View Full Version : Fish in a bag

07 July 2003, 05:11 PM

I have a question dealing with a digital fish being composited into a plastic bag filled with water.

I have an idea on an approach though I'd like to get some other opinions on how you guys would tackle such a problem.

Any response would be great.



07 July 2003, 06:42 PM
Reference man... Go buy a goldfish for 3 bucks, and bring it into work... Set it on your desk (preferably not above anything electrical, 'cause that would be bad) and look at it.

I think you'll find that a plastic bag doesn't really refract much, so maybe just a tiny bit of blur and displacement will be all you need.

07 July 2003, 03:37 AM
Thanks for the response Jason.

I've broken down everything I can think of that I'll be requiring its just a matter of how to get those layers that I'll require.

Oh and before I go any further explaining I'll list the software I'm using. For the Fish I could use either Maya 5 or MAX 5. For the compositing software I've got the choice of Combustion 2 & AfterEffects.

THE PROBLEM ---> Splitting what you see through the bag and the reflection on and within the bag.

We havn't shot the live action yet and will be doing preproduction in a few months time so I'm just preparing for it all.

I was thinking for the reflections on the bag, the bag could be filled with a black opaque liquid whatever that could be, to be used for the outer reflections.

For the other layers such as what you see through the bag I'm not exactly sure if the live action will be shot with a lock down as the briefing for this has been unbelievably brief and rushed. Though if locked down was the case I was thinking you could shoot a plate shot with and without the bag.

The last few layers that I think will be important for giving depth, would be the inner reflections and the displacement and subtle distortion the bag has over the live action. I'm not sure about how I would go about getting the inner reflections. I keep thinking by just shooting a bag filled with water, both the inner and outer reflections could be extracted by using levels to over expose certain features. Then allowing it posibble to removes sections that are not requires and blending all the layers together.

Finally (I think & Hope) for the displacement. I was thinking of modelling the basic form of the bag and tracking that to the live footage depending whether its moving, though hopefully not.

I think thats about it. I did some test work in the early hours of this morning on just a still shot. Just blending a model within a helicopters cockbit. I did the most simplest method to just take a look and get started on the problem solving Which the problem after duplicating the cockpit layer, lowering the opacity and placing it over the model was, the model seems to be transparent due to the transparent cockpit layer on top of it.

This is where I start thinking if you break down the lights and darks of the cockpit using levels you could utilise both inner and outer reflections.

I don't know, back to testing. If anyone could explain their approach that would be priceless!



07 July 2003, 03:57 AM
yeah, it all depends on the footage. If it's a close up, yeah, you're going to need all the layers. If it's further off, just the fish would do.

If you have access to a video camera, shoot some tests yourself.

Luma keying the reflection in and out of the bag might not be as easy as all that, but shoot as much reference as you can on the shoot.

A bag of black paint will get you reflections (mercury would be better, but i have no idea how you would get a bag of mercury!) , a bag of milk will get you lighting information and color temp. Reflections inside the bag might just be reference footage, for you to duplicate in CG. Perhaps modelling a CG bag, and then use it as a ref gen element.

It might just be best to do the whole thing in CG, or at least the majority of it. What if you used mostly CG, and then just roto'd in some water surface element shot on set? The bag, fish, and all reflections etc could be CG, and then you just add a bit of splashy water as a surface in the bag as a real element... Might be easiest.

Best of luck.

07 July 2003, 10:02 AM
and after you have finished your work you can still eat the goldfish :D

07 July 2003, 01:15 PM
Do you know what is going on in the shot as there would be better ways of doing things for different things.

-If there is no interaction with the back or only from the fish then it might be better to go all CG then you don't have to worrie to much about intergrating the fish in as it could all be done in 3D.

For that you could use a refelction map. Using a crome ball on set. for the displacement then just displace the background plate.

Only thing would be the water might be a bit tricky depending on how much the fish is moving.

-If you want to go for a real bag, ie. for interaction then the black liquid sounds good, with a back ground plate for behind it. With the diplace ment of the back ground you don't have to worrie to much about it as long as its worped in someway then it'll look ok. people wouldn't be able to work out if its a phisically correct image.

for the inner reflection might be a bit tricky as you would have to have a CG counter part and track it. also to get some good refractions of the fish.

post some of ur tests might be easier to help.

Good luck

-Matt :surprised

07 July 2003, 03:55 PM
Thanks for your input Jayk2k and Harrad!

I've started modelling up the fish for some preproduction tests. Still havn't heard too much about the integration of the shots(Finding out late this week) so I'm trying to cover all areas as I'm new to all this. This is the next level for me, so all your input it great.

I've got some questions to ask about this whole process, some things I've always wondered about.

First up the Chrome ball used to get the reflections as Harrad mensioned. I've seen some behind the scenes shots of minature sets used for compositing, and the Chrome ball sitting within the shot and always wondered about its use, and what you do with it. As in how do you apply the reflection information of the Chrome ball and apply that into the compositing stages. I've got a brief understanding, but a walk through would clear things up.

The other thing is the white foam ball. How I'm thinking that it helps is to do with lighting set ups within the 3D application. So firstly camera matching the shot then trying to replicate the lighting in the shot using the ball as the guide. Correct? Is that all its used for?

All this is all new territory to me so starting from the basics to trying and get a firm grip on all this. Fortunately enough I've recently got the assistance of a visual effects company here, who will mentor me through the production. Which will be invaluable.

I'm just trying to get some understanding of the process. Not as much as putting it all together but more so on the shoot, what I should be recording and just a check list of things I should do and how I should go about them.

If anyone could give a guide as to how to execute such a procedure that would be fantastic. Doesn't have to be in depth, anything would help!



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