Game Development Reference
In-Depth Information
the perceptual properties of HD video have not been fully investigated. Generally,
the viewing experience of HD video should be more dependent on the viewing
environment, such as the distance, device and the illumination. How to utilize these
factors to optimize the video codec need to be further studied.
12.4.4 Screen Content Coding
After HEVC, the Joint Collaborative Team on Video Coding (JCT-VC) also work
towards high efficiency compression on new media content, such as screen and high
dynamic range (HDR) video. Typical screen images from HEVC test sequences are
shown in Fig.
12.9
. Different from the conventional video content, the unique screen
video contains more text and graphics information. In addition, chrominance down-
sampling may introduce annoying artifacts to screen content. Therefore, for screen
video, 4:4:4 color format is usually used to preserve the quality of color compo-
nent. Many specific designed coding techniques for screen content compression are
proposed, such as transform skip (Mrak and Xu
2012
; Lan et al.
2012
), intra copy
Kwon and Budagavi (
2013
) and layered coding (Wang et al.
2012
). Usually, the
coding efficiency is much higher when the screen content is compressed in spatial
domain instead of the transform domain. In HEVC, the transform skip technique is
adopted to avoid the DCT/DST transform, and the residuals can be directly quan-
tized and compressed in spatial domain. Though many compression algorithms are
developed, as screen content is usually not generated from natural scene, the prob-
lem of quality assessment of screen content is still unresolved. To apply screen video
compression in real applications, there are also many issues for screen encoder opti-
mization, such as rate control, low-complexity codec optimization and perceptual
inspired optimization.
12.4.5 Compact Representation of Feature Descriptors
For cloud-based video coding techniques, the feature descriptors should be extracted
and transmitted frame-by-frame together with the video content. Thus it is crucial to
Fig. 12.9
Screen images (SlideEditing and PCBLayout)
