Panasonic AJ-HPX3700, AJ-HPX2700 manual C I n t r a T e c h n o l o g y

A V C - I n t r a T e c h n o l o g y

Sample Images of Intraframe Preduction

Left: Original image Center: Intra-frame predictive image Right: Difference image obtained from subtracting the intra-frame predictive image from the original image. This shows the high accuracy of intra prediction.

Intra-Frame (I-Only) Compression Superiority

Conceptual Illustration of Luminance Signal (Y) Intra Prediction Mode

Motion-image compression can be divided roughly into two methods: I-Only compression, which completes all processing within each frame, and Long GOP compression, which processes across multiple frames. AVC-Intra and DVCPRO HD use I-Only compression, while HDV uses Long GOP compression.

The MPEG-4 AVC/H.264 standard encompasses both methods. When the images of adjacent frames are similar, Long GOP compression achieves an advantageously low bit rate. However, this trait is not often seen in broadcasts like flash-filled press conferences, fast-action sports, and music shows with confetti and electronic displays.

Also, because processing is performed frame-by-frame in I-Only, new-generation multi-core CPUs offer high-speed parallel processing. This makes I-Only compression more suitable for

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Non-linear editing than Long GOP, for which parallel processing is difficult due to its inter-frame dependence.

With its I-Only compression, AVC-Intra produces remarkably stable images that are unaffected by adjacent frames, and meets professional needs in virtually all situations and workflows.

Twice the Compression Efficiency of MPEG-2

By selecting the most effective compression techniques from among those in compliance with the H.264 standard, AVC-Intra has doubled the compression efficiently over earlier Intra frame compression schemes. Its intraframe predictive and context- adaptive entropy coding are particularly effective methods for boosting compression efficiency.

Intraframe predictive coding (intra prediction)

This process generates predictive images based on adjacent blocks of 8 x 8 pixels. Selecting the most suitable predictive mode from among nine luminance signal modes (see illustration) and four color signal modes, it generates accurate predictive images. The residual data (obtained by subtracting a predictive image from the original input image) is recorded together with the

This process generates predictive images based on adjacent blocks of 8 x 8 pixels. Selecting the most suitable predictive mode from among nine luminance signal modes (see illustration) and four color signal modes, it generates accurate predictive images.

predictive image. Because the prediction accuracy is high, there's minimal residual data, and thus high compression is achieved. This process is conducted within the frame, so prediction accuracy remains high even with fast-motion images.

Context-adaptive entropy coding

The entropy coding process used in MPEG-4 AVC/H.264 utilizes CAVLC (Context Adaptive VLC) and CAVBAC (Context Adaptive Binary Arithmetic Coding), both of which are context adaptive.

MPEG-2 uses a fixed table when performing the VLC coding, with the result that compression efficiency is low with some types of images. In context-adaptive coding, on the other hand, operation varies with different kinds of images and high compression efficiency is maintained at all times.

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