Flat Field Calibrat...
 
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Flat Field Calibration not possible  

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(@biggen)
White Dwarf Customer
Joined: 10 months ago
Posts: 17
January 5, 2020 21:17  

So I captured some raw subs last night using Sharpcap.  I'm wanting to process those through APP.  I didn't use Sharpcap to capture my flats, darks, or dark flats.  I use Astro Photography Tool to capture those.  After I load everything into APP I hit "calibrate" and everything runs along normally.  When its done I see I have a master flat, dark, and dark flat at the bottom of the window as normal.

However, after the calibration if I choose one of my lights and hit the dropdown at the top that goes from linear to l-calibrated, I get this error message: 

Flat field calibration is not possible. The masterflat and the light frames aren't compatible.  The masterflat has 1 channel and the light frame has 3 channel.

I'm not sure why this is. Looking at the CFA column of APP, the lights are showing up as RGB while the flats, darks, and dark flats are showing as "NO".

I just checked Astro Photography Tool and its showing the output as RAW16 which is exactly the same setting Sharpcap was using.  Why is it showing as only 1 channel for flats and other calibration frame?

This topic was modified 3 months ago 2 times by Mabula Haverkamp - Admin

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(@mabula-admin)
Quasar Admin
Joined: 3 years ago
Posts: 2369
January 6, 2020 14:44  

Hi @biggen,

You will need to create those Master Frames with the correct CFA pattern and this is very crucial.

Different capture programs can work differently on how the sensor is read and how the data is stored in the FITS file, and which Bayer Pattern needs to be used then...

Furthermore, if you mix your light frames and calibration frames using different capture software, you will run into all sorts of trouble, especially with OSC/color sensors, but also with mono sensors. Sometimes the gain and offset values don't match or are incorrectly reported. An important rule in data calibration is that you will need to shoot your calibration data with the same capture software as your lights. If you don't, trouble will occur sooner or later...if it does not, you will be very lucky 😉

I know for a fact that SharpCap and APT are NOT fully compatible here as well when it comes to Bayer CFA sensors.

If you create your masters, before doing so, in 0) RAW/FITS, enable force CFA for the APT calibration frames ( APT does not store metadata to indicate it's Bayer CFA data, so you will need to tell APP) and set the correct Bayer Pattern for your sensor. You need to be very careful here, chances are big that you need to use a different Bayer Pattern here compared to the pattern for your SharpCap data.

Kind regards,

Mabula

 

This post was modified 3 months ago by Mabula Haverkamp - Admin

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@biggen)
White Dwarf Customer
Joined: 10 months ago
Posts: 17
January 6, 2020 15:05  
Posted by: @mabula-admin

Hi @biggen,

You will need to create those Master Frames with the correct CFA pattern and this is very crucial.

Different capture programs can work differently on how the sensor is read and how the data is stored in the FITS file, and which Bayer Pattern needs to be used then...

Furthermore, if you mix your light frames and calibration frames using different capture software, you will run into all sorts of trouble, especially with OSC/color sensors, but also with mono sensors. Sometimes the gain and offset values don't match or are incorrectly reported. An important rule in data calibration is that you will need to shoot your calibration data with the same capture software as your lights. If you don't, trouble will occur sooner or later...if it does not, you will be very lucky 😉

I know for a fact that SharpCap and APT are NOT fully compatible here as well when it comes to Bayer CFA sensors.

If you create your masters, before doing so, in 0) RAW/FITS, enable force CFA for the APT calibration frames ( APT does not store metadata to indicate it's Bayer CFA data, so you will need to tell APP) and set the correct Bayer Pattern for your sensor. You need to be very careful here, chances are big that you need to use a different Bayer Pattern here compared to the pattern for your SharpCap data.

Kind regards,

Mabula

 

Thanks Mabula.  Yeah, I figured it out this morning.  APT isn't storing metadata like you said.  I need for force the CFA RGGB Bayer pattern in APP.  That gave color to my lights.

I did get another calibration warning after I started over.  I'm using Flats, Darks, and Dark Flats.  My Dark Flats and Flats were taken at the exact gain and exposure length.  I made sure of this when I took them.  APP even shows them with matching gain/exposure numbers in the columns when loaded into APP.  However, when APP got to calibrating them, I got an error popping up saying that the Flats/Dark Flats were mismatched (I don't remember exactly how it was worded).

Can this also be attributed to APT not storing all the correct metadata for in the .fits file?

Here is an example dark flat: https://www.dropbox.com/s/47cpxaaamnwnvu5/DF_2020-01-05_19-38-49_Bin1x1_3.1875s__-10C.fit?dl=0

Here is an example flat: https://www.dropbox.com/s/2tw4cjafoedcavz/F_2020-01-05_19-33-04_Bin1x1_3.1875s__-10C.fit?dl=0

 

Well I just ran the calibration again, and I didn't get the error message so perhaps I assigned the wrong calibration file when I loaded them.

This post was modified 3 months ago 2 times by Biggen

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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 1435
January 7, 2020 14:46  

It seems there are compatibility issues between the packages, unfortunately not all software follows the fits standard correctly or uses unique names for some commonly used labels. My advice would be to use a different package to take the data... might be a bit extreme maybe, but it would likely solve all issues you're having.


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