The Heart and Soul Nebulas are two bright nebulas on the border of
Cassiopeia and Perseus. They are cataloged in the Sharpless
catalog of bright Hydrogen rich areas. Portions also have NGC or
IC designations.
I imaged these in an earlier project in 2012,
but at that time I was using an 8300 based camera with a narrow Field
of View. Consequently the project required 9 separate
segments. When I was not able to complete it I realized that the
8300 was not suitable to the type of projects I was interested in
shooting. This led to my acquiring the 16803.
The processing of these images was greatly influenced by the 2014
Katonah NY workshop. The 2012 project was up to this point one of
my favorite works. Applying what I learned in Katonah gives an
image that is much richer in color. Green (Hydrogen)
dominated the previous image, hiding the rich colors along the edges of
the
nebula that become apparent in the more balanced image. Also note
the Purple area on the upper
right of the Heart. This was lost before the Katonah processing.
Annotated Image
Choice of Palettes
For this image I only used the SHO Palette. Otherwise known as
the Hubble Palette. This maps
Zoomable Image in SHO
The full size image is 6457 x 4954.
The following will allow the reader to zoom into the image to
explore it more closely.
Soul Nebula (SH 199)
This is a reduced resolution image of just the Soul (Sharpless 199).
Note the yellows (S+H) along the edges of the nebula and the aquas
(O+H) in the center. Some regions contain enough Sulfur to be
reddish (with this processing).
Note the Open Cluster on the right side of the nebula.
Heart (SH 190)
The Heart (Sharpless 190). I was not able to complete the Heart
with the 8300 and thus it remained a monocolor Hydrogen project.
Like the Soul the edges have hints of yellow with Aqua in the centers.
Note especially the purple bands on the upper right corner. Those
are regions rich in Sulfur and Oxygen. This framing crops the full
structure. Please consult the zoomable image above.
Processing Details
Data was collected between November 2014 and January 2015 at
-30C. While collecting data for this project I switched to using APCC.
This greatly improved my tracking and reduced the number of rejects.
Still I took about 50% more images than what I used.
Filter
Exposure
Hydrogen
21x900
Oxygen
21x900
Sulfur
24x900
Color Calibration
As I learned in Katonah instead of trying to preserve the relative
levels of the filters we
used color calibration on the strong nebula as a "white"
reference. In addition before color calibration I adjusted the
SHO levels by ratio of 5:1:2. This brought them closer to even
before Color Calibration was done. Adjusting the levels this way gives
more balanced image. Otherwise Hydrogen would be the only thing
displayed.
Managing star shapes and size
One of the most important things we learned at Katonah was how to build
good star masks. PixInsight provides a tool for doing this directly,
but it is difficult to fine tune the results of the tool. At the
workshop we learned to use MLT to perform an initial extract. We
then used Curves, MT, and convolution in whatever combination gave us a
satisfactory mask. Once I had the masks I protected the stars
particularly from the
sharpening operations. Different operations required different
masks. Sharping operations used relatively broad masks while
color operations used narrow masks.
Many of these techniques are also covered in IP4P section 3 PI-11 and
PI-12.
Managing star colors
One of the other uses for the mask was to correct the horrid star
colors that result from using the narrowband filters after aggressive
color calibration. With a
suitable mask from above one can then apply corrections. We were
taught to do this either by removing saturation or by overwriting with
a luminance. For this project I used the latter.
Here is an example of before and after. The Before image is 2x to
make the rings easier to see
Before
Repaired
Ultimately the root problem with "raccoon eyes" is that "color" in the
image is formed by combining two images that are red (Hydrogen and
Sulfur) and one that is aqua (Oxygen). Thus we start far from
anything that would produce a balanced white result. This is
compounded by greatly
magnifying some channels which increases the area at the edges of
stars. That is data loss and there may be little that can be
done.
At Katonah we learned to fix the star colors immediately after color
calibration. An image produced using that technique was almost
the final image in
this project. I decided to go back and instead try making the
color
correction late in the processing. The "H" version being
displayed is
the result of that change. To my eyes the halos are eliminated
without
substituting gray rings around the stars. Some rings remain, but
remember the halos are a data loss. Your choice is rings or
larger
stars. The "H" version opted for slightly larger bright stars,
but
better small stars.
In addition I am following the IP4P set of tutorials. Section 3 PI-12
contains a number of suggestions on using the Color Saturation tool to
correct the star halos. This allows the precise color of the halo
to be mitigated. In addition this tutorial and the previous also cover
some of the same mask techniques covered at Katonah.
MidLevel details.
Using curves on a Luminance extract it is possible
to isolate the mid level intensities (25-60%) and then apply color
saturation or boost the luminance. Either or both bring out details in
the more subtle portions of the nebula.
