Information Technology Reference
In-Depth Information
should be avoided. Due to the dependency between frames in such formats, a sig-
nificant delay can occur when the material is randomly accessed. Indeed, decoding
an arbitrary frame may require the additional decoding of several other frames
which are directly or indirectly needed to complete the decoding process. In other
words, an intra-only compression format should be favoured for edit-friendly HD
recording and production. Finally, for optimal interoperability, the use of open,
international standards is warranted.
In this chapter, two state-of-the-art intra-only compression formats for HD re-
cording and production will be reviewed and compared: Motion JPEG 2000
(ISO/IEC 15444-3:2007/ ITU-T Recommendation T.802: Information technology
-- JPEG 2000 image coding system: Motion JPEG 2000, ) and H.264/AVC Intra
(ISO/IEC 14496-10:2009 Information technology -- Coding of audio-visual ob-
jects -- Part 10: Advanced Video Coding / ITU-T Recommendation H.264: Ad-
vanced video coding for generic audiovisual services). Section 3 provides a
detailed overview of the H.264/AVC standard with an emphasis on Intra-only op-
eration. Similarly, section 4 discusses the Motion JPEG 2000 standard. In section
5 both compression schemes will be evaluated in terms of rate-distortion perform-
ance, recompression loss and functionality. Finally, in section 6 the conclusions of
this work are presented.
2 720p vs. 1080i
Since full HD production and emission is not yet economically viable, two differ-
ent alternatives are currently being put forward: 720p50/59.94/60 (1280 x 720
pixels per frame, 50, 59.94 or 60 progressive frames per second) or
1080i25/29.97/30 (1920 x 1080 pixels per interlaced frame, 25, 29.97 or 30 inter-
laced frames per second). The benefits and drawbacks associated with each alter-
native largely stem from the different characteristics of interlaced and progressive
video transmission.
To avoid flickering and to obtain visually smooth motion, a minimum number
of frames per second needs to be displayed. This minimum frame-rate depends on
the ambient lighting and on the average luminance of the frames [5]. For televi-
sion, the commonly accepted minimum lies between 50 and 60 frames per second.
In the early days of analogue television, the bandwidth needed for progressive
scan transmission, which corresponds to sending 50 or 60 complete frames per
second, was deemed to be too high. To solve this problem, interlacing was intro-
duced. Interlacing implies recording, transmitting and presenting only half of the
lines for each frame, thereby effectively halving the pixel count. For each pair of
consecutive frames, the even-numbered lines of the first frame and the odd-
numbered lines of the second frame are retained. The retained lines of each frame
form a so-called field. Two consecutive fields are grouped together into one inter-
laced frame. The resulting interlaced video material consists of 50 to 60 fields per
second or 25 to 30 interlaced frames per second. Because of the inherent inertia of
the human visual system, the missing lines in a displayed interlaced image are not
visible because they coincide with the fading lines of the previously projected im-
age, thus retaining the spatial resolution of the original images. On a CRT screen,
