Saturn, trying new technique

[rustigsmed]

hi all,

have been getting more used to registax 6, originally i was reluctant to push it too far in the settings. getting some interesting results now, definitely seem to lose the (yellow / bright) colour a fair bit in the quest for sharpness ... so its either a nice fuzzy yellow saturn or a sharp 'grey' saturn. perhaps i need to record my data 'brighter' to allow for a colour / brightness reduction when sharpening? any way these things are going through my head, hopefully i eventually get there.

saturn cropped, from May data, canon 600d eos, 12" skywatcher goto, 5x and 2x barlows, registax 6.

colour probably off, as i am trying to emphasis (unsuccesfully) the 'blue' band.
:screwy:


http://www.flickr.com/photos/80336656@N07/

[syousef]

First, even as is, it's better than any image of Saturn I've managed (though I admit I haven't tried in years and I was using horrible webcams).

The trouble is that there colour noise in the data. So when you bump up the saturation it comes out as looking grainy which to the eye does not look sharp. If you split the image into red, green and blue channels, you'll see blue is very blotchy, and red a little blotchy, but green is good. The more you sharpen the more this blotchiness is standing out and the less sharp it looks.

You've got a few options here. (I'm using GIMP and old version of Paintshop Pro terminology. The ideas are the same though).

1) Greyscale the image and recolourise. The trouble is the easiest way to colourise - basically change it to yellow - doesn't look at all natural and you lose detail. I wouldn't bother with this one.

2) Decompose into channels. Copy and individually blur the blue, and perhaps the red channels AND BLUR THEM. Copy them back in and recompose them. The trouble is if you blur 2 out of 3 channels you're going to end up with a less sharp image.

3) A better way is to posterize or decrease the colour depth. It looks better to me if I decrease the colour depth to 256 colours (using whatever options best smooth the changes between colours do it doesn't look like a mess) then apply moderate saturation. This worked well for me on your image...but you can do better...

4) Finally consider how you're sharpening. You don't want to sharpen the colour noise. There are techniques for sharpening just the edges. If you use a mask to just sharpen the edges you want to, your image will look sharp but noise in the less defined parts won't be affected.

Here's one of the most comprehensive reviews of different sharpening techniques I've seen:
http://ronbigelow.com/articles/sharpen1/sharpen1.htm
through
http://ronbigelow.com/articles/sharpen1/sharpen6.htm

Here's a simpler one
http://bythom.com/sharpening.htm

[rustigsmed]

thanks for taking the time out and replying syousef! I really appreciate it.

some really good tips, i've had a quick read of those links (starting from the simpler one) and it is quite obvious i've made some fundamental 'errors' in my processing order / technique. am looking forward to having another crack over the w'end when i get some more time. i've only been using the DSLR for a couple of months ... its very steep learning curve!

Its fair to say that i have so much more respect for the quality astrophotos that I see.

[syousef]

Let me just say that is brilliant for such a short time using a DSLR.

I got into photography because I ended up with manual film cameras trying (badly, and in the wrong way) to do astrophotography. I went to the zoo one day and was hooked.

I haven't given up on astrophotography (even took some photos of the Venus transit) but I'm not trying to do long exposure stuff. Life is just too busy right now with a young family. And to be honest I'm spoilt as there is so much good professional and amateur astro work that if I'm honest the only thing I'll gain is a sense of personal accomplishment. Planetary isn't a bad starting point.

Also do not forget the moon. Here's one I got with a point and shoot held up against the eyepiece of my dob, then overlayed with Virtual Moon Atlas

http://www.progsoc.uts.edu.au/~sammy/photography/IMG_1488_ImprovedPositionOverlayAni mation.gif

It's amazing what you can do without highly specialised gear IF you're willing to give up deep sky.

[syousef]

I've edited the first reply to add something I meant to write but didn't. See the words in ALL CAPS.

[rustigsmed]

thanks again, and nice work with the moon! yes i've taken a few shots, one i'm really happy about. but i need to get the atlas out and familarise myself with the features! the gif would be a good learning feature!

cheers

[syousef]

Sorry when I said aligned with Virtual Moon Atlas, I mean I took a screenshot and did created the animated gif in GIMP and a gif animation tool. Virtual Moon Atlas is an amazing piece of software though. Well worth getting to know.