CG blood?

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Old 08 August 2013   #1
CG blood?

Hi,

I'm practising scenes with actors and trying to make it as close to the real thing as possible. Assume I'm not able to do this as a special effect.

There is a scene where someone slits their wrist and blood runs down their arm. I haven't shot this scene yet and am wondering how would I do this using CG blood? What would be the process?


Thanks for any help,
Jules
 
Old 08 August 2013   #2
Very rough workflow:
Recreate a geometry for the arm, recreate the movement of the arm, create a fluid sim, shade/light/render the fluid sim.
If you are using digital double of the arm, you'll need to shade/light/render that too.

Try to do it as a practical effect, there's a lot of ways to make it believable with clever editing.
 
Old 08 August 2013   #3
Originally Posted by scrimski: Try to do it as a practical effect, there's a lot of ways to make it believable with clever editing.

Quoted for agreement.
If you haven't shot it yet.
All it takes is some pretty dramatic arm movement and you will spend hours, days, or weeks trying to make the sim track the arm in a realistic yet artistically appealing manor.
If this is something you want to study go for it. If you 'just' need some blood-make it practical.
What software do you have access too? Its quite possible you'd need to buy something (plug-in or software) you don't already own to do good liquid dynamics...

Last edited by circusboy : 08 August 2013 at 02:49 PM.
 
Old 08 August 2013   #4
Originally Posted by circusboy: Quoted for agreement.
If you haven't shot it yet.
All it takes is some pretty dramatic arm movement and you will spend hours, days, or weeks trying to make the sim track the arm in a realistic yet artistically appealing manor.
If this is something you want to study go for it. If you 'just' need some blood-make it practical.
What software do you have access too? Its quite possible you'd need to buy something (plug-in or software) you don't already own to do good liquid dynamics...

It's for previz of a scene really and for possible promotional use in a trailer etc.

Shot 1:
Close-up of one forearm and a knife (rubber) cuts down the forearm and blood seeps out.

Shot 2:
Actor has both arms resting on a table top leaking two blood pools that spread out.

In both cases I guess the actor can keep the arms as still as possible and the camera fixed on a tripod. Nice to be good quality as we are shooting on a cinema camera under studio lights.

Everything to be done in Maya. Do recommend any plugins if it can help.


Thanks,
Jules
 
Old 08 August 2013   #5
Practical blood isn't that hard or expensive to do and since you are shooting it would be an important part of your learning process on an indie set to deal with it.
By the time you compromise the shot to make it easier to do it in CG you would have compromised it less for better results if you had done so to deal with practical.

Corn syrup with food colouring, a thick needle syringe and packing satchels, or pouring from a vial if the source is off-screen, is all you need.

You can then augment it with CG drips and rivulets once they are off arm if you want to, but you won't have to go through the rather time consuming process of tracking geometry for the fluid sim running down the arm.

There are plenty good tutorials on the web on how to do fake blood on the cheap given gore and slash are so common in the indie scene. I would strongly recommend you at least take a peek and give it a shot (no pun intended).
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Old 08 August 2013   #6
Simple solution is to go practical if at all possible.
There are a lot of recipes for fake practical blood.
Most just involve Karyo (clear Corn Syrup), water and food coloring.
There is also Red velvet Cake mix and water.
If you really want to go all out rig up a Surgical tube to a syringe or pump.
Then attach that to the back side of a stage knife, one that's been dulled so it won't harm anyone. Place the pump in the actors hand and when he runs it across his wrist he pumps the fake blood out. With a bit of editing and camera placement it should work ok.
 
Old 08 August 2013   #7
Youtube has a ton of practical fx things. I can't testify to their efficacy, but if you are asking about doing it all CG, then a little so-so practical, plus a little cg might be the right ticket.

I would rather roto/erase a small flesh colored tube spouting blood than add flowing blood elements under most circumstances I can think of.

Considering you are asking this question, it is safe to assume that it isn't an over the top slasher flick. Rewatch Resevoir Dog's ear scene or Heat's Natalie Portman suicide scene. Do you really need or want to show blood spurting from an open wound.

ooopp...I just read your breakdowns.

Shot 1, blood comes out of a trick knife. Add the cut with cg (a red dark streak *edit) after the knife moves...the more blood that pours out of that knife, the less cut to add. Maybe some gum arabic wound started that is obscured by the knife.

Shot 2, gum arabic wound plus lots of "thinner" blood, with occasional "heavy" Blood streaks. Lots of Blood on the arm. Tube under arm emits blood to form pool. In comp, wiggle/morph/displace, ever so slightly those heavy streaks, to give the idea that it is flowing. If you light the heavy streaks to catch more of a spec highlight, all the better, or add the spec highlights and massage/wiggle them to indicate the flow. By wiggle/morph/displace I mean like he does to the cloud in this: http://www.videocopilot.net/tutorial/animating_a_still/ I think less would be more in your case.

Honestly...I like the Reservoir Dogs ear philosophy better than either of my suggestions.

Also...have you ever donated blood?...it is insane how much blood you can give, eat a cookie and leave....like...you could paint a good sized wall with the amount they take. I bring this up because honestly, cutting a wrist and watching it on a table isn't a real suicide attempt...that is cry-for-help-baloney. Natalie Portman's character in Heat is not asking for help...there are gruesome details to the little girl's process of attempting suicide that are part of a really well told story there.

Last edited by Stankluv : 08 August 2013 at 04:35 AM.
 
Old 08 August 2013   #8
Very good advice given by the above and others. I was going to ask to see storyboard because any VFX solution is dependent on chosen angle.

But yeah, I do agree, trying it as a Special Effect first is probably a good idea for something like blood.
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Old 08 August 2013   #9
It's also a lot more fun.
Be warned it will make a sticky mess, but nothing you can't easily work around with the simplest of split shot on a static camera if the location can't be messed up.
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Old 08 August 2013   #10
Originally Posted by ThE_JacO: It's also a lot more fun.
Be warned it will make a sticky mess, but nothing you can't easily work around with the simplest of split shot on a static camera if the location can't be messed up.


My personal experience with Special Effects was that I had to play the Devil in a stageplay... And, in the Philippines there's a tendency to just "jump on the first thing that comes to mind".

So.... without research..... but identifying the need that I should have RED skin, they decided to coat my body in LIPSTICK.

Somehow I think anything these guys do for their little slashed wrist experiment cannot get as sticky or as messy as what happened to me.
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Old 08 August 2013   #11
I approach anything practical with fear and apprehension the same way I approach putting up a shelf. I'm much better with computers.

In the real situation you'd pay for someone who already has the skills to do blood special effects? As the film is not really that blood based, I don't feel I'm missing out if I don't learn how to do it.

However I'm tempted to have ago with my own arm for the close up (showing just the forearm) with the special effect (some good instructions in this thread). Then use AE for the wide shot. I assume AE can do this sort of thing?

Cheers,
Jules


P.S. The cut is not across the wrist. It's going down the forearm along the vein, and you die from that kind of wound in real life quite quickly.
 
Old 08 August 2013   #12
Originally Posted by Jules123: I approach anything practical with fear and apprehension the same way I approach putting up a shelf. I'm much better with computers.

In the real situation you'd pay for someone who already has the skills to do blood special effects? As the film is not really that blood based, I don't feel I'm missing out if I don't learn how to do it.

However I'm tempted to have ago with my own arm for the close up (showing just the forearm) with the special effect (some good instructions in this thread). Then use AE for the wide shot. I assume AE can do this sort of thing?

Cheers,
Jules


P.S. The cut is not across the wrist. It's going down the forearm along the vein, and you die from that kind of wound in real life quite quickly.


Well Jules... it might be nice to know that the original ILM team came from people who did architectural dioramas and toys and other things.... Everybody starts from not knowing.

I am not much of a Special Effects person (as I've narrated, I am more a Special Effects victim hehehe). But to be fair the descriptions for the blood FX stated above sound like fun. Unless you have particular issues about messes/cleaning up....

The cut you described also sounds like the famous "Forearm Cut" scene from "The Terminator". I'm sure there's data on that also online.
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Old 08 August 2013   #13
Here's one technique:

Shoot trickling syrup on a white piece of cardboard (dilute with water to get good consistency). Then just grade and comp it into the shot. Depending on the shot, you might need to track the arm and project the effect on to a geo, or warp it a bit to match the contours.

Of course, this only works if the shot isn't a close up. For real close stuff, where you need to see the depth of the blood flow with spec hits and such to sell the shot, you probably have to go 3D. Fluid sims are the only way I can think of. Unless you plan your shoot really carefully so you can match lighting and volume of the live action plate with your separately shot blood effect work. Track and match them together, with maybe some careful massaging in comp. But at that point, you might as well do it as a practical gag.
 
Old 08 August 2013   #14
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