Let there be light: and there was light.
Color representation of narrowband emitters
Why color calibration?
Color
calibration
of
astronomical
targets
is
an
essential
step
in
getting
reproducable
results.
The
most
often
used
methodology
is
the
so
called
„photometric
color
calibration“.
Based
on
star
colors,
which
are
obtained
from
a
database
after
a
platesolving
process,
the
image
is
corrected
in
a
way,
that
the
colors
of
known
stars
have
a
best
fit
to
reality.
This
process
is
based
on
white
point
calibration
and
therefore
only
makes
sense
for
desaturated colors, i.e. continuum emitters like stars, star clusters or galaxies.
This
method
will
strongly
fail
for
narrowband
emiiters.
Why
this
is
the
case,
and
how
colors
of
narrowband
emitters
are
best
approximated
on
common
imaging
devices
(monitors,
printers),
is
deduced
in
the
following
paper:
A numerical solution for correct color rendering of narrowbandemitters in applied astrophotography.
(download as pdf)
The image below shows a comparison of conventional color rendering (left side) and the physically correct color
rendering (right side). If you have ever oibserved M42 in a larger aperture instrument under good skies, you will
remeber the grey-blue greenish tint of the outer regions of the Orion nebula, as you can see them in this image.