Digital Imaging and Communications in Medicine (DICOM)

6.2 Image Compression 99
times is always eclipsed by increased processing times. This is not usually an
issue (and herein lies the reason you need a faster computer anyway!), but
some compression techniques (such as JPEG2000) are known to take much
longer to compress/uncompress compared to others (such as JPEG-LS).
2. When images arrive at their destinations and need to be viewed, they will
have to be uncompressed. This means that all (7FE0,0010) buffers return to
their original data size, as large as it can be. Therefore, compression will
not make your viewing workstations more efficient; they still need sufficient
memory and hard disk space to handle the uncompressed data. The main
beneficiaries of image compression are always your image archives (storage)
and networks, but not the viewing workstations.
This temporary nature of compression can be confusing. You could walk into
your ultrasound room and hear something like: “Why does my computer work
so slow? My ultrasound files are only about 30 MB in size!” Well, these image
files are 30 MB because they are compressed with some 10:1 ratio. When they
are loaded into computer memory for display, they are uncompressed to the
original size of 300 MB – enough to start dragging your computer down.
If the advantages of image compression for storage are obvious (you cut
your storage size by the factor of R comp ), compression gains for networks is a bit
trickier. Look at Fig. 24.
Fig. 24 Using image compression on networks