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Messages - jkmorse

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46
General / Re: Flats, Darks, etc..
« on: 2016 December 20 14:26:39 »
So long as you collect sufficient ADU, you don't need to go crazy with Flats.  I target 150k total ADU which I get from 5 sky flats shot at around 30k each (if my set up had the option of a light panel like the one Rob describes, I would shoot more, but you can only cram in so many when using the sky).  Like Rob says, 30k ADU per flat is a great target since its a little less than half of the full well depth of your camera/CCD and should be well within the linear range of your camera/CCD.  But, since you don't need to shoot them nearly as often, don't scimp on the darks and bias frames. 

One other point worth mentioning, Niall is right that you don't need to shoot flats every day BUT ONLY if you have no dust donuts.  But if you have dust donuts anywhere in the image chain and do any changes to the chain, such as change the rotation of your camera or switch between filters, then the dounts do not stay put and you might end up creating more problems than you solve if you don't shoot new flats for each change you make.  In my case, where my system sits in a remote observatory that inevitably gets a bit of dust on the primary mirror, I shoot different flats for each position angle and different filter, though things stay the same for the most part that I only need one set for each image run, even it is takes several weeks to capture all the light subs. 

Flats are the most confusing part of the imaging process but getting the process right deserves your attention and study since they really help when done properly.

Jim

47
General / Re: Problem Cleaning Up Dark Columns
« on: 2016 December 14 08:32:53 »
Wayne,

Try using the CanonBandingCorrection script.  It is not just for Canon cameras but works on any horizontal band in your image.  You may need to play with the settings a bit to get the right effect but it works really well for what you are seeing if we are talking about your image of the Horsehead region.

Jim

48
General / Re: Color calibration/hist equalization on NB images?
« on: 2016 December 14 08:25:57 »
Wayne,

NB images often require a different approach on color balance.

A couple of things you can try.  One that I particularly like is after stretching to create a star mask to protect the stars, then use the Hue function in Curves Transformation (its the button labeled with H towards the right).  Depending on the curve you create, and it may take a couple of iterations, you can do some nice color adjustments, though that is a bit of a blunt force approach. 

The second way involves adjusting the color mixes when you combine the images.  I am not sure what you used to combine your channels but one method that gives you complete freedom to tweak the mix is by using PixelMath in stead of ChannelCombination.  Its actually an easy process, once you get it set up initially.  To use it, open Pixel math, clear anything that may be written, then click on expression editor.  Then for each color, simply insert your images (easiest by using the "image" tab on the right).  So if you have Ha as red, just drop the Ha image in the Red column.  For Green, assuming you are using a mix of Ha and OIII, then put in both images in the format [Ha image]*0.5 + [OIII image]*0.5.  Do the same for Blue, though that will likely just be OIII.  Now accept the expressions to get back to the main PixelMath screen from the beginning.  Make sure that you open the bottom tab and check create new image and that it should be RGB.  Now you can play to your heart's content, making adjustments to the percentage contributed by each of the individual colors, so long as they add up to 1 (i.e, you can change the 0.5 and 0.5 to 0.2 and 0.8, for example).  In fact, you can even go over 1 if it doesn't blow out that color.

A third way is with the SHO-AIP Script.  There, again after stretching, you do much the same thing with mixing that you can do with PixelMath. 

Good luck.

Jim   

49
General / Re: Losing Hair Over Deconvolution
« on: 2016 December 14 07:45:21 »
Geoff,

You may very well be right, but I have never done it that way.  I have always only worked on a lum image.

Jim

50
General / Re: Losing Hair Over Deconvolution
« on: 2016 December 13 08:54:05 »
Decon is one of those processes where each image requires you to tweak the settings to get it right.  When you introduce the added data from the combined image, things change and it requires you to change as well.  But Egnaz is on the right track in that I always find it easier to work on a monochrome image with Decon than a combined image.  That doesn't mean you are out of luck though.  There are a couple of ways to tackle this:

1.  Use the combined image and tweak your settings.  You most likely have to fix the local support slider to get rid of the rings, going really low (say 0.002) and slowly working your way up;

2.  Take the combined image, use Channel Extraction with the Lab setting.  This will give you three images, the Luminance frame and the a and b color channels.  Put the color images aside (but don't close them as you will need them in a bit).  Now take the L image and make a clone (simply left click on the name in the upper left corner and pull a new image over to the right.  Its best to experiment on a clone, not the original).  Now you have extracted the L image which is where all the detail is and you can run Decon on it.  Hopefully working on the monochrome will make the Decon process easier.  Then, when you get what you want, simply open Channel Combination, select Lab and recombine the three images.

Hope that helps.  By the way, I do have a 70+ page workbook that goes into a lot of this, including details on Decon and the other major processes, workflows, etc, etc.  I share it freely with around 200 people around the world.  If you are interested, just drop me a line at jkmorse57@gmail.com.

Best,

Jim 

51
General / Re: Dark frame optimization and amp glow?
« on: 2016 December 13 08:15:29 »
Mangus,

If you are using a Dark with the same iteration time there is no need to use the bias since it is already built into the dark.  At the same time, it wont hurt anything to include it since what the program will do is subtract the bias from the dark, then substitute the bias frame you included.  Still I prefer the simpler method of just using the Dark since using it alone eliminates one more place for read noise to sneak into your images. 

I have been doing it this way for years and I can assure you it works.

Jim 

52
General / Re: problem integrating manually BIAS frames
« on: 2016 December 09 07:20:56 »
A couple of things.  What do your individual bias frames look like?  Is this an issue before you integrate?  If not, try unchecking the "clip lower range" setting and see what happens.

53
General / Re: Dark frame optimization and amp glow?
« on: 2016 December 08 07:34:51 »
Magnus,

Don't take this as gospel, but if you have matched the iteration times as well you don't ever need to use optimization.  I have found after lots of trial and error (lots of error) that I personally am better off having a suite of dark masters set at my typical iteration times for lights (my set includes 60, 120, 180, 300, 600, 900 and 1200 sec dark masters, the shorter ones needed for bloom correction since I don't have an antiblooming gate on my CCD).  Then I never need to use the optimization routine which for me results in some strange results (no correlation warnings).  Also, note, if you match the iteration times you do not need to include a bias frame since it is already built into the master dark.

Hope that helps,

Jim 

54
Tips & Tricks / Re: Red noise in image - any way to get rid of it
« on: 2016 December 07 19:09:34 »
There is a quick, way to fix the problem, though it is not entirely true to the data.  But it will save your image.  First, make a clone of your image, then convert it to greyscale and invert it so that the clone shows the background white and the target and stars as dark.  You are likely going to need to use Histogram Transform to get it right.  Once you have it set, apply the clone to your main image as a mask.  Now you are protecting the stars and target and can work on the background alone.  Open Curves Transformation and choose the saturation button on the far right (labelled "S").  Now just lower the curve to desaturate your background.  It may take a couple of iterations but in the end you will have a nice grey background.

Jim 

55
Not all is lost.  Depending on what you are shooting, that may be just fine.  Actually you often see the brightest stars showing color only on the edges.  That does not mean that you are necessarily over exposed.  Rarely are you able to avoid any fully exposed cores.  Especially in something like the Beehive, those stars are just too bright.  If you want to avoid any oiver exposure however, more subs with shorter iterations are the way to go.

56
Image Processing Challenges / Re: what is going on?
« on: 2016 December 07 18:52:34 »
Greg,

Hadn't thought of it that way, but I really like your idea of using BN and CC to identify the background, then apply it to the uncorrected version.  That is the best of both world's clever  ;)

Best,

Jim

57
Image Processing Challenges / Re: what is going on?
« on: 2016 December 07 08:57:15 »
Carlos,

I must just be lucky, imaging at 7300 ft from some of the darkest skies in the US, but I take your point.

Jim

58
A couple of questions.  Is your scope achromatic or apochromatic.  If the former, color issues are normal due to failures to focus colors at the same point.  Second, where on the image is the star in question, dead center or off in a corner.  That sometimes has an impact due to field rotation, though it looks relatively minor.

As to the blown out cores, that just goes to interation time and the well capacity of your camera.  If you are looking to avoid blowing out the cores, try shorter subs and also try using histogram transform so you can watch what is happening with the histogram as you stretch the image.  Also, see what the stars look like with STF turned off.  If you are seeing the stars without any stretching, those are blown out cores.

Best,

Jim

59
Image Processing Challenges / Re: what is going on?
« on: 2016 December 07 08:30:58 »
Also, there is no reason you can't do background neutralization and color balance first, before you do DBE.  That should clean up the color problem as well.  Note also that if the flats do their job, you may not need DBE at all.  I rarely use it any longer since the flats flatten my images already.

Best,

Jim

60
Greg,

Great image but one tweak you might try.  On my computer it looks like you have some blue running in the background, particularly towards the bottom.  One way to fix that is to clone your image, convert the clone to grey scale, invert it and then stretch to protect everything but the background.  Then apply that mask to your main image.  Once you are working on the background only, use Curves Transform to desaturate the background.  It will turn the background a consistent grey.

Best,

Jim

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