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In Production
HD Problems

BBC Blows Up Human Body

by David Fox

The BBC is moving on to the really big screen with its first IMAX production. Plus how High Definition video works at IMAX resolution.

The BBC has started production [late 2000] on its first IMAX film, The Human Body, co-produced with the Discovery Channel. The film is based on its award-winning eight hour TV series of the same name, which itself broke new ground using new techniques, many of them from medicine.

When it is released sometime next Autumn [2001], the film will be projected on 15-perf/70mm film, but only some of the material will have been shot on 15/65mm film (the 70mm allows for an audio track), with parts of it shot on HD and other formats.

Director, Peter Georgi, has used macro photography, microscopy, electron microscope shots which have been digitally enhanced, high speed and time lapse, computer graphics, and a thermal imaging camera from the UK's Ministry of Defence, which he claims is the most sensitive temperature sensing camera in the world.

For one sequence of an embryo's hand growing, he scanned four print images at a print bureau (because print works at much higher resolutions than film), before morphing the four together over 40 seconds. This reveals one benefit of IMAX, that you can hold shots for a long time on the large screen, as viewers can't take in the whole screen at one glance. "The screen is so large that it brings a whole new meaning to the imagery we had. It just shows so much detail. It allows viewers to see something they couldn't see otherwise," said Georgi.

Indeed, with the scanning electron microscope, which takes 20 to 30 minutes to capture a single frame, material has to be used sparingly, holding each shot for about 10 seconds - which was possible because it was so detailed. "You can do things more simplistically than 35mm or TV if the subject matter allows it," he said.

"Large format has traditionally been a medium where the camera and technology rule, but we wanted to do things that can't be done with 15/70 cameras," he said. Instead, he used whatever technology gave the best results, including Canon still lenses for macro photography (in one motion control shot, they had to glue the model's fingernails to a mould to ensure he couldn't move while they did a macro shot of his fingerprint), 8-perf 70mm and 5-perf 65mm at 100 frames per second (which an IMAX camera can't do), for high-speed diving and basketball sequences. These will be letterboxed across the screen, as will interviews shot on HD, although where HD was used for other insert shots it won't be shown full screen.

He believes that many IMAX films are impersonal, concentrating on great images of space or landscapes, but "because of our background as documentary makers, we're not scared of humans," he said. He wants to turn the camera inwards and tell us more about ourselves.

Much of what he is doing is experimental, but he feels he has to try it to tell the story properly. He is telling some of the story in panels on the screen, because he's using HD, which is "better than film for shooting interviews, because it has longer run times and stock is cheaper." Having done tests, he says the blown-up 24p (24 frames per second progresively scanned) footage looks "sublime" in the panels. It has limitations, but if used correctly it is "excellent". Within the story, they are following a woman through her pregnancy, and he believes it is vital to interview her as part of that, to hear what she experienced in her own words.

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HD's Big Screen Problems

The introduction of HD has caused a lot of IMAX producers to experiment with video, but the big screen reveals the format's problems more than ever before.

At the VFX 2000 conference in London, Chris Reyna, president of both Imagica USA and the Large Format Cinema Association, showed delegates material shot on Sony's 24p camera (using a Panavision zoom) which had been converted to IMAX. "They look better than they deserve to. The wider shots, the longer shots, definitely display some limitations in contrast and definition, but it's amazing this shot looks as well as it does," he said.

The testing revealed that the 24p camera is particularly sensitive to changes in temperature, which means having to recalibrate regularly, and that back focus is critical.

Imax Corporation is financing large format digital experiments, including using 1080i (interlaced) for very deep underwater work, where large format cameras couldn't fit in the small submersibles and using any film while waiting for something to happen would be expensive. Again, the HD cameras had to be calibrated beforehand in special cooling tanks to ensure they worked correctly at depth.

"Some animal close-ups held fairly well at full screen width, but some were only 70%," said its head of digital technology, Gord Harris. Surprisingly little line structure was evident after de-interlacing, although some interlace artifacts were noticeable at the edges. The small size of the cameras has also made them useful for Steadicam work, for which the large format cameras are too big.

It has also been doing 3D tests, which Harris hopes will hide the defects of shooting in HD. He found that using 1080i for a live 3D test made the results look more realistic - due to the higher frame rate. "HD did well at capturing dim interior details with more depth of field than film, which is extremely useful for 3D," he said.

Imax has also done side-by-side tests between 24p and film with the help of Titanic director, James Cameron, which merely proved just how much sharper and colour-rich 15/65 film is. The HDCAM exhibited some blue/yellow fringing, especially on white objects at the side of the screen - which may have been partly due to the lens quality (using a Canon Cine 9x5.5 zoom) - as well as slight vertical rippling, which he thought could be due to the power supply. Reyna believes that HD filters could have been a cause of problems, especially fringing, as they are not built to the high specification IMAX uses. But "with careful attention to detail, all these things can be improved," said Harris. There was also some compression noise and the results were softer than film. But HDCAM can be run for a long time at low cost compared to film, and users can exaggerate the contrast and colour electronically, which is particularly useful underwater to sharpen the picture, where its extra sensitivity in low-light conditions also helps.

Although shooting on HD tape is cheap, converting the results to 15/70 is not, with colour registration a major issue at such large screen sizes. HD material was up-rezzed to 4k and sharpened using Shake or custom software. "HD is a great step, but eventually we're going to be talking 4k minimum," said Reyna.

The current generation of HDCAM uses small CCDs, as it was rushed in to use to meet the deadline of Star Wars (which is reducing its stock and processing budget from $5 million to just $15,000 in tape costs thanks to HD), but Reyna believes the next generation will use larger chips (possibly 35mm size) which will help solve a number of optical problems, such as back focus. Today's HDCAM is also more difficult to set up than a film camera, because of the need for adjustments and fine tuning the colour on the HD monitor. "There are a lot of variables," said Harris.

"The 24p system is a great evolution. It opens new horizons. It makes some shots possible that maybe were not before," said Kommer Kleijn, Belgian freelance visual effects cinematographer. However, he believes it still has drawbacks for effects work, due to its lower contrast ratio and lack of headroom compared to 35mm film. There is also a limited choice of 24p lenses. Angenieux has recently launched an adaptor for prime lenses, but it is long and heavy. There is also lower resolution than 35mm. "For visual effects, we often prefer to have more resolution than needed, to allow us to play with the image," he said.

He put a 24p camera on a motion control rig and found that it impossible to mount precisely because parts of the body were plastic and he was afraid to clamp it too much. He also criticised the viewfinder for being monochrome and low resolution. It is not easy to change recording speed, and there are fewer choices than film. There is also, currently, a lack of HD screening rooms to view the full resolution of the camera.

Instead, Kleijn has created his own digital camera for frame-by-frame work using an Eastman Kodak 3k digital photography back to which he's added video assist. There is now a 6k back available. Although it has limited contrast, this is a minor problem for studio work. It can work with a much wider range of lenses and uses no data compression, is small and lightweight (ideal for miniature work). He has already shot an animation output to 35mm on it and has tested it for IMAX use. He believes it is better than film, "because we have immediate verification and control of what we're doing," using a high-resolution monitor, and sees digital capture evolving rapidly to become dominate that part of the industry.

© 2000 - 2010

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David Fox