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Blood work: Attaching a PNG to a roto shape/mask
Blood work: Attaching a PNG to a roto shape/mask
by Ward DeMartino on Nov 26, 2019 at 7:47:57 pm

Hey all,
Newbie-ish here....this is probably something relatively simple, but I'm racking my brain over here.
I am working on a vfx shot where I need to paint blood onto a doctor's latex gloves (they didn't do this in production...oof). There is SO much movement, closeups, etc etc. And the clip is long. They didn't use tracking markers or anything either on the white latex gloves. I tried to track areas in Mocha to basically attach a PNG of a bloody brush that I made in Photoshop so that I could create some splotches on the gloves, but it was really too hard to get a good track without spending the next few years of my life manually getting it right.....
So...I decided to roto the doctor's fingertips (where the blood mostly needs to be) and to change the levels to color them like blood, changed the opacity, etc...

1) But is there a way that I can just use the roto masks and actually just attach my blood brush splotch PNGs to them? The brushes look a lot better than just coloring the rotos.
2) If I just use my colored rotos as the bloody areas, is there a way to apply a gradient only to the roto shape? I feel like there is but I can't figure it out.
3) Am I overlooking a much easier way to create the illusion of blood on white latex gloves that are moving around a lot?
4) What would you all recommend as the best way to give a shiny texture to the roto shapes? I have been trying the glass effect, but I'd love to get a nice shine on the rotos (maybe it's not possible).

Thank you in advance for any and all input on this. A bit lost here......

Re: Blood work: Attaching a PNG to a roto shape/mask
by Graham Quince on Nov 30, 2019 at 10:52:04 am

Oof. That’s difficult and kudos for not wanting to just colouring the roto.

Taking 4) first, try adding static noise to a duplicated layer of the fingers. Corridor Crew on Youtube recently used this technique to improve the Scorpion King’s appearance in the Mummy Returns.

3). I think you either colour the fingers or apply textures and I you can’t track then you might be stuck. One option you could try, is using the fingers as a displacement map for a blood texture. It wouldn’t track the texture into the fingers, but it would give a sense of movement and wrapping around the gloves.

2). Fractal noise can add texture to colour, if you go that way and see 3)

1). Tracking something like this feels really difficult, but you could try AE’s mask tracking and see you get anywhere. Failing that there are pay-for plugins like Red Giant’s King Pin tracker that might help. I’ve not used it, but it looks pretty good. - Free FX for amateur films - FX blog

Re: Blood work: Attaching a PNG to a roto shape/mask
by Max Haller on Dec 2, 2019 at 6:38:41 pm

that sounds like a nightmare. If you roto'd the fingertips using masks (vs shape layers as alpha mattes) you can use the feather tool to customize the feathering on the masks. So you could use that to keep the end of the fingertips sharp, while making the part closer to the palm feathered out. You'll find the feather tool as a feather icon if you hold down on the pen tool.