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Using Primatte in Nuke
Here’s another list of tips for using Primatte in Nuke.
-Instead of using sliders to adjust the matte, use the “Operation” pull-down and key out the areas on each section, starting with “Select BG Colour” and working your way down the list.
-BG Colour: Get a single pixel key on the main greenscreen for the overall key-BG Noise: Do box selection to get rid of all the BG noise around the character. It’s helpful to bump up the gamma to really see what’s going on here.
-FG Noise: You want to select areas within the character you are trying to keep in the FG, so you get a solid core. Slam the viewer gamma down to make sure there aren’t any holes in the core.
-Spill Sponge: Control-Click select along any edges of FG meeting the BG to get rid of the spill.
-Spill(-): Use to remove spill within the core. This will not effect the alpha. ONLY use single pixel selections, no drag selections or it will mess up the colour space.
-Spill(+): Puts the spill back into the image. This works well if there are discoloured pixels from using Spill(-). Select only the discoloured pixels.
-Matte Sponge: Used to define areas that are to be 100% opaque. Which to alpha channel when using. Click and drag sections in the core to make it 100% opaque.
-Matte(+): Use to increase the matte core, good for wispy hair. Again, this is for finer adjustments only so only do single pixel selections.
-Matte(-): Good for softening the edges in a motion blur so the alpha isn’t so sharp. Drag+click is ok for this-Restore Detail: Pops detail back into the comp that was already completely transparent.
-Detail(+): Like “Restore Detail” only much more finer adjustments.
-Detail(-): Pulls detail very finely out of the comp. Good to crank up the gamma when using this.
-Fine Tuning Sliders: Whatever colour you pick, the sliders will operate on that colour.
-L-Poly(Large Poly)Spill: Only affects the spill, but not affecting the matte.
-M-Poly(Middle Poly)Trans: Affects the middle core of the matte will move in and out.
-S-Poly(Small Poly)Detail: This effects the outside of the matte. This affects the boundary edge detail of the matte.
Primatte Autocompute Button: Makes a quick matte for you based on math.
-Auto BG factor: Affects where the matte meets the black. Adds or removes detail. You have to press the autocompute botton again before it takes effect.
-Auto FG factor: Moves the core of the matte in and out from the edge.-Viewer checkbox: Shows you visually the polygone that is your key
Spill Process: replace with:
-Compliment: Replaces greens spill with magenta, bluescreen with yellow, etc -Solid colour: Use any colour you want to replace with -defoucused background: uses the BG as the spill and it’s blurred
Garbage matte: Make a roto node under the FG footage. Select output of roto to “Alpha” only. -In Primatte, check of “use mask” and select “rbga.alpha” as the input
-You probably want to use the “premultiplyed” option for this step
-You have to colour correct outside of Primatte. Make a grade node below Primatte.
-Make sure to check the (un)premultiplyed by “rgba.alpha” on the Grade Node
-To add the BG, add a merge node to the Grade Node and plug the BG into it as well
Basic tips on using Keylight in Nuke
-Tuning adjusts the spread of the shadows and midtones, and highlights.-For the tuning tab, uses 0.18 for the midtones which works better with Nuke’s linear lightspace than the default 0.5
Used with serious discoloured elements.
-Alpha Bias would work if there is too much red in the Key, pull the colour from the FG element
-Despill Bias: Sample the source image, not the keyed image. Fixes hair spill issues, on the edges.
-Get a core matte from the FG element, then set it to “Intermediate Result” for export of Keylight node.
-Connect this as the Source of the other Keylight which is plugged into the BG-Key it and then select “Combined Matte”
-On the “Inside Mask” tab, enable the Inside Mask from the source alpha
-Use the “Inside Replace Colour” to fix any alpha issues when viewing the “Status” level
Forground colour correction:
-Add a Grade node after Keylight
-Make sure to select premult by rbga.alpha channel
-Add a merge node and connect it to the BG
-Now you can colour correct outside of Keylight prior to the composite.