[AZ-Observing] Re: Dual stream answers
- From: Chris Schur <comets133@xxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Fri, 4 Jan 2008 07:33:04 -0800 (PST)
Victor and Dean, sorry about the lack of response in
the past week, my email program suddenly decided that
AZ observing messages were spam and promptly deleted
them.
Anyway, Heres the deal with "Dual Stream" processing.
Heres the problem: You'll find lots of faked images
of encounters of moving comets with non moving deep
sky objects. An example is one recent encounter of
comet SW3 with the ring nebula. A well known imager
manufactured an image of the event by taking some old
ring nebula images, some new comet images taken after
the event, cutting and pasting them together in what
was claimed to be the "exact position during the
event", and proclaiming this concoction as a true
image of the event. More horrifying is some of the
images of the Tuttle/M33 encounter posted on
Spaceweather.com, a very popular place to show off
latest event type images on a NASA forum. Several of
the images posted were created by imagers that were
clouded out during the close approach, so they took
images from the night before of the comet, an old
galaxy shot, and pieced it together, sending to space
weather as an actual recording of the event. Gee.
So what I did with the M33/ Tittle event was start
shooting 2 minute exposures consecutively for 3 hours
straight, starting at 7:02 pm, closest approach. I
then took every other frame in the sequence (two data
streams) and processed them alternately by taking
every other image and median combining it one image at
at time directly over the comet image in the 7:02
shot, about 25 frames. The Galaxy is almost invisible
when you do this. That is because of the 2 minute gap
between the data streams cancels out any thing that is
not the same in consecutive images in median or sigma
reject combine mode. Then I took the other alternate
frames (second stream) and aligned and median combined
them on to the 7:02 image again but aligning the
galaxy. The resulting image is both a sharp galaxy
and comet, frozen in time over the 7:02 closest
approach frame. So I essentially recorded the event
with a series of movie like frames and brought them
all back one step at a time to the start frame. I
believe this to be a far more responsible and
reputable way to generate an image of the event, data
actually taken at the time!
Chris
>
> With reference to Chris Schurs's technical
> specifications for his Comet
> Tuttle 8P image of December 30:
>
> "... Camera: Hutech Modified Canon XTi @ ISO800
> Exposure: 45 x 2m Continuous dual stream ..."
>
> and Dean Ketelsen's question January 1:
>
> "... I assume when you say "two data streams ...
> were brought
> together" that you mean that you removed the comet
> from each frame and
> co-added and realigned it to the co-added shot of
> the galaxy? ..."
>
> --------------------------------------------
>
> Does "dual stream" refer to an operating mode where
> the camera produces
> simultaneously files in 2 different formats ??
>
> For example, a video camera specification might say:
>
> " ... 30 frames per second on dual stream mode of
> MJPEG and MPEG 4 data
> ..."
>
> I am also interested in how the two streams were
> brought together,
> thank you.
>
> Victor Herrero
>
>
>
>
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