Hi Paul,
There may be a tool that already does what I'm about to describe, but I've done
something like what (I think) you want in the past by cropping to the small
area that you want to analyse then put a sufficient blur on that small area to
smooth it all out, then reformat the small crop up to a full size image. Then,
take a "frameHold" on that image on some reference frame, then divide the one
by the other and you now have a full frame image that you can use to multiply
against anything else to CC it in a way that will mimic the frame by frame
difference of your little sampled area over the course of the shot, so you can
(for example) reproduce flickering, or even remove flickering if you flip the
order of the inputs on the "divide". Anyway, this may give you other ideas too.
Regards,
James Rowell
________________________________
From: Paul Schoen <[email protected]>
To: [email protected]
Sent: Saturday, May 12, 2012 5:26 AM
Subject: [Nuke-users] Analyze Brightness in a Region of Pixels to drive Grade
Node
Hello,
this is my first post to the mailing list, so I hopefully get everything right
in explaining my particular problem:
I have a composite of a Background in which feet are moving over a pavement. As
they move they make shadows on the pavement. The foreground is moving spider
that was filmed on the same pavement later on. Now I want the brightness of my
foreground to change exactly like the shadows of the moving feet change the
brightness of the pavement in the background.
Long time ago, there was a node in Shake called AnalysePixel or something like
that which could read out a certain area of pixel over the whole length of a
shot. With this data one could drive the ColorCorrect-node to automatically
change the the brightness or any other value. I used it once to match a
non-flickering shot to a flickering one (NOT FLICKER REMOVAL!!!).
I found nothing similar in Nuke except the Spotmeter-function in the Viewer.
But I found no hint to read its values and use it in an expression. I need
something to constantly analyze the brightness over a given range of frames in
a certain region of pixels and to drive a Grade or ColorCorrect-Node with this
values via an expression.
Does anyone have any hints on this? I'm using Nuke 6.2v1.
For convenience I uploaded the comp layout:
http://dl.dropbox.com/u/1891745/dpadb_022_lay_v01.mov
Thanks,
Paul Schoen, Vienna
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