Surfing the web for something completely unrelated, I came upon the blog
BigJimmy's Brain, wherein i found a
photo of the Moon. Not one of the usual familiar moons (for those of
us working on the Cassini-Huygens mission) but the Earth's moon! Hey, i don't look
at that old thing too often. Strange, hard to recognize.
Anyway, it wasn't the best exposed photograph, and being a professional image enhancer,
i thought i'd have a go at bringing out the details, if there indeed were any in there.
Here is the original photograph, taken at f/2.8 Here is my "improved" version: Pushing it a little bit more... The small bright dot with a sort-of fan shape on it is probably Jupiter or one of the brighter stars.
When i get around to it, and assuming BigJimmy's camera's clock is at least loosely accurate, that spot
could be identified. The processing i did was something like this:
I like the way the moon looks bright, almost hurts my eyes though
it is merely white (hex #FFFFFF) on my screen just like all the text editor window backgrounds and doodads
appearing on my screen, no brighter or dimmer just #FFFFFF, but don't seem that bright. The way
the brightest white falls off radially somehow cues the visual system to think "bright". Though there
is a lot of research on how Human (and other) visual systems work, i don't recall much particularly on the
sensation of brightness.
Is hard - the light coming from the halos or clouds illuminated by a full moon, is but a small
fraction of the light coming directly from the moon. A common digital camera that creates 8-bit/channel JPEGs
isn't going to cover the dynamic range. To see the halo requires overexposure of the moon. But the general
stray light from a full moon tends to wash out everything - though we can see halos just fine with our eyes. Cameras
normally can't handle it. Maybe if the clouds are thick enough the moon will be dimmer, and the halo or other
nifty optical phenomena will be brighter. What can you do to take the best photo possible?
The best way to make a pretty image of the moon, without it being washed out, where the craters are visible,
and also capture a halo without
it getting grainy or posterized-looking, is to take two photos.
Tutorial on blending different
exposures in GIMP
another tutorial
from Digital Secrets
Commercial software named Photogenics HDR by
Idruna Software Inc, runs on Windows and Linux, is a good tool for
working on 32-bit-floating point images, allowing extremely wide dynamic ranges. Combining different shutter speeds
to make pretty fully-good-looking images from extremely contrasty reality,
is the least of its capabilities.
Cinepaint is a freeware app based on a GIMP version
of yore, somewhat buggy, but used by some film studios, astronomers and mad scientists.
I claim to be adding VICAR-reading capability to it, but that darn ol' Cassini mission
keeps me (all of us at CICLOPS) busy, busy busy...

8sec exposure, f/2.8, ISO 100
photo by Jim Kane


Photographing Moon and Clouds
These images of the same scene with different exposure can be combined to made
a final image that shows the best of each. You can buy software to do this. Links are below.
Details of how to do this by hand in Photoshop/GIMP/other is beyond the scope of what i care to
write about today, but you do want to use one or more of: histogram equalizations, gamma adjustments,
and masks to blend the images.
Further Reading