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Messages - CraigNZ

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General / Re: How to Add stars
« on: 2016 July 20 01:37:16 »
Thanks Andres.  I found another method, using StarMask.  This process looks to pull out the faint stars and 'magnify' them.  The number of stars brought out depends on the noise threshold.  Makes for a very nice 'mask'.  I then used PixelMath to add the stars back to the image and the net effect was leaving the extended objects untouched but bringing out the faint background stars.

General / How to Add stars
« on: 2016 July 19 19:02:45 »
I am doing an artistic image which needs some stars to an otherwise black background.  I was able to use ImageSolver to register the image and the star mask generated does show lots of other stars.  Question now is how do I use this to map the stars on to the image so that they look as if imaged.  In other words, I would like them to have a FWHM shape of say 3 arcsec and show as faint and bright by boosting their appearance.  I find lots of articles on how to remove stars but not necessarily how to add them back in.

General / Re: HDRComposition question
« on: 2016 July 19 03:16:24 »
After reading through the explanation of how HDRComposition works and after analyzing my images I decided to try 80, 20, and 5, by adding them in that order and then turning off the automatic exposure setting.  This worked and I got a good HDR.

General / Re: HDRComposition question
« on: 2016 July 19 01:54:32 »
Never mind that last post, I found the articles detailing the development of HDRComposition and the use of LinearFit.

I think where part of my problem comes in is the images were taken on different nights with different sky conditions.  Ideally they should all be taken on the same night under the same sky conditions.  When I use blink and scan through the images I can clearly see changes in the brightness due to high level cloud passing through at different times and on different nights.  This may be confusing the LinearFit algorithms.

General / Re: HDRComposition question
« on: 2016 July 19 01:44:11 »
How does HDRComposition know if a pixel is saturated?

General / Re: HDRComposition question
« on: 2016 July 18 18:13:33 »
So if I understand correctly, if I select images of 320, 40 and 5 for example, it will start with the longest exposure time (320 seconds) and identify all saturated pixels.  It will then move to the next exposure (40 seconds in this example) and try to resolve those pixels with unsaturated ones.  Then if there are no saturated pixels in the 40 second image it will stop because nothing is added by the 5 second image.  Is this right?

General / Re: HDRComposition question
« on: 2016 July 17 13:19:06 »
I tried 320, 40, and 5 and it failed.  I lowered the threshold down to .13 and I get a linear fit error and .14 it gets the cannot integrate error message.

It does work with 320 and 20 (or any other one as long as there are only two being combined).  But with the 320 and 20 I get a red image.  Do I need to color correct each of the subs before I use HDR?  No white balance has been performed on the images. The red channel is dominant in all of the subs and maybe the red is saturating somehow the HDR algorithms?

General / HDRComposition question
« on: 2016 July 17 04:18:53 »
Using a DSLR I have recorded sets of 5,10,20,40,80,160 and 320 seconds, each with 20 images and all taken at ISO 100.  The images have been calibrated, registered and integrated, so I now have a single image for each exposure time.

If I now use HDRComposition to combine them it fails after the second image with the message:

** This HDR composition cannot integrate further images - aborting process.

It works okay if I use any two images (e.g., 5 and 40 seconds).  It also works if I use any three images as long as they are less than 160 seconds in length (e.g., 5, 40 and 80).  But I cannot do any 4 images (e.g., 5, 10, 20, 40).

Does this mean there is some sort of math limit to the function?

General / Re: Aperture Photometry question
« on: 2016 June 28 14:29:45 »
Andres, cancel that request, I came up with a different solution.  So there is no need to flag the proper motion correction in the output table.

Thanks for helping on this and clarifying my misunderstanding.

General / Re: Aperture Photometry question
« on: 2016 June 28 14:06:35 »
Sorry, I missed that .. reading equinox but thinking epoch.

Is it possible then to indicate in the output file if CATRA and CATDEC are the epoch of the image, ie, corrected using proper motion values.  This would make it easier when doing differential astrometry to know if the reference stars are using positions corrected for proper motion.  Ideally if the proper motion is used, a flag is set and reported in the output table.

General / Re: Aperture Photometry question
« on: 2016 June 28 01:23:31 »
Where I was concerned was in the documentation it stated that IMGRA and IMGDEC are the equatorial J2000 coordinates of the star, and were calculated by 'unprojecting' from IMGX and IMGY.  I wasn't sure if 'unprojecting' meant applying only the distortion correction of the image or if also applying proper motion in reverse to show the equatorial coordinates had it been measured in J2000.

Would it be correct then to say that IMGRA and IMGDEC are the equatorial coordinates of the star at the epoch of the image?

General / Aperture Photometry question
« on: 2016 June 27 18:19:20 »
In the output Image Table there are 4 columns: CATRA, CATDEC, IMGRA, IMGDEC.  Quoting from the documentation:


Equatorial J2000 coordinates of the star as stored in the catalog.


Equatorial J2000 coordinates of the star as measured in the image. This value is calculated unprojecting the measured pixel coordinates of the star.

When converting the IMGX and IMGY pixel values to IMGRA and IMGDEC, is the proper motion of the stars used in the calculation?

General / Re: Aperture Photometry, Initializing ImageSolver
« on: 2016 June 26 13:34:30 »
Thank you Andres .. that looks great.  I'll keep an eye out for the update.

General / DynamicPSF problem
« on: 2016 June 25 15:08:32 »
I am measuring the separation of visual double stars and have one star that DynamicPSF is having trouble resolving.

The location (pixels) of the first star is: 1794, 1258
The location of the second star is: 1794, 1273

The center of the stars are separated by 15 pixels.

When using STF Autostretch the stars almost touch each other (ie, the outer faint fringes of the stars are separated by 1 pixel).

When I run Dynamic PSF and click on the first star it draws a box around the correct star but puts the x on the other star.  It reports cx,cy as: 1794, 1273.

I changed the star detection search radius to 4 but it still did it.  I would have thought that it would have remained centered on the top star, the one I clicked.

The script 2DPlot clearly shows two peaks, one for each star.

Anyway to fix this so DynamicPSF will measure two distinct stars?

General / Re: Aperture Photometry, Initializing ImageSolver
« on: 2016 June 22 22:17:31 »
I found a script, FITSKeywords.js, that could be used by the AP script to get the OBJCTRA and DEC values.  Now all I need is a way to forward them to IS when it is called.

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