Transcript Document 9655442

Matakuliah
Tahun
: UO666 / DKV Visual FX
: 2009
Supervising a VFX Shoot
Pertemuan 04
Supervising Shoot
BE PREPARED
Before you even reach the set, know your shots inside out, including
know which elements you’ll need to shoot and how they’ll be
photographed. You’ll need to have every unit of photography
covered, and depending on the complexity of the shoot, you may
need assistants for each unit. While one is taking notes, another
could be setting up tracking markers, and a third helping queue
camera moves on the motion control rig. Make sure each assistant
has access to all the equipment they’ll need.
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Supervising Shoot
MEASURE EVERYTHING
You can never collect too much data. Not only will you need to know everything
about the camera settings, you’ll also need to know the camera’s relationship
to the set, positions of the primary lights, the set’s layout and the positions of
the actors. Don’t rely on the Camera Assistant for their camera reports. If they
miss vital lens information on a take, you’ll be the one struggling in
postproduction. Any data you capture will be used in a variety of situations,
from reconstructing precise models of the set in 3D, to matching on-set
lighting or camera positions, or tracking live-action footage. While tape
measures are fi ne for miniature shoots, it’s worth investing in the more
expensive laser range-fi nder for live-action shoots. Also carried by the
Camera Assistant, these are good for measuring distance up to about 150m,
and are accurate to 1cm or less. When you next need to measure the height
of a cathedral ceiling with a tape measure, you’ll wonder why you never made
the investment earlier. (You can buy laser measuring devices from
www.microglobe.co.uk.
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Supervising Shoot
TAKE REFERENCE PHOTOGRAPHS
Shoot everything you can with a good quality digital stills camera
– something capable of taking shots in excess of 4MP, and that
can shoot in RAW format (we recommend digital SLRs that offer
exposure bracketing and interchangeable lenses). You’ll need
general reference stills showing each lighting and camera set-up,
as well as the layout of the set. If there’s any possibility you’ll need
to reconstruct elements of the set in 3D, shoot as many texture
references as you can. However great the temptation is to fi re
off the camera fl ash in low-light conditions, don’t use one on set
without warning everyone fi rst. And, as obvious as it may sound,
never fi re a fl ash while fi lming! (This has reportedly been done.)
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Supervising Shoot
SHOOT HDR PANORAMAS
High Dynamic Range (HDR) images, created from multiple exposures
of the same shot, provide a means to light a 3D scene to match a
real-world reference (for more details, see the tutorial on page 58).
Set up your digital camera on a panorama head and take a series of
stills by rotating the camera around its optical centre. Bracket each
exposure fi ve to seven times, either manually by incrementally
varying the aperture one stop from the previous image, or by using
your camera’s auto exposure bracketing function. Overlap the sets
of images to create a 360-degree panorama. The rotation between
overlapping tiles will depend on the lens and resolution. When the
bracketed images are combined using a tool such as HDR Shop, the
HDR log image has a greater dynamic range than the individual
exposures, affording more defi nition to rendered highlights.
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Supervising Shoot
MAKE USE OF LIGHT PROBES
Grey, chrome and white lighting reference balls are used to set up
3D global illumination in the VFX studio. They’re mostly used
mounted on sticks to avoid unnecessary issues with fi ngerprints,
and should be photographed for each lighting and camera set-up.
Leave the fi lm camera in its set-up for the shot; have the Camera
Assistant shoot a VFX slate marked up with the shot number, lens
and focal length; place the lighting reference ball where the main
action occurs, then run a few frames of fi lm. If the action moves
across a large area, shoot the reference balls in positions that span
its breadth. If the camera set-up is far from the action, and the
reference balls are small, you can request a 4K version of the scan.
If you’re striving for perfection, take care when using balls that
aren’t optically perfect. Secondary refl ections caused by ripples on
the surface are quite diffi cult to fi x.
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Supervising Shoot
MAKE USE OF LIGHT PROBES
Grey, chrome and white lighting reference balls are used to set up
3D global illumination in the VFX studio. They’re mostly used
mounted on sticks to avoid unnecessary issues with fi ngerprints,
and should be photographed for each lighting and camera set-up.
Leave the fi lm camera in its set-up for the shot; have the Camera
Assistant shoot a VFX slate marked up with the shot number, lens
and focal length; place the lighting reference ball where the main
action occurs, then run a few frames of fi lm. If the action moves
across a large area, shoot the reference balls in positions that span
its breadth. If the camera set-up is far from the action, and the
reference balls are small, you can request a 4K version of the scan.
If you’re striving for perfection, take care when using balls that
aren’t optically perfect. Secondary refl ections caused by ripples on
the surface are quite diffi cult to fi x.
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Type Of Light Probes
THE GREY BALL
Images of the grey ball are used to fi gure out the direction of the
keylight when setting up a 3D scene for global illumination. The
18 per cent grey tone appears neutral to the human eye, and is
equivalent to the average Caucasian skin tone. There’s no need to
buy a special-purpose visual effects grey ball – any medium-size
spherical, wooden or Styrofoam ball, available from a crafts shop,
will serve the purpose. First, coat the ball with a white base-paint,
then paint with an 18 per cent grey, matching the swatch to a grey
reference card (this can be purchased from www.amazon.com).
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Type Of Light Probes
THE CHROME BALL
As an alternative to shooting a HDR panorama of the set, the
chrome ball (or ‘mirror ball’), provides the necessary data needed
for setting up 3D refl ection environments. To get full, complete
coverage of the set, you’ll need to shoot the ball twice, from
opposite sides, so that each hemisphere is represented. Specialpurpose
chrome balls come in a range of sizes, so choose the sizes
you’ll need according to your camera set-ups and location. If there’s
only time to shoot one angle, photograph it matching the fi lm
camera’s aperture for equal depth of fi eld, and from as far away as
possible with a fairly small ball (6-8cm). Calibrate your chrome ball
for colour by placing a white card visible in both the frame and the
refl ection within the chrome bal
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Type Of Light Probes
THE WHITE BALL
Many VFX supervisors just shoot grey and chrome balls. Shooting a
white lighting reference ball provides additional information about
multicoloured lights.
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