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TUTORIALS | VFX supervision tips

054 | 3D WORLD3D WORLD July 2006

On-set reference material is the key to realistic visual effects. Discover what data to record – and how to record it – with this complete set of expert tips

Supervising a VFX shoot TIPS & TRICKSTIPS & TRICKS

Our experts this issue…

● The key role of the on-set VFX Supervisor is to gather all the data needed to complete the job. This month, four supervisors share their hard-earned expertise to provide a full checklist

hether working on a major feature, where camera data is collected by on-set wranglers, or on a smaller production, where you alone will collect all the data you’ll need, knowing

what to record on set is essential to the role of the Visual Effects Supervisor. Without the right information, you’ll waste days in the studio later trying to track shots, match on-set lighting, or replicate textures.

All too often, something unexpected happens

mid-shot, and it’s at just those times that the VFX team are

called in to rectify the problem. If you’ve documented what

went wrong, you’ll understand what it is that you need to

fi x, and how you can do so. And this is just the beginning.

How many times has a ‘simple 2D comp’ escalated into full-on

3D in post, when the director decides that the shot is “missing

a little something?”

Preparation for a VFX shoot starts in early preproduction,

before you’re anywhere near the set. You will already have

gone through the storyboards with the director, rendered

up previsualisations, and planned which elements to shoot

separately. You’ll have a good idea of each camera and lighting

set-up and, on a professional shoot, may have arranged for a

motion control rig to capture multiple elements. You’ll also know

which shots need to be tracked, in 2D or in 3D. Miniature shoots

come with their own challenges, but without the actors on set,

there’s more opportunity to get involved in supervisory work.

In this article, we set out 15 essential tips on how to record

all the necessary data, as provided by our international team

of experts. We will conclude with a checklist of everything

you need to bring along to the shoot, while further reference

material, including examples of lens grids and camera report

sheets you can copy for yourself, can be found on the CD.

WCRISTIN PESCOSOLIDO

Cristin joined Meteor Studios as a VFX Supervisor in 2004,

where she’s supervised Catwoman and Elektra.www.meteorstudios.com

NICOLAS AITHADINicolas is a VFX Supervisor at the Moving Picture

Company, currently supervising X-Men: The Last Stand.www.moving-picture.com

OYSTEIN LARSENOystein is VFX Supervisor at Toxic in Norway. Former credits

include the Matrix sequels, Catwoman and The Ladykillers.www.toxic.no/toxic.html

FRANK WEGERHOFF Frank is an independent VFX Supervisor, with credits including Das

Wunder von Bern. He’s working on Blood and [email protected]

TDW79.t_tips 054TDW79.t_tips 054 10/5/06 4:46:39 pm10/5/06 4:46:39 pm

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BE PREPAREDBefore 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.

OBSERVE ON-SET ETIQUETTEBe friendly, know who’s who, and don’t pester the wrong people

for information they don’t have. Your allies will be the Camera

Assistant, who will provide you with much of the camera information

you’ll require, and the Script Continuity Supervisor, who will also be

recording camera data. Remember, there’s no reason why the crew

should understand visual effects jargon, so talk in a language they

understand. Explaining what you’re doing, and why you’re doing it,

is a good way to build productive relationships.

BE FAST, AND BE INVISIBLEFilm shoots are extremely expensive and, unfortunately, the VFX

crew (however unfairly) have the reputation of being the ones to

hold up the shoot. Since time is money, work as fast as you can. Let

the shoot run smoothly as you gather data from behind the scenes.

ASSIST THE DIRECTORDo whatever you can to help the Director get the images he needs.

You’ll need to help in creative decision making, as well as ensure

you’ve got the visual effects shots covered technically. Set-ups

you’ve proposed in preproduction may not work out as planned,

so you’ll need to think on your feet. A background in photography

helps, as does a good eye for composition. If your knowledge of

cinematography is sketchy, now’s the time to do some homework.

Start by purchasing the American Cinematographer Manual edited

by Rod Ryan (1993, ASC Holding Corporation, ISBN 0935578110).

MEASURE EVERYTHINGYou 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.)

SHOOT LENS GRIDSUnless you’re trusted by the Director of Photography, and

experienced enough to operate the fi lm camera yourself, ask the

Camera Assistant to shoot a lens grid, full frame, for each lens. (An

example can be seen at the top of this page, and is also included on

the CD.) Lens grids are a way of measuring the barrelling distortion

of any particular lens, and are used back in the visual effects offi ce

to ‘undistort’ the scans when compositing. Shooting a lens grid is

particularly important for wide-angle lenses with greater distortion.

● Lens distortion grids can be made by mounting a printed A3 grid on polyboard. The cross is lined up with the crosshairs in the viewfi nder

● Shoot a visual effects slate before HDR or photogrammetry stills. It can be as simple as handwritten notes on paper

VFX supervision tips | TUTORIALS

IN FOCUS | The camera report sheet

The camera report sheet is the fi rst place you’ll go when looking for information about a shot. Always record all of the information from the slate, as it will be removed in the rough cut. In the sheet shown on the right (a full-size version can be found on the CD for you to adapt to your own projects), 28 is the scene number (from the shooting script); 001 refers to the fi rst FX sequence; and 005 means this is the fi fth shot in that sequence.The sheet should also contain the following information about the set up of the shot:

• Shot description: a brief aide memoire when reviewing your notes in the offi ce

• Lens information: particularly for zoom lenses. Include any serial numbers

• Frames per second: was the shot normal, high speed or slow motion?

• Camera roll number: found on the mag• Any fi lters placed on the camera lens• Height and focus distance of the camera:

measured from the fi lm-back• Tilt of the camera: measured with an

inclinometer placed on the base plate of

the camera. Some camera heads have a scale to show this, but it’s rarely accurate

• Shoot dates: on longer shoots, fi ling reports by date, unit and location is vital

July 2006 3D WORLD3D WORLD | 055


TUTORIALS | VFX supervision tips

Slate the lens grid with a note of its make, model and focal length.

There should be a ‘grid warping’ tool in your compositing software

that enables you to ‘undistort’ the plate using the distortion you’ve

captured in the lens grid. All you have to do is create the same

number of lines as your lens grid and pin its points to match, before

fi nally applying the warp effect.

TAKE REFERENCE PHOTOGRAPHSShoot 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.)

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.

ALLOW FOR SET RECONSTRUCTIONHDR images are used in 2.5D reconstructions, or photogrammetry,

where photographs of the set are re-projected back onto 3D

geometry, then rendered with a virtual camera. Shoot the set from

a similar angle to your 3D virtual camera, matching the lens. You’ll

need to photograph at least six or seven images, which should have

overlapping features visible in at least a few of the images. If you

don’t have the time to work with HDR images, single exposures will

do. If your virtual camera moves signifi cantly through the scene, you

may need to shoot image tiles from key points along its move.

MAKE USE OF LIGHT PROBESGrey, 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.

● 8cm diameter Christmas tree baubles make excellent light probes on a miniature shoot. To create the grey ball, spray the bauble with an 18 per cent grey automotive primer

IN FOCUS | Drawing up a plan

If you’re shooting on a stage, ask the art department for a copy of its fl oor plan. Out on location, survey the site as accurately as possible, and sketch out both plans and elevations. You’ll need detailed measurements of anything you may need to reconstruct in 3D. Additionally, for each lighting set-up, mark the locations of the primary lights on the plan. It’s always helpful when you’re back in the offi ce, matching the scene in 3D, and trying to determine where exactly to put the keylight. Sketches are also vital in describing camera tracks or dollies on the camera report.

● It pays dividends to have a notebook handy for all manner of data collection – in this instance, for noting on-set camera and light positions

056 | 3D WORLD3D WORLD July 2006


IN FOCUS | The supervisor’s survival kit

Here’s your complete checklist of what you’ll need to bring with you to the set. It’s a mixed bag of handy gadgets and absolute necessities. Some things may seem superfl uous, but you’ll be a long way from the offi ce, and you’ll need to be prepared for all the situations you’ve planned for. One of your best investments will be a good quality digital camera, capable of shooting high-resolution reference stills and HDR images. Make sure it’s able to shoot roll images in their RAW, uncompressed format. A laser pointer is also handy in quickly pointing out a problem in-shot, particularly if you’re with a foreign crew and don’t speak the same language.

• Digital stills camera, various lenses, spare batteries, memory cards and a battery charger

• Tripod and lighting fl ag stands• Tracking markers• Light meter

• Printed templates for shoot notes• Visual effects slates and a clipboard• Pocket-size notebook or PDA• Sharpies, pens and pencils• Gaffer tape and camera tape (you never know

what you might need to fi x)• Lighting reference balls: grey, chrome and

possibly white balls• A laptop with your compositing software

of choice• Lens grids• Tape measure and a laser range fi nder• Grey glass and various coloured fi lters• Video cameras on a miniature shoot, spare

batteries and tapes • Leatherman and scissors• An LED torch• A laser pointer• An inclinometer (to measure camera tilt)• A spirit level• The American Cinematographer Manual

THE GREY BALLImages 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).

THE CHROME BALLAs 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. Special-

purpose 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 ball.

THE WHITE BALLMany VFX supervisors just shoot grey and chrome balls. Shooting a

white lighting reference ball provides additional information about

multicoloured lights.

SET UP WITNESS CAMERASOn a miniature shoot, bring or borrow as many video cameras as you

can. Set up a video camera pointing at the lens of each fi lm camera,

so you can shoot and record the speed of any zooms, particularly

when they’re not constant. It’s also good to set up a video camera

encompassing the whole of the working area on the stage. If

anything unexpected happens mid-shot, you’ll have it recorded on

tape for later reference. ●

VFX supervision tips | TUTORIALS

● Oystein Larsen makes the fi nal checks to one of the cameras in the UCAP rig, capturing Halle Berry’s facial performance for Catwoman. A good example of the complexity of a professional VFX shoot

● Reference photos are vital. Here, they show the layout of

the miniature set for the subway crash sequence on

Final Destination 3

July 2006 3D WORLD3D WORLD | 057


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