Wednesday, 13 January 2010
Odd radius snow surface display in Tampere
Stacking revealed the odd radius halos better. The one above - a stack of 138 photos - is made with lighten mode in Photoshop, and shows 9, 20, 24 and 35° odd radius halos. The 24° one is not well separated from the 22° halo and it shows better in 293 frame stack by average mode using Registax ( 1 ).
The lighten method (introduced by Jari Piikki for snow surface halos), which chooses the brightest pixel of the stacked photos, provides more realistic looks with the crystal glitter and here the realism is somewhat enhanced due to high number stack. It has the downside is losing colors: colored pixel is replaced if it overlaps with a white one. But you can still see plenty colored crystal glitter in the 46° halo in the larger image that opens by clicking the photo.
For the lighten method stack photos are taken low down where most of the halo is formed of separate crystals. From standing height the halo becomes more solid, especially near the horizon and then average stacking mode works better.
Having seen a couple of snow surface odd radius displays now it seems they can be expected when the snow surface has been fed with water fog. The odd radius halos rarely show up clearly visually, but a broad 22° halo, that is not well defined from its inner edge, seems to be a sure sign.