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THEORY OF A CGI OBJECT INTERACT WITH LIVE PLATE FOOTAGE


First, I want to tell you briefly what my understanding of good composition is. It is a combination of other images (elements) married together to give the illusion of one complete whole image. As if a camera photographed that image in one go. That all the elements which make the illusion of one whole image fit seamlessly and not at odds with each other. These separate elements could include a mixture of video, film, photographs, computer animation or paintings.

I want to create an image, which will convincingly integrate a CGI object into a real world image. For this exercise I used my coffee mug placed on a coffee table for the live plate. The coffee table is good because it is slightly reflective which makes my job harder. So, this task involves matching lighting, shadows and reflections. I won't go into software specific details her. I have tutorials planned for the tutorial section.

Take notes on the lighting positions on your live set and their colour temperatures. Is it daylight, tungsten, fluorescent or a mixture? This will help you reproduce the lighting interacting with you CGI object match the real lighting on your live shoot. Also, take note of you camera positions including distance and rotation (pan/tilt degrees) from your object. Write down your camera details such as lens type. You set your virtual camera to these settings.

A good 3D program can save out various elements of the computer animation out separately for compositing in another program. You can have a separate sequence of images for the object, shadows, luminosity etc. Why do this? It gives you more control over specific elements. You could make your shadows softer or harder in an imaging program. Batch processing this one element in Photoshop is much quicker than re-rendering a whole scene which could take hours or days. The elements can be finally married together within Adobe After Effects which takes less time than a full re-render.

Now here is the process I used to composite my bikini girl into the video footage of the table.

1. The video footage is loaded as the background plate and the CGI object is the foreground. As you can see, the figure at the moment does not look part of the background image. More like a stick on cut out.


2. Then we rearrange the virtual lighting in the animation program to match the set lighting.


3. The lighting colour has to be altered to match the lighting temperature of the background plate. For the shadow I created a dummy object in the 3D program to represent the table. The image still does not look quite right.


4. Next, using the dummy table object I added reflection to match the real table and softened the shadow.


5. Something is still not quite right. The Hi8 footage has a lot of noise so the CGI object stands out as too crisp and clean. By adding noise/film grain I can improve this.


This concludes the basic theory of adding a CGI object to a live background image. I'll add to this as I learn more.

COMING SEPTEMBER - WORKING WITH BLUE SCREEN