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Messages - drmikevt

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General / Re: Proper Exposure
« on: 2018 June 06 06:00:45 »

Hello.  Most people, I think, think about this question a bit differently.  When trying to determine optimal sub exposures, it is considered a better idea to think about what the minimum exposure needs to be to differentiate signal from noise.  Or, said another way, what is the minimum exposure needed to get your weakest signal off the 'noise floor' of the camera?  In this way, you would have the best chance of capturing the faintest details with the smallest possible exposure - thus giving you the least chance of over-exposing anything in the image.  Stars will probably still be clipped, but there should not be any clipping in the nebula areas.  Of course, there are outliers like M42 that may require an HDR approach (using short and long exposures) to avoid saturating the nebula, but in almost all cases, this approach should work well.  There is a script in PI, CalculateSkyLimitedExposure, that can help you determine your minimum possible exposure while still getting all the details above the noise. 

I'm sure others with more experience will chime in, but I hope this helps.


General / Re: masked stretch problem
« on: 2017 November 25 19:44:47 »

Allow me to spell things out in a little more detail.  First of all, it does not sound like you are ready for Vincent's tutorial and would be better served by the tutorials on the LightVortexAstronomy website.  There is an tutorial for Masked Stretch there.
Basically, you want to
1) Create an preview in your linear image that is only background - no nebula. 
2) Open Masked Stretch and leave everything at default.  For Background ref choose the preview you just created.
3) Zoom in on the preview and using your cursor, measure the background level. You might need to select 'readout mode'.  On the bottom of the screen there should be a K value - maybe .02 or something.  Enter that value in the Upper Limit box.  Leave the lower limit at 0. 
4)  Disable the screen transfer function on the image and apply Masked Stretch - should work just fine.  You can get more or less contrast by adjusting the clipping fraction. 

I hope this helps

General / Re: INDI Device Controller
« on: 2017 November 17 05:01:54 »
If you are lucky enough to be on a Mac, you can find an open source INDI server here:

General / Re: Masking question
« on: 2017 November 12 11:26:32 »
That video is pretty interesting.  You can also try making a star mask and a range mask.  In Pixelmath:  range_mask - star_mask  will give you exactly what you are looking for.

General / Re: issues with drizzle
« on: 2017 October 27 11:56:55 »
Good luck - its hard to say if the drizzled image looks right without seeing the difference between it and your integrated image.  Does it look hazy?  Sure it does, but its a very dense star field.  I don't see any major artifacts, though (but you have some funky diffraction spikes and bit of a coma issue).  If you still have trouble, post both the drizzle and integrated image, and your subs if possible - that might allow folks to better help.  And again, make sure to use Blink - making sure that you are applying the same histogram to all images (rather then applying a custom one to each).  If you looked at the images using a tool that automatically applies an STF, then you can easily miss when one image is much brighter then the others because the auto-STF will try to make it look the same. 


General / Re: issues with drizzle
« on: 2017 October 27 10:57:32 »
Yes, so, just to check myself I re-downloaded one of your images. You will see that when you open it in PI, there is a green line next to the name tab on the left of the image.  This tell you that the image is linear, i.e. - it has not been stretched.  In this case, we would expect the extracted L image to also be linear (not stretched).  If you saved the image as a .fit instead of .xsif, you would see that when you re-open it, it will be black. 

If you have questions or confusion around the stretching of images, the tutorial about this on the LightVortexAstronomy website will help tremendously. 


Gallery / Re: M31 LRGB 19hrs - PCC and ArcsinhStretch
« on: 2017 October 27 05:39:36 »

That looks quite nice.

One small point: I find arcsinh stretch a bit too heavy and have been blending it with a conventional HT stretch and find that looks more natural.  Some of your big orange stars have the look that I'm trying to avoid with a saturated blobby star with a hard core.  They look a bit like a pimple  :)  It's not a big deal  but I think there is a small improvement you could make.


Thank you, and thank you for the tip!  I do think that will improve things.  I also used the HSV Repair script before stretching and then did a slightly Convolution to the big star cores to deal with some clipped pixels after AS - I think things would have been even worse without those (but maybe the convolution is contributing to what you are seeing as a problem).  Plus, my stars are not yet as crisp as I'd like (I think my reducer is at play, but not sure yet) so that doesn't help either. 


Gallery / Re: M31 LRGB 19hrs - PCC and ArcsinhStretch
« on: 2017 October 27 05:34:01 »

I'm processing also a M31. Roughly 12h with a FSQ106 f3.7 and a Moravian G3-16200. It's my second try after a first attempt some years ago.
The colour balance in my images of M31 is like yours. Im not able to obtain that saturated blue color on the periphery of the galaxy that you can see in many images out there.
I wonder what I do wrong and I do not find the reason....



Mikel - I think that the saturated blue that you see in many images is a fabricated color effect to make a pretty image.  The goal of this image was to try to present a 'natural' color profile, as determined by PCC, without altering the colors too much.  Its not that those other images are 'wrong', its just that that heavy blue does not really reflect reality (or, what we would see if we were floating in space).  As it is, this image is probably a bit saturated compared to what we would see in space, but I'm good with that.  In the end, make the image that you like.  If you don't already know this trick, to boost color, you can try making the areas you are interested in and then use MLT, slightly increasing bias (.05-1.5) on layers 5-8 with it set to target Chrominance. Then, saturate slightly - that should help bring out your blues. 


General / Re: issues with drizzle
« on: 2017 October 27 05:18:16 »
I am not exactly sure what is going on here, but:

 - I was able to stretch your image (using a standard STF transferred to Histo. Transformation, and then applied to the image). 

 - After stretching, I was able to exact a lightness, and it was stretched (non-linear) - like normal.

 -One issue is that you need to crop off the border areas of the image - use Dynamic Crop to do this. 

 - Another issue might be your subs.  Did you go through each sub visually (using the Blink process) to look for images that were all washed out?  It looks like you may have one or more subs that have captured too much sky glow, maybe from clouds?  Another way to do this is to open all images in SubFrameSelector and then look at the median and noise values - you should see the outliers.  Eliminate them, then integrate and drizzle the stack again. 

If you then crop the resulting image, I think all will be back to normal.  How were you trying to stretch your image?  Again, everything seems normal when I stretch it.  The border areas look like they don't stretch, but they do - they just have very little signal.  I hope this helps!


General / Re: DrizzleIntegration process takes more than 3 hours
« on: 2017 October 25 09:44:44 »
Ok, so for the moment, we are going to ignore your hard disk because your numbers are still not making any sense.

A 254mb Ramdisk is very, very small.  Very small.  Did I mention its small?

Open PI, go to Global Preferences and look at the Directories and Network tab. What is listed for your Swap directories?  If the only thing listed is your Ramdisk, then this is definitely the problem (probably).  Your Ramdisk should be at least 8gb, and even that is not very big.  You will probably get better results if you use a swap directory folder on your hard drive.  This is the default configuration.  The best results may come from listing your RAMdisk first (assuming you increase it to 8GB) and then a swap folder on your hard drive second in the 'Swap storage directories' section.  Some people even list their RAMdisk 2 or 3 times before listing the hard drive folder, but I do not have personal experience with this.  Even if it is not the only swap directory listed, a RAMdisk that small is most likely slowing things way down.  I don't know what camera you are using, but it would not even fit one of my subs, which are around 330mb.

I should say that if anyone else thinks the above is incorrect, please chime in.


General / Re: DrizzleIntegration process takes more than 3 hours
« on: 2017 October 25 06:59:26 »

Your answers are confusing :(

 - How can you have a 232GB SSD hard disk, but also have 500GB left on your hard disk?  Perhaps you can see that this makes no sense.

 - If, in fact, you only have 254MB of RAM, then I think this is the problem.  Most people here have 16GB of RAM, about  64 times what you say you have.  PI is a very RAM intensive program.  Re-check this number.  If its correct, you need to look into how to upgrade your RAM to the max that your computer can handle.  If your computer can not handle at least 8GB, it is time for new computer.


General / Re: DrizzleIntegration process takes more than 3 hours
« on: 2017 October 25 04:59:17 »
It does not look as if you have done anything wrong.  I think you just have a slow computer....

On my quad core i7 it takes about a half hour with that many images.  3 hours is a lot longer, but what is your processor?  Are you using an SSD drive?  How much RAM do you have? How much space is left on your hard drive? Is the data on an external hard drive?  Have you tried using a swap disk?  Are you sure you have not restricted PI's use of your processors? all of these things will greatly affect your speed in processing. 


General / Re: the 'Inside PixInsight' book for a complete beginner
« on: 2017 October 19 16:49:04 »
+1 for LVA website - easy to follow and well explained.  It assumes you know nothing.  Work through the first 4 item on the tutorials page and you will have a very good understanding of how to use and navigate PI.  You will get a lot more out of the book that way.  I recommend learning how to calibrate and stack subs manually first, instead of using the automated script (BatchPreProcessing).  There are also a lot of good vids on youtube, but some are better than others.  Check out the AstroImaging Channel for some good ones.

Good Luck!

General / Re: StarRegistration not working on dithered subs?
« on: 2017 October 17 05:10:13 »
You must have forgotten to set a reference for the first run.  Try it again on a non-registered set of subs.  Make sure to set a reference frame.  If it works, then that is what happened.

Gallery / M31 LRGB 19hrs - PCC and ArcsinhStretch
« on: 2017 October 16 20:57:08 »
Continuing the processing of my big M31 project, which  was very unfortunately taken while I was still having some flatness issues.  It affects some of the outside stars if you look (don't look). 
L : 72x300 + 120x30
RGB : 24x600 each
MyT, SV80ST, QSI 683wsg-8
Luckily, I was just about to start this when ArcsinhStretch was released.  It is very easy to use - I like it already.  I compared it to Masked Stretch and Hist.Trans and it clearly provides much better color information.  Color in this image was not touched except for a very, very light curves saturation to the whole image; otherwise, it is exactly what the (also new) PCC tool and ArcsinhStretch produced.  It begs the question -  is is just bringing out color to a more natural extent than the others are able to or is it saturating things beyond what is 'really' there?  I'm not sure, but the results are nice either way.  Please enjoy and I'll take any and all suggestions for improvement or rework.  Of course, the full version, linked below, is much nicer (as always)

Thanks for looking

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