The International Archives of the Photogrammetry. Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
(a) (b) 
Figure 2: Performances comparisons according to the intercomponent transform. Using a precomputed KLT on huge set of similar data 
enables a bitrate gain of a factor of 1.75 to 2. 
• LRCP: progressive quality on the whole image; 
• RLCP: progressive resolution on the whole image; 
• RPCL: progressive resolution with a more localized access; 
• PCRL: fast random accès on the image; 
• CPRL: fast random access by component. 
The five progression order are compared in term of speed access 
and quicklook generation. On Fig. 4, the quicklook generation 
time is detailled for different progression order. Differences be 
tween progression remains small as the access was on hard drive 
which are quite efficient for random access. Differences arë ex 
pected to be much bigger when data are accessed through a net 
work. 
4.5 
Order 
Figure 4: Quicklook generation time for a compressed Quickbird 
image of size 27504 x 26636. The quicklook correspond to a 
reduction in pixel number by 32 in each direction. 
4.4 Visualization session 
The interest of using compressed data is also studied in the situa 
tion of normal data visualization. A typical visualization session 
with ENVI is simulated and it appears that using directly com 
pressed data enables a gain of 20 in time. Results are presented 
in Fig. 5. The increase in computational complexity for the de 
compression is more than balanced by the reduced data transfer 
required from the disk. This advantage of compressed data would 
be even stronger in the case of distant usage of data through a net 
work. 
Order 
Figure 5: Simulation of navigation session in a JPEG 2000 im 
age with random access. Despite the computational cost of the 
decompression, it is still faster to work directly with compressed 
data (disk access is reduced). 
4.5 Tiling impact 
Tiling is an important concept to ease memory constraints at the 
compression and decompression steps. For such images, where 
holding the whole image into memory is out of question, tiling 
is mandatory. The impact of tiling on visual quality is explored 
for the common rates. Three different tile sizes are compared on 
Fig. 6(a) and 6(b): 8192 x 8192, 4096 x 4096 and 1024 x 1024. 
Using smaller tiles enables a reduction in memory requirements 
without a loss in image quality. A block effect could arise for low 
bitrate but above 0.5 bpp these are not visible. 
5 A NEW COMPRESSION PARADIGM 
With these end-users requirements in mind, this study leads to 
perceive the compression in a new way. The main purpose is not