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Topics - astroedo

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Gallery / From Here to there
« on: 2013 March 30 11:23:41 »
Hello to all forum readers and writers.

This post does not contains a great picture like those we are used to see here, but wants to be an homage to all guys of the forum who help newbies to climb PI learning curve.

This picture was taken almost one year ago on a moderately light polluted sky in northern Italy with a more than 30 years old Leika telephoto lens and a Modified Canon 350D DSLR.
It was processed with IRIS and GIMP software: most used commercial software is too expensive for my pockets and software piracy is not an acceptable shortcut for me.

Since first processing the image showed a strong green cast and even with white balance the green hue remained mostly on the tiny stars in the background (they were green like peas  :o ).

Every attempt to correct this hue turned my picture to magenta: after a lot of work I obtained the firs picture showed here: this was my best of.

Then i knew and bought Pixinsight a i began to climb the learning curve thanks to the forum contributors help.
I know that you cannot get diamonds from manure and if you have a poor data set you cannot get an APOD but in my opinion PI has done a small miracle!

The second picture is the final result from the same raw data of the firs one.
Unfortunately the strong green cast has faded away most of the nebula color.

As I said it's clearly not an APOD, but for me is a giant leap!

Thank you guys!!   a great forum for a huge software!

Any advice is welcome!


30 x 2 min frames
Leika 180mm
Modded Canon 350D

Completely processed in Pixinsight.

From Here

To There

General / Command Line Reference
« on: 2012 September 24 08:00:24 »
Hello All!

Does exits a command line reference list?
I would like to learn more about this.

Second, i know that an official reference of PJSR does not exists at the moment, but does a tutorial or an unofficial reference exists ?.



General / Strange Statistics
« on: 2012 September 10 14:43:25 »
Hello to the forum.
My name's and i'm new to pixinsight: this evening i was playing with Menus, processes and so on.

I tried to get statistics from an image (A dark frame) and i get strange results:
The image is a single 60 seconds dark frame from an Black and white Orion CCD (16 bit pixel depth).
If i use statistics i get this results:

Mean         34360.0
Median      34359.0
AvgDev     17.2
StdDev      118.3
Variance    0.2
Minimum    34252.0
MinPos      14,218
Maximum   62044.0
MaxPos     198,551

If i do the same with another software (Maxim) i get

Maximum    29276.000
Minimum     1484.000
Average     1591.988
Std Dev      118.309

As you can see Average, maximum and minimum values are completely different and the only consistent data is the standard deviation.

I tried the same with a color Meade DSI II camera obtaining an even odder result:


Mean          497.209
Median       456.776
AvgDev       91.703
StdDev        828.911
Variance     10.484
Minimum      0.000
MinPos        516,456
Maximum    65535.000
MaxPos      678,9

Maximum    65535.000
Minimum     5018.200
Average     5477.336
Std Dev      765.438

Another strange thing is the Variance value: the StdDev value is the square root of variance, but in the results this simple relation is completely missing.

Can someone explain me this odds results?


Cieli sereni
Edoardo Radice

General / Possible workaround for color flats with DSLR
« on: 2012 August 16 13:28:46 »
Hello to all forum users,
My name's Edoardo Radice from Italy.

I am a beginner with pixinsight (at the moment i have only a trial licence) and i'm learning basics.
Being a DSLR user one of my first concerns was about colored flats (taken on morning sky or with light pollution filters).

I usually use Iris for frame calibration: here exists a GRAY_FLAT command that turns a colored flat in a gray one.
in Maxim exist a "boxcar filter" that does something similar.

In PI it seems that does not exist something similar (i have found a few forum topics about this, i hope i haven't missed something important  :P ).

Although many PI expert says that colored flats are not a problem (obviously i can correct color hues with color balance and background neutralization), i prefer starting with a gray flat.

Googling on the internet i have found somewhere that a low pass filter with the scheme

1 1 0
1 1 0
0 0 0

can fix the problem, so i've tried to create it with pixel math.
Following the PM tutorial i wrote this expression that works quite well

x = XPos();
y = YPos();
left = x-1;
top = y-1;
plt = Pixel( $target, left, top );
pt = Pixel( $target, x,   top );
pl = Pixel( $target, left, y   );
p = Pixel( $target, x,   y   );

(you can find GrayFlat.xpsm as attachment).

Just to test the procedure, i opened a master flat from my canon 350D with an Astronomik CLS filter.

in sflat_RGB_VNG.jpg   you can see the debayered version of the flat with the blue hue caused by the filter.

in sflat_RGB_VNG_gray.jpg  you can see the debayered version of the flat after application of the pixel math instace.

finally sflat_flattened_with_gray.jpg you can see the debayered version of the "blue" flat flattened with the gray flat: there is no change in color hue after flattening and the field appears well flattened.

Obviously applying a low pass filter some information in your original flat is loosen, so you cannot anymore use your calibrated frames for scientific uses like photometry.
But if your goal is only to produce a nice picture to share with friends this procedure can be useful.

Comments and advice are welcome



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