Flats processing is not working.

Discussion in 'Image Processing' started by Brian Atteridge, Jan 31, 2017.

  1. Brian Atteridge

    Brian Atteridge Cyanogen Customer

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    Jan 23, 2017
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    I am running into an issue when trying to process calibration images with Maxim DL v5.24 (cant afford the new version just yet). When i try to process Flats taken in Maxim DL it says it cannot find any images that apply even though i have correctly specified them and the header window for them appears to be correct. Bias and Dark frames apply correctly but not flats. What could i be doing wrong? What do you need from me to be able to answer this question? Everything else works great but not being able to apply the flats has made my images not turn out as stellar as i would like (Pun Intended).
     
  2. William B

    William B Cyanogen Customer

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    Hi Brian.

    Just another customer replying...

    The only time I remember getting this message (many years ago now) was because I had a captured the flats with a different binning to the lights darks and bias. I sometimes see this today with a different image processing package (not Maxim DL) with DSLR images that are imported still carrying the camera orientation information and the lights, darks, flats and bias might have been recorded at different landscape/portrait orientations.

    If you can attach to your post a sample light, dark, bias and flat raw fits image then anyone can look at them and comment, but depending on file size, if too large to attach here in a post, then you would need to upload to the Diffraction ftp server a sample of your raw fits lights darks flats and bias frames with an easily identifiable file name for Diffraction people to look at them and let them know you have done so in your new post.

    Alternatively, if you have a free Dropbox account or Google Drive then place your images in a shared folder on there and post back a link to the folder in your reply.

    William.
     
  3. Brian Atteridge

    Brian Atteridge Cyanogen Customer

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    I have uploaded the files you suggested to the following link. Hopefully i got the dropbox sharing right. Let me know.
     
  4. William B

    William B Cyanogen Customer

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    Had a quick look at your post (using Safari on a Mac) but I can't see the link to the folder?
     
  5. Brian Atteridge

    Brian Atteridge Cyanogen Customer

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  6. William B

    William B Cyanogen Customer

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    Brian.

    Sorry to make you wait, I turned in for a few hours, just had a look before setting off for work.

    The problem is the ISO speed of the flats does not match the ISO speed of the lights, darks and bias.
    Lights, darks and bias are ISO 800 while the flats are ISO 100 so calibration fails when you include flats in the Set calibration tool.

    I loaded your images into a virtual Windows 7 installation on my Mac and ran a copy of Maxim DL v5-24, all calibration groups were created automatically but on applying to the lights I get the message, "Could not calibrate all images" so calibration failed.

    If you load your flats in Maxim, select each flat and use the "Fits header window" tool from the "View" menu, click on the "Edit" tab then click on the ISOSPEED item, change the value from 100 to 800 and press the SET key then close and save the flat image, you need to to that for each flat, next reopen the Set Calibration tool and press the "Auto generate (clear old)" button a new set of calibration frames will be generated using the new ISO 800 speed for the modified flats, apply to the lights and the calibration will succeed.

    You can manually edit the ISO speed in all your flats one at a time in this way or batch process them if you have a lot, or retake your flats using ISO 800. I don't use a DSLR much these days and can't say whether editing the ISO speed in the fits header for the flats will actually produce a different calibration result to using ISO 800 and retake the flats, I will leave that for one of the experts to answer (or yourself to try).

    Hope this has helped, sorry if it seems a little rushed, have to dash off for work...

    William.

    Edit flats header.jpg
     
    Last edited: Feb 1, 2017
  7. Brian Atteridge

    Brian Atteridge Cyanogen Customer

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    I did that and it is working now. However i still need to experiment with actually taking the flats as it is still leaving way too much vignetting in the image and isn't processing properly. The odd part is i didn't think that the settings made a difference with the flats since everything i have seen online suggested taking the flats at a low ISO to limit the noise and the main images could be taken at a higher ISO without issues in processing. I guess Maxim requires it to be all the same to process. Good to know for future setups. Thanks for the help! :)
     
  8. Doug

    Doug Staff Member

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    You need the imaging conditions to be identical between the flat and the flat-dark. If not then you will get a pedestal offset and the flat won't be scaled properly.
     

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