There is no Master Flat filter function

Stacking program, astrometric (plate) solver, fits file viewer

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There is no Master Flat filter function

Forum: General discussions ASTAP

Created: 2021-05-01

Updated: 2021-07-19

bedu - 2021-05-01

Why is there no longer the Master Flat filter function in the stack method tab?

Astap 2021-05-01 115233.jpg

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han.k - 2021-05-01

Hello Bedu,

After studying literature and testing the "master flat filter" function has been removed. Due to inequality between pixels it is now concluded it is better not to filter the master flat. Only for a few flats it makes sense but as soon you have more then a few flats the final noise will be lower without filter.

After combining the flats the dark current noise will quickly lower the noise caused by unequality of the pixels. The same unequality in flat and light will compensated each other. But only if the flat is not filtered.

I have posted the test results somewhere but I can't find at the moment.

Han

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bedu - 2021-05-01

thanks for the technical answer, and I agree. Unfortunately, having a qhy-10 camera that behaves strangely, I would need to reactivate that function if it is possible.
let me explain better, with my camera, if I make a flat over 8 seconds the 2 green pixels That is RGGB the two GG are not the same and it creates a sort of lattice on the final image

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bedu - 2021-05-01

In the images below, the flat matrix at 10 seconds and the one at 8 seconds

Bayer 8-10sec-mod.jpg

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han.k - 2021-05-01

The flats should be RAW. Not colour. In ASTAP the RAW flat will used to correct the light, then the debayer is applied.

That one set of green pixels is different is very strange. The light is longer exposed then the flat so you will get strange effects. What you could do is apply a box blur on the flat and save it again. See tab pixel math 2. That will solve it. See screen shot.

Last edit: han.k 2021-05-01

Untitled.png

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han.k - 2021-05-01

Apply a 2x2 box blur

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bedu - 2021-05-01

thanks anyway but it doesn't make sense to double pass and just a waste of time, i will continue to use version 0.9.525 which still has the function I need.

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han.k - 2021-05-27

In the next ASTAP version (0.9.546) the master flat filter will be reinstated. The requirement is for the case where the light source is not equally exposed the red, green and blue pixels. It will be a fixed box filter 2x2.

Han

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han.k - 2021-05-28

Normalizing the R, G, G, B pixels is probably a better option. Raise the signal of the weak colours in the raw to the brightest colour.

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han.k - 2021-05-28

Test version:
http://www.hnsky.org/astap_setup.exe

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bedu - 2021-05-28

Very well, thank you for putting back the OSC filter for Flat. I just tried it and it works. Thank you again

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han.k - 2021-05-29

Just note in version 0.9.547 it moved to the "Raw one shot colour images" section of the tab "Stack method".

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bedu - 2021-05-29

yes i saw, thanks again for the availability, and for creating this software. Good day

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han.k - 2021-06-12

There was major bug in the last versions regarding OSC filter/flat normalisation. Try version 0.9.552 just released.

Han

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