Don't give up on an image too quickly

Geoff45 (Geoff) · #1 25-02-2008, 04:18 PM

Here are three pics of NGC 1365 from the same set of raw files. The problem was stupid error#27 in my list of stupid errors--forgetting to switch the moving speed of the mount from visual to photographic. The stars are pretty much all over the place when I did a straight align and average combine in ImagesPlus (left pic). Also there is a satellite trail in one of the frames, which still shows in the combine. So I tried a different combine method--Sigma clipped average in ImagesPlus. This basically throws out the outliers for each pixel and averages the rest, so the satellite trial goes and since the tracking errors are random, most of them appear as outliers and so the result (middle pic)is better. I then found the best 4 frames (out of ten), sigma combined them and pasted them as a layer over the middle pic with the blending mode set to darken. This got rid of a few more tracking errors. Next was to round off the stars a bit in the usual way and finally to remove the gradient, using Russel Croman's Gradient Xterminator plug-in for Photoshop (well worth getting at about $40).
The final result (right pic), while not the greatest pic in the world is still presentable.
Geoff

skwinty (Steve) · #2 25-02-2008, 05:29 PM

Hi geoff
You are right.Dont give up on an image too quickly. You can often rescue an image with a bit a clever manipulation.
That is why I like the track and stack method because you can ditch the satelite frames and continue. I also like AIP4WIN software as the software has loads of tools and utilities for exactly these reasons.
The last pic as you say is not the best but certainly presentable.
I have played around with lots of raw data but as yet still to take my own.
Regards
Steve

RB (Andrew) · #3 25-02-2008, 05:39 PM

Good advice there Geoff.
Also a good idea to archive your old RAW data so you can always come back to it as your skills and techniques in processing increase.

EzyStyles (Eric) · #4 25-02-2008, 06:06 PM

great method being used there Geoff. I havent tried sigma clipped method before might give that a go as i can see a huge difference. Gradient Xterminator is the best tool i have ever used

Geoff45 (Geoff) · #5 25-02-2008, 07:28 PM

Quote:

Originally Posted by skwinty

Hi geoff
You are right.Dont give up on an image too quickly. You can often rescue an image with a bit a clever manipulation.
That is why I like the track and stack method because you can ditch the satelite frames and continue. I also like AIP4WIN software as the software has loads of tools and utilities for exactly these reasons.
The last pic as you say is not the best but certainly presentable.
I have played around with lots of raw data but as yet still to take my own.
Regards
Steve

Hi Steve
Actually, if you use a combine method that removes the outliers, you don't discard the whole frame--you only discard those pixels in a frame that are wildly different from the corresponding pixels in the other frames. In the case of a satellite trail, all the pixels in the frame except the satellite ones are used.
Geoff

skwinty (Steve) · #6 25-02-2008, 07:40 PM

Hi Geoff
Thats pretty neat and new to me. I dont use photoshop at all as it is quite pricey. Plus you need to purchase lots of Astro plugins. (I dont use pirated software).
I bought AIP4WIN for $99 US and got a complete and dedicated astro software package with all the bells and whistles plus a 700 page Book on CCD's and DLSR's. The next upgrade comes for free if you buy version 2.
This way I find it easier to come to terms with the intricacies of image processing.
Great to hear about the capabilities of Photoshop
Regards
Steve

Geoff45 (Geoff) · #7 25-02-2008, 07:58 PM

Hi Steve
Actually its ImagesPlus that is doing all the fancy stacking and combining. I much prefer it to AIP4Win, but that's a personal choice. I only use Photoshop once the images have been stacked. I think IP comes in at about $200 (R1200).
Geoff

skwinty (Steve) · #8 25-02-2008, 08:11 PM

Hi Geoff
Thanks for that info.
Is there a trial version of images plus?
I would like to preview before I spend another R1200.00.
Will imagesplus handle the canon 40d 14bit raw files?
Regards
Steve

RB (Andrew) · #9 25-02-2008, 08:22 PM

Quote:

Originally Posted by skwinty

Is there a trial version of images plus?
I would like to preview before I spend another R1200.00.
Will imagesplus handle the canon 40d 14bit raw files?
Regards
Steve

Yes Steve IP 3 will handle the 40D RAWs.
To make sure you can email Mike.U and ask him.
He's usually very quick with his responses.

Demo version here.

skwinty (Steve) · #10 25-02-2008, 08:39 PM

Thanks RB
Will check it out
Regards
Steve

Kal (Andrew) · #11 25-02-2008, 08:52 PM

Thanks for showing the process instead of just the final product there Geoff, an interesting demonstration of what you can do with data that you might be tempted to discard

Alchemy (Clive) · #12 25-02-2008, 08:54 PM

the third image is the best, but how much of the image in the final is just the 4 best images?

Geoff45 (Geoff) · #13 25-02-2008, 09:06 PM

Quote:

Originally Posted by Alchemy

the third image is the best, but how much of the image in the final is just the 4 best images?

Good question. My original thought was all of the ten pics contrbuted, but now I'm not sure. I'll sleep on it.
Geoff