Dot Product

[forkazoo]

Okay, so I can do some math in Nuke like add, subtract, multiply using a merge node. Is there an easy way to do a dot product?

[pingking]

nice one



for what do yu need it? try the expression node (under Color->math)

[jeremybrown]

my first impression was to write this into an expression node:

a=(r1*r2)+(g1*g2)+(b1*b2)

however, the expression node only takes one input and (as far as i can tell) you can't pass rgb values per pixel through expression links.

so, i got a little carried away and made a dot product gizmo (attached to this post).

just plug two images in, and it puts the result in the alpha channel. people should check my work though... i did this in about 10 minutes =)

on a related topic, why do you want to take the dot product in a merge node? i've never really heard of needing something like that for compositing. and looking at the output of the dot product, it didn't look terribly useful, although I am fully open to the fact that i could be missing the point, or doing it wrong.

here are the images i tested it with:
image a:

image b:

output:

[pingking]

however, the expression node only takes one input

but you can shuffle/copy the second input into a new layer and use that as second input

[Diogo Girondi]

Just use a Merge Expression instead.

MergeExpression {
 inputs 2
 expr0 Ar*Br
 expr1 Ag*Bg
 expr2 Ab*Bb
 expr3 (Ar*Br)+(Ag*Bg)+(Ab*Bb)
 name MergeExpression1
 selected true
 xpos -288
 ypos 53
}

[jeremybrown]

ack! i can't believe i never found that node before! thanks diogo.