Technology
Intra-Frame (I-Frame Only) Compression Superiority
Motion-image compression can be divided roughly into two methods:
I-Frame 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-Frame Only compression,
while HDV and XDCAM HD 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, fast-action sports, and music
shows with confetti and electronic displays.
Also, because processing is
performed frame-by-frame in I-Frame Only, new-generation multi-core
CPUs offer high-speed parallel processing. This makes I-Frame Only
compression more suitable for nonlinear editing than Long GOP, for
which parallel processing is difficult due to its inter-frame dependence.
With its I-Frame 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 ratio of MPEG-2, even with I-Frame Only compression. Its
intra-frame predictive and context-adaptive entropy coding are particularly
effective methods for boosting compression efficiency.
Intra-frame 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 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 CABAC (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.
For further information about MPEG-4 AVC/H.264, including an
explanatory video, please visit:
https://eww.pavc.panasonic.co.jp/pro-av/technology/
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.
Versatile Playback Functions Meet Diverse Needs
• Format Auto Playback:
This automatically detects the video format and codec
for each video clip when starting playback and signal output.
• Variable Speed Playback:
For slow-motion and double-speed playback.
• Resume Playback:
If you press the Stop key during playback, the AG-HPG20
temporarily "bookmarks" the stop position until another operation is performed.
When you press the Play key, playback resumes at the bookmarked position.
* The bookmark memory is reset when the power is turned off. The Resume Playback function is
factory-set to OFF.
• Single-Clip Playback:
This convenient function plays back one video clip with
a one-touch operation.
• Repeat Playback:
For presentations and demonstrations, use AG-HPG20
(P2 Portable) for repeated playback of a selected clip or multiple clips.*
Playback is seamless, with no need for rewinding or cueing. There is no wear or
image deterioration even after extended, continuous playback.
*The clips must be in the same format.
mode 0
mode 1
mode 2
mode 3
mode 4
mode 5
mode 6
mode 7
mode 8
Adjacent pixels
Copy of below pixel
Predictive pixels
Average
