Dodgy fix for bad flats.

[ollypenrice]

Our present imaging guest had the bad luck to have a dust bunny which shifted between shooting luminance lights and flats. It's a galaxy widefield so there was no nebulosity affected. The bunny is just in a field of stars. This was embarrassing so I felt I needed to find a Photoshop fix! OK:

Using star removal, make a completely flat and objectless background sky at the same brightness as the real image. (23 in this case, but easily adjusted.)

Paste the real image on top.

Use Select - Colour Sampler to select the background sky of the entire bunny.

Erase this selection over the bunny.

Adjust the noise in the bottom layer (using Add Noise) till it matches the top layer.

Flatten.

Better than binning a full night of nice luminance and pretty much invisible.

Olly

[harry page]

Hi

don't tell anybody but I have done something similar

 

Harry

[andrew s]

Olly, your a very naughty boy (and so are you Harry) - Regards Andrew

(NB to be read in a Monty Pythonesque voice.)

[carastro]

Needs must.

Carole 

 

 

[frugal]

Olly, I presume you could use a similar technique to cut and paste the dust bunny into the old location? I.e. if the dust bunny has hopped from position A to position B; can you cut it out of the flat at position B and then add it back into a copy of the flat at position A? Then so long as you know if your light has the bunny at position A or B you know which flat to use.