In one of sound rooms of the CEDIA exhibition hall was Sim2, the Italian home theater projector specialist. R&D Director Domenico Toffoli showed us the brightest HDR monitor currently available in Sim2 production and a new set-up they have been working on, that uses two 3-chip projectors to achieve a high dynamic range (HDR) image projection.
Sim2 and Toffoli has been working on HDR for a long time – since 2007. This started with the company Brightside, developing a flat panel display solution that featured a direct backlight with LEDs that could be individually controlled. Dolby later bought the company and continued development work, showing improved prototypes for a number of years.
Meanwhile, Sim2 continued the development work, showing improved prototypes and solutions for a number of years, until the product with features that Sim2 was looking for was ready for production.
The result was being demonstrated outside of the company’s sound room. It is a 47” LCD flat panel that has 8-bits per color. But behind it is a backlight unit that has 2200 individually controllable white power LED that can create a range of luminance with 12-bit control. These two levels of modulation multiply, so the display offers 20-bits per color of brightness control.
Peak luminance is rated at 6000 nits and contrast is measured at 220,000:1. This measurement is done using a black background with five peak brightness white squares located in the corners and center of the black background. The area of each white square is about 1% of the total area, so very small. This is the pattern Dolby developed for evaluating HDR contrast.
Toffoli says the display meets the REC. 709 color space. Needless to say, this was a very bright display. The company was running a skiing clip that showed really bright and very white snow that looked great.
Inside the sound room, we found the two-projector HDR demo running. Currently, the two projectors, which are modified Sim2 SuperLumisPro models, were stacked in a rig that includes very fine mechanical adjustments to align the two images. That is not a very good long term solution as this set up will drift with temperature so will be a real pain to maintain in any actual home theater. Content was shown on a Matte white gain 1 screen from Draper that was 3.5 meters wide.
Toffoli was showing The Great Gatsby movie, which was a good choice as people have seen this in HDR and is a good reference point. The images looked quite similar to other HDR demos I have seen of this movie – but Sim2 was generating this from an SDR Blu-ray disc!
According to Toffoli, the Blu-ray signal was simply split and sent unaltered to each projector. Inside the projectors, the HDR magic happens. Naturally Toffoli was hesitant to disclosure exactly what they are doing. But the gist of the solution is that one projector is dedicated to showing the higher luminance values and the other to the lower luminance values, preserving the black level. If these projectors had only been superimposed, it would not be an HDR solution as they would merely shift the total contrast range up by having a higher peak white but also a higher black level.
To overcome this and create a real change in the contrast, the lower luminance projector was modified in the optics in order to reduce stray light with new dedicated electronics to differentiate the video processing inside the two projectors. In a projector, that typically means the addition of apertures and baffles, so that may be what he is doing. The final contrast ratio of the paired solution was not revealed, but the images on the screen definitely had that “HDR look”.
Taking an SDR signal and creating an HDR image in real time is not easy, so this method will never be as good as one where a colorist is involved. In essence, the electronics in the projectors need to stretch the existing dynamic range of the content to the new dynamic range. Toffoli said he played with this quite a bit but finally ended up with a new gamma curve that is pretty close to the 2.4 gamma used in cinema.
This was the first demo of the HDR solution and an impressive and important step ahead. But Sim2 should consider ways to add the PQ and HLG gamma curves so differently mastered HDR content can also play on this set up. Toffoli has considered these already, plus improved alignment solutions. The set up can be purchased today for $110K.
Sim2 has offices in the US, UK and China. Recently, it announced a new CEO for the US office – Greg Nicoloso. (CC)
