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Jellis100
12-28-2009, 12:01 PM
Hey everyone,

I'm a 3D hobby-ist, completely self taught with Maya and Realflow.......I'm trying to composite my models onto a real life video of the step outside my door, just a simple chrome ball or a ball on fire to learn the technique but it's driving me absolutely mad.

The software I'm using is PFTrack-Maya 2009 Unlimited-Adobe Master Collection CS4.........I've got the camera tracking, the fire rendered against a black background (See photo) All I want to do is the equivalent of 'Background select' in Photoshop and delete the black bits, not really bothered how realistic it looks as I can then play around with it and take it away from there. I can use both After Effects and Premiere Pro, I'm just not sure how to do this.

Many thanks in advance,

Jack.

http://www.perthstreetbikes.com/73387/firei.jpg

danielHinton
12-29-2009, 10:21 AM
Hi Jack,

1. My suggestion is to pick up The Art and Science of Digital Compositing (http://www.digitalcompositing.com/) as it will school you better than I can explain..

2. There's no easy way to do this. Your goal is to "sell the shot" - make something unbelievable look like it's happening, right? Consider the following (by no means exhaustive) list:

- lighting - is the object going to cast shadows/illuminate the background

- colour - is the rendered object going to match the RGB and luminance values of the
background

- reflections - is the rendered object going to have any obvious reflective surfaces - if so you're going to need to get a sample reflection map from the shot so that the object reflects the background

- any other basic interactions between the object and the background - ie are bits falling off the object and onto the ground?

- grain/depth of field/ field of view/lens inconsistencies - basically dirty up the rendered footage to match the video you have. If you have DV then there will be plenty of noise in the green channel of your footage. What you're aiming to do here is make your object look like it's been shot with the same equipment as your background.

I'm certain that if you've rendered the shot correctly, Maya will produce a matte or alpha channel for the object, this enables you to cut out the object and place it in the foreground of your video. After effects can use this matte channel as a track matte for your foreground object.

Finally - you lucky bugger! You must be pretty rich to be able to afford all that software for your hobby..

pingking
12-30-2009, 06:52 AM
for your very simple example. just render from maya the fire with alpha channel, put your rendering on top of your real footage in AE and your done

Midgardsormr
12-30-2009, 05:01 PM
Pingking has described the correct way to do this, however I'd like to take the opportunity to suggest that you never try to "delete" the black, whether in AE or Photoshop. Trying to do that will never work, especially with something translucent like a flame. Instead, explore the blend modes. The additive modes will work best for fire on black.

As regards proper workflow from Maya to After Effects, render to a format that permits an alpha, like a tiff or iff sequence (iff is Maya's native format; AE and PS can both read it just fine) and be sure you are rendering an alpha. When you bring the element into After Effects, make sure it interprets the alpha as premultiplied with black (assuming you didn't change the camera's environment color).

Jellis100
12-30-2009, 05:28 PM
Hi Daniel, Thanks for your reply - I shall be taking all those into account in the future, at the moment I'm just trying to get the shot composed and itwas proving to be extremely difficult and frustrating. I may have some more questions for you in the future if you don't mind! :applause:

Pingking and Mid - I tried rendering it as a Tiff and I'm pleased to say it worked! Albeit a bit weirdly but it's worked none the less, now I'll just fiddle with it and see what does what.

To render in Alpha, do I have to tick the box under 'Renderable Cameras' that says 'Alpha Chanel (Mask)' ?

Thanks again! :thumbsup:

Take care and have a happy new year, Jack. :)

bobzilla
12-30-2009, 06:16 PM
In Photoshop (don't know if AE has something like this), in Layer Styles (click the fx button at the bottom of the Layers palette, or double-click in the empty space on the layer in the Layers palette), it will come up with Blending Options highlighted. Go to the Blend If area and play with the sliders in This Layer. You can hold down Option (or ALT on PC) and split the sliders. Then move them around to adjust how much of the dark or light shows through.

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12-30-2009, 06:16 PM
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