Author Topic: New tutorial: Master Calibration Frames: Acquisition and Processing  (Read 35932 times)

Offline Harry page

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Hi Juan

Can I upload to your new ftp or not I will put them on mine

Harry
Harry Page

Offline harist

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Hi Harry, Juan,

The peculiar thing is that the light, flat, and dark frames are OK (all taken with AA4). It is the bias frames that PI misinterprets their value. I will try to provide an ftp link tomorrow.

BR,
Tasos

Offline Juan Conejero

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Can I upload to your new ftp or not I will put them on mine

For security reasons we have disabled anonymous ftp on our new server. While I figure out how to overcome this limitation, better upload your images to your website.
Juan Conejero
PixInsight Development Team
http://pixinsight.com/

Offline Juan Conejero

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The peculiar thing is that the light, flat, and dark frames are OK (all taken with AA4). It is the bias frames that PI misinterprets their value.

Hmm, this is really weird. Are you sure these are 16-bit FITS files? Anyway, as soon as you upload the image I'll know what's happening.
Juan Conejero
PixInsight Development Team
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Offline Niall Saunders

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Hi Hans,

Agreed, BatchConversion is an 'extra step', but it is an essential step as PI was written to work in the 'FITS' environment - and your Canon images are very definitely NOT 'astronomical' images as such.

Fortunately it is a step that you only need to execute once, right at the start of your post-processing cycle. I have to do something very similar myself, becuase Meade created the Envisage program with a 'bug' that has remained uncorrected for several years now (and which will now be likely to remain uncorrected forever), which requires me to batch-convert all of my 'raw data' from 32-bit Float to 16-bit Unsigned Integer after every image capture session.

Fortunatley these 'batch conversions' are quite 'robotic' after a while - they don't really take up enough effort or time to be worth complaining about in the first place ::)

HTH

Cheers,
Cheers,
Niall Saunders
Clinterty Observatories
Aberdeen, UK

Altair Astro GSO 10" f/8 Ritchey Chrétien CF OTA on EQ8 mount with homebrew 3D Balance and Pier
Moonfish ED80 APO & Celestron Omni XLT 120
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9mm TS-OAG and Meade DSI-IIC

Hans Pleijsier

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Niall,

you are quite right ... and yes, I should buy a camera more fit for the job ... donations are welcome ...  8)

Hans

Offline Niall Saunders

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Hans,

I am even further down the 'camera ladder' than you are - I am still imaging with only 775 x 577 pixels, with no TEC cooler (at least, not one that is reliable to better than 5degC), and with everything else in my arsenal (other than my LX90 and my Moonfish ED80) being 'home brew'  ::))

So, no, I do not believe that you need a new camera - you (like me) may just have to accept that there have to be some 'extra stages' in the process of trying to obtain decent astronomy images :'(

Cheers,
Cheers,
Niall Saunders
Clinterty Observatories
Aberdeen, UK

Altair Astro GSO 10" f/8 Ritchey Chrétien CF OTA on EQ8 mount with homebrew 3D Balance and Pier
Moonfish ED80 APO & Celestron Omni XLT 120
QHY10 CCD & QHY5L-II Colour
9mm TS-OAG and Meade DSI-IIC

Offline Juan Conejero

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The peculiar thing is that the light, flat, and dark frames are OK (all taken with AA4). It is the bias frames that PI misinterprets their value. I will try to provide an ftp link tomorrow.

Hi Tasos,

Thank you for uploading the image. The file you have uploaded is a 16-bit signed FITS image. However, its minimum sample value is 32768. This is indeed 'peculiar' for a bias frame. It is quite evident that the people who wrote the software that has created this image forgot to include the necessary BZERO and BSCALE header keywords in the main HDU of this FITS file. Another example of PixInsight being blamed for the mistakes made by other poorly coded applications :)

Fortunately, converting these images to the correct [0,65535] 16-bit unsigned range is very easy in PixInsight:

1. Define a PixelMath instance with the following parameters:

RGB/K expression: $T - 0.5
Rescale result disabled

Drag the blue triangle to create a PixelMath icon on your workspace.

2. Make sure that your FITS module writes unsigned integer images by default. Open the Format Explorer window and double-click the FITS item. On the FITS Preferences dialog, be sure the Default integer signedness option is set to Write unsigned integers.

3. Define an ImageCointainer with all your incorrect bias frames. The output template should be something like:

&filename;_u.fit

to ensure that the output images will be written in the FITS format. The _u postfix is of course optional, but I would include it to better identify the corrected files (_u stands for 'unsigned' here).

4. Drag the blue triangle from ImageContainer to the icon you created in step 1. This will convert all your bad bias frames into valid unsigned 16-bit FITS files that you can use with ImageCalibration.

As a side note, I personally would complain very seriously to the authors of the software that creates these images. I'll better stop talking at this point...
Juan Conejero
PixInsight Development Team
http://pixinsight.com/

Offline Harry page

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Hi Juan

Thanks for looking at that and the answer :D I will have a word with FAbio at astroart , I personaly have always found him very helpful and has alltered some software before at my behest before

Regards Harry
Harry Page

Offline vicent_peris

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The peculiar thing is that the light, flat, and dark frames are OK (all taken with AA4). It is the bias frames that PI misinterprets their value. I will try to provide an ftp link tomorrow.

Hi Tasos,

Thank you for uploading the image. The file you have uploaded is a 16-bit signed FITS image. However, its minimum sample value is 32768. This is indeed 'peculiar' for a bias frame. It is quite evident that the people who wrote the software that has created this image forgot to include the necessary BZERO and BSCALE header keywords in the main HDU of this FITS file.

Hi,

this happens also in Iris exactly as you have described. Iris works in 15 bit, so original pixel values are automatically remaped from 32768 to 65535.

¿Perhaps Astroart works also in 15 bit precision?


Vicent.

Offline Nocturnal

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Could it be AA has an Iris Compatibility mode? Nebulosity does.
Best,

    Sander
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Offline harist

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Hi Juan,
Thanks for the thorough response.

AA4 automatically decides on wether to save images as 16 or 32 bits depending on pixel values (an annoying feature which in many instances has prevented me from transfering AA4 debayered frames to PI).

I examined the flats, darks and lights all coming from the same session (including the bias frames) and all being 16 bits (AA4 supports up to 96 bits), and for some peculiar reason (probably related to this automatic fits formatting) the bias frames do not have the BZERO keyword while all the others do!

I will follow your procedure since I would like to keep all my processing under PI, and apparently IC is fine for OSC CCDs. AA4 is excellent (and cheaper than MaximDL) for integrating all the motorised gear (Mount, CCD, AO, Filter Wheel, Focuser) but not so much to my taste for processing.

Thanks,
Tasos

Offline Nocturnal

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Would it be possible to manually (or with a script) add the required keywords to your FITS files? I would probably go that route.
Best,

    Sander
---
Edge HD 1100
QHY-8 for imaging, IMG0H mono for guiding, video cameras for occulations
ASI224, QHY5L-IIc
HyperStar3
WO-M110ED+FR-III/TRF-2008
Takahashi EM-400
PIxInsight, DeepSkyStacker, PHD, Nebulosity

Offline harist

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Would it be possible to manually (or with a script) add the required keywords to your FITS files? I would probably go that route.
Well, I did what Juan suggested and took no time really!

BR
Tasos

Offline Cheyenne

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So.. I've been following this thread.. and have a question.. dealing with DSLR (but probably applicable to other formats).

Any suggestions on the process for creating a library of darks to create a master dark frame?  And can I assume that bias frames in this case are not really applicable?
Cheyenne Wills
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