NHK Develops 8K Square Sensor
NHK has made a contribution to the 4K HDR Summit with something new every year usually about 8K and this year came the announcement of a new camera system ‘beyond 8K’. The presentation was made by Kodai Kikuchi – Research Engineer NHK Science & Technology Research.
The latest camera chip supports 8K x 8K and is for expanding vistas. Up to now a rectangular shape, typically 16:9 has been normal, but there are more and more full size Imax screens and high resolution domes used for information and entertainment. 360 deg VR is becoming an important application and it’s essential in that application to have more vertical resolution.
The sensor is quite new and in the early stages of testing, so there are not many example cameras yet. Kikuchi looked at the development of 8K sensors in cameras.
In the history of development, zoom lens compatibility has been essential. However, the bigger the sensor, the more difficult it is to make a very high level of zoom available.
The first 8K cameras used three sensors of 2.5″ which meant huge lenses with limited zoom of just X5. Then a Super 35 single chip was developed and that allowed some x10 zooms. Next came a 1.25″ three chip architecture that saw zooms reach X50 – and they were used for 8K by NHK. However, the sensor was still bigger than most professional TV cameras which use 2/3″ sensors and have x100 zoom capability – the level that is desired by TV producers. This is, Kikuchi said, the ‘last frontier’, but is it the end?
The new 8K square sensor can capture at 60fps with a 14 bit ADC and uses ‘open gate readout’. The 5/6″ size matches 2/3″ when the square image is cropped to 16:9 to support ‘ITU 8K’. The chip was designed to require relatively low power and was developed jointly with Sharp Semiconductor Innovation Corporation.
Compared to other sensors for example from Gpixel Teradyne NHK is dramatically smaller withh 1.25um pixels. The others have much larger sensors.
The sensor has been used to make a prototype camera which is useful for gimbals and drones and compatible with C Mount lenses. It has been tested with 25mm and 3mm (fisheye) lenses. The current prototype uses an external electro/optical (e/o) unit to transmit images, and an external processor and recorder. Future versions will have integrated e/o unit to processor. Later system are intended to include integrated recording. There are no 8k x 8k square monitors so the testing was done with dual 8K displays mounted one above the other.
Although the displays in headsets are just 4K, the original content needs to be in 8K to allow users to look around. Kikuchi sees applications for virtual tours, XR attractions etc
The group has also tested close up use and sees further applications for the sensor in education, science, museums, medical, industrial etc.
This is far from the end for NHK which is planning 15K to 30K cameras to push resolutions right up to ITU recommendations for 360 degree content. It is also ready to push beyond traditional applications.
In respons to a question Kikuchi said that 8K capture for domes is an early target. The sensor has already been tested in an endoscope. There are challenges but if they can be overcome, a square imager is better because it can capture the full round endoscope image.
