We describe an image-comparison technique of Heidemann and Ritter (2008a, b),
which uses image compression, and is capable of: (i) detecting novel textures
in a series of images, as well as of: (ii) alerting the user to the similarity
of a new image to a previously observed texture. This image-comparison
technique has been implemented and tested using our Astrobiology Phone-cam
system, which employs Bluetooth communication to send images to a local laptop
server in the field for the image-compression analysis. We tested the system
in a field site displaying a heterogeneous suite of sandstones, limestones,
mudstones and coal beds. Some of the rocks are partly covered with lichen. The
image-matching procedure of this system performed very well with data obtained
through our field test, grouping all images of yellow lichens together and
grouping all images of a coal bed together, and giving 91% accuracy for
similarity detection. Such similarity detection could be employed to make maps
of different geological units. The novelty-detection performance of our system
was also rather good (64% accuracy). Such novelty detection may become
valuable in searching for new geological units, which could be of
astrobiological interest. The current system is not directly intended for
mapping and novelty detection of a second field site based on image-
compression analysis of an image database from a first field site, although
our current system could be further developed towards this end. Furthermore,
the image-comparison technique is an unsupervised technique that is not
capable of directly classifying an image as containing a particular geological
feature; labelling of such geological features is done post facto by human
geologists associated with this study, for the purpose of analysing the
system's performance. By providing more advanced capabilities for similarity
detection and novelty detection, this image-compression technique could be
useful in giving more scientific autonomy to robotic planetary rovers, and in
assisting human astronauts in their geological exploration and assessment