Can I make an artificial flat in PI?

[astrovienna]

I have some dust donuts (yeah, I forgot to take flats a couple nights . . . )  I take care of this in PS by making an artificial flat:  clone out the stars, crop the galaxy and paint it in with the surrounding areas, blur it a bit, then subtract that flat from the original with an offset value.  Is there a way to do this in PI?  Something with PixelMath?

Kevin

[TobiasLindemann]

Hi Kevin,

Dave has posted this for a couple of weeks:
http://trappedphotons.com/blog/?p=756

I have not tested it yet, but it looks good.

Greetings
Tobias

[oldwexi]

Hi Kevin!
The quick and dirty way WITHOUT PAINTING(!) by using the data itself is:
Take your RAW Image from the mono camera (or debayered RAW from the OSC)
1. Prozess ABE or DBE  - this creates a longwave background model without any stars very similar to a real flat field. (Downsampling Factor to 1.0 instead of 2.0)
2. USE PixelMath      $T / backgroundmodel       
These 2 steps are the basic idea, you can expand it with your own ideas to increase quality.

Gerald

P.S.: Thanks to Rob (pfile) you can reduce the steps. i did it already in this message...  (I have not seen until today the Downsampling factor for the Background)
        Thank you Rob for pointing me to that!

[pfile]

also you should be able to tell ABE (or DBE) to produce a full size background model by changing "Downsampling Factor" to 1.00 under the Interpolation and Output tab of the ABE process window.

the problem with the ABE/DBE method is that it's not going to correct dust donuts. but depending on the f/ratio of your system, you may not see any dust donuts in your images.

rob

[astrovienna]

Thanks for the help, folks.  I'll try that next time.

[dnault42]

I did the synthetic flat tutorial for those cases where ABE & DBE are not able to fully correct the field due to the structure sizes involved (too small) and as Gerald says it requires painting (i.e. CloneStamp) and sometimes a lot of it.  ABE and/or DBE are the better and faster solutions for most issues, but if you find they aren't able to correct your image you may venture into the synthetic flat territory.

Regards,
David