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Topics - astroedo

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31
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 ?.

Thanks

Edoardo

32
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:

K
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:

Pixinsight

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
Maxim

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?

Thanks

Cieli sereni
Edoardo Radice

33
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   );
(p+pl+pt+plt)/4

(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

Bye

Edoardo


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