  The ISOGAL project is a survey of the stellar populations, structure, and
recent star formation history of the inner disk and bulge of the Galaxy. ISOGAL
combines 15 and 7micron ISOCAM observations with DENIS IJKs data to determine
the nature of a source and the interstellar extinction. In this paper we report
an ISOGAL study of a small field in the inner Galactic Bulge (l=0deg, b=1.0deg,
area=0.035 sq. deg) as a prototype of the larger area ISOGAL survey of the
inner Galaxy. The five wavelengths of ISOGAL+DENIS, together with the
relatively low and constant extinction in front of this specific field, allow
reliable determination of the nature of the sources. The primary scientific
result of this paper is evidence that the most numerous class of ISOGAL
15micron sources are Red Giants in the Galactic bulge and central disk, with
luminosities just above or close to the RGB tip and weak mass-loss rates. They
form loose sequences in the magnitude-colour diagrams [15]/Ks-[15] and
[15]/[7]-[15]. Their large excesses at 15micron with respect to 2micron and
7micron is due to circumstellar dust produced by mass-loss at low rates. These
ISOGAL results are the first systematic evidence and study of dust emission at
this early stage (''Intermediate'' AGB), before the onset of the large
mass-loss phase. It is thus well established that efficient dust formation is
already associated with such low mass-loss rates during this early phase.
