Most people probably still remember the incredible special effects in Hollywood movies such as Jurassic Park, Independence Day and Twister. But movie makers may sometimes employ computer technology in such a subtle way that audiences are unaware of it. The Soong Sisters from Hong Kong director Mabel Cheung Yuen-ting is one example. The film is about the lives of the Soong sisters - Ailing, Chingling and Meiling - who played a role in shaping recent Chinese history. Unlike science fiction, this historical story seems an unlikely candidate for advanced technology, but in fact, many computer-enhanced special effects are used in the film. Choi Kwok-keung, digital graphics designer with Centro Digital Pictures, said the film contained 40 special effects. The company spent more than six months working on The Soong Sisters. The 3-D animation requirements alone took three to four months to create. The film contains two major computer animation sequences: one 'reactivates' the first Chinese-made aeroplane, making it fly. The other is an air battle between Chinese and Japanese warplanes. Since the director could not obtain the aircraft from those historic flights, (they were either destroyed or are kept in museums), she could only bring the flights to the screen by constructing models and relying on digital wizardry to make them fly. Centro's computer graphics animator Karl Mak said computer graphics for the planes had been created from photographs which gave detailed information about their exterior and interior design. 'We have to study how they fly to work out the motion, and pay attention to the details - colour, lighting, texture and even small marks, dirt or holes on the planes that have to be consistent,' Mr Mak said. The company has a number of Silicon Graphics Indigo workstations running on the PowerAnimator of Alias Wavefront. These are networked to an Onyx 1000 supercomputer which features 12 CPUs in order to achieve parallel rendering. Seamlessly integrating computer animation with live action is regarded by digital effects designers as their most challenging task. Mr Choi cited a scene which shows Soong Chingling flying in the first Chinese-made aeroplane. The computer-generated plane is integrated with the actress' action, and a grassland background with the aircraft's shadow. 'Instead of simply putting the different parts together, we had to simulate the effect of shooting the top view of a real flying scene,' Mr Choi said. 'We created a multi-layer effect by adding air currents and changing the focus from the shadow on the ground to the actress sitting in the plane, moving in gradually from the left of the screen.' Another example was pasting a computer-drawn painting of the actor playing the role of Sun Yat-sen into the background of the wedding ceremony of Chiang Kai-shek and Soong Meiling. Mr Choi pointed out that it was difficult to keep resizing and repositioning the picture in sync with the movement of the camera. Centro Digital's president and chief executive John Chu stressed that the objective was not to show off technology, but to make the special effects play a role in enhancing the storytelling. He said computer technology could help film-making in two ways. It could turn the impossible into the visually possible. For example, actors could perform against a background of long-demolished buildings, and with long-dead people. It also helped economise on production costs since digital 3D effects could be used to create an entire army on screen by using a few people and horses. So far the company has invested $30 million in digital production equipment. Centro Digital operates a 15,000-square-foot studio in the Hong Kong Industrial Technology Centre. The studio houses Domino, a key digital machine from Quantel worth US$2 million. The Domino film optical system consists of a film scanner for real-time full-resolution display, a recorder for re-imaging digital information for motion pictures, and workstations for image compositing and effects manipulation. There are also Domino support systems for Ethernet connection, film monitoring, and local and D16 film resolution storage and archives. Mr Chu said the company was the first in Asia to use Domino, the same tool employed by movie makers in Hollywood. He said finding equipment was easy; the real task was searching for talent and training 'local digital dream kids' to operate the technology. Graphics designer Mr Choi: 'We are able to keep abreast of the latest technology. It is only inexperience that makes our work not quite up to Hollywood standards.' Mr Chu said the digital production industry was still in its early stages here. 'It takes time to educate film makers about the capabilities of technology,' he said. 'We have to give them confidence and provide solutions at affordable prices.' The company is now concentrating on a local special-effect movie, Storm Riders, which is expected to be completed this year. It is also involved in projects in other countries and a project with Chinese director Chen Kaige. In addition to digital production in advertising, television and film industries, the company is active in interactive multimedia services and on-line applications. It has designed the digital interface for Hongkong Telecom's upcoming video-on-demand service, which will be launched officially later this year.