Just found this site – http://www.skyhunterdave.com/webtutorials
Got links to some great Pixinsight tutorials 🙂
I have never really bothered about running the fan on the back of my Altair F4 Newt, always thought that since the ‘scope was in an observatory it would be ‘near enough’ ambient temperature. Well tonight I put it on, just for a few mins whilst I was focussing, all was good, I unplugged it and let the subs roll in…… Then on looking at a couple of them I could see that the stars looked a little like comets, the stars when focussing were lovely and round???? Then I remembered the fan and so nipped outside and plugged the fan back in. Below are a before and after image, I think you will agree the difference is quite noticeable!
I always wished that noise reduction could be applied at the linear stage, afterall why go to the bother of stretching all the noise only to then try and get rid of it? Better to remove the noise at the linear stage then it is not included in the stretched image at all!
Pixinsight of course, has the answer in the form of the K-Sigma noise reduction in the ATrois Wavelets function. Open up ATrois wavelets on an image that has only a screen transfer stretch applied (This stretches the displayed image but the underlying image is still in its linear form) and click the K-Sigma noise reduction and marvel at the dissapearance of the noise! You can also apply some sharpening by increasing the detail layer bias by small amounts. Here is a before and after image, it’s from a 30 second exposure of the Orion Nebula (The sample is a tiny portion of the full image).
Here is the setting you want to enable:
Noise Reduction at this level also solves the patchy noise reduction artefacts that NR functions like ACNDR produce, the image below has been stretched then had ACNDR applied, it’s quite tricky to show in a low res shot but hopefully it shows some very dark, faint blobs, which are not present in the images above when K-Sigma NR has been applied.
I find a lot of pixinsight images have a night smooth, almost ‘creamy’ background to them – I found out how to create this!
Select the background, open the convolution tool and use that to blur the background slightly…
I may have a went as little too far in the examples below, the effect should be subtle but this is to show the difference it makes, also this is a 100% zoom, it will be less obvious when the image is viewed at normal resolution.
I have tried for years to get deconvolution working in various astro and non astro processing apps and never had ANY success, until now! After much reading of the docs and other tutorials I finally have a process that seems to work with my images…..
Deconvolution, what is it? Think about it for a minute, if we could work out all the errors in our optics, and tracking, and atmosphere, we could apply the inverse of this to get a perfect image… Deconvolution attempts to do just that, the results do vary and the settings are VERY sensitive, but give it a try as I do think the results are worth the little bit of time it takes to get it right.
So, my method…. First up, this needs to be applied at the LINEAR stage
1. Create a synthetic Point Spread Function – choose the Dynamic PSF Function from the Process menu
2. With your image, and a screen stretch only (remember this is to be applied at the Linear stage), double click on some stars to add them to the PSF function, say around 20, spread all over the image
3. click the Export Synthetic PSF button (Looks like a little ball)
4. Now, you want to create a star mask so…. apply the screen stretch to the histogram trasfer function then run the create star mask function, THEN…. undo the previous 2 steps so you are back to a linear image with a seperate star mask.
5. Open the Deconvolution process, enable de-ringing and local de-ringing, set the Local Support to the star mask you created previously
6. Now the tricky bit – Global Dark value in de-ringing, I usually scroll about the dark areas of the image and find the lowest values, then set the Global Dark value just lower than this, it does need a play around with but thats the good thing about Pixinsight and previews!
7. Leave everything else at default, other than the Iterations, I usually start at 10 and watch the preview, watch for ringing/dark areas starting to appear around the protected stars then back it off a few iterations
Check these out!!!
Anna Moris has some fantastic Photoshop tutorials for all levels of astro imager and also does her own set of actions, similer to the well known Noels Actions, the site also has some fantastic images as well of course!
Found this site – http://www.eprisephoto.com/videos
Lots of nice video examples and she also has a set of actions Annies Actions for sale, which I shall be purchasing very soon!
This is the first time I have tried M45 with my QHY8, the previous image was taken with my Canon 350d. The image is composed of 6X 15 minute shots and 2X 10 minute shots, along with Flats and Dark frames.
The illumination (Nebulosity) is due to the stars in this open cluster moving through a region of space with dust and the light of these stars is reflecting in the dust. This open cluster is around 370 light years from us in the constellation of Taurus and is easily seen high in the south on a crisp winters night.
OK, so you have taken your long exposure images and stacked ’em all up only to find you have big black holes in your image! These are tiny pieces of dust on one of the glass surfaces which block the light hitting the CCD Sensor. The BEST way to deal with these is with FLAT files – these are images taken of a uniformly white/grey scene taken without moving the anything in the image train. These flat files will show up the ‘Dust Bunnies’ as they are known and by using these images you can correct and repair the image. BUT…. say something goes wrong, you don’t have enough time to take flats (BTW, look back shortly for a tutorial on taking Flats), you move the CCD and the flats don’t work… Is there another way?
Thankfully there is! – Photoshop CS5 Content Aware Fill to the rescue!!!!
In Photoshop CS5 there is a new feature named content aware fill. This is really intended to remove lampposts and signs and things like this from normal daytime photographs but it does a fantastic job of removing dust bunnies from long exposure images. One caveat……. Content Aware works by sampling the surrounding area and replacing the selection with what it ‘thinks’ should be there. So, if you are looking for astronomically correct images, this process may not be for you as it could, potentially remove or add an extra star from the image. So… with that out of the way, how do you do it?
OK, First off, open your image in Photoshop CS5 and look at select the dust bunnies with the standard lasso selection tool
Once you have drawn a circle round your dust bunny – It does not have to be accurate BTW, very rough is fine, Press Shift & F5 (or from the Edit menu, select Fill). In the screen that pops up, drop down the ‘Use’ box and select ‘Content Aware’, then click OK and be amazed!
Here’s an example, I have drawn round a couple of the offending bunnies with a brush tool.
Here is the full image, showing the dust bunnies before and after removal – I think you will agree Photoshop has done a good job?
Here’s the image, after removing the bunnies