"Non-blooming
Rotational Composite (NBR Composite)"
proposed
by Uto & Okano
Mototsugu Motoki, M.D.
The messiest thing we are facing with NABG CCD cameras
is the blooming phenomenon. Against this issue
Uto and Okano, Ph.D. proposed the "Non-blooming
Rotational Composite (NBR Composite)" which removes
the blooming almost completely away. This method
utilizes the fact that the bloomed area extends upward
or downward on the same line from the bright stars.
To perform the NBR Composite we need to prepare two
sets of images(LRGB, RGB, etc.) taken with the different
rotating camera position. Namely, after taking
LRGB images with the usual camera position we need
to rotate the CCD camera 90 or 270 degrees and take
one more set of LRGB images with the same exposure.
Then compose two set of images by the command of
"select minimun pixel value." In my test
series of ST-10E, I tried the NBR Composite in some objects and
got satisfying results. Here I introduce this method
and share my tiny experience with those who are
interested in anti blooming.
Object;
M8; 2001/05/17, 1:38(JST)
Set 1; L=5min+4min, R=G=2min, B=4min
Set 2; L=4min+4min, R=G=2min, B=4min
System;
Newtonian reflector(f=1500mm, F5), Takahashi EM-500 Temma
PC, CFW-8A, ST-10E, CCD temp.; -20C
(double Pertier and water cooling)
Software;
CCDOPS 4.30, StellaImage
3
L images(Left:Set1, Right:Set2) with the different rotating camera
position
Magnified bloomed area; L image(Set1)
Cool or cold pixels surrounding saturated area should be painted white.
Otherwise, this dark band will be remained after NBR Composite (select
darker pixels).
L image(Set1) after painting white the cool or cold pixels existing
peri-saturated area
Final L image got by the NBR Composite of L image(Set1) and L image(Set2)
Align both of L images (Set1 and
Set2) perfectly, and carry out the command of "select darker one" (in other
words, " select minimum pixel value")
by the image processing software StellaImage 3. Bloomed area is
almost completely removed. The
same procedure should be done in each frame of RGB and finally we get a
blooming less LRGB image as below.
Another example of NBR Composite (Rosette nebula) by newly released StellaImage
3.1
No
more painting dark band white, and easy preview adjustment of each image
brightness!
Conclusion
The NBR Composite not only erases the blooming completely but also
vividly reproduces the star image
buried in the blooming. Though it takes double longer time than in
the usual photographing, the S/N ratio
is expected to be improved a little bit. I do hope this anti blooming
method proposed by Uto & Okano will
be helpful to all of the NABG CCD users and the colleges who are worrying
about which one should they
choose, ABG or NABG.
Acknowledgment
Thanks to Masaaki Uto, Kunihiko Okano, Ph.D. who proposed NBR Composite
and permitted me to introduce
this method, and to Mr. Barry Gooley at KOKUSAI KOHKI for his offering
me the chance of ST-10E test.
