M31 Comparison Image for Mr Geake

Apologies for posting the second link twice, this was an afterthought.

The unprocessed image prior to digital enhancement.
http://homepage.ntlworld.com/taylor_.../M31unproc.jpg

The processed image
http://homepage.ntlworld.com/taylor_...31_resize2.jpg

Hope this demonstrates the rationale behind the application of digital
filters. I still hope to improve on these techniques someday. Its a lengthy
learning curve.

Regards


Chris

"Chris Taylor" wrote in message
...
Apologies for posting the second link twice, this was an afterthought.

The unprocessed image prior to digital enhancement.
http://homepage.ntlworld.com/taylor_.../M31unproc.jpg

The processed image
http://homepage.ntlworld.com/taylor_...31_resize2.jpg

Hope this demonstrates the rationale behind the application of digital
filters. I still hope to improve on these techniques someday. Its a lengthy
learning curve.

thanks chris, this is really useful. How did you remove the blue bias? In the processed image I
can still see a little blue gradient, but it's a fine image!
--
Martijn (astro-at-pff-software.nl)
10" LX200GPS-SMT
ETX105
www.xs4all.nl/~martlian

"md" not given to avoid spam wrote in message
...


thanks chris, this is really useful. How did you remove the blue bias? In
the processed image I
can still see a little blue gradient, but it's a fine image!

My biggest problem at the moment is light pollution, the original images had
an orange glow. I used a white balance on the RAW images to remove this and
when the resultant images were stacked the blue halo remained.

This is a quick and dirty demo that still leaves a little of the blue. I
usually use 'levels' also before doing this but the principle laid out below
is fine for this demonstration:

Here's the original again
http://homepage.ntlworld.com/taylor_.../M31unproc.jpg

Using paint shop pro, use a salt and pepper filter to remove most of the
stars.
http://homepage.ntlworld.com/taylor_...SaltPepper.jpg

Select the area around the galaxy and reduce the curve with a large feather.
Then copy and past over remaining stars from adjacent areas. Reduce the
brightness a little (say -2 or -3) and perform a guassian blur at around 10
to 15 radius. This leaves you with:
http://homepage.ntlworld.com/taylor_...brightblur.jpg

Then re-open the unprocessed image and use the arithmetic function to
produce the difference between the images:
http://homepage.ntlworld.com/taylor_...M31submask.jpg

Regards


Chris

"Chris Taylor" wrote in message
...
Apologies for posting the second link twice, this was an afterthought.

The unprocessed image prior to digital enhancement.
http://homepage.ntlworld.com/taylor_.../M31unproc.jpg

The processed image
http://homepage.ntlworld.com/taylor_...31_resize2.jpg

Hope this demonstrates the rationale behind the application of digital
filters. I still hope to improve on these techniques someday. Its a
lengthy
learning curve.

Regards


Chris



Chris,

I noticed you had about 30 odd minutes of expsoure (74 x 30s) on your image!
How come so many smaller ones instead of one bigger one? Again, i realise
that filters have their place and obviously in this case have improved
detail no end. I have (somewhere at home) a 15 minute ISO 400 film
exposure(200mm FL) of M31 that i took on a crystal clear night(similar to
last night after rain that shows similar detail to your modified image. I
will dig it out and scan it and publish a link to it over the weekend.

We have seemed to miss the main point of my post! The question i pose is
basicly how much proccesing is too much. The differences between your M31
pre and post proccessing are clear, at that point i would say thats far
enough, the image looks far better than the original and indeed, far better
than any of us will see with our 1/60 eyes!

R

How come so many smaller ones instead of one bigger one?
Because it's very hard to accurately track for 30 minutes, whereas a
reasonable well polar aligned mount will track adequately for 30 secs or so.
Also the s/n ratio is improved by the square root of the number of
exposures. Additionally there is much less chance of a plane or satellite
(gust of wind, brief cloud cover etc) ruining the shot during the 30th
minute of exposure! (just throw out the short exposures that are ruined).

Regards
Ian
http://www.astro-sharp.com

"Robert Geake" wrote in message
...
"Chris Taylor" wrote in message
...
Apologies for posting the second link twice, this was an afterthought.

The unprocessed image prior to digital enhancement.
http://homepage.ntlworld.com/taylor_.../M31unproc.jpg

The processed image
http://homepage.ntlworld.com/taylor_...31_resize2.jpg

Hope this demonstrates the rationale behind the application of digital
filters. I still hope to improve on these techniques someday. Its a
lengthy
learning curve.

Regards


Chris



Chris,

I noticed you had about 30 odd minutes of expsoure (74 x 30s) on your
image!
How come so many smaller ones instead of one bigger one? Again, i realise
that filters have their place and obviously in this case have improved
detail no end. I have (somewhere at home) a 15 minute ISO 400 film
exposure(200mm FL) of M31 that i took on a crystal clear night(similar to
last night after rain that shows similar detail to your modified image.
I
will dig it out and scan it and publish a link to it over the weekend.

We have seemed to miss the main point of my post! The question i pose is
basicly how much proccesing is too much. The differences between your M31
pre and post proccessing are clear, at that point i would say thats far
enough, the image looks far better than the original and indeed, far
better
than any of us will see with our 1/60 eyes!

R

On Fri, 26 Aug 2005 09:53:45 +0100, "Robert Geake"
wrote:

We have seemed to miss the main point of my post! The question i pose is
basicly how much proccesing is too much. The differences between your M31
pre and post proccessing are clear, at that point i would say thats far
enough, the image looks far better than the original and indeed, far better
than any of us will see with our 1/60 eyes!

My own personal belief is that many imagers are confused souls. What's
the point of taking an image? Is it to create something of beauty or
is it to reveal hidden details locked away inside all of that data.
The two don't necessarily go hand in hand.

Do you balance your photo to make it look aesthetically pleasing - a
work of art - or do you push it hard to reveal those elusive details?

DSO's are a strange target in this respect because, unless you're
actively doing something for scientific recording purposes (which 95%
of DSO imagers aren't), then the purpose, logically, has to be to
create a thing of beauty. This requires balance and finness in the
final image, something that's constantly fighting against the inner
yearning to see just how far you actually did go, or can go with
additional processing.

Perhaps I'm just tired - it was a late and breezy night last night ;-)

--
Pete
http://www.digitalsky.org.uk

"Robert Geake" wrote in message
...
"Chris Taylor" wrote in message
...

I noticed you had about 30 odd minutes of expsoure (74 x 30s) on your
image!
How come so many smaller ones instead of one bigger one? Again, i realise
that filters have their place and obviously in this case have improved
detail no end.

Ian Sharp covered this one pretty well. There are two additional reasons
that 30 seconds was used. The first being that light pollution here is so
extreme. Here's 30 seconds of uncombined, unenhanced exposure taken at
around midnight but with a wider field (interestingly M31 is just visible to
the top right of this image also):
http://homepage.ntlworld.com/taylor_...opix/NoLPR.jpg . Much more
than 30S would have far too much light pollution for a retrieval of the
galaxy.

Another reason is that the Canon 350D software allows programmable remote
control of the camera for a maximum of 30s. I now have a light pollution
filter and a programmable solution for longer exposures but alas, no camera.
Makes you laugh; doesn't it...

I have (somewhere at home) a 15 minute ISO 400 film
exposure(200mm FL) of M31 that i took on a crystal clear night(similar to
last night after rain that shows similar detail to your modified image.
I
will dig it out and scan it and publish a link to it over the weekend.

I'd love to see the picture. I've always admired the additional skill
requried to work with film and its apparent limitation compared with the
digital world. How would film have coped with the light pollution I'm
experiencing? Also, living so close to Heathrow, Gatwick and Farnborough any
extremely long exposures would leave a mass of unwanted intruders in any
widefield shot.

We have seemed to miss the main point of my post! The question i pose is
basicly how much proccesing is too much. The differences between your M31
pre and post proccessing are clear, at that point i would say thats far
enough, the image looks far better than the original and indeed, far
better
than any of us will see with our 1/60 eyes!

I got the point of your main post and agree; almost. There is so much more
that can be done to improve contrast etc. Some of which I'm still trying to
learn. Take a look at this guy's tutorial:
http://www.waid-observatory.com/article-psp-sharp.html for instance.

I agree that images can, and are often overdone but without the knowledge
and practice to begin with where to we get the experience from to determine
when the best has been achieved?

Looking forward to your M31.

Regards


Chris

"Robert Geake" ha scritto nel messaggio
...
I noticed you had about 30 odd minutes of expsoure (74 x 30s) on your
image!
How come so many smaller ones instead of one bigger one? Again, i realise
that filters have their place and obviously in this case have improved
detail no end. I have (somewhere at home) a 15 minute ISO 400 film
exposure(200mm FL) of M31 that i took on a crystal clear night(similar to
last night after rain that shows similar detail to your modified image.
I
will dig it out and scan it and publish a link to it over the weekend.

If I'm allowed, I would put my two cents in. Last week we also took some
pictures of M31 (and M33 too) using a Canon 350D with 200 mm telephoto lens.
The results are on http://www.antareslegnano.org/profondo.htm . It's a sum
of 7 exposures, 4 minutes each, at 800 ISO, autoguided by vesta pro webcam,
processed with Iris and photoshop. We still have to shoot a film picture for
comparison. Hope to do next new moon.
Clear skies,

--
Beta Persei
45° 35' N
08° 51' E

Remove "_nospam" to reply

Additionally there is much less chance of a plane or satellite
(gust of wind, brief cloud cover etc) ruining the shot during the 30th
minute of exposure! (just throw out the short exposures that are ruined).

Isnt that what we(I) use a big black hat for???

Perhaps I'm just tired - it was a late and breezy night last night ;-)

Breezy....Blimey, my hands where as ice just after polar alignment