I posted this over at the offical forums but I thought some of you might like to read it too. http://forum.blackmagicdesign.com/vi...121899#p121899
Here is an example of a diy blackshade:
With dark frame subtracted:
In particular, look at the difference in the FPN in the out of focus areas of the left hand side. There is a shift in the overall exposure that could be attributed to doing the subtraction not in linear gamma.
This also masks out any hot pixels!
You can create the dark frame either in photoshop, as Scott has explained, or via imagemagick, an open source swiss army knife of image processing.
1) Record about 5-10 seconds of footage @ 4k with the body cap on
2) Render the dark clip out of Resolve as 16bit tiff files
from the directory that has the tifs in it.
convert *.tif -evaluate-sequence median dark-frame-median.tif
This will take a long time
4) Import the median file as an external matte in resolve and set up your node graph like this: http://imgur.com/q8JHudY
I'm sure smarter minds than mine can improve the process.