Diffusion is a tool that, as its name says, allows you to diffuse whatever it is connected to. It is perfect for a misty effect.

Expand Diffusion
Group {
name Diffusion1
onCreate "\nif nuke.thisNode()\['f_created'].getValue()==True:\n nuke.thisNode()\['f_created'].setValue(False)\n nuke.thisNode().showControlPanel()"
tile_color 0xffbb9eff
selected true
xpos -286
ypos 340
addUserKnob {20 Diffusion}
addUserKnob {7 diffusion_size R 0 100}
diffusion_size 40
addUserKnob {7 diffusion_amount}
diffusion_amount 0.4
addUserKnob {26 ""}
addUserKnob {22 mask_input l "Toggle Mask Input" T "# Toggle Mask Input\nfrom __future__ import with_statement\nn = nuke.thisNode()\n# Disconnect Mask Input\nn.setInput(1, None)\nwith n:\n mask_input = nuke.toNode('InputMask')\n if mask_input:\n nuke.delete(mask_input)\n else:\n mask_input = nuke.nodes.Input()\n mask_input\['name'].setValue('InputMask')\n mask_input.setXpos( 1280 )\n mask_input.setYpos( -177 )\n mdot = nuke.toNode('mask_dot')\n mdot.setInput(0, mask_input)" +STARTLINE}
addUserKnob {41 mix T NodeWrapper1.mix}
addUserKnob {6 f_created l "First Created?" +INVISIBLE +STARTLINE}
f_created true
}
Input {
inputs 0
name InputMask
xpos 1280
ypos -177
number 1
}
Dot {
name mask_dot
label "Mask Input"
note_font_size 42
note_font_color 0x7f7f7f01
xpos 1314
ypos -44
}
Input {
inputs 0
name Input
label "\[value number]"
xpos 1940
ypos -162
}
Dot {
name Dot17
label "BG INPUT"
note_font_size 42
note_font_color 0x7f7f7f01
xpos 1974
ypos -80
}
Dot {
name Dot4
note_font_size 42
note_font_color 0x7f7f7f01
xpos 1974
ypos 64
}
set Nb7ec520 [stack 0]
Dot {
name Dot12
note_font_size 42
note_font_color 0x7f7f7f01
xpos 1754
ypos 64
}
set Nc86c6b0 [stack 0]
Shuffle {
red white
green white
blue white
alpha white
name WHITE
tile_color 0xfefefeff
xpos 1500
ypos 60
}
Switch {
inputs 2
which {{"\[exists parent.input1]"}}
name MaskSwitch
xpos 1280
ypos 60
}
Dot {
name Dot15
note_font_size 42
note_font_color 0x7f7f7f01
xpos 1314
ypos 604
}
Dot {
name Dot1
note_font_size 42
note_font_color 0x7f7f7f01
xpos 1314
ypos 892
}
push $Nb7ec520
Dot {
name Dot10
note_font_size 42
note_font_color 0x7f7f7f01
xpos 2414
ypos 64
}
set N8fe2090 [stack 0]
Keyer {
invert true
operation "luminance key"
name Keyer1
xpos 2380
ypos 702
}
Dot {
name Dot11
note_font_size 42
note_font_color 0x7f7f7f01
xpos 2414
ypos 892
}
push $Nb7ec520
Dot {
name Dot2
label Diffusion
note_font_size 42
note_font_color 0x7f7f7f01
xpos 1974
ypos 136
}
Dot {
name Dot3
note_font_size 42
note_font_color 0x7f7f7f01
xpos 1974
ypos 208
}
set Nbb24510 [stack 0]
Blur {
channels {{{parent.NodeWrapper1.channels}}}
size {{parent.diffusion_size}}
name Diffusion_Blur
xpos 2050
ypos 204
}
push $Nbb24510
Dissolve {
inputs 2
channels {{{parent.NodeWrapper1.channels}}}
which {{parent.diffusion_amount}}
name Diffusion_Dissolve
xpos 1940
ypos 276
}
Dot {
name Dot7
note_font_size 42
note_font_color 0x7f7f7f01
xpos 1974
ypos 604
}
set Nb7db940 [stack 0]
Dot {
name Dot8
note_font_size 42
note_font_color 0x7f7f7f01
xpos 2084
ypos 604
}
set Nc1b3200 [stack 0]
Dot {
name Dot9
note_font_size 42
note_font_color 0x7f7f7f01
xpos 2194
ypos 604
}
Dot {
name Dot18
note_font_size 42
note_font_color 0x7f7f7f01
xpos 2194
ypos 820
}
push $Nc1b3200
Defocus {
channels {{{parent.NodeWrapper1.channels}}}
defocus 10
name Defocus1
xpos 2050
ypos 672
}
Blur {
channels {{{parent.NodeWrapper1.channels}}}
size 10
name Blur1
xpos 2050
ypos 744
}
Merge2 {
inputs 2
operation min
name Merge17
xpos 2050
ypos 816
}
push $Nb7db940
Keymix {
inputs 3
channels rgba
mix 0.4
bbox B
name Keymix1
xpos 1940
ypos 888
}
push $Nc86c6b0
Keymix {
inputs 3
channels rgba
bbox B
name Keymix2
xpos 1720
ypos 890
}
set Nc8291c0 [stack 0]
push $N8fe2090
Dot {
name Dot5
note_font_size 42
note_font_color 0x7f7f7f01
xpos 2854
ypos 64
}
Dot {
name Dot6
note_font_size 42
note_font_color 0x7f7f7f01
xpos 2854
ypos 1216
}
NodeWrapper {
inputs 2
channels rgb
name NodeWrapper1
xpos 1720
ypos 1212
}
Output {
name Output1
xpos 1720
ypos 1500
}
push $Nc8291c0
Viewer {
input_process false
name Viewer1
xpos 1940
ypos 1047
}
end_group