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welcome to this overview of PXF Vector Etchblur
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so here I have a clip of someone playing basketball
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and I want to
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cut the player out and replace the background
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with a roto
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so so I have a roto prepared here
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I'm using the copy node to combine the RGB
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and the Alpha together
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and I'm using the premolt node to have an RGBA
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premultiplied image that's ready to be put on
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top of a background using n over
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so far so good
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so that's great
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however there's a problem
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if I look at the footage it's got motion blur and my
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Roto does not have motion blur
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so if I look at the basketball
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the inside is blurry and the edge is sharp
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that's a problem
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so typically we would turn on the motion blur
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in the Roto node
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so if we go back in the Roto node
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we can turn on Global Motion Blur
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and now I have
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a blurry
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alpha so my alpha has motion blur so that's great
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but there's a problem when I combine the blurry
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alpha with the blurry picture
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I can see in my result here parts of the ground
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showing through the edge
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and that's normal
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see
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you can see the lines from the basketball court here
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so that's normal
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that's expected
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because when you turn on
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the motion blur
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the alpha
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grows and we end up with parts of the background
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so a mistake would be to try to fix this
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by shrinking
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the roto making the shape of the ball smaller
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so that the blurry areas stay on the opaque bits
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this will
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of course fix my issue of seeing the ground but
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my ball will end up looking smaller than it should
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so that's a problem
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the reason we're having the problem is because
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in the this image here
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in the blurry parts we're having a mix of the ground
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and the ball
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and we just want the ball we don't want the ground
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so we're stuck here
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we can just use the motion blur on the roto side
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we need to apply motion blur here after
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the premultiplication and that's where PXF Vector
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Edge Blur comes in
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so let's copy our branch here to compare
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I'm gonna turn off the motion blur in the roto
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and we're gonna bring in a PXF Vector Edge blur
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and I'm gonna connect it here
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and we can compare
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we don't have the same shutter speed
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so I'm gonna slow down the shutter here
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here we go
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so now we should be able to compare apples to apples
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so now this is the version with
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Vector Edge and this is the version without
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so you can see there's quite a difference
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between the two
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let's comp it on top of our background
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here we go
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so this is the old way using the motion blur from
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Nux Roto
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and this is the new way using vector edge blur
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so what's happening here
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basically what we're doing is now we're
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turning off the motion
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blur in the Roto
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and doing only the opaque areas in the alpha
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so the Alpha or Doroto has been
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made as tight as possible to include only
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the opaque bits and not
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to include the motion blur
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once we have that
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we're using a vector generator
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under the hood to analyze the motion
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and a vector blur to basically blur the edges
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so not only are we blurring our alpha channel
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we're also blurring
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RGB values so essentially we're taking
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the opaque bits of the ball
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to recreate the transparent bits
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which we cannot use from the
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footage because it's mixed
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with the ground
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so this is giving us a pretty good result
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so let's look at the
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knobs and settings in Vector etular
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so the first one here is
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which channel to analyze for motion so basically
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where are the motion vectors coming from
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are we analyzing the motion of the alpha only
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or the RGB it's up to you
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usually alpha gives better result
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but you can also analyze the motion
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of the RGB image
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so that's your first option
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second option is whether or not to apply
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the blur only on the edges
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so if you turn that off you can blur the inside
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this would be a mistake here
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because now we're applying motion blur
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to pixels that already have motion blur from the
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footage so we don't want double blur here
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but if you wanted to you can turn that off
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you can choose which method to apply motion blur so the
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Vector Blur 2 method is using the GPU
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accelerated recent
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Vector Blur node
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this one uses the old node so it might be
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useful if you're having bugs or
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if you want slightly different results
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this is the old Vector Blur node
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and you can use the Nuke Motion Blur node
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which uses multi sampling here
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so you can adjust a number of samples
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so if you have two low samples you're gonna see
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doubled up edges here
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so make sure to adjust that
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if you're using the vector blur method this doesn't
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make any difference
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shutter time is how
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slow or fast your shutter is
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so the smaller the value this
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less blur you're gonna have
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so if you set it 2.5
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this is equals to
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180 degree shutter angle this is a 360 degree
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shutter angle and this is would be a
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90 degree shutter angle
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the adjust B box
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feature is
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to fix errors on the edges of the bounding box
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so let's create a bounding box here
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I have a bounding box on my roto
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so we're gonna use the copy B box
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feature
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and we're gonna copy the bounding box from our roto
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to our pre multiplied image here
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so now we have a tight bounding box around our
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basketball player and if we
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use our vector edge if we don't
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grow the bounding box
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you might have these kinds of artifacts
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streaks on the edges
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this seems to be an artifact of the vector blur node
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so we need to grow our bounding box a little bit
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we have the option here
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so for example here I'm adding 50 pixels of
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extra size to my bounding box to
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get rid of the artifacts
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so this is there for those types of problems
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lastly we have to mix slider
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just like most nuke nodes we can mix
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our effect with the original
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so that way we can blend between the original and
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final effect so there you go
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that was an overview of PXF Vector Edge Blur
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I hope you've enjoyed it and I'll see you in the next
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video goodbye
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