The visual impact of invisible CG-effects (Video below)
First of all watch the end result. The actor is walking towards the camera with a leaf blower and autumn leaves are whirling on the lawn. A garden during the fall. So it appears.
Then watch the original scene (original plate). This whole sequence was shot in the midst of summer on a very hot day. The actor moved around like a ballerina in a sweater. He had a hard time, sweating like a pig in a bacon factory, the colours were pale and the artificial leaves didn’t move in a natural fashion.
Our VFX artist Gregoire went to work. He moved the whole scene into a particle system (Camera tracking, 8 seconds). During the actual shoot, three rotating autumn leaves had been shot separately against a chroma key background, in the backyard. These leaves were inserted in the particle system (18 seconds) and after processing, the leaves fly and whirl towards the camera.
Next you’ll see the same image from the POV of the camera. The particle engine creates the digital effects in a 3D environment (20 seconds).
Subsequently the digitally generated leaves were imported in the original source, and depth of field and motion blur were added to emphasize the suggestion of movement. Our color correction man Barry got going and created a warm, red autumn hue (32 sec.).
At the start you will see the end result: The actor throws up the leaf blower towards the camera hanging over the lawn. Next you’ll see the original shot: The actor pretending to throw up something (42 sec.). The leaf blower, while turning around its axle, had been shot separately against a chroma key background. During the following process, Gregoire retimed and adjusted that swirling, circular movement, so it would progress upwards in a straight line towards the camera. Motion blur was added, suggesting speed. He removed the blue reflections in the leaf blower and applied depth of field. Barry corrected the colors and you can watch the result at 54 seconds.
This sequence is all about erasing a lump on the extreme left side of the image. Watch the original shot at exactly 1 minute and 7 seconds. That’s the sandbag keeping the ground sheet in it’s place during the sliding. The whole sequence was digitalised. The green stripes define the image. The longer the stripe, the faster the movement. With those elements the software calculates, the difference in speed between the background and the foreground, caused by the viewing angle and is able to recognize the depth in the scene.
After that Gregoire generated a point cloud (van 1 min. 16 seconds) in a three dimensional surrounding. The green points define the hedge, the orange dots, the leaves.
The next scene shows the point cloud again from the POV of the camera. Gregoire projected rectangular cards with the actor and the leaves. The second camera moves from left to right and digitally records the scene. At 1 minute and 27 seconds the bulgy sandbag has been replaced by a patch with leaves (projection patch rendered), resulting in a beautiful autumn sliding.
Watch the original shot (1 minute 41 seconds). The actor with a pursed mouth, pretends to be blowing something. A whole lot of thin air. The leaf had been shot separately against a chroma key background with the proper lighting, turning around its axle. In the next sequence you’ll see the camera track in a digital 3D- environment. There we have those green stripes again, defining speed and depth of field.
In the next scene the leaf has been inserted in the 3D-environment and animated manually, so that It whirls and twirls towards the digital camera (1 min 57 seconds). Subsequently the chroma key blue was removed, the colors of the pale yellow leaf were changed into a warm red tint, matching the autumn atmosphere. Watch the end result at 2 min. 6 seconds.