  The efficient storage of digital data is becoming very challenging over the
years due to the exponential increase in the generation of data which can't
compete with the existing storage resources. Furthermore, the infrequently
accessed data can be safely stored for no longer than 10-20 years due to the
short life-span of conventional storage devices. To this end, recent studies
have proven DNA to be a very promising candidate for the long-term storage of
digital data. Several pioneering works have proposed different encoding methods
for the specific encoding of images into a quaternary DNA representation while
first compressing the image using the classical JPEG standard to reduce the
high cost of DNA synthesis. However this type of compression is not optimized
with respect to the quaternary DNA code and results in an open-loop workflow.
In our previous works we have introduced the first closed-loop solution for
generating a constrained fixed-length quaternary code which allows controlling
the synthesis cost thanks to a source allocation algorithm. In this paper, we
extend our studies to proposing a variable-length encoding solution which is
based on the JPEG standard.
