Bedienungsanleitung Panasonic ag hmc 151 (Seite 6 von 12) (Englisch)

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High-Quality AVCHD Recording, Plus the Professional PH Mode Boosts the Quality of HD Images

AVCHD Format for High-

Quality, Efficient HD

Recording

Panasonic AVCCAM

camcorders use the AVCHD

format for tapeless recording

with high image quality and

low bit rates. This format

complies with the latest

H.264 motion image

compression standard, and

employs the High Profile

standard to improve

compression efficiency.

Featuring twice the

compression efficiency of

HDV (MPEG-2), the

AG-HMC151 achieves

extended HD recording.

The following four new

technologies make this

possible.

MPEG-4 AVC/H.264 Technologies

Intra-Frame Prediction

This process generates predictive pixels based on the adjacent pixels

within each frame. It then selects the optimal predictive mode. The

generated predictive image is subtracted from the original input image,

and the residual data is compressed and recorded at a low bit rate.

The entire process is conducted within the frame, so prediction

accuracy remains high even with fast-motion images.

Variable Block Size Motion Compensation

In contrast with MPEG-2, in which inter-frame compression based on

the correlation between adjacent frames uses fixed blocks of 16 x 16

pixels, AVCHD divides the blocks into multi-sizes as small as 4 x 4

pixels. In this method, it is able to use large blocks to process images

that show only slight changes on the screen, and smaller blocks to

process images that have considerable change. This raises the

accuracy of motion compensation to boost the quality of fast-motion

images while increasing compression efficiency.

Loop Filter Prevents the Propagation of Compression Distortion

Because MPEG-2 uses a decoding image that contains compression-

induced block distortion as a reference image for motion

compensation, it exhibits residual distortion — even within the same

frame — when a large amount of block distortion is generated.

MPEG-4 AVC/H.264 detects block distortion in the decoding image

and removes it with a context-adaptive filter that functions according

to the degree of distortion. This prevents the propagation of block

distortion by keeping the reference image clean at all times.

New CABAC Entropy Encoding

The AVCHD format uses CABAC (Context Adaptive Binary Arithmetic

Coding) for its variable-length encoding. Compared with the variable-

length encoding of MPEG-2, in which the compression efficiency is

greatly affected by subject type, CABAC provides lossless

compression with constantly high efficiency and no distortion for

virtually all subject types. Because MPEG-2 compresses and converts

data according to the standard's fixed conversion rules, the

compression efficiency may drop for image types other than those that

were considered when the standard was established. In place of fixed

conversion rules, CABAC provides the best possible conversion

method by constantly optimizing and automatically tracking the image

that is being processed, in parallel with the compression process.

HDV AVCHD

Pixel (H x V) 1440 x 1080 1920 x 1080

Compression Method

MPEG-2 MPEG-4 AVC/H.264

Comparison of HD Recording Formats

Sample comparison: When a flash causes large contrast differences and reduces depth perception, HDV shows considerable block noise, while AVCHD in the

PH mode minimize break-up.

MPEG-2 (fixed block size)

Blocks of the same size are used to process parts both with and without motion.

MPEG-4 AVC/H.264 (variable block size)

Block size is precisely varied to match the size of the moving part contained in each block.

16×16

16×8 8×16 8×8

8×8 8×4 4×8 4×4

MPEG-2 MPEG-4 AVC/H.264

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