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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-HMC150
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
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
8×8
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.
16×16
16×8
8×16
8×8
8×4
4×8
4×4
Comparison of HD Recording Formats
HDV
Pixel (H x V)
1440 x 1080
Compression Method
MPEG-2
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.
MPEG-2
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.
AVCHD
1920 x 1080
MPEG-4 AVC/H.264
MPEG-4 AVC/H.264