In this contribution we discuss image quality in the context of the vi
suo-cognitive system as an information-processing system. To this end,
we subdivide the information-processing as performed by the visuo-cog
nitive system into three distinct processes: (1) the construction of a
visual representation of the image, (2) the interpretation of this re
presentation by means of a confrontation with memory, and (3) task-dir
ected semantic processing of the interpreted scene to formulate a prop
er response. A successful completion of these processes can be ensured
only when two main requirements are satisfied: (1) the visual represe
ntation of the image should be sufficiently precise, and (2) the degre
e of correspondence between the visual representation and ''knowledge
of reality'' as stored in memory should be high. We then relate these
requirements to the attributes ''usefulness'' and ''naturalness'' of t
he image and give a functional description of image quality in terms o
f naturalness and usefulness. To conclude, experimental results suppor
ting this description of image quality will be discussed.