Focusing difficulty has become a critical issue in 8K ultra-high definition television (UHDTV) production. Especially in 8K high-speed shooting, defocus blur significantly degrades a user's experience of slow-motion playback video. For this reason, incorporating a sensor-based phase detection autofocus (PDAF) system that can adjust the focus of a lens quickly into an 8K UHDTV camera has been strongly desired. Although conventional sensor-based PDAF systems have been designed for single-chip cameras capable of using optional color filters, the application of phase detection (PD) in professional broadcasting cameras with three-chip imaging has not been studied, in which incident light separates into three color components (red, green, and blue) by a separation prism. This paper presents an investigation into the PD property among the color channels using a newly prototyped 1.25-inch 8K 240-fps complementary metal-oxide-semiconductor (CMOS) image sensor with two types of horizontal PD pixels (left- and right-phase). Our experiment showed that crosstalk over angler responses of the PD sensor became larger as the wavelength of light increased, and that the crosstalk in each color component reduced the accuracy of the PD amount between a set of stereo images. Consequently, these results demonstrated that utilizing the phase-differential information from the blue component enables a high-precision sensor-based PDAF operation in three-CMOS imaging when shooting black and white objects
KEYWORDS: Signal processing, Camera shutters, Video, Cameras, Modulation transfer functions, Light sources, Imaging systems, Image sensors, Light, Signal generators
This study proposes a flicker reduction method for 120 fps shooting under 100 Hz light fluctuation. In 120 fps videos, a 100 Hz light fluctuation causes a 20 Hz flicker, which is an aliasing artifact induced by its sampling frequency. In this method, the frame period of 1/120 s is divided into 1/150 s and 1/600 s exposure by using a double rolling shutter. Each pixel alternatively outputs 1/150 s and 1/600 s exposure signals which are readout by a readout circuit operated at double the rate of a normal 120 fps operation. A 120 fps signal with an exposure time of 1/100 s is obtained by summing three consecutive signals with exposures of 1/600, 1/150, and 1/600 s. This method is effective for flicker reduction even in the presence of several light sources with different amplitudes and phases. We implemented this method to an 8K camera and examined the flicker reduction effect for an 8K 120 fps video. As a result, the 20 Hz flicker was suppressed to less than one-tenth.
We have been researching and developing a CMOS image sensor that has 2.8 μm x 2.8 μm pixel, 33-Mpixel resolution
(7680 horizontal pixels x 4320 vertical pixels), 120-fps frame rate, and 12-bit analog-to-digital converter for “8K Super
Hi-Vision.” In order to improve its sensitivity, we used a 0.11-μm nanofabricated process and attempted to increase the
conversion gain from an electron charge to a voltage in the pixel. The prototyped image sensor shows a sensitivity of 2.4
V/lx•s, which is 1.6 times higher than that of a conventional image sensor. This image sensor also realized the input-referred
random noise as low as 2.1 e-rms.
KEYWORDS: Cadmium sulfide, Image sensors, Video, Digital electronics, Data conversion, Analog electronics, Digital signal processing, Signal processing, CMOS sensors, Copper indium disulfide
We have developed a CMOS image sensor with 33 million pixels and 120 frames per second (fps) for Super Hi-Vision (SHV:8K version of UHDTV). There is a way to reduce the fixed pattern noise (FPN) caused in CMOS image sensors by using digital correlated double sampling (digital CDS), but digital CDS methods need high-speed analog-to-digital conversion and are not applicable to conventional UHDTV image sensors due to their speed limit. Our image sensor, on the other hand, has a very fast analog-to-digital converter (ADC) using “two-stage cyclic ADC” architecture that is capable of being driven at 120-fps, which is double the normal frame rate for TV. In this experiment, we performed experimental digital CDS using the high-frame rate UHDTV image sensor. By reading the same row twice at 120-fps and subtracting dark pixel signals from accumulated pixel signals, we obtained a 60-fps equivalent video signal with digital noise reduction. The results showed that the VFPN was effectively reduced from 24.25 e-rms to 0.43 e-rms.
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