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Messages - Ignacio

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Wish List / Re: Linear plane manual background extraction
« on: 2019 March 20 15:10:31 »
Interesting idea. I use first order background models a lot with ABE, but with the "limitation" that you don't get to pick directly the reference points, and sometimes is hard to capture the right background areas. I would rather have that built into ABE, than manual sliders. Or have DBE work with various order models, rather than splines.


General / Re: Location and Scale estimators
« on: 2019 February 22 14:27:55 »


I am not familiar with this- can you give a few more details on what you are doing? (What process?)

It is actually quite simple, Adam. I use the script SubframeSelector to add weights to the fits headers, and I choose StarSupport/max(StarSupport for the whole series). So you end up with weights <=1, which I then use in ImageIntegration. When there is much dispersion in quality, I take the square root of that fraction as weight.


General / Re: Location and Scale estimators
« on: 2019 February 22 08:49:26 »
Good. Maybe a hot pixel count would be another quality proxy for my setup? (assuming the true hot pixel count doesn't change much across frames)

It might. In any case, I do the quality ranking/weighting with subframe selector after full calibration (including cosmetic correction), so hot pixels should be gone by then.

I am quite happy with this approach, giving very consistent results. What I am still debating is the weighting scale: linear? square root? etc. I tend to use linear when frames are quite even, and square root when there are large differences. But no technical argument behind this.


General / Re: Location and Scale estimators
« on: 2019 February 21 13:34:57 »
Yeah, if you undersample it won't work. My typical fwhm is around 1.5 pixels or higher, so don't have that problem.


Wish List / Re: Noise reduction like this would be nice!!!
« on: 2019 February 21 09:10:24 »
Very interesting. I have some AI background and have been thinking about this lately. Will look into the technical details. Thanks.


General / Re: Location and Scale estimators
« on: 2019 February 21 08:56:39 »
FWIW, I have been using StarSupport as a proxy for frame quality. I find it interesting as it combines SNR, transparency, and FWHM aspects of the subexposure.

In the past I have encountered weighting issues due to thin clouds, optics dew, and changing gradients from imaging at different elevations.


Gallery / Re: M83, the Southern Pinwheel
« on: 2018 June 15 09:43:26 »
Spectacular, Rick/Martin! The fullres version is so detailed and clean.


Gallery / Re: NGC 2736 - the Pencil Nebula aka Herschel's Ray
« on: 2018 April 08 10:30:40 »
Fantastic, Rick! The best I've seen of this object.


Gallery / Re: M78 - LHaRGB
« on: 2018 March 02 07:12:32 »
Excellent! Super sharp for the aperture, and great color resolution.


Gallery / First image of 2018 - A classic if there is one
« on: 2018 January 22 14:20:42 »

This would be my first image of 2018 (hopefully of many to come). I had the privilege to spend three nights at a friend's observatory, located under very dark skies in Argentina. We enjoyed three consecutive clear nights, and was able to image one object per night (summer nights are very short!)

This image was acquired in the first night, after eluding a pretty strong summer storm by no more than 20 miles (with the full setup deployed!). After the southern celestial pole cleared of clouds, I polar-aligned, and enjoyed a very transparent night, although a bit windy.

I love how the image of this beautiful classic turned out. Its an LRGB (130:30:30:30) with a rather neutral (G2V) color calibration.

Usal setup: AP167FLZ + AP1100 + Apogee U16M + Astrodon 2nd Gen filters. Usual data reduction and processing with Pixinsight 1.85.

Here is a link to the full-res version, hope you like it.



Gallery / First NB images with renewed setup
« on: 2017 September 22 14:39:28 »
After much planning and a significant effort, I managed to renew all of my setup. Starting with my AP167 FLZ, which I have introduced to you already, I now added an AP1100 CP4 mount, and an Apogee U16M with deep cooling and a populated 7-filter wheel! This is no small feat for someone based in Argentina (anyway, not without breaking many banks!). I was able to take advantage of some level of mercy from the local customs, after being stationed in the USA for almost 2 years, which I took full advantage of.

A cooled monochrome CCD with NB filters allows me to start exploring the possibilities of NB imaging from my LPed backyard. These are my first two attempts: an SHO M16, and a bicolor Helix.

Hope you like them,

Gorgeous image, Rick! Very clean and balanced.


Color calibration is always an engaging topic, that can easily bring out passionate views and opinions.
The way I see it (no pun intended), color is about spectral information within a certain bandwidth. So if one is able to piece together a procedure from detection to final reproduction (say, through a display), that reproduces accurately such information, then that is the ideal case. Now, in astrophotography we like to go beyond human vision capabilities so that frequent astrophysical phenomena is not left out (ie, H-alpha emissions). Then the question arises as how to remap such part of the spectrum into the visible range. One possible approach is to compress the spectral information around some middle point in the greens, so that all information is preserved (and could be recovered by an inverse transformation). This, again, is the ideal case.

In practice, we detect color through three components (typically RGB), that result from passing the signal through three different filters before hitting a detector. Such filters and detectors are not standardized among amateurs, and they add their own idiosyncrasies to color registration. In fact, the problem becomes infinite dimensional if different filter/detector profiles are to be taken into account (to match those used in photometric catalogs). On top of this, we like to filter out unwanted additive signals, such as LP and air-glow, and the question of spectral information becomes even more intractable.

What I really like about color calibration using photometric data from different spectral type stars, is that it deals with many of the these problems at the same time, if a rich enough model if fitted.

So, the question remains if a model with three scaling parameters is good enough to recover accurate color balance, given the infinite dimensional nature of the problem. I know for a fact this is not the case with DSLRs (whose filters have significant cross-talk), where at least a matrix transformation is required. But given the unstandardized nature of color filters transmittance, and detectors spectral QE profiles, I wonder... And now that we will have access to hundreds of data points via photometric catalogs, maybe is time to get more ambitious!


This is amazing! I was just working on something along these lines, using the AperturePhotometry script!

Now, my motivation was driven by a DSLR issue with color calibration, that stems from the fact that the CFA has no clean frequency cut-offs and there is significant cross-talk between color channels. Proprietary digital development software inside the camera processors, and in software like adobeĀ“s camera raw and dcraw, partly correct this by means of a color calibration matrix that maps the camera raw data onto some standard color space (ie, XYZ). This is camera and illumination dependent. Although one can find sources for such matrix data for different camera models and illuminations,  these are not useful with modded DSLRs in astroimaging situations. Hence, I was working on the idea of using catalog photometric data to determine such matrix via a multilinear regression approach, including pedestals in the model that could take care of background neutralization at the same time:

[RGB]_xyz = M [RGB]_raw + [RGB]_bias

where the elements of the 3x3 matrix M, and 3x1 vector [RGB]_bias, are obtained by fitting the detected data to the catalog photometric data.

Is this something that could be accomplished by the new module, or white balance will be handled in the standard three (RGB) multiplicative factor?


Gallery / Re: NGC3718, NGC3729 and Hickson 56
« on: 2017 May 13 09:40:59 »
Terrific image, Sergio! Seriously good.


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