  Context: Measuring amplitudes of solar-like oscillations and the granulation
power spectral density constitute two promising sources of information to
improve our understanding and description of the convection in outer layers of
stars. However, different instruments, using different techniques and different
bandpasses, give measurements that cannot be directly compared to each other or
to theoretical values. Aims: In this work, we define simple response functions
to derive intrinsic oscillation amplitudes and granulation power densities,
from photometry measurements obtained with a specific instrument on a specific
star. Methods: We test this method on different photometry data sets obtained
on the Sun with two different instruments in three different bandpasses.
Results: We show that the results are in good agreement and we establish
reference intrinsic values for the Sun with photometry. We also compute the
response functions of the CoRoT instrument for a range of parameters
representative of the Main Sequence solar-like pulsators to be observed with
CoRoT. We show that these response functions can be conveniently described by
simple analytic functions of the effective temperature of the target star.
