1. Steve Cannistra, Dark Halo Removal
Dark halos around stars can result from overly aggressive
use of deconvolution or unsharp masking.

2. Steve Cannistra, Dark Halo Removal
Setting up the technique in Photoshop:
1. Duplicate the layer (Layer, Duplicate Layer).
Smooth the top layer (Filter, Noise, Median). A radius of 5
is a good starting point.
3. Assign the top layer to “lighten” mode.
4. Create a top layer mask (Layer, Add Layer Mask, Hide All).
5. The layer should now look like this (next slide):

3. Steve Cannistra, Dark Halo Removal
Lighten mode
Original layer
Mask
Median smoothed layer

4. Steve Cannistra, Dark Halo Removal
Removing the halos is accomplished by painting the mask
white in the areas of affected stars:
1. Select the paint brush tool. Make certain color is set to white.
Adjust the paint brush diameter so that it is approximately
the same size as the stars.
3. Click on the black mask area to make it active.
Paint over the affected stars to reveal the overlying
lighter regions of the smoothed top layer. The dark halos
around the stars should nicely fill in.
5. The layer should now look like this (next slide):

5. Steve Cannistra, Dark Halo Removal
Final image with halos removed
Mask with white areas
representing locations of
affected stars