibility of a major gain in performance to justify the step from H.264 to H.265. Though the necessary scope of H.265 is yet to be determined, it is agreed that among the goals will be [AA01]:

• simplicity and “back to basics” approach
• high coding efficiency, e.g., two times compared with H.264
• computational efficiency, considering both encoder and decoder
• loss/error robustness
• network friendliness
• other considerations as necessary 

Backward/forward compatibility is not assumed to be required for H.265, as H.265 is a brand [......]

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Permanent Link: Current Status of H.265 (as at July 2008)