Download Acceleration Techniques for Numerical Flow Visualization

3.3. DEDICATED CHANNEL IMAGE TRANSMISSION
81
Table 3.1 Framerates of gears for different scenarios. Left: 802.11b WLAN,
240×320 viewport (Compaq iPAQ display size), right: Fast Ethernet, 512×512
viewport. CCC LZO denotes LZO-compression of CCC-compressed image data.
Compression
none
LZO
ZLIB
CCC
CCC LZO
BTPC
Ratio
–
17
40
8
52
30
WLAN
PSNR
FPS Ratio
–
0.6
–
9.0
–
9.4
37
7.5
37 10.0
31
3.5
–
33
79
8
89
58
Ethernet
PSNR
–
–
–
42
42
34
FPS
10.2
170.0
72.0
138.0
138.4
20.0
compression and decompression to keep latencies low. Second, the algorithm
should result in high image quality and it should be able to preserve pixel-wide
lines. Third, the compression ratios should be high (or even adjustable) in order to be usable in low-bandwidth networks. In this work, five algorithms were
integrated and evaluated.
The class of general-purpose compression algorithms is represented by the
ZLIB library and LZO. ZLIB [26] is generally known for good performance and
high compression ratios. Since it is readily available on most Unix installations
it can serve as a fall-back solution. LZO [62] is optimized for speed instead of
compression ratio and especially designed for real-time data compression and decompression. Another benefit of LZO is that decompression is computationally
simple and, accordingly, very fast—a highly welcome property for a remote visualization system which, by its very definition, assumes that the client (interaction
server) has low performance.
For general image compression we integrated Binary Tree Prediction Coding
(BTPC). BTPC [75] is advertised to be fast and to generally perform moderately
well with regard to compression ratios. On average, the algorithm performs better than other image compression for lossy compression of photographs (which
medical volume visualizations resemble) and significantly better than JPEG for
lossy compression of graphics (which is relevant for engineering applications like
numerical flow visualization). For lossless image compression BTPC performs
comparable to state-of-the-art JPEG-LS and PNG. In the context of remote visualization, the ability to switch between lossy and lossless compression is advantageous since it allows for an adaptation to network bandwidths and client/server
performance. Another general image compression algorithm integrated is Color
Cell Compression (CCC). The main benefit of CCC [9] is a fixed compression