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Messages - MortenBalling

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General / Re: Help with a image capture problem?
« on: 2015 February 03 00:02:17 »
With all due respect, I find it hard to understand, how a USB cable could cause this. It's a digital signal, and it should be a lot less fragile than an analog signal. On my old Orion Starshoot Pro, I've seen dropouts, due to lack of USB bandwith, but that shows up as black pixels. Anyways, what do I know about cucumber salads? ;)

I have a similar problem as mads0100's example show, but more like a single wide "line" towards the edge of the image. I live (and image) in an extremely light polluted area, so I think my problem is due to some sort of false light entering the telescope/camera, probably through the gap in the crayford focuser on my refractor. I've seen that happen, when I shoot flats indoors during the day.


Morten :)

General / Re: ImageIntegration lags before starting
« on: 2015 February 02 15:43:16 »
It sounds like the cache. Have you tried clearing memory cache?

Be aware that normally cache is your friend, and that even though PI waits for a while, when you hit global, once things start going, cache really speed up the process!



General / Re: Pixinsight workspace question
« on: 2015 January 30 18:48:40 »
Hi Tom

It's meant to divide the workspace, so that you can keep minimized icons in the right hand border it creates. If you tile or maximize images, the stay within the orange line.



General / Re: StarMask - dealing with large star
« on: 2015 January 30 18:19:53 »

I have to admit, that after getting started using Harry's excellent videos, I've been using the trial and error method ever since, so I don't know much about available tutorials.

The PI learning curve is so steep, that it's more than vertical in some cases, but hang in there. It gets a lot easier ;)


Exactly  ;)

General / Re: Dealing with salt and pepper noise?
« on: 2015 January 30 18:15:16 »
Hi Callum

I think, the problem is, that you're trying to remove all the noise in one sweep. Actually, I'm impressed that you are able to do that! :)

Try to accept a little noise, and adjust your MLT settings carefully, one layer at a time, using a realtime preview.

I think you should be able to remove even the salt/pepper noise. I tried that using the example in your post, and it works fine. Problem arises when I try to regain sharpness using the detail layers.

Try to reduce the amount of noise reduction on each layer to 0.5, and then increase the value until you get the best result.

I've personally found, that I get the best results in PI, using small careful steps. If it wasn't enough, I can add more later.


Morten  :)

General / Re: StarMask - dealing with large star
« on: 2015 January 29 23:11:26 »

Wavelet Transform can also be used, disabling the R layer, together with convolution and Pixelmath.



Off-topic / Re: Drizzle vs smaller pixels
« on: 2015 January 29 22:49:21 »
This is purely empirical,but:

Drizzle is great! However it was invented for undersampled images. I personally like to postprocess images oversampled/upsampled. That makes me jugde my settings more critical, like deringing etc. Therefore I try to work at a resolution at least twice (on both axis), the resolution I aim for with the final image. Before Drizzle in PI, I upsampled my calibrated lights to 200% (using a lanczos algorithnm that introduce a slight ringing) before staraligning. To be honest I find it very difficult to tell the results of those two methods apart, even though Drizzle is a far more complicated process. Nasa don't use simple cowboy tricks like mine  ;)

Undersampling doesn't rely on pixelsize alone, but on a combination of pixelsize and FL. It's the final image pixel scale that counts. Using large pixels with a short refractor will quickly get you in the undersampled territory, but with a wide field.

Until recently I've used an older Orion Starshoot Pro, which have pretty large pixels (7.8 microns). The chip is cooled, and have a reasonable SNR, and with an ED80 refractor reduced to F/5.6 the image was undersampled @3.62"/pixel. Perfectly suited for Drizzle.

Then I bought an Atik 428M and even though it has much smaller pixels (4.5 microns), it produce much better results. First of all, the microlenses seem to do their job pretty good these days, so SNR is better with the same amount of exposure time, as with the Orion camera:

There are a lot of different factors at work here, like mono/osc etc, but my gut feeling is that pixel size isn't the only one parameter worth considering.

I live in a city center, so seeing is horrible here. I also have a C8 sct and even reduced @0.66x it still gives me a resolution of 0.69"/pixel. Combined with the awful seeing, that makes an oversampled image on most nights. Then Drizzle doesn't really make much of a difference.


Morten :)

Btw. do you know this one?

General / Re: Documentation lacking
« on: 2015 January 29 21:40:47 »

Excellent! Thanks for sharing  :)


It's a process we all go through. Honestly it's a pain, and it's often debated. On the other hand, I have to admit, that getting my telescope to work, with ascom drivers, autoguiding, strange "angles" on the mount etc. was a bit of a challenge as well, and that was part of what inspired me to keep going. Also remember that to keep PI affordable to amateurs, and a much smaller customer base than Excel and Word, there has to be a few compromises here and there. So, forget about rocket science! This is the real deal ;)

General / Re: Keyboard shortcuts??
« on: 2015 January 29 21:30:09 »
This is as close as it gets:

The ones for masks are invaluable, but it would be nice with a shortcut for showing/hiding previews.

Morten  :)

General / Re: StarMask - dealing with large star
« on: 2015 January 29 21:23:17 »
Hi Joel

One "cowboy trick", that I've used in situations like this, is to clone the image I'm working with. Then I resample the cloned image to 50%, and use the smaller downsampled image to make my starmask. You might also want to try to lower the values for Structure Growth and especially Smoothness. Then you get square stars in the mask, but "no free lunch, and minor problem". The downsampling makes the bigger stars easier to handle, and also speed up the whole trial and error process (by a factor of four! :)).

Once you have a good starmask, you resample that back to the size of the original image (using resample = 200%). Be aware that PI can't work with half pixels, so if the original image had odd numbers of pixels in one or both dimensions, for example 2997x1999 pixels, you will have to manually enter the resolution of the original size, when upsampling the starmask.



General / Re: Donuts like stars
« on: 2015 January 05 07:16:51 »
I'm not sure that you need to throw away your work. Donut like stars like these can i some cases be restored by using MorphologicalTransform carefully. The trick is not to overdo it, and to use a good starmask.

Generally the subjective visual sharpness of an astrophoto can be divided into the stars, and all the rest. A large portion of the percepted sharpness lies in the stars. Nebulae etc. are much less critical when you look at the final image. Furthermore, you can try to deconvolve the nebulae and galaxies using a sampled PSF, or even one that you make yourself by experimenting with the dials.

Nothing beats focusing the telescope, but many of the tools available in PixInsight are designed to fix a "not so perfect" image.


Morten  :)

General / Re: Terrible Banding/noise and haze
« on: 2014 December 27 16:13:13 »
Hi Adam

It's really difficult to see any banding at the image you've attached, but you might try to shoot more bias frames (like 100). It's quickly done, and you can even do it on a cloudy night. Basically, 10 calibration frames is too little.

Also try and blur your flatstack slightly. Or run TGVDenoise on the Flatstack and try to calibrate again using that.

Do you dither your mount? That can have tremendous results, especially with DSLR.



General / Re: Drizzle
« on: 2014 December 27 13:46:03 »
I think an important point is how to present the final image. For a final version, I would normally resample to 66 or even 50% for the internet. Working at full resolution has some advantages though. You work a lot more critical with your settings, and it is easier to see what you're doing.

Drizzle is a great tool, but before that, I used to resample my registration reference frame to 200%, and reached pretty similar results after deconvolution.

All in all: Do exactly what you feel looks right. I think most of us started doing all this, because we looked at all those Hubble photos and went uhhh! and ahhh! :) The point is that a large majority of the astro photos I see, seems to be made to show the strange aesthetic beauty of our Universe. Even though we feel very scientific while we make them.



General / Re: Integration using FWHM weights?
« on: 2014 December 27 11:36:01 »

In the first post, I wrote that I'm working with a special technique, where I search the Internet for as many Creative Commons astro photos of one deep sky object I can find, and then combine all the images into one. The idea is to try and take collaborations even further.

Combining several hundred images, even though they are nonlinear JPGs, results in an amazing SNR due to the combined integration time. Often more than 500 hours in total.

Someone at the danish astronomy forum, mentioned that the method should be called Crowd Imaging, and that name stuck. I've done quite a few so far, but because it's sort of Big Data projects, it's pretty time consuming. I constantly find newer, smarter and faster ways to make it work.

Basically I gather as many images as I can find. Then I crop the edges, and flip the ones who need it. After that I StarAlign all the images to a single image with a large field.

Next I use SubFrameSelector to measure FWHM of the aligned frames. The images I use, vary quite a lot, both regarding color, sharpness, resolution, SNR etc. A funny thing though, is that people are pretty precise with how they rotate the field. I therefore normally end up with eight spikes. :smiley:

The SFS FWHM weights are then used for ImageIntegration. In theory I should loose SNR, but in practice the images I find with low FWHM often have better SNR. I integrate using black clipping, add/scale normalization and no rejection.

You can see some results here:

I wanted to share the FWHM weight idea, because it might come in handy in some other cases as well.

One is Lucky Imaging. I tried to shoot a 300x1sec frame series of Trapezuim with small pixel resolution, and sorted out the 200 with best eccentricity and FWHM. Then I integrated using weight=1/FWHM^2, and used Pixelmath to "replace" with the sharp stack on a normal stack, using the normal stack as mask. I need way more frames to make it work, but so far it looks promising. I can even see the proplyds.

Another way to use this is when you combine several nights of exposure, with different seeing, or when you use different exposure times. Then you mix in the sharp stack in the bright areas of a stack with max SNR, like mentioned above.

My formula is very primitive and homemade, so there's a lot of room for improvement. But I guess the first pancakes weren't perfect either ;)

Best regards


General / Re: Observations from a Newbie
« on: 2014 December 27 06:07:01 »
Hi Joel

Welcome to the wonderful world of PI. Hang on, and you won't regret it. Even though I still find some of the math behind PI complicated, I start to feel safe and at home, once the software starts up. I come from a similar software as you, and work very much in a visual way, and therefore a word like transformation used to mean moving the image along an axis. Things like that takes a little while to get used to, but once you learn the lingo, a whole new universe lies ahead.

Nice gallery btw.

And once again. Thanks a googolplex^n to Harry. If you ever run for president, you can count on my wote! :smiley:

Best regards


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