M83 Southern Pinwheel - With and Without Gradiant Processing

[dcalleja]

Hi
I thought this might be of interest to some. I took this image of M83 the other night (40x40s Guided, Orion ED80, DSI Pro II) and intially processed with curves and levels in PS.

I've been playing around with gradiant mask subtraction as well and put both images up here for comparison. In the processed image though I still have countour lines from the blurred mask I've used. Any thoughts on how to get rid of them would be appreciated.

[jase]

Dan,
You're on the right track. You've done a decent job using a PS mask to remove the radial gradient. Analysing your before and after processing shows a significant improvement, but as you indicate (and can be seen) a slight gradient still exists (see first two attachments for analysis).

Typically, radial gradients such as this are subtracted using flat calibration/reduction frames. You can still use gradient maps and post processing to remove them, but you waste a lot of processing time which could be spent on other tasks in the routine. Are you taking any flat frames?

If you *must* use processing to remove this type of gradient, I wouldn't use the blur filter, go with median when creating the layer mask to subtract. I've attached a version which I played around with. It’s not perfect (actually a little difficult due to jpg compression). The analysis show a background average pixel value count of 55 - reasonably flat. Yours averages close to 33 as the pixel value as you've made the background darker. I didn't bother with this, just performed a quick stretch with curves to see how much detail you got in the galaxy arms.

Keep at it. Nice image by the way. You may need to collect more data to better your S/N ratio. Look forward to seeing more of your work.:thumbsup:

[leon]

I don't quite know what you guys are talking about with Gradient stuff etc, however a pretty good effort you have there Dan, well done.

Leon

[ballaratdragons]

Wow, I didn't understand a word of it either! Waayyy over my head. So is the program shown.

[rat156]

Hi all,

M83 should be easy to get a great image of. This is why we are so critical of the images posted. It's not that easy actually. I've got an image which I'm quite proud of because I know what went into it, but I won't show anyone 'cause it's not quite right.

Anyway this is a great DSI image of a galaxy.

I've owned one I know they are not the best for this type of object. But it shows one of the problems my images of galaxies show. Burnt out stars. Stars that are obviously saturated detract from the image. Anyone know how to fix this??????????

I also had shedloads of gradient from LP in my images, so much so that I bought a LP filter. It's been cloudy since so I don't know if it works yet!

Keep up the good work.

Cheers
Stuart

[Ric]

Hi Dan, nice images of the Pinwheel.

Ken, the program is MaximDL. I think it is a wonderful program, although after 12 months with it I still live in the user manual and probably only use 50% of what is available. I'm a bit slow with this type of software but I'm getting there. I might have to pay Jase for tutoring :lol:

Cheers

[ballaratdragons]

Hmmm, think I'll stick with capturing in 'Desire', stacking in Registax 3, and processing in both Photoshop and PaintShop Pro.

I still don't know how to use all of them properly yet, but they are the easiest ones I know of :lol: and I like easy :)

[Ric]

It's like a jigsaw to me, you have to stick with it and slowly bits start to fall into place and open up new sections to explore.

Cheers

[ballaratdragons]

and your saying this to the bloke who keeps leaving his Moon Filter in the scope and wondering where everything else in the sky dissappeared to :lol:

[Garyh]

Well done Dan!!! :thumbsup:
Not having top software like MaximDL and using mainly PS and freeware, I had a bit of a play in PS..
Basically I just clipped off the darker tones with the curves function. there would be no data lost as its from vignetting. Took 2 goes and a very light gaussian blur of .7 pix. You will have to be very careful not to clip any data.
Cheers....:thumbsup:

[dcalleja]

Thanks to all for the comments:

Jase
Many thanks for your efforts & two questions - 1. should I spend the $$ on Maxim if I want to be serious about processing (its not cheap!) as it looks better suited to astro processing and 2. How can i generate a flat field (I just do darks in the DSI SW).

Gary
Thanks for having a play with - it looks much better. I have to pay attention to clipping.

Stuart
Whats a better CCD for this type of imaging? I got the DSI to ease myself into imaging and I'll stick with it for a while but I wouldn't mind some views on what the next step up should\could be.

Thanks

[jase]

Dan,
You can get serious about processing without MaximDL. Investigating gradient problems and colour shifts can be performed in Photoshop without much effort. MaximDL does take some of the guesswork out of determining problems, but you still need to understand what you are looking for. Like most astronomical software, its functions are overwhelming at first and takes time to understand how they work and when to apply them (which is important as some tasks will introduce noise if performed in the wrong order).

For me MaximDL is the backbone in my imaging projects. I use it for CCD camera control, guiding, image reduction and specific processing functions. While you could potentially use it for your entire image processing routine, I find that certain functions perform better in other applications (this of course is a matter of opinion and experience). For example, even though MaximDL has an image align function, I use other software (Registar) as it performs the task with great accuracy and can scale images as required. Similarly, for deconvolution, I use CCDSharp instead of MaximDL’s deconvolution function. You’ll still need Photoshop for image cleaning, creating filter/layer masks etc to reduce noise, smoothing and bring out subtle details etc etc.

I really do enjoy batch processing script capabilities of MaximDL. You can automate so much work. Finally, there is a lot of plug-ins for MaximDL that extend functionality. One which I use is designed for taking sky flats. I simply enter the desired ADU count and it alters the exposure as the sky brightens or darkens to ensure the ADU count remains consistent.

Which leads me on to your flat field query. I recommend you look at the following IIS article to give you a grounding of darks / flats. http://www.iceinspace.com.au/index.php?id=63,211,0,0,1,0
They’re not hard, but you need to ensure you do it right. If you’re going to introduce a calibration error, it will usually be with your flats. So carefully analyse each frame. Again, I use MaximDL to validate a good flat sub before I combine them. This can be achieved through MaximDL’s animate feature where images a “blinked” in succession. (This is also a great way of check for possible discoveries in your sub frames after calibration/reduction – now and then I get a satellite in a few subs. These are removed once a median combine function is performed).

[dcalleja]

Thanks Jase
I've read through the article and it's given me some new work to do! I'll stick with PS for now and consider Maxim down the track.

Thanks

[h0ughy]

gee wizz there is a heap of useful information given in this. I wonder how IP would rate against Maxim

[dcalleja]

Is that the Meade IP program?

[Dr Nick]

Nice, I got some shots of this one last night. I'll post them here in Ice In Space as soon as i get colour data. ;)