After the IBC Big Screen Experience screening of ‘Baby Driver’ in Dolby Vision and Dolby Atmos, delegates were out in force for two special Big Cinema sessions.
Michael Bradbury, head of cinema technology at Odeon Cinemas opened the first, explaining that after receiving feedback from various directors of photography to the effect that the pictures being screened at some cinemas didn’t accurately reflect the pictures that they had signed off after the final grading process, he had undertaken a number of investigations to find out why this might be the case.
Extraneous illumination from exit lights and safety lighting had turned out to be one explanation, but side by side tests of images from xenon and laser projectors had also shown up differences. Mike had assembled a panel of experts in all the areas that might be relevant, and asked each of them to make a short presentation before joining a discussion — which turned out to be one of the liveliest and sometimes most contentious at IBC.
Brian Claypool from Christie talked about the Christie range of laser projectors then used their new CP4325 direct-coupled RGB laser projector with its wide colour gamut and capabilities for high dynamic range and high frame rates to show a familiar clip from Pixar’s Inside Out at 14fL, illustrating its highly saturated colour palette.
Mark Clowes from Sony gave some good explanations as to how their SRX-R500 series projectors work with EclairColor to provide high contrast images. He introduced their new SRX-R500 laser-phosphor projector pointing out that this has a 10,000:1 contrast ratio, DCI P3 colour space, and similar brightness to lamp-based projectors. Sony are still working to produce an RGB laser for cinema use, and are seeking to use a true green laser in their design. They are also currently working on a dual-engine
RGB laser which has six chips on a single optical substrate, which could produce simultaneous L-R 3D images with none of the disadvantages of ‘flashing’ 3D systems.
Mark Kendall from NEC discussed the three types of laser projector in the manufacturer’s current range, laser-phospor, R-B laser phosphor, and RGB laser. He explained the advantages of each type of projector, providing solutions for all cinemas from low-cost to highest performance.
A brief history of lasers in time
Goran Stojmenovik from Barco gave a brief history of laser-projection from 2012, explaining why laser projectors can provide a cure for existing disadvantages of xenon systems, and higher quality images. He said that Barco’s market research had shown clearly that cinema audiences gave higher marks for picture quality when they watched laser projection, and that this was particularly true for their flagship 6P RGB laser projectors.
Nic Knowland, cinematographer, said that speaking from a lectern effectively put him ‘on the wrong side of the camera’! He stressed the importance of the cinema environment to ensuring that the all-important storytelling experience is undisturbed, saying that there should be no distractions from things like extraneous lighting, which could spoil the experience that the director wanted the audience to have. DoPs are involved in the final grade of a picture, which is usually done in a darkened preview theatre with a white screen and a skilled projectionist, after which the movie is ‘signed off’. But some cinematographers are later surprised to see how different their work looks when projected in a standard cinema. Silver screens can produce hot spots and the images are significantly less bright at the edges than in the centre. Extraneous lighting is a real pain, and he said that it is not a legal requirement to keep exit lights on during a performance — Odeon has established this with some local councils and will be incorporating a system where exit lights only come on when required in some of their new cinema upgrades.
Laser and xenon compared
Nic and BSC colleagues had put together a number of test charts and clips (in DCP format) allowing visual comparisons to be made on known material between laser projectors and xenon projectors. These included colour charts, grey-scales and speckle tests. He showed a range of clips from Murder on The Orient Express showing a range of different lighting situations, and then a number of comparative test charts, some putting laser and xenon images side by side. It was noticeable that the laser images showed a slight magenta bias in the whites compared to a slight green bias in the whites of the xenon images. He did accept that a viewer soon adapted to the colour bias and subsequently didn’t notice it, and he knew that it was possible to create different grades for different types of projector, but didn’t think this solution would appeal to the industry.
Nic then went on to discuss speckle, saying that he and colleagues had looked at their test images on four different types of laser projector, and all had shown unacceptable amounts of speckle when shown on silver screens. He said that the 3P RGB projectors showed noticeable amounts of speckle even when used on a white screen. Such a situation is not acceptable, it is not in keeping with the creative aims of the cinematographers, and cinema customers should not be expected to put up with or even get used to watching these degraded images.
Calling for more work to be done to eliminate speckle in projection systems, he compared the situation unfavourably to what has happened in the cinema camera area, where digital camera manufacturers had worked hard and taken great care to reduce noise successfully. Speckle in projectors has similarities to noise in cameras, and manufacturers should find ways of eliminating it. Vibrating the cinema screen works, but is hardly a practical solution for most cinemas. Nic said he would prefer all films to be screened on white screens, without hot spots, and concluded by re-iterating that speckle needs to be sorted and auditorium lighting needs attention.
Peter Doyle, supervising visual colourist at Technicolor, gave further support to the ‘creative’s’ argument, saying that there is no point in having a great projector or display device if you haven’t defined the screen, and he cited the enormous differences that can occur between images on white and silver screens. He bemoaned the fact that film-makers have to do so many different grades, quoting 2D 14fL, 3D 14fL, 3D 7fL, 3D 4.5fL, Dolby 2D and 3D, IMAX and EclairColor for grades for one recent movie. At the current time a director knows only what he has graded on a white screen in the preview theatre, whereas there is a real need to know what these images look like in the average cinema. The move towards a wide colour gamut will see the need to create a separate grade to take account of the different colour space — why do we really need this WCG?
As the lone exhibitor, Mike Bradbury said that exhibitors are currently being offered a range of technologies by the manufacturers — but what should he buy? Manufacturers themselves seem split on the use of RGB/ phosphor technologies to achieve the best results. Brian Claypool from Christie said that all cinema screens will eventually need to be ‘refreshed’ technically. The new technologies allow exhibitors to choose solutions that they can afford and which will best enable them to present the HDR and WCG images that the creatives will be learning to provide. Mark from NEC said that the variety of projection types that are offered is a good thing , allowing exhibitors to choose the most appropriate solution for each cinema marketplace. Goran agreed, telling Mike ‘buy what you need’, taking into account total cost of ownership, cost savings, and adequate image quality for some sites, but Barco also offers the choice of paying more to impress your premium customers, so you have the choice. Mark Clowes from Sony reminded us that Sony don’t yet have an RGB laser offering. He said that laser phosphor has a place, but there is still room for increased contrast and so far we are restricted to P3. Different manufacturers are using different laser suppliers, so it is likely that metamerism will continue to result in different colour perceptions. The creative side of the industry will learn how to cope with and get the best from the new technologies.
Dominic from Pixar noted that the new technologies provide exciting new tools — no-one would want to go back to a system with more flicker or more grain, for example. Pixar currently prefers the laser projector solution.
In further discussions it was agreed that green lasers are currently difficult to manufacture — Brian explained that getting the specific wavelengths required for cinema is a challenge. There was no clear answer to Mike’s question as to whether laser speckle will be fixed — Nic asked whether the laser source could itself be vibrated, in a similar way to which cinema cameras had adopted a half pixel vibration to smooth the images. NEC agreed that speckle still does need fixing, and that its latest RGB lasers were a considerable improvement on earlier models. Brian felt there was progress being made in terms of wavelength diversity and diffusion, and there was general agreement that ‘we are getting there’. But Goran put the situation into practical perspective by saying that Barco had installed over 200 RGB laser projectors and there hadn’t been a single customer complaint. To which Nic replied that customers don’t yet know about the problem — once they see speckle they won’t ignore it.
A fascinating session that summed up the state of the industry with regard to laser projection — we are getting where we want to be as far as image quality is concerned, but the whole industry still has much work to do.
The need for WCG?
Dominic Glynn, senior scientist at Pixar, believes that enhancing a premium experience is a major reason to use WCG. Film-makers would like to use more colours than DCI P3 provides, since this will give them more creative freedom, and it stands to reason that we need new projectors to cope with the extra colours — he felt that WCG might become the primary grading system one day. Metamerism, where two people see different colours, remains a problem, and colour scientists are working on new measurement techniques for light sources that will allow us to understand the reasons better and to make appropriate adjustments.
In Dominic’s view such a premium grade would be hard to market today because of the lack of standardisation. Peter Doyle noted that we need to open up wide gamut discussions between creatives and projector manufacturers so that we can convince the creatives that their intentions can be faithfully recreated on cinema screens.