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.
The full-specification Super Hi-Vision image sensor realizes 4320 lines of 7680 pixels at 120 frames per second with 12-
bit resolution. This sensor requires both high sensitivity and high frame rate, because the illumination per frame
decreases as the frame rate increases. Sensitivity of the back-side-illuminated sensor is estimated to be 1.65 times higher
than that of the front-side-illuminated sensor, which is calculated from the product of light gathering power of 1.32 times
and internal quantum efficiency of 1.25 times. The advantage at high frame rate is that the rising time of the driving
voltage waveform of a pixel in the back-side-illuminated sensor is three times faster than that of the front-sideilluminated
sensor. To realize a back-side-illuminated structure with a 10 μm-thick photo-electric conversion element,
we investigated the cross-sectional potential profile using an np double epitaxial layer structure. Concentrations of the nand
p- epitaxial layers were studied, aiming to achieve a transit time of less than 2.3 ns and a potential barrier height of
more than 0.117 eV.
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.
We developed an experimental ultrahigh-definition color
video camera 7680H4320V pixels using four 8-million-pixel
charge-coupled devices (CCDs) to increase the camera’s resolution.
This involves attaching four CCDs to a special color separation
prism. Two CCDs are used for the green image; the other two
are used for the red and blue images. Our prototype camera attains
a limiting resolution of more than 2700 television lines, both horizontally
and vertically. Camera sensitivity is F/2.8 at 2000 lux, with a
luminance signal dark-noise level of approximately 50 dB in high
definition television format. To analyze camera performance, we estimated
the spatial position error between the two green CCDs and
the chromatic aberration. Based on these estimations, the cause of
resolution deterioration and ways to improve resolution are
We developed an experimental single chip color HDTV video image acquisition system with 8M-pixel CMOS
image sensor. The imager has 3840 (H) × 2160 (V) effective pixels and built-in analog-to-digital converters, and its
frame rate is 60-fps with progressive scanning. The MTF characteristic we measured with this system on luminance
signal in horizontal direction was about 45% on 800 TV lines. This MTF was better than conventional three-pickup
broadcasting cameras, therefore the enhancement gain (the "enhancement area" in MTF) of the 8M single-chip HDTV
system was about a half of the three-pickup cameras. We also measured the color characteristics and corrected the color
gamut using matrix gain on primary colors. We set the color correction target similar to that of three-pickup color
cameras in order to use multiple cameras to shoot for broadcasting, where all cameras are controlled in the same manner.
The color error between the single-chip system and three-pickup cameras after the correction became 2.7, which could
be useful in practice.
We have developed an experimental single-chip color HDTV image acquisition system using 8M-pixel CMOS image sensor. The sensor has 3840 × 2160 effective pixels and is progressively scanned at 60 frames per second. We describe the color filter array and interpolation method to improve image quality with a high-pixel-count single-chip sensor. We also describe an experimental image acquisition system we used to measured spatial frequency characteristics in the horizontal direction. The results indicate good prospects for achieving a high quality single chip HDTV camera that reduces pseudo signals and maintains high spatial frequency characteristics within the frequency band for HDTV.
We have developed color camera for an 8k x 4k-pixel ultrahigh-definition video system, which is called Super Hi- Vision, with a 5x zoom lens and a signal-processing system incorporating a function for real-time lateral chromatic aberration correction. The chromatic aberration of the lens degrades color image resolution. So in order to develop a compact zoom lens consistent with ultrahigh-resolution characteristics, we incorporated a real-time correction function in the signal-processing system. The signal-processing system has eight memory tables to store the correction data at eight focal length points on the blue and red channels. When the focal length data is inputted from the lens control units, the relevant correction data are interpolated from two of eights correction data tables. This system performs geometrical conversion on both channels using this correction data. This paper describes that the correction function can successfully reduce the lateral chromatic aberration, to an amount small enough to ensure the desired image resolution was achieved over the entire range of the lens in real time.
We describe a precise alignment method of attaching imagers to a prism to produce an ultra-high definition color camera system. We have already developed a prototype camera with 4-k scanning lines using this alignment method.
To increase its spatial resolution, this camera has four 8-megapixel imagers (GGBR), which are attached to a prism with a half-pixel pitch offset so that their pixel arrangement is equivalent to that of a single-chip color-imaging sensor with a Bayer-pattern color filter. The precision of their positioning influences the resolution of the reproduced images. The small pixels in the latest imager make it more difficult to maintain precise imager positions. A precise alignment method for attaching imagers to prism is therefore essential for developing a camera system with high resolution. We propose a method with high detectivity using a sinusoidal pattern chart that easily reproduced by one imager, and a signal process. Images from this camera can attain a limiting resolution of more than 3200 TV lines.
In an integral three-dimensional television (integral 3-D TV) system, 3-D images are reconstructed by integrating the light beams from elemental images captured by a pickup system. 160(H) x 118(V) elemental images are used for reconstruction in this system. We use a camera with 2000 scanning lines for the pickup system and a high-resolution liquid crystal display for the display system and have achieved an integral 3-D TV system with approximately 3000(H) x 2000(V) effective pixels. Comparisons with theoretical resolution and viewing angle are performed, and it is shown that the resolution and viewing angle of 3-D images are improved about 2 times and 1.5 times respectively compared to previous system. The accuracy of alignment of microlenses is another factor that should be considered for integral 3-D TV system. If the lens array of the pickup system or display system is not aligned accurately, positional errors of elemental images may occur, which cause the 3-D image to be reconstructed at an incorrect position. The relation between positional errors of elemental image and reconstructed image is also shown. As a result, the 3-D images reconstructed far from the lens array are greatly influenced by such positional error.
An experimental ultrahigh-definition color video camera system with 7680(H) × 4320(V) pixels has been developed using four 8-million-pixel CCDs. The 8-million-pixel CCD with a progressive scanning rate of 60 frames per second has 4046(H) × 2048(V) effective imaging pixels, each of which is 8.4 micron2. We applied the four-imager pickup method to increase the camera’s resolution. This involves attaching four CCDs to a special color-separation prism. Two CCDs are used for the green image, and the other two are used for red and blue. The spatial image sampling pattern of these CCDs to the optical image is equivalent to one with 32 million pixels in the Bayer pattern color filter. The prototype camera attains a limiting resolution of more than 2700 TV lines both horizontally and vertically, which is higher than that of an 8-million-CCD. The sensitivity of the camera is 2000 lux, F 2.8 at approx. 50 dB of dark-noise level on the HDTV format. Its other specifications are a dynamic range of 200%, a power consumption of about 600 W and a weight, with lens, of 76 kg.
We have developed an experimental progressive-scanning color camera system that has three 2/3-inch-2M-pixel-CCDs. A multiple frame interline transfer CCD was used because its structure enables the charges of each pixel to be handled separately. This CCD has 1,920 X 1,036 active imaging pixels and it was successfully driven at 148.5 MHz to reproduce sixty frames a second of a progressive-scanned picture. The limiting resolution was 1,000 TV lines in both the horizontal and vertical directions.
An ultra-high definition experimental camera system has been designed with double the horizontal and vertical resolution of HDTV. An 8M-pixel CCD with a progressive 60 frame-per- second scan-rate has been developed for the system. The 34 mm X 17.2 mm image area has 4046 (H) X 2048 (V) active imaging pixels with 8.4-micrometers squares. This CCD has a split- frame transfer structure and sixteen 37.125 MHz outputs so that the vertical and horizontal transfer frequencies are almost the same as those of HDTV. The split-frame transfer structure halves the required VCCD clock speeds and thus improves charge transfer efficiency. The multiple-output structure with its 16 outputs enables high data-rate imaging for ultra-high resolution moving pictures. In the signal processing section, analog gain adjustment circuits correct for the mismatches in the characteristics of outputs, and a correlated double-sampling technology is employed on each of the 16 CCD output signals. The output signals are digitized by 12-bit ADCs. The converted signals are then sent to the digital signal processing (DSP) circuits. In the DSP circuits, the upper half of the captured image is vertically inverted. All of the output data is then merged into a 4K X 2K pixel image and reformatted to create twenty-four 640 (H) X 480 (V) pixel sub-images for image processing. After contour compensation processing, the video signals are converted into an analog signal and presented on two ultra high resolution video monitors.
This paper describes the development of an experimental super- high-definition color video camera system. During the past several years there has been much interest in super-high- definition images as the next generation image media. One of the difficulties in implementing a super-high-definition motion imaging system is constructing the image-capturing section (camera). Even the state-of-the-art semiconductor technology can not realize the image sensor which has enough pixels and output data rate for super-high-definition images. The present study is an attempt to fill the gap in this respect. The authors intend to solve the problem by using new imaging method in which four HDTV sensors are attached on a new color separation optics so that their pixel sample pattern forms checkerboard pattern. A series of imaging experiments demonstrate that this technique is an effective approach to capturing super-high-definition moving images in the present situation where no image sensors exist for such images.
A dynamic range expansion method for charge modulation device (CMD) imagers has been proposed and an experimental circuit was evaluated. As active pixel sensors, CMD imagers offer significant advantages in terms of non-destructive readout and high-speed operation. Furthermore, the CMD imager used in this study has built-in dual vertical shift registers which can start their scanning independently. We applied our newly developed source reset method to the imager, which enables each pixel charge to be reset by external circuits. By using these functions, we have obtained our dynamic range expansion method. THe source reset method enables each pixel of a CMD imager to be reset selectively. We use it for a regional electrical shutter. For instance, if there is an overexposed pixel, its accumulated charge is reset from outside the imager, so that the pixel charge is prevented from becoming saturated. The non-destructive readout and high-speed operation enable the CMD imager to be read multiple times without destruction of accumulated charges. For instance, if the imager is driven twice in one field period, each pixel's accumulations can be checked and reset selectively from external of the device at the first scanning, then, all the signals are obtained at the second scanning and output through a small process circuit. This dynamic range expansion method for CMD imagers needs only a simple feedback circuit but does not need complex equipment externally nor adding reset circuits on a chip. An experimental circuit with this method was successfully evaluated here.
We have developed a 60 frame/sec 2 K multiplied by 2 K progressive-scan color camera system. Two new key technologies have been applied in the design process. One is high-data- rate imager operation technology in which each of four charge modulation device (CMD) chips is driven at 167 M pixel/sec in progressive scan mode. One chip consists of 1920 (H) multiplied by 1035 (V) pixels. The other technology is the four-imager pickup method in which two CMD imagers are used for green and the other two for red and blue. Spatial offset imaging is applied in the vertical direction to the two green imagers so that the equivalent number of vertical lines reaches 2070, twice that of one CMD. The above technologies enable the construction of a very-high-resolution camera with a data rate of 334 M pixel/sec and a vertical limiting resolution on a color monitor of more than 1500 lines.